Fire Protection - Knauf Insulation

Section 6.0 

Fire Protection 

Structural steelwork 

Product: Knauf Fireboard 

Fp01 


Product: Rocksilk FireTech Slab 

Fp02 

Mezzanine floors 


Fp03 

Small cavity barriers 

Product: Earthwool Cavity Barrier 

Fp04 

Large cavity barriers 

Product: Rocksilk Smoke and Fire 

Barrier 

Fp05 

Refurbishment of timber 

separating/internal floor 

Product: Earthwool Flexible Slab 

Fp06 

Steel Duct Encasement 

Product: Rocksilk Pyroduct Slab 

Fp07

6.1 


Fire protection of structural steel 

Fire protection design 

Knauf Insulation are members of 

the Association for Specialist Fire 

Protection, and our fire protection 

products are listed in the Yellow 

Book, which presents economical 

methods for the fire protection of 

structural steelwork to provide 

compliance with Building 

Regulations 

266 

Structural steel requires fire protection because 

it loses structural strength at temperatures that 

can be rapidly reached in a building fire. This 

will consequently have a negative impact on the 

structural integrity of the building. Protecting the 

structural steel from the heat of a fire will delay 

the onset of this loss of strength and the possible 

collapse of the building. This is essential 

because it allows extra time for both the 

occupants of the building to escape and fire 

services to tackle the fire. It could also prevent 

the actual collapse of the building minimising 

insurance losses. Building Regulations covering 

fire safety are concerned with the preservation 

of life. 

With the increasing use of structural steel in 

construction, designers need fire protection 

solutions that provide a combination of fast 

installation and cost-effectiveness whilst 

achieving the desired finish. 

Whatever the application Knauf Insulation has 

a range of board products and systems to cater 

for any project. 

When used for the fire protection of structural 

steelwork, board systems offer several 

compelling advantages over site applied paint 

and spray coating systems. 

Board systems: 

• Are manufactured to factory tolerances – this 

enables the specifier to be certain that the 

correct thickness of fire protection is being 

applied, by simply checking the thickness of 

materials supplied 

Technical Advice and Support Centre 01744 766666 

• Can be installed prior to the building being 

sealed and made watertight, in all 

temperature and humidity conditions – this 

is in contrast to paint and sprays which are 

often restricted by normal UK winter 

conditions, causing potential delay to 

site programs 

• Are fast, clean, and dry to install, with 

negligible dust levels, allowing other trades 

to work in close proximity 

• Are quick and easy to check (by visual 

inspection) that all relevant areas have 

been protected 

• Are fully compatible with drylining systems 

and allow easy integration with partitioning 

schemes 

Fire protection 

Any steel section which is an element of 

structure and is deemed by any of the following 

regulations to require fire resistance can be 

protected with a fire protection system of dense 

rock mineral wool slabs or fibre reinforced 

gypsum based boards. 

1. The Building Regulations (England and 

Wales) Approved Document B (Fire Safety) – 

Volumes 1 and 2 (2006) 

2. The Building (Scotland) Regulations, 

Technical Booklets, Section 2, 2011 

3. The Building Regulations (Northern Ireland) 

Technical Booklet E, 2005 

4. The Building Regulations (Republic of Ireland) 

Technical Guidance Document B (2006) 

www.knaufinsulation.co.uk 

5. Loss Prevention Council Code of Practice for 

Construction of Buildings 

Steel sections can include universal beams, 

columns and joists (plain and castellated), 

structural and rolled tees, angles, channels and 

round, square or rectangular hollow sections. 

Benefits 

Both rock mineral wool slabs and fibre 

reinforced gypsum boards offer a number of 

advantages for the fire protection of structural 

steelwork that make them ideal for fast track 

projects. 

Rock mineral wool 

• Lightweight product – at less than half the 

weight of calcium silicate slabs – rock 

mineral wool fire protection boards are easy 

to handle and fit on site particularly for 

overhead work 

• Ease of cutting and fixing: Rock mineral wool 

slabs are easy to cut with either a saw or a 

sharp knife, furthermore there are four fixing 

methods, all involve square edge butt joints 

between the boards which enables a fast and 

simple system to be installed without delaying 

other trades and activities 

Fibre reinforced gypsum 

• Smooth surface – only requires decorative 

finishes for completion 

• Robust and impact resistant – ideal for 

columns and all exposed surfaces 

• Easy to cut to size – can be scored and 

snapped to speed up cutting and reduce 

dust levels

Fire Protection 6.1 


Solution optimiser and pathfinder 

Key 

Pb01 

Find online. Visit knaufinsulation.co.uk and key in construction code to find the 

most up to date information on your chosen solution. 


Period of fire resistance (mins) 

Knauf Insulation solution 

0 mins 30 mins 60 mins 90 mins 120 mins 150 mins 180 mins 210 mins 240 mins 


Product: Knauf Fireboard 

See page: 268 

Fp01 



See page: 274 

Fp02 



See page: 280 

Fp03 

Fp04 


Product: Rocksilk Smoke and Fire Barrier 

6.1 

See page: 286 

Fp05 

Refurbishment of timber separating/ 

internal floor 

Product: Earthwool Flexible Slab 

See page: 292 

Fp06 


Product: Rocksilk Pyroduct Slab 

See page: 294 

Fp07 



267

6.1 




Knauf Fireboard 

• Quick and easy to install 

Fp01 

NEW BUILD 

REFURB 

• Dry fix system providing up to 2 

hours fire protection 

• Combined fire protection and 

aesthetic finish 

Knauf Drywall Screws at maximum 

100mm centres into backing strips 



• Non-combustible with a Euroclass 

A1 reaction to fire rating 

• Zero Ozone Depletion Potential (ODP) 

• Zero Global Warming Potential (GWP) 

Abutment angles: light gauge 

steel angle provides support at 

soffit and wall junctions. Fixed to 

adjoining soffit or section flange. 

Edge fix the boards using 

either Knauf Drywall Screws 

at maximum 150mm centres 

or proprietary staples at 

120mm centres. 

Products 

Knauf Fireboard is a gypsum based board 

specially developed for high performance lining 

and encasement, providing up to two hours of 

fire protection. 

Knauf Fireboard has a high quality white 

smooth surface finish ideally suited as a self 

finish. Its surface allows direct decoration with 

most paint finishes or it can be plastered*. 

Knauf Drywall Screws are gold passivated 

screws with spoon tips and ‘hi-low’ threads. 

Knauf Fireboard can also be installed using 

proprietary staples. 

*Consult plaster manufacturer prior to application of plaster 

finish. 

Typical construction 

Knauf Fireboard is used in frameless 

encasements. The product has been specially 

developed to accept direct edge fixings. 

Casings consist of Knauf Fireboard screwed or 

stapled to itself at abutting corners. 

For steelwork encased on all four sides, Knauf 

Fireboard is fixed at each corner directly 

through the material, independent of the column 

or beam. For partial encasement, involving wall 

or ceiling abutments, Knauf Fireboard is fixed to 

light gauge steel angles. 

Knauf Insulation recommend the use of Knauf 

Drywall Screws, essential for fast construction, 

solid fixing and tightly closed edge joints. 

268 


www.knaufinsulation.co.uk


Typical specification 

Knauf Fireboard, ...…mm thick, to be used to 

provide fire protection to structural steelwork. 

Stagger joints by 300mm minimum 

Knauf Fireboard casing 

It is to be installed on beam*/column* as a 

complete 4 sided*/3 sided*/2 sided* 

encasement (*specifier’s choice) to provide 

......minutes fire protection as detailed in the 

Installation section. 

Alternatively, consult the National 

Building Specifications, Standard 

version clause/clauses… 

K10/265…………… 

Knauf Insulation specification clauses can be 

downloaded from knaufinsulation.co.uk/nbs 

Direct edge-fixing with Knauf Drywall 

Screws at 200mm centres or 

proprietary staples at 120mm centres 

Performance 

Fire performance 

The system can provide up to 2 hours fire 

protection. For precise calculation of fire 

protection periods, please contact Knauf 

Insulation Technical Advice and Support Centre. 

Operating temperatures 

Continuous long term exposure to temperatures 

over 50ºC can induce a change of state which 

would reduce the physical performance and 

serviceability of the boards. 

Knauf Fireboard is non-combustible 

to BS 476: Part 4: 1970 (1984) and Class 1 

surface spread of flame to BS 476: Part 7: 

1997. Knauf Fireboard complies with the Class 

‘0’ requirements of the Building Regulations 

when tested to BS 476: Part 6: 1989 and Part 

7: 1997 and with the limited combustibility 

described in the Building Regulations. 

Health and safety 

Knauf Fireboard must be installed with care. 

Ensure adequate ventilation during installation, 

particularly when cutting boards. Avoid harsh 

body contact with sharp cut edges of metal 

components. Refer to Knauf Insulation Material 

Safety Data Sheets and to the Health and Safety 

Executive publications. 

6.1 

Humidity 

Constant humidity over 95% or subjection to 

continuous water will reduce the serviceability 

of the boards. 

For Hp/A tables please visit 

knaufinsulation.co.uk 



269

6.1 



Installation of column system 

Installation sequence 

Cut two boards to 

1 the width of the 2 

column flange. 

Hold in place the 

first 2 boards 

with clamps. 

3 

After measuring the 

size of the remaining 

2 sides, cut another 

two to the depth of 

the column plus 

twice the thickness 

of the board. 

4 

Apply the remaining 

boards, adjusting 

the length of 

adjoining boards to 

ensure that board 

joints are staggered 

by at least 300mm. 

5 

Edge-fix the boards 

using either self 

drilling Knauf 

Fireboard Gripper 

Screws at 200mm 

centres or proprietary 

staples at 120mm 

centres. Knauf 

Fireboard Gripper 

Screws should 

penetrate into the 

casing by at least 

30mm 

Installation 

Steelwork encasements must be installed in full 

accordance with Knauf Insulation’s 

recommendations and in compliance with 

BS 8212: 1995 and BS 8000: Part 8: 1994. 

The installation procedures outlined here relate 

to normal single layer applications. 

Knauf Drywall Screws 

Knauf Drywall Screws should penetrate into the 

casing by at least 30mm. 

Four-sided column encasement 

• Cut two boards to the width of the column 

flange. Cut another two to the depth of the 

column plus twice the thickness of the board 

• Adjust the length of adjoining boards to 

ensure that board joints are staggered by at 

least 300mm 

• Edge-fix the boards using either Knauf 

Drywall Screws at 200mm centres or 

proprietary staples at 120mm centres 

Partial column encasement 

Assuming a typical three-sided encasement 

where one of the column flanges straddles a 

wall, follow the same procedure as outlined 

for four-sided encasement with the following 

differences: 

• Fix 25 x 25mm light gauge steel angles, 

in continuous lengths, to either the abutting 

wall face or the inner flange of the column. 

Use appropriate proprietary fixings at 

600mm centres 

Double layer application 

Install the first layer as described for either full 

or partial encasement. Secure the second layer 

to the first with fixings spaced as for the first 

layer but avoid coincident fixing positions. 

It is good practice that board joints are 

staggered – as with the first layer – between 

adjoining boards and also between the two 

layers. In the case of structural steelwork, 

double layer encasement will obviate the need 

for joint backing strips. 

270 





Installation of beam system 

Installation sequence 

1 

Install continuous lengths of 

25 x 25mm angle using 

appropriate proprietary 

2 

Cut two boards to the depth 

of the section plus twice the 

board thickness plus l0mm. 

3 

Cut a soffit board to the 

width of the steel flange. 

The length of this board must 

4 

Cut board off-cuts 100mm 

wide as joint backing strips. 

Fit these, half lapped, behind 

fixings at 600mm centres, fix 

further lengths of 25 x 25mm 

angle at any end abutment. 

Screw-fix these to the angles 

at 150mm centres with 

35mm Knauf Drywall 

Screws. 

differ from the side boards to 

ensure adjacent board joints 

are staggered by at least 

300mm. 

all butt joints at the sides 

and soffit of the beam. 

Fix with Knauf Fireboard 

Gripper Screws at maximum 

Edge-fix horizontal board to 


the two vertical boards using 

either Knauf Fireboard 

Gripper Screws at 150mm 

centres or proprietary staples 

at 120mm centres. 

Beam encasement 

Assuming a typical three-sided encasement, 

where a beam is exposed directly below a level 

soffit, fix light gauge steel angles to either the 

adjoining soffit or the top flange of the beam. 

Install continuous lengths of 25 x 25mm angle 

using appropriate proprietary fixings at 600mm 

centres. 

• Cut board off-cuts 100mm wide as joint 

backing strips. Fit these, half-lapped, behind 

all butt joints at the sides and soffit of the 

beam fixed with Knauf Drywall Screws at 

maximum 100mm centres 

Double layer application 

Install the first layer as described for either full 

nominal 150mm centres, screw lengths should 

be equal to the thickness of the second layer, 

plus 30mm. Where two different thicknesses of 

Fireboard are applied, the thicker layer is 

installed first. 

6.1 

• Fix further lengths of 25 x 25mm angle at any 

or partial encasement. Secure the second layer 

end abutment 

to the first with fixings spaced as for the first 

• Cut two boards to the depth of the section 

layer but avoid coinciding fixing positions. 

plus twice the thickness of the board plus 

It is good practice that board joints are 

l0mm. Screw-fix these to the angles at 

staggered – as with the first layer – between 

150mm centres with 35mm Knauf Drywall 

adjoining boards and also between the two 

Screws 

layers. In the case of structural steelwork, 

• Cut a soffit board to the width of the steel 

flange. The length of this board must differ 

from the side boards to ensure adjacent 

board joints are staggered by at least 

300mm. Edge-fix this horizontal board to the 

two vertical boards using either self-drilling 

Knauf Drywall Screws at 150mm centres or 

double layer encasement will obviate the need 

for joint backing strips. 

The second layer of boards across the webs are 

fixed to the angle attached to the upper flange 

using 55mm long Knauf Drywall Screws at 

150mm centres and the second layer across the 

bottom flange using Knauf Drywall Screws at 

staples at 120mm centres 



271

6.1 



Application details for beams 

Beam with partition abutment 

25 x 25mm angle secured to top flange 

of beam, or alternatively to soffit 


100mm centres 

Fireboard casing 

Backing strip 

10mm gap 

Direct edge fixing with Knauf Drywall 

Screws at maximum 150mm centres or 


C-Stud partition with standard 

U-Channel head track 

Beam with wall abutment 

25 x 25mm angle secured to top flange of 

beam, or alternatively to soffit 


100mm centres 


Direct edge fixing with Knauf 

Fireboard Gripper Screws at 

maximum 150mm centres or 


Continuous 25 x 25mm Knauf 

Fireboard Angle secured to substrate 

using appropriate fixings 

Masonry wall 

272 




Column with partition abutment 




Knauf C-Stud toggle-fixed to Knauf 


Knauf Wallboard not fixed to this C-Stud 

Column with wall lining abutment 

Continuous 25 x 25mm Knauf 

Fireboard angle at each corner 


6.1 






273

6.1 




Rocksilk FireTech Slab 

• Flexible system with four installation 

methods 

• Maintenance free, passive system 

• Clean installation process with 

negligible dust generation 

Fp02 


REFURB 


• Non-combustible with a Euroclass A1 

reaction to fire rating 



Pig tail screws 

Noggin of Rocksilk FireTech Slab 

or Rocksilk FireTech Dry Fix Noggin 

Slab 

Product 

Rocksilk FireTech Slab is a dense rock mineral 

wool slab. It is available unfaced or faced with 

a bright Class ‘0’ reinforced aluminium foil, for 

applications above clean rooms, within air 

plenums, or for aesthetic purposes. 

Plaster manufacturers advice and guidance 

should be followed regarding pre-treatment of 

Rocksilk FireTech Slabs before application of 

plaster finishes 

Rocksilk FireTech Dry Fix Noggin Slab is an ultra 

high density rock mineral wool slab used for the 

noggin in the Rocksilk FireTech Dry Fix Noggin 

System. 


The exposed surfaces of any steel section are 

fully enclosed in Rocksilk FireTech Slab, using 

any of the fixing systems shown on the following 

pages. 

Rocksilk FireTech Slab can be used to provide 

up to 4 hours fire protection to structural steel 

and cast iron columns, beams and trusses. Steel 

sections may include universal beams, columns 

and joists (plain and castellated), structural and 

rolled tees, angles, channels and round, square 

or rectangular hollow sections. 

Installation 

Rocksilk FireTech Slab can be used with four 

types of fixing methods for the fire protection of 

structural steelwork and each system has its own 

performance characteristics. 

Fixing methods: 

• Dry Fix Noggin System 

• Adhesive Noggin Fixing System 

• Combination Fixing System 

• Welded Pin Fixing System 

274 




Technical specification 

Rocksilk FireTech Slab, ...…mm thick, to be 

used to provide fire protection to structural 

steelwork. 

Noggin of Rocksilk FireTech Slab or 

Rocksilk FireTech Dry Fix Noggin 

Slab 

Pig Tail Screws 

It is to be installed using the dry fix noggin 

system*/adhesive noggin fixing system*/ 

combination fixing system*/welded pin 

fixing system* (*specifier’s choice) as 

detailed in the Installation section. 




K11/885…………… 




Performance 


Rocksilk FireTech Slab is classified as 

non-combustible to BS 476: Part 4: 

1970(1984), Class 1 surface spread of flame 

to BS 476: Part 7: 1997, and Class ‘0’ to the 

Building Regulations. Rocksilk FireTech Slab is 

designed to provide up to 4 hours fire 

protection to structural steelwork, thereby 

satisfying the Building Regulations and 

insurance demands for periods of fire 

resistance. 

Durability 

Rocksilk FireTech Slab is rot proof, does not 

sustain vermin and will not encourage the 

growth of fungi, mould or bacteria. 

Rocksilk FireTech Slab is odourless and 

non-hygroscopic. 

Rocksilk FireTech Slab is non-wicking when 

tested to BS 2972: 1989: Section 12. 

When exposed to 90% relative humidity and 

20ºC, Rocksilk FireTech Slab absorbs less than 

0.004% of moisture. 

6.1 

For Hp/A tables please visit 

knaufinsulation.co.uk 



275

6.1 



Installation of Rocksilk FireTech Slab 

Dry Fix Noggin System 

Up to 2 hours fire protection 

Adhesive Noggin Fixing System 


100mm wide noggins of 

Rocksilk FireTech Dry Fix 

Noggin Slab friction fitted 

between the flanges. 

Attach web pieces to 

noggins with pig tail 

screws at 100mm centres. 

Attach flange pieces to web 

pieces using pig tail screws 

positioned 25mm in from 

each end and at 150mm 

centres. 

Attach web pieces to noggins 

with pig tail screws at 


100mm wide noggin of 


glued into place using 

suitable adhesive 

Attach flange pieces to 

web pieces using pig tail 

screws positioned 25mm 

in from each end and at 


Combination Fixing System 


Welded Pin Fixing System 


Attach the Rocksilk FireTech 

Slab web pieces by impaling 

over the welded pins and 

securing in place with 38mm 

spring steel washers. 

Attach flange pieces to web 

pieces using pig tail screws 

at 150mm centres. 

Adhesive should be used at 

the joint between subsequent 

web pieces. 

Attach the Rocksilk FireTech 

Slab web and flange pieces 

by impaling over the 3mm 

diameter welded mild steel 

pins and securing in place 

with 38mm spring steel 

washers. 

Adhesive should be used at 

the joint between subsequent 

web pieces. 

Alternative installation methods 

The Dry Fix Noggin System 

Is a fast and efficient friction fit noggin system 

that does not require adhesive. It can give up to 

2 hours fire protection to BS 476: Part 21. 

When installing 20, 25 and 30mm Rocksilk 

FireTech Slab, noggins should be cut from a 

30mm Rocksilk FireTech Dry Fix Noggin Slab. 

When greater thicknesses of Rocksilk FireTech 

Slab are used, the noggins are cut from a 

corresponding thickness of Rocksilk FireTech Dry 

Fix Noggin Slab. 

The Adhesive Noggin Fixing System 

Can be used to provide up to 2 hours fire 

protection to all sizes of structural steelwork. 

The Combination Fixing System 


protection to all sizes of structural steelwork, 

and up to 3 hours fire protection to steelwork 

with section factors (Hp/A) of up to 133m -1 for 

columns and 143m -1 for beams. 

The Welded Pin Fixing System 


protection to all sizes of structural steelwork, 

and up to 4 hours fire protection to steelwork 

with section factors (Hp/A) of up to 172m -1 for 

columns and 184m -1 for beams. 

If section factors are above 260m -1 contact our 

Technical Advice and Support Centre. 

The use of a dense rock mineral wool slab 

requires no special vee cuts, drilling or 

sub-frames, making it fast and easy to install. 

Rock mineral wool slabs can be easily cut using 

hand or power tools. 

Note: Rocksilk FireTech Dry Fix Noggin Slab has a density 

of 200 kg/m 3 . 

276 




Greater 

than 

500mm 

Full 

depth 

Greater 

than 

500mm 

Y 

100mm 

100mm 

X 

Solid noggin formed from one or more pieces 

of Rocksilk FireTech Slab 

T-shaped noggin formed from two pieces of 

Rocksilk FireTech Slab joined at right angles 

using pig tail screws 

Insert noggins as described at 600mm 

centres and if practicable leave for 4 hours 

for adhesive to cure. 

Cut Rocksilk FireTech Slab to size as follows: 

Beams: flange pieces to dimension X, web 

pieces to dimension Y + t (t = thickness of 

board) 

Columns: flange pieces to dimension X, 

web pieces to dimension Y + 2t 

Attach web pieces to noggins using pig tail 

screws at 100mm centres 

Attach flange pieces to web pieces using pig 

tail screws positioned 25mm in from each 

end at 150mm centres. 

Note: For flanges greater than 400mm use welded pin 

and spring steel washers to provide extra retention of 

the flange piece of insulation. The welded pins should 

be located along the centre line of the flange at 300mm 

centres. 

Adhesive noggin fixing system 

Noggins are cut 100mm wide from 20mm thick 

Rocksilk FireTech Slab. They should be cut to a 

suitable length relative to the web size to give 

a tight compression fit. 

Noggins are glued top and bottom using a 

typical adhesive thickness of 0.5mm and friction 

fitted between the flanges at 600mm centres. 

The noggins should be installed in such a way 

that they are slightly 'proud' of the flange (by 

about 2mm) and such that they coincide with 

joints between the boards. 

It is preferable to leave the noggins in position 

for 4 hours to allow the adhesive to cure. 

However, where this is impractical Rocksilk 

FireTech Slab can still be fitted before the 

adhesive cures since the noggins are essentially 

friction fitted. 

For web depths greater than 500mm, T-shaped 

or solid noggins should be used, formed from 

Rocksilk FireTech Slab, and screwed together 

using pig tail screws. 

6.1 



277

6.1 



Application details for beams 

Partition abutment using a noggin fixing system 

Pig tail screws at maximum 

100mm centres 

Rocksilk FireTech noggin 


Direct edge fixing with pig tail screws at 


Attach flange piece to web piece by 

impaling over welded pins and securing 

the board to board joint with pig tail 

screws at 150mm centres. Spring steel 

washers are used over the welded pins to 

retain the insulation, any excess pin 

length being trimmed off 

C-Stud partition with standard U-Channel 

head track 

Wall abutment using a noggin fixing system 

Pigtail screws at maximum 100mm centres 

Masonry wall 




Attach flange piece to web piece by impaling 

over welded pins and securing the board to 

board joint with pig tail screws at 150mm 

centres. Spring steel washers are used over 

the welded pins to retain the insulation, any 

excess pin length being trimmed off 

278 




Adhesive detail 

The adhesive used for gluing Rocksilk FireTech 

Slabs should be a thixotropic paste type based 

on soluble solids of silicate and potassium 

mixed with clay or refractory mineral filler to an 

approximate ratio of 70:30 by weight. 

Steelwork should ideally be dry but the 

presence of condensation will merely prolong 

the cure time, not weaken the bond strength. 

Since only the top and bottom surface of each 

noggin is glued with a typical adhesive 

thickness of 0.5mm, excellent rates of usage are 

achievable. 

Note: Steelwork should be clean and free from grease prior 

to the application of adhesive. 

*For further details contact our Technical Advice and 

Support Centre. 

Pig tail screws 

The spirally wound or pig tail screws are 

made from 16 gauge galvanised wire and 

are available from stockists. A specification 

is available on request from our Technical 

Advice and Support Centre. 

The screws should be installed flush at 150mm 

centres on board to board joints and 100mm 

centres over noggins, using either power or 

hand tools. There is no need to countersink the 

screw heads. 

Column with partition abutment 





Column with wall lining abutment 

6.1 

Masonry wall 







279

6.1 





• Simple, clean and quick to install 

• Provides up to 3 hours fire resistance 

• System covers section factors up to 

310 Hp/A - (A/V) 

Fp03 

REFURB 







Product 

Rocksilk FireTech Slab is a dense rock mineral 

wool slab specifically designed for the fire 

protection of structural steelwork. 


The exposed surface of a steel section is fully 

enclosed in Rocksilk FireTech Slab, using a 

metal clip, snap-lock system. 

Installation 

The column case is pre-fabricated to suit the 

specific beam or column. It is lined with Rocksilk 

Firetech Slab which is pre-bonded to the steel 

skin. Note that no adhesive is applied to the 

joints between individual slabs. The column 

case is made of galvanized or PVC coated steel 

minimum 0.7mm thick. For columns, the casing 

is normally supplied in two pieces with the 

closing face fixed with snap-lock joints. 

Three-sided encasements are secured at 300mm 

centres to continuous galvanized steel angles, 

or the flange of the steel section, or to the wall 

or floor at 500mm nominal centres. 

Alternatively the casing may be secured using 

an integral lip on the casing. 

Performance 


Rocksilk FireTech Slab is classified as 

non-combustible to BS 476: Part 4: 1970 

(1984). Class 1 Surface Spread of Flame to BS 

476: Part 7:1977, and Class ‘O’ to the 

Building Regulations. Rocksilk FireTech Slab is 

designed to provide up to 3 hours fire 

protection to the mezzanine floor column 

support system, thereby satisfying the current 

Building Regulations and insurance industry fire 

resistance performance standards. 

Performance 

Rocksilk FireTech Slab is rot proof, does not 

sustain vermin, will not encourage the growth of 

fungi, mould or bacteria and is odourless and 

non-hygroscopic. 

280 




Table 1 - Mezzanine floors 

Time - mins Board Thickness (mm) Hp/A 

60 20 224 

25 260 

30 310 

35 310 

40 310 

45 310 

90 20 91 

25 115 


Rocksilk FireTech Slab….mm thick, to be 

used to provide fire protection to structural 

steelwork in a mezzanine floor system. 




K11/885………… 



30 139 

35 165 

40 190 

45 217 

50 244 

55 260 

60 270 

65 310 

120 20 57 

25 72 

30 87 

35 102 

40 117 

45 133 

50 149 

55 165 

60 181 

65 198 

180 30 49 

6.1 

35 58 

40 66 

45 75 

50 84 

55 92 

60 101 

65 110 



281

6.1 


Cavity barriers 

Cavity barrier design 

Design considerations 

Every building must be designed and 

constructed in such a way that in the event of 

an outbreak of fire within the building, the 

unseen spread of fire and smoke within 

concealed cavities in its structure and fabric is 

inhibited. The Building Regulations require 

cavity barriers to sub-divide voids if they extend 

beyond certain dimensions. 

In addition cavity barriers are also required to 

be placed above fire resisting partitions. Both 

glass and rock mineral wool products are ideal 

to act as cavity barriers due to their inherent 

non-combustibility. 

In the case of fire stopping minor imperfections 

of fit between construction elements or 

components, it is acceptable to seal small gaps 

with unfaced glass or rock mineral wool 

products. However, for specific periods of fire 

resistance in small and large voids (as required 

by the Building Regulations) it is necessary to 

use specific products that have been tested and 

assessed to offer the required performance 

when installed in a specific way, if necessary, 

using specific fixing components. 

Concealed cavities 

Fire and smoke spread in concealed spaces is 

particularly hazardous because fire can spread 

quickly throughout a building and remain 

undetected by the occupants of the building. 

Cavity barriers are used to sub divide 

cavities and so prevent smoke and flame from 

by-passing fire-resisting walls and partitions. 

The maximum distance between barriers must 

be appropriate to the location of each cavity. 

Also, due consideration must be given to the 

class of surface exposed within the cavity. 

Cavity barriers should achieve at least 30 

minutes fire resistance, providing a minimum of 

30 minutes integrity and 15 minutes insulation. 

Detailed requirements are complex. For full 

details about the position and spacing of cavity 

fire barriers refer to the relevant sections of the 

appropriate Building Regulations. 


Small voids include the cavities in external walls 

and voids beneath raised access floors. Larger 

voids include the spaces between suspended 

ceilings and soffits or roofs. 

In cavities in external walls the resilient 

properties of glass mineral wool mean that it 

can be compression fitted, between the outer 

leaf and the inner leaf or frame. The noncombustible 

nature of glass mineral wool allows 

it to resist the effects of fire, enabling it to 

remain in place during the fire and effectively 

block the transfer of fire through the cavity. 


In England, Wales and Northern Ireland, all 

cavity barriers should be constructed to provide 

at least 30 minutes fire resistance and 15 

minutes insulation. In Scotland large cavity 

barriers, which are defined as being greater 

than 1m x 1m in size, must provide the same. 

Fixing systems 

Any product used for fire protection can only be 

considered to be offering a specific period of 

fire protection when it is installed in the manner 

specified in the appropriate fire test report. This 

includes the specification of all associated 

fixings and supporting frame work. 

282 




Photograph courtesy of Henley Building Systems 

30 minutes fire resistance 1 hour fire resistance 

Definitions 

The following definitions are taken from 

Approved Document B (Fire safety) - Volume 

2: Buildings other than dwellinghouses 

(2006) 

50mm Rocksilk 

Smoke and Fire 

Barrier 

Suspended ceiling 

of 12.5mm plasterboard 

50mm cavity 

50mm Rocksilk 

Smoke and 

Fire Barrier 

Cavity barrier 

A construction, other than smoke curtain, 

provided to close a concealed space against 

penetration of smoke or flame, or provided to 

restrict the movement of smoke or flame 

within such a space. 

Fire stop 

Seal provided to close an imperfection of 

fit or design tolerance between elements or 

components, to restrict the passage of fire 

or smoke. Any unfaced glass or rock mineral 

product can be used as a fire stop. 

Period of fire resistance (mins) 

6.1 

Knauf Insulation solution 0 mins 30 mins 60 mins 90 mins 120 mins 150 mins 180 mins 210 mins 240 mins 

Small cavity barriers - to be deleted 

Fp04 


Product: Rocksilk Smoke and Fire Barrier 

See page: 286 

Fp05 



283

6.1 




Earthwool Cavity Barrier 

• Meets Building Regulation 

requirements for fire, acoustics and 

party wall bypass applications 


• Colour coded for easy identification 

Fp04 

NEW BUILD 

Earthwool Cavity Barrier 



• A+ Generic BRE Green Guide rating 



Earthwool Cavity Barrier stapled through top flange to 

sheathing to fully fill the cavity 

Brick outer leaf 

Product 

Earthwool Cavity Barrier is manufactured from 

a continuous length of non-combustible glass 

mineral wool which is compressed within a 

resilient polythene sleeve incorporating two 

flanges designed for ease of fixing. 

The polythene sleeve is colour coded to suit a 

variety of cavity widths from 50mm to 100mm 

and eliminates the need for weather protection 

during installation. 

The barriers are 1200mm long and can be 

used in both vertical and horizontal 

applications, and are available in two standard 

widths (100mm and 300mm). 100mm barriers 

are used for normal fire stopping and noise 

reduction applications. 300mm barriers are 

used where higher performance levels are 

specified and at party wall/external wall cavity 

junctions. 


Earthwool Cavity Barriers are engineered to 

prevent the spread of smoke and fire through 

walls, floors and cavities in timber frame, metal 

frame and masonry buildings. 

They are also suitable for reducing flanking 

noise transmission in these concealed cavities. 

The use of the correct size of Earthwool Cavity 

Barrier is essential. Earthwool Cavity Barriers 

are designed to compress to a tight fit in 

cavities and in the event of fire breaking into 

the cavity, Earthwool Cavity Barriers do not rely 

on the polythene flanges to hold them in place, 

but on their compression between the inner and 

outer leaf. 

It is, therefore, essential to specify the Earthwool 

Cavity Barrier by reference to the actual 

constructed cavity width. 

Installation 

In vertical applications, both flanges of the 

Earthwool Cavity Barrier should be fixed to the 

inner leaf. 

In horizontal applications, the top flange of 

the polythene sleeve should be fixed to the 

inner leaf. 

All joints and intersections of Earthwool Cavity 

Barriers should be closely butted. 

284 




Typical junction with party wall 

300mm wide Earthwool 

Cavity Barrier - stapled to 

sheathing board either 

side of party wall 

Earthwool Timber Frame 

Party Wall Slab 

Earthwool FrameTherm 


Timber frame construction 

Earthwool Cavity Barrier 100mm*/300mm* 

wide, coloured yellow*/ blue*/white* to be 

friction fitted in the positions shown on the 

drawings. Earthwool Cavity Barrier to fully fill 

the depth of the cavity. 

Polythene flanges to be stapled to the 

timber*/sheathing board* to hold the cavity 

barrier in place. 

All joints and intersections of Earthwool 

Cavity Barriers should be closely butted 

together. 




P10/420…………… 



Masonry construction 

Earthwool Cavity Barrier 100mm*/ 300mm* 

wide, coloured yellow*/ blue*/white* to be 

friction fitted in the positions shown on 

the drawings. 

Performance 


Earthwool Cavity Barriers are manufactured 

from glass mineral wool which has a Euroclass 

A1 rating when classified in accordance with 

BS EN 13501-1. 

Earthwool Cavity Barriers have been tested for 

fire resistance in accordance with BS 476: Part 

8: 1972 and will provide 60 minutes stability, 

integrity and insulation. 

Acoustic performance 

Table 2 - Colour coding 

Cavity width (mm) 

Colour 

50-65 yellow 

66-80 blue 

81-100 white 

Earthwool Cavity Barrier to fully fill the depth 

of the cavity. 

All joints and intersections of Earthwool 

Cavity Barriers should be closely butted 

together. 




P10/420…………… 



6.1 

Building Regulations require the use of a cavity 

closer to reduce flanking noise transmission 

along party wall cavities and external wall 

cavities in masonry and timber frame 

constructions. 

Earthwool Cavity Barriers meet the generic 

description for cavity closers and will therefore 

ensure compliance with Part E and Robust 

Details in timber frame and masonry wall 

constructions. 



285

6.1 



Large cavity barrier 

Rocksilk Smoke and Fire Barrier 


• Provides both fire and acoustic 

performance 

• Versatile, flexible and adaptable 

system 

Fp05 

Metal angle fixed to soffit 

REFURB 


• Non-combustible with a Euroclass 

A1 reaction to fire rating 




50mm airgap 

Rocksilk Smoke and 

Fire Barrier fixed to 50mm 

timber spacer 

Product 

Rocksilk Smoke and Fire Barrier is made from 

rock mineral wool and formed into a flexible 

mattress faced on one side with galvanised 

wire mesh stitched in position. 

Rocksilk Smoke and Fire Barrier is also 

available foil faced on one or both sides. 

Rocksilk Smoke and Fire Barrier must be 

installed in accordance with the specifications 

detailed below and on the following pages. If 

these specifications are not strictly followed the 

installation cannot be deemed to offer any 

specific period of fire protection. 

Fixing components: 

Angle: Mild steel - 50mm x 50mm x 2mm or 

60mm x 40mm x 2mm 

Strip: Mild steel - 40mm x 2mm 

See Table 3 for suitable method of fixing angles 

and strips to substrate. 


For half an hour fire resistance 

A single layer of 50mm Rocksilk Smoke and 

Fire Barrier, applied as a hanging curtain, 

supported continuously from above and both 

sides, using the fixings listed in the Table 3. 

At the base Rocksilk Smoke and Fire Barrier is 

either lapped freely on to the back of a 

suspended ceiling or fixed to a partition head. 

Suitable for drops up to 7 metres. 

For one hour fire resistance 

Two layers of 50mm Rocksilk Smoke and Fire 

Barrier, separated by a 50mm air space, 

applied as a hanging curtain with wire mesh 

to the outside, supported continuously from 

above and both sides, using the fixings listed in 

Table 3. At the base it is either lapped freely on 

to the back of a suspended ceiling, or fixed to a 

partition head. 

Use foil faced Rocksilk Smoke and Fire Barrier 

when the ceiling void is used as an air plenum. 

Installation 

See page 288 - 291 for installation details. 

See Table 3 for specification of fixings and 

supporting metalwork. 

286 




Metal angles 

fixed to soffit 

Rocksilk Smoke 

and Fire Barrier 


fixed to timber spacer 


Half hour cavity barrier 

A single layer of 50mm Rocksilk Smoke and 

Fire Barrier (*foil faced) to be installed in the 

positions marked on the drawings, and fixed 

in accordance with the manufacturer’s 

recommendations. All joints either tightly 

butted, overlapped, or with edges returned, 

and stitched in a continuous spiral loop with 

1mm diameter galvanised lacing wire. 

(* delete as appropriate) 

One hour cavity barrier 

Two layers of 50mm Rocksilk Smoke and 

Fire Barrier (*foil faced), separated by a 

50mm air space to be installed in the 

positions marked on the drawings, and 

fixed in accordance with the manufacturer’s 

recommendations. All joints either tightly 

butted, overlapped, or with edges returned, 

and stitched in a continuous spiral loop with 

1mm diameter galvanised lacing wire. 

(* delete as appropriate) 




K10/545…………… 



Performance 


Rocksilk Smoke and Fire Barrier is made from 

rock mineral wool and is classified as noncombustible 

to BS 476: Part 4: 1970. Rocksilk 

Smoke and Fire Barrier has a Class 1 Surface 

Spread of Flame to BS 476: Part 7: 1997 and 

is Class ‘0’ to the Building Regulations. 

When subjected to full scale fire resistance tests 

to BS 476: Part 22: 1987, a system comprising 

one layer of 50mm Rocksilk Smoke and Fire 

Barrier, fixed by using the components and 

methods detailed on the following pages 

achieved 19 minutes insulation, and retained its 

integrity for 35 minutes, after which time the test 

was discontinued. 50mm Rocksilk Smoke and 

Fire Barrier thereby satisfies the criteria laid 

down in the Building Regulations for cavity 

barriers, by exceeding the minimum 

requirement of 15 minutes insulation and 30 

minutes integrity . 

When subjected to full scale fire resistance tests 

to BS 476: Part 22: 1987, a system comprising 

a double layer of 50mm Rocksilk Smoke and 

Fire Barrier, fixed by using the components and 

methods detailed on the following pages, 

achieved 61 minutes insulation, and retained its 

integrity for 66 minutes, after which time the test 

was discontinued. 

A double layer of 50mm Rocksilk Smoke and 

Fire Barrier thereby satisfies the criteria laid 

down in the Building Regulations for one hour 

cavity barriers. 

These tests incorporated vertical and horizontal 

joints between barriers. Fire resistance is 

effective from either side of the barrier. When 

tested, the wire side was exposed to the furnace 

as this is the side most vulnerable to fire. 

6.1 



287

6.1 



Installation of half hour cavity barrier 

80mm 

minimum 

1. Metal angle fixed to purlin 2. Fixed to purlin 3. Fixed to rib of coffered slab 

4. Fixed across coffered ceiling 5. Perimeter fixing with steel strip 6. Junction with ceiling 

Installation 

The following information and illustrations 

outline typical details for the installation of large 

cavity barriers. In case of uncertainty, refer to 

Knauf Insulation. 

Metal deck with overdeck insulation 

If Rocksilk Smoke and Fire Barrier runs with the 

slope of the roof, a supporting steel angle 

should be fixed between purlins and the smoke 

and fire barrier clamped to this with steel strip 

(Figure 1). The insulation should project 80mm 

beyond the strip to ensure a good seal. 

If fitted across the sheeting profile, Rocksilk 

Smoke and Fire Barrier should be bolted to the 

purlins (Figure 2). It is returned at the top, to a 

length equivalent to 3 times the profile depth, to 

allow for cutting at troughs and pushing 

securely into profiles. Alternatively, proprietary 

profile fillers may be used. 

Concrete decks 

Rocksilk Smoke and Fire Barrier is clamped 

between the deck and steel angle secured by 

expanding bolts. If the deck is coffered it should 

usually be possible to locate the cavity barrier 

along one of the ribs (Figure 3). If fitted across 

the coffering it should be clamped by steel strip, 

to the steel angle which is secured to the ribs. 

If the depth of coffering is less than 100mm, 

Rocksilk Smoke and Fire Barrier should be 

returned at the top by 300mm, to allow for 

cutting at the ribs and pushed securely into the 

coffering (Figure 4). If the depth of coffering is 

greater than 100mm, Rocksilk Smoke and Fire 

Barrier should be fixed around the coffering 

using steel angle, as described above. 

Alternatively, proprietary profile fillers may be 

used. 

The perimeter of the barrier should be secured 

with steel strip (Figure 5). 

At the ceiling junction, Rocksilk Smoke and Fire 

Barrier is cut and draped on and between the 

joists, and secured by fixing to steel angle, 

which is itself fixed to the joists (Figure 6). For 

suspended ceilings, see Figure 11. 

At partitions or wall heads, if a secure fixing is 

available, as at soffits, Rocksilk Smoke and Fire 

Barrier should be clamped with a steel strip 

Two layers of 50mm Rocksilk Smoke and Fire 

Barrier with a 50mm air space between them 

are needed for one hour fire resistance. In 

general two separate layers should be installed 

back to back, each in a manner identical to that 

shown for half hour fire resistance. The joints in 

the two layers should be staggered and Rocksilk 

Smoke and Fire Barrier returned outward at the 

top and bottom. The wire reinforced sides 

should be placed outward, see Figure 7. 

288 





Installation of one hour cavity barrier 

7. Fixed to concrete slab 8. Fixing to wall head 

9. Fixing to timber spacer 

10. Fixing at perimeter 

Partitions and wall heads 

If possible, Rocksilk Smoke and Fire Barrier 

should be secured with steel strip to the partition 

or wall head so as to maintain the 50mm air 

space (Figure 8). If this is not possible, it should 

be draped with a return of at least 150mm, or 

fixed to a timber spacer which is fixed to the 

partition or wall head (Figures 6 and 9). 

Perimeter fixing 


secured with steel strip to the sides of the 

perimeter wall, so as to maintain the 50mm air 

space (Figure 10). 

Fixing system specifications 

Table 3 - Specification of angles and strips 

Angle: Mild steel - 50mm x 50mm x 2mm or 60mm x 40mm x 2mm 

Strip: Mild steel - 40mm x 2mm 

Angle fixings to concrete decks and steel sections: angles 50 x 50 x 2mm 

Fire resistance 

Maximum spacing of fixings (m) for the following drop heights (m) 

period (mins) 3 3.5 4 4.5 5 5.5 6 6.5 7 

30 2 2 2 2 2 2 2 2 2 

60 2 2 1.75 1.5 1.5 1 1 0.75 0.75 

Key: 

M8 M6 

bolts bolts 

Angle fixings to timber beams and trusses: angles 50 x 50 x 2mm 

Fire resistance Maximum spacing of fixings (m) for the following drop heights (m) 

period (mins) 3 3.5 4 4.5 5 5.5 6 6.5 7 

30 2 2 2 2 2 2 2 2 2 

60 2 2 1.75 1.5 1.5 1 1 0.75 0.75 

Key: 

Buildex HT screws, minimum 25mm thread penetration into timber 

Buildex HT screws, minimum 40mm thread penetration into timber 

Steel strip fixings: To masonry and concrete Buildex Tapcon 4H masonry anchors 

To timber 

Buildex HT range of fixings 

To steel angle 

Steel bolts 

6.1 

Minimum return of Rocksilk Smoke and Fire Barrier - When clamped to flat surface (vertical or horizontal) 

80mm. When loose laid over horizontal surface - 150mm. 



289

6.1 



Jointing Rocksilk Smoke and Fire barrier 

11. Junction with suspended ceiling 

12. Vertical butt joint 13. Vertical returned joint 14. Vertical lap joint 

500mm 

minimum 

overlap 

15. Perpendicular joint 16. Horizontal joint at a drop 

Suspended ceilings 

With suspended ceilings where positive fixing 

to wall heads or partition heads is not possible, 

the weight of Rocksilk Smoke and Fire Barrier 

and the stiffness of wire facing are such that it 

will form an effective seal if it laps the 

horizontal surface by a minimum of 150mm. 

Lapped joints are only permissible where the 

suspended ceiling has the same fire resistance 

as the cavity barrier. Rocksilk Smoke and Fire 

Barrier must be slit and fitted around any 

crossing tees to eliminate gaps and ensure that 

excessive loads are not transferred to the ceiling 

(Figure 11). 

Jointing 

This section describes the approved methods for 

joining adjacent pieces of Rocksilk Smoke and 

Fire Barrier. The methods are applicable to both 

half and one hour large cavity barriers. 

Vertical and horizontal joints 

Three methods of securing the joints between 

adjacent pieces of Rocksilk Smoke and Fire 

Barrier are approved. 

Joints are tightly butted together and stitched in 

a continuous spiral loop with 1mm diameter 

galvanised lacing wire. The stitching should 

pass through the reinforcement mesh and the 

wool on each side of the butt joint at centres not 

exceeding 100mm (Figure 12). 

Alternatively the Rocksilk Smoke and Fire 

Barrier edges are returned at least 80mm and 

wired together (Figure 13), or they may be 

lapped at least 100mm and wired together 

(Figure 14). 

Perpendicular joints 

The junction between two barriers should be 

securely wired together (Figure 15) with a 

return of at least 80mm. 

Drops 

All barriers can be used for drop heights up to 

5m without additional support. For drops 

between 5m and 7m it is necessary to introduce 

additional supporting members in order to 

support the weight of the fire barriers (Figure 

16). 

Services 

Services which are permitted by Building 

Regulations to penetrate barriers, should 

be provided with collars of Rocksilk Smoke and 

Fire Barrier at least 300mm long, sewn to the 

main barrier and then strapped or wired so as 

to avoid any possibility of gaps (Figure 17). 

A half hour barrier requires a collar on 

one side of the barrier. A one hour barrier 

requires one collar on both sides of the barrier 

system. 

290 





Penetrating pipes and ducts 

300mm 

minimum 

17. Penetrating pipe 

18. Penetrating steelwork 

19. Temporary framework to ease handling 

Penetrating steelwork 

Handling 

Following trades 

This should be provided with a collar of Rocksilk 

Smoke and Fire Barrier at least 300mm long 

Depending on the size of the barrier and the 

working space available, it is sometimes difficult 

The integrity of barriers must be restored if 

disturbed by following trades, either during 

6.1 

(Figure 18). The collar is fixed to the concrete or 

to hold the material in place while top fixings 

the building process or after completion. 

metal deck by clamping against these surfaces 

are being secured. It will be found helpful to 

This instruction should be incorporated into 

behind steel angle. The voids in the steelwork 

make a temporary prop from, e.g. slotted 

the building handbook. 

are filled with Rocksilk Smoke and Fire Barrier 

angle. This may comprise a crosspiece of length 

(figure 18). A half hour barrier requires a collar 

appropriate to the width of the Rocksilk Smoke 

on one side of the barrier. A one hour barrier 

and Fire Barrier, with studs on the top which will 

requires one collar on both of the layers of the 

hook into the wire mesh of the Rocksilk Smoke 

barrier system. 

and Fire Barrier. This may be swivelled on the 

Access 

Where permanent access is needed through the 

barrier, a fire door and frame, rated to the 

appropriate fire resistance, must be used. 

Rocksilk Smoke and Fire Barrier should be fixed 

securely to the frame. 

top of a handle, and secured horizontally or to 

the angle of the roof by an adjustable brace. It 

is used to hold the Rocksilk Smoke and Fire 

Barrier up, 100mm or so behind the fixing 

location, while fixing is being carried out. 

When fixing to a sloping deck, the top of the 


trimmed to the correct angle to ensure that joints 

are truly vertical (Figure 19). 



291

6.1 


Internal floor 

Refurbishment of timber separating/internal floor 

Earthwool Flexible Slab 

• Existing ceiling can be 

retained, avoiding disruption 

to rooms below 

• Provides thermal and acoustic 

insulation as well as fire 

resistance 

• 

Meets the requirements of 

Approved Document E for sound 

resistance of internal floors 

Fp06 

REFURB 




• A+ Generic BRE Green Guide rating 



Support mesh 

stapled to joists 

Existing ceiling 


Minimum 18mm Chipboard 

Products 

Earthwool Flexible Slab is a multi-purpose rock 

mineral wool slab designed to be friction fitted 

in a wide range of acoustic, thermal and fire 

resistant applications. 

Introduction 

Where the loft space of a two storey house is 

converted into habitable accommodation, the 

floor to the new rooms must have 30 minutes 

fire resistance over any part of the escape route 

directly below. This is often the case when, for 

example, the floor of the new room extends 

over a landing in the stairway enclosure below. 

The solution on this page provides the required 

period of fire protection without having to 

upgrade the existing ceiling. 


The use of Earthwool Flexible Slab in a 

suspended timber floor achieves one hour fire 

resistance, whilst allowing the existing ceiling to 

be retained. 

To achieve one hours fire resistance: 

• The floor deck should be at least 18mm thick 

tongued and grooved chipboard or timber 

boarding 

• The joists must be at least 200mm deep and 

37mm wide 

• The wire mesh should be stapled to the sides 

of the joists at least 40mm above the ceiling 

level 

• Any ceiling can be used 

Installation 

After removal of the floor deck, line the voids in 

the floor with 25mm wire mesh, to form a 

support tray for the insulation. Staple the wire 

mesh to the sides of the joists, at least 40mm up 

from ceiling level. 

Cut 100mm Earthwool Flexible Slabs to size 

and lay onto the wire mesh support, so that 

there are no gaps between the insulation and 

the joists. Butt joint the insulation slabs so there 

are no gaps between them. 

Fix a chipboard floor deck, at least 18mm thick, 

over the entire floor area. 

292 




Typical wall floor junction 

Existing wall 

Earthwool Flexible Slab cut and friction 

fitted between last joist and wall 

Minimum 18mm chipboard 


Lay 100mm Earthwool Flexible Slab on 

25mm chicken wire mesh, stapled to sides of 

joists at least 40mm up from ceiling level and 

at 600mm centres. The joists should be at 

least 200 x 37mm and spaced at not more 

than 600mm centres. The flooring board to 

be at least 18mm thick. 




P10/250…………… 



Earthwool 

Flexible Slab 

Wire mesh stapled to joists to provide 

support for Earthwool Flexible Slab 

Existing ceiling 

Performance 


Earthwool Flexible Slab is classified as 

Euroclass A1 to BS EN 13501-1 and noncombustible 

to BS 476: Part 4: 1970 

(1984), Class 1 Surface Spread of Flame to BS 

476: Part 7: 1997 and Class ‘0’ to the Building 

Regulations. 

Acoustic 

The acoustic performance of an internal floor 

containing 100mm of Earthwool Flexible Slab 

(and 12.50mm standard plasterboard ceiling) 

will be at least 40dB and therefore, meet the 

requirements of Approved Document E of the 

Building Regulations. 

6.1 



293

6.1 




Rocksilk Pyroduct Slab 

• Lightweight, mineral wool has 

approximately one half to one third of 

Fp07 

Blockwork compartment 

wall 

NEW BUILD 

REFURB 

the weight of traditional silicate and 

vermiculite boards 

• Fast and simple fixing system makes the 

slabs quick and easy to install 

• Provides excellent acoustic and thermal 

performance insulation 

Rocksilk Pyroduct Slab 





RS33 Slab as packing 

Steel angle rivetted at 150mm centres 

Rocksilk Pyroduct fixed to duct 

Rocksilk Pyroduct glued to wall and insulation 

Product 

Rocksilk PyroDuct Slab is a 160 kg/m 3 density 

rock mineral wool slab. The slabs are faced 

with a bright Class ‘O’ reinforced aluminium 

foil, making it suitable for applications above 

clean rooms, within air plenums or for aesthetic 

purposes. 


The exposed surfaces of steel ductwork are fully 

enclosed in Rocksilk PyroDuct Slab using the 

fixing system shown on the following pages. 

Rocksilk PyroDuct Slab can be used to provide 

up to 2 hours fire protection to steel ductwork. 

Installation 

Rocksilk PyroDuct Slab is applied in a single 

thickness, removing the need for multi layer 

applications. This provides assurance of a 

uniform thickness and therefore the integrity of 

the system and allows for easy verification of 

correct installation on site. 

Individual slabs are 1200mm long and 600mm 

wide making them easy to carry around site. 

Their lightweight nature also makes them easy 

to use.The fixing system of welded pins and 

square edge butt joints gives a fast and simple 

system which requires no special vee cuts, 

drilling or sub-frames and also makes the slabs 

fast and easy to install. 

Performance 

Fire 

Rocksilk PyroDuct Slab is classified as 

non-combustible to BS 476: Part 4: 1970 

(1984), Class 1 surface spread of flame to BS 

476: Part 7:1997 and Class ‘O’ to the Building 

Regulations. 

Rocksilk PyroDuct Slab has been tested in 

accordance with BS 476: 24:1987 and can 

provide up to two hours fire resistance for steel 

ductwork exposed to fire either inside or outside 

of the duct. 

Moisture resistance 

Rocksilk PyroDuct Slab is non-wicking when 

tested to BS 2972: 1989: Section 12. When 

exposed to 90% relative humidity and 20ºC, 

Rocksilk PyroDuct Slab absorbs less than 

0.004% of moisture. 

294 





Rocksilk PyroDuct Slab...........mm thick to be 

used to provide up to 2 hours fire protection 

to steel ductwork as detailed in this schedule 

(specifier to state which ducts require fire 

protection). 

It is to be installed using the fixing system as 

detailed, and at a thickness with due regard 

to the duct size, orientation and period of fire 

protection required. 

Foil facing omitted for clarity 

Table 4 - Required thickness of Rocksilk PyroDuct Slab 

Period of fire 

resistance (hours) 

Thickness of insulation (mm) 

Vertical ducts Horizontal ducts Kitchen extract 

ducts 

0.5 - - 45 

1.0 45 45 90 

2.0 90 90 - 

Table 5 - Weight of slabs 

Thickness 

(mm) 

Weight 

(kg/m 2 ) 

45 7.20 

90 14.40 

Weight 

Table 5 shows the weight per square metre of 

Rocksilk PyroDuct Slab. 


Any vertical or horizontal, rectangular or 

square steel ductwork associated with 

ventilation and/or air conditioning systems, 

including ducted supply and extract systems 

(whether through ducts or plenums), 

mechanically assisted systems and those 

relying on natural convection can be 

protected with Rocksilk PyroDuct Slabs to 

provide the required degree of fire protection. 

Achieving the required fire 

performance 

The required thickness of Rocksilk PyroDuct 

Slab depends upon the orientation of the duct 

and the period of fire resistance required. 

Table 4 displays the thicknesses required for 

vertical and horizontal ducts and also for 

kitchen extract ducts for the commonest 

periods of fire resistance. 

6.1 



295

6.1 



350mm 


350mm 

350mm 

50mm 

500mm 

max 

350mm 

Greater 

than 

1000mm 

50mm 

500mm 

max 

350mm 

X 

Greater 

than 

1000mm 

1. Weld 3mm diameter steel pins at 350mm longitudinal centres 

along the centre line of the vertical sides of the ductwork. 

2. Where the dimension of the vertical sides Y exceed 1000mm, 

the steel pins should be in rows starting 50mm in from the edge 

and spaced apart at a maximum of 500mm centres. 

50mm 

350mm 

Greater 

than 

1000mm 

X 

500mm 

max 

Y 

X 

350mm 

500mm 

max 

Y 

50mm 

350mm 

500mm 

max 

50mm 

3. Weld 3mm diameter steel pins at 350mm longitudinal centres 

along the horizontal surfaces of the ductwork in rows starting 

50mm in from the longitudinal edge and spaced apart at a 

maximum of 500mm centres. 

4. Cut Rocksilk PyroDuct Slab to size as follows: 

horizontal surfaces to dimension X, 

vertical surfaces to dimension Y + 2t, 

where t = thickness of insulation. 

500mm 

max 

350mm 

50mm 

6 

7 

8 

5. Attach the insulation by impaling over the welded pins and 

securing with 38mm spring steel washers. 

6. Glue all board to board joints using a thixotropic silicate 

based adhesive. 

7. Trim off pin lengths to about 30mm excess and bend this 

excess to form a right angle with the insulation. 

8. Although not essential, it is good practice to offset the joints 

for each surface. 

296 






– 

Vertical ducts 

The installation detail on the previous pages for horizontal ducts is 

also relevant for vertical ductwork, though the horizontal and vertical 

surfaces referred to for horizontal ductwork will be the longest and 

shortest surfaces respectively in vertical ductwork. 

Ductwork passing through compartment 

walls or floors 

In accordance with The Building Regulations, when ductwork passes 

through any element of construction which has a designated period 

of fire resistance, the integrity of that compartment should be 

maintained. In these situations, the ductwork in the immediate vicinity 

of the penetration should be stiffened as follows: 

a) When the flange is within 100mm of the penetration then a 

50 x 50 x 3mm steel angle should be rivetted to the top edge 

of the duct using a single row of rivets with washers starting 

50mm from the edge and at 150mm centres. 

Earthwool Building Slab RS33 should be used to pack any gap 

between the main insulation and the blockwork. 

120 x 90mm sections of Rocksilk Pyroduct Slab is glued to the 

wall and main Pyroduct insulation. 

6.1 

b) When the flange is greater than 100mm from the penetration, 

two angles should be used, fixed as described in a) above, and 

45mm Rocksilk Pyroduct Slab installed perpendicular to the duct 

at the penetration. 



297

Knauf Insulation Ltd Customer Service (Sales) Technical Advice and Support Centre Literature 

PO Box 10 Tel: 0844 800 0135 Tel: 01744 766 666 Tel: 08700 668 660 

Stafford Road Fax: 01744 612007 Fax: 01744 766 667 Fax: 0870 400 5797 

St Helens Email: sales.uk@knaufinsulation.com Email: technical.uk@knaufinsulation.com Email: info.uk@knaufinsulation.com 

Merseyside 


WA10 3NS

Fire Protection - Knauf Insulation

Create successful ePaper yourself

Delete template?

Save as template?