guide to specification - Reid Construction Systems

www.flexus.co.nz 

guide to specification 

modular flooring system 

innovative | flexible | versatile | superior | flexus

Ryman Health - Gisborne 

Contents 


Introduction 4 

ECC 4 

Pryda Truss Systems 6 

Pryda Span Trusses 6 

Pryda Longreach 7 

Other Joists 7 

S1: Compliance with the New Zealand Building Code (NZBC) 8 

S2: Acoustics 8 

S3: Fire Rating 9 

S4: Flexus Design Considerations 10 

4.1 Factors Affecting Floor Performance 10 

4.2 Span Tables 11 

4.3 Floor Diaphragm Action 12 

4.4 Components 12 

4.5 Materials 12 

4.6 Accessories - Installation 13 

4.7 Conditions 13 

S5: Internal Walls 14 

S6: External Walls 14 

S7: Pryda Truss Design Considerations 15 

S8: Support and Connection Details 16 

S8(a): End Support Details - Diagrams 16 

S8(a): End Support Details – Fixings Notes 17 

S8(b):Edge Connection Details 18 

S9: Stability Bracing 18 

S10 Design Request Form 19 

3

4 

Introduction 

The Flexus Modular Flooring system are prefabricated 

modules comprising of a 30mm thick Flexus ECC 

(Engineered Cementitious Composite layer supported on a 

Pryda Truss (either PrydaSpan or Longreach Truss system) 

or LVL Joist system. 

The patented system forms a sub or mid-floor for typical 

structures such as timber, steel, concrete, masonry or brick 

and is suitable for use in: 

• Light Commercial Buildings 

• Low-rise Construction 

• Apartments 

• Residential Housing 

• Pre-fabricated Buildings 

The Flexus Modular Flooring system can be used 

on either new buildings or retrofit interior and exterior 

situations. 

Flexus Modular Floors are manufactured under strict 

quality control standards by approved fabricators. 

ECC 

Flexus is an engineered cementatious composite 

(ECC) material that has unique properties unlike other 

cement / sand products. 

It has a high compressive strength (like concrete) and 

features a tensile strength much higher that concrete. 

When the nominal tensile strength of Flexus ECC 

material is exceeded, it micro-cracks and gains 

in strength as more load is applied. Unreinforced 

concrete and timber, in comparison, cracks and gives 

way suddenly. ECC exhibits ductility more like steel; 

providing a safer more appropriate structural material 

that is ideal for the Flexus Modular Floor. 

The fine materials allow an F5 smooth finish to be 

formed from a steel casting bed on the top surface. 

The 30mm thick ECC topping is attached to the 

supporting floor trusses or joists through regularly 

spaced Pryda connectors. 

Flexus test beam in deflection

6 

Pryda Truss Systems 

Pryda Floor Truss Systems are a complete structural 

system for timber floors made up of flooring material, 

floor trusses, strong-backs, connections and bracing. 

They have been proven for many years and provide 

occupiers with floors that have an excellent and 

predictably reliable performance. 

All trusses use commonly available timber and most 

floor trusses in New Zealand are made from 90mm 

Kiln Dry timber. 

There are two types of web systems for these trusses 

using timber chords. Pryda Longreach uses all timber 

webs, while Pryda Span uses metals webs for the 

diagonals and timber webs for the verticals. 

Both systems of Pryda Floor Trusses are generally 

made to order by licenced fabricators. While there are 

standard end details that allow trusses to be trimmed 

on-site, this practice is not common. This is not only 

because all trusses are designed for an exact span 

for economic reasons, but the interaction between 

the true span of the trusses and the flooring should 

be considered for proper dynamic performance 

assessment. 

Pryda Span Trusses 

Flexus Modular Floor 

Pryda Span trusses have metal diagonal webs for 

lighter weight and cost-effectiveness. They are ideal 

for shallower trusses where there is a need for more 

clearance room to accommodate services and for 

trusses where the chord design has some reserve 

capacity. In some instances, some diagonal metal 

webs may have to be replaced by timber webs as load 

or geometry considerations dictate. 

Webs may be on both sides of the truss, or just on 

alternate sides. In the latter case, this allows for the 

webs to overlap. 

Pryda Span trusses are referenced as PS25, PS30 

or PS40, where “PS” means Pryda Span, and “30” 

is the nominal overall depth (cm). The overall depths 

are in specific steps, but are actually 260mm, 310mm 

and 420mm (note - the 30mm ECC topping must be 

added to give overall floor module depth).

Pryda Longreach 

As the name suggests Pryda Longreach trusses are 

suitable for longer spans. Overall truss depth may 

increase depending on the span and performance 

required. Longreach trusses also have open webs 

allowing easy installation of services. 

Flexus Modular Floor manufactured with LVL for a sub floor. 

Other Timber Joist Systems 

LVL Joists 

Flexus is suitable for use with a LVL joist system. New 

Zealand’s major LVL suppliers provide joist design 

software suitable for residential situations and a design 

service for specific design. 

Solid Timber Joists 

If preferred, Flexus Floor Modules can be designed to 

use solid timber joists. For design information contact 

Reids Engineering Design office. 

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8 

S1: Compliance with the New Zealand Building Code (NZBC) 

If designed, used, installed and maintained in accordance with statements and conditions contained in this 

document, the Flexus Modular Flooring System will meet the following provisions of the New Zealand Building 

Code. 

Clause B1 – Structure : Performance B1.3.1, and B1.3.2. The Flexus Modular Flooring System meets 

requirements for loads arising from self-weight and impact (i.e. B1.3.3 (a), (b) and (j). 

Clause B2 Durability : Performance B2.3.1 (a) not less than 50 years. 

Clause C3 Spread of Fire: Performance C3.3.1. 

Clause F2 Hazardous Building Materials: Performance F2.3.1. 

Clause G6 Airbourne and Impact Sound : Performance G6.3.1 and G6.3.2. 

S2: Acoustics 

For inter-tenancy applications the Flexus Modular Flooring System achieves an STC of 57 and IIC of 81. A full 

acoustic report compiled by an independent acoustic consultant is available at www.flexus.co.nz. 

In summary, performance requirements of the NZ Building Code are: 

Clause G6 Airbourne and Impact Sound : 

Performance 

G6.3.1 The Sound Transmission Class of walls, floors and ceilings, shall be no less than 55. (STC 55) 

G6.3.2 The Impact Insulation Class of floors shall be no less than 55. (IIC 55) 

TABLE 1. 

Construction Test 

(Airborne/Impact) 

30mm ECC floor; m x 260mm timber trusses; 

Pink Batts; 13mm Gib Noiseline with rubber isolation clips 

STC 

Performance 

Airbourne STC55 

Table 1 : Flexus Composite Modular Flooring System Laboratory Test Results - STC 

The results of the Flexus Floor System Acoustic Airborne testing demonstrates that; “30mm ECC floor, 90mm 

x 260mm timber trusses, Pink Batts, 1 Layer of 13mm Gib Noiseline with rubber isolation clips” complies with 

G6.3.1.” N.B. 20mm particle Board requires 2 layers 13mm Noiseline. 

TABLE 2. 

Floor Covering Test 

(Airborne/Impact) 

IIC 

Performance 

Loop Pile carpet with underlay Airbourne IIC 81 

Table 2 : Flexus Modular Flooring System Laboratory Test Results - IIC 

The results of the Flexus Flooring System Acoustic Impact testing demonstrates that; “30mm ECC floor plus Floor 

covering of Loop Pile carpet and underlay complies with G6.3.2.”

S3: Fire Rating 

The Flexus Modular Flooring System comprises of two 

main elements, a support structure and a floor topping. 

The support structure is either a timber or steel joist or 

timber truss layout as per a normal built up floor. 

The plywood or particle board sheet flooring of a built 

up floor is replaced by a monolithic cementatious floor 

sheet (Flexus material) that spans the length of the 

joists and up to 2400mm in width. 

The whole of the Flexus floor sheet (span x width) is 

made as a module complete with the supporting truss 

or joist system in a factory environment and delivered to 

site ready for installation. 

Once the Flexus flooring modules are in place and 

secured, services can be run through the floor space 

and a ceiling installed to the underside of the modules. 

For fire rating we follow the recommendations of the 

Winstone Wallboards Ltd publication Gib® Fire Rated 

Systems for fire rated floor/ceiling systems and any 

specific recommendations from the joist/truss supplier/ 

manufacturer. 

Gib® fire rated systems use a 20mm particle board 

floor or a 17mm plywood floor as a minimum. 

The Flexus floor sheet is a non combustible 

cementitious material 30mm thick. By common 

engineering knowledge of materials, Flexus has a 

superior fire resistance than the wood based thinner 

materials used for the Gib® fire rating. Therefore, Reid 

are comfortable using in accordance for the situation, 

the fire ratings for Gib® board ceilings as per the Gib® 

Fire Rated Systems publication for Flexus flooring 

modules until specific fire tests are completed. 

Flexus Modular Flooring System can be used to 

provide passive fire protection in accordance with the 

requirements of NZBC Clause C3 – Spread of Fire. 

In order to satisfy the requirements of NZBC Clause C4 

– Structural Stability during Fire, designers must ensure 

that fire rated elements are supported by elements 

having at least the same Fire Resistance Rating (FRR). 

Collapse of elements having a lesser FRR shall not 

cause the consequential collapse of elements required 

to have a higher FRR. 

Underneath a Flexus Floor with open webs 

9

10 

S4: Flexus Design Considerations 

The Flexus Modular Flooring System has been designed for use with Pryda Span Floor Trusses. For spans outside 

of the following tables and construction using steel or laminated timber joists, please use the free engineering 

advisory service available to our clients to assist with your specification. 

For further detailing, CAD drawings and specification, please refer to www.flexus.co.nz or call us on 0800 88 22 12. 

Flexural Stress First Cracking >5MPa 

Flexural Stress First Ultimate >8MPa 

Compressive Strength (f’c) >40mpa at 28days 

Crack width at Ultimate Flexural Strength 15GPa 

4.1.1 Factors Affecting Floor Performance 

Floor liveliness, or bounce, has been an intermittent issue over the years with lightweight residential floors – for all 

forms of timber and steel construction. To eliminate these problems, Pryda Floor Systems are designed to stringent 

dynamic performance criteria. 

Pryda Floor Systems have three options for floor performance that can be selected by the designer; 

• AS/NZS 1170: 2002 as the minimum criteria. 

• “Pryda Build” truss design software design option of “normal” is more stringent 

• “Pryda Build” truss design software design option of “Enhanced” is used for those who want a superior performance 

overall. 

The floor truss is only one component that can affect the floor performance. The engineer should also consider the 

vibration performance of the supporting structure. On-site conditions are always important and proper attention to 

detail must be taken at the time of installation. 

Flooring Material 

The flooring material has a significant effect on the perceived bounce of a floor. It has the ability to spread human 

impact loads depending on the material and the thickness. Plywood acts differently to particle board, and T&G acts 

differently to both. A simple way to improve floor performance is to select flooring that is stiffer (e.g. thicker) than the 

minimum for your chosen application.

S4.2 Span Tables 

Residential Application 

Floor Load = 1.5kPa / 1.8kN Dead Load = allow 0.8kPa 

30mm Flexus Modular Floor and MSG12 Timber 

Module o/a depth (mm) Truss Type / 

Spacing 

Truss Spacing Maximum Span (mm) 

290 PrydaSpan PS25 up to 600 crs 4800 



290 Longreach up to 600 crs 4800 









Commercial Application 

Floor Load = 3.0kPa / 2.7kN Dead Load = allow 0.8kPa 

30mm Flexus Modular Floor and MSG12 Timber 

Module o/a depth (mm) Truss Type / 

Spacing 

Truss Spacing Maximum Span (mm) 




380 PrydaSpan PS25* up to 400 crs 6200 



600 Longreach* up to 400 crs 8500 

630 Longreach* up to 400 crs 8800 

*90mm x 90mm MSG12 Chords 

Notes: The span tables above are a guide only and all Flexus Modular Flooring designs must be checked 

by our Authorised Manufacturer or Reid’s engineering team. Module widths may need to be adjusted to 

keep module weight within lifting or site constraints. 

11

12 

S4.3 Floor Diaphragm Action 

Flexus Floor Modules can be used for diaphragm action to transfer loads to boundary shear walls. Specific 

information is required for detailing module connections to suit the application. 

This information from the engineer must include location of shear walls in relation to floor diaphragm support 

structure and predicted shear flows in kN/m. 

S4.3.1 Information required by fabricator for Flexus Floor design 

• Detailed plans with dimensions of Flexus Floor location. 

• Sections through support locations 

• Ceiling construction 

• Any super dead loads/live load 

• Any braced walls and concentrated loads to be carried by floor modules 

• Design shear flow in kN/m. 

S4.4 Components 

PrydaSpan or Longreach Timber truss designed by Pryda 

LVL or timber Joist LVL 

Flexus ECC topping 

Pre-cast ECC 30mm in depth 

S4.5 Materials 

Timber : Longreach Webs MSG8, MSG10, MSG12 

Timber : LVL joist Refer supplier product data sheets 

Timber : solid timber joist MSG8, MSG10, MSG12 

Metal Webs : PrydaSpan Webs : PS25, PS30, TW16 

Metal Connectors : Pryda Claw Plates as specified in Truss design 

ECC : 30mm Flexus topping 

Casting Mix

S4.6 Accessories - Installation 

4.6.1 75mm and 90mm Timber Nails 

A number of 75mm and 90mm timber nails are 

required to provide adequate fixing between the timber 

floor trusses where the modules meet. These nails are 

required through the bottom chords. 

4.6.2 Metal tek Screws 

Metal Tek Screws are required if specified in any fixing 

details. 

4.6.3 Coach Bolts and Screws 

For applications where the Flexus Floor is required 

to be fixed to an I-Beam, timber packers are required 

within the I-Beam flanges. Coach Screws and Bolts 

can be specified as the fixing method for the stringer 

on the module into the timber packers. 

4.6.4 Metal Timber Connectors 

For timber to timber or concrete connections use Pryda 

Knuckle Nailplates, Multigrips, Sheet Brace Straps, 

Joist Hanger, Tim-Con Brackets, Framing Bracket, 

Concealed Purlin Cleats as specified. 

4.6.5 Reid 2FA170 Swiftlift Anchor 

For shear connection of Flexus Modular floor. 

4.6.6 Non-shrink grout 

Ramset Premium Grout MP for jointing modules if 

required. 

S4.7 Conditions 

4.7.1 Moisture Content 

Maximum moisture content of timber framing to 

NZS 3602. 

4.7.2 Building 

Ensure foundations or wall frames are constructed in 

accordance with NZS3604. 

4.7.3 Storage 

Timber expands in thickness and depth when allowed 

to get wet. 

To ensure the Flexus Floor Modules stay dry, straight 

and true at the time of installation, the following 

recommendations regarding storage are made : 

• Stack on evenly spaced level bearers to keep flat 

and straight. 

• Provide a surface for the materials to be placed on 

that is in plane. 

• Stack well clear of the ground for good ventilation. 

• Store under cover to keep dry prior to installation. 

4.7.4 Handling 

• Handle with extreme care. Protect edges, 

corners, truss and surface finish from damage. 

• A crane or Hiab is required for the placement 

of modules – for example a 6mx2.4m Module 

weighs approx. 1.1 tonne. 

• Module weight = approx 82kg/m2 (based on 

module with overall depth of 450mm) 

• Specially Modified Reid Swiftlift Face Lifting 

anchors (installed into 30mm ECC topping) are 

used with a Reid Swiftlift Lifting Clutch to safely lift 

the Modules. 

• Standard Personal Safety Equipment applicable 

to the activity must be worn when handling 

Flexus Floor modules. Refer Department 

of Labour Health and Safety in Employment 

regulations and information. 

4.7.5 Substrate 

Do not commence work until the substrate is of the 

standard required by the relevant manufacturer’s 

technical literature for the specified finish; plumb, level 

and in true alignment. Maximum moisture content of 

timber framing to NZS 3602. 

Fastening the modules to the framing. 

13

S5: Internal Walls 

Internal Non-loadbearing Walls. 

The Flexus Modular Floor system requires no additional 

stiffening when supporting non-loadbearing walls. 

For situations where these walls act as wind bracing walls 

then consult the Reid Engineering Design office. 

Internal Loadbearing walls. 

If the Flexus Modular Flooring modules are going to be 

supporting Internal Loadbearing walls then consult the Reid 

Engineering Design office. Information on vertical and shear 

loads from these walls will be required. 

Non-Loadbearing Walls under. 

Floor trusses must be adequately supported on the 

loadbearing supports nominated in the design. There may 

be a detrimental effect on the walls and the flooring system 

if the trusses bear on a non-loadbearing wall. The tops of 

internal non-loadbearing walls need lateral stabilising by 

fixing to the truss bottom chords. The trusses must be 

allowed to deflect downwards. 

Loadbearing Walls under 

Should an internal wall be required to support floor trusses 

and/or behave as a shear wall to transfer diaphragm loads, 

this intention should be made abundantly clear on both the 

trusses and the truss layout. 

When the floor modules are designed, any internal 

loadbearing wall under has to be factored into the truss 

design. 

S6: External Walls 

External Loadbearing Walls. 

Where external loadbearing walls are being supported by 

the floor modules the floor detailer needs to be made aware 

of this so that additional roof and wind load can be factored 

into the floor truss design. 

14

S7: Pryda Truss Design Considerations 

Flexus Modular Flooring System has been designed for use with Pryda 

Span Floor Trusses. For spans outside of the tables provided and 

construction using steel or laminated timber joists, please use the free 

engineering advisory service available to our clients to assist with your 

specification. 

For further detailing, CAD drawings and specification, please refer to 

www.flexus.co.nz or call us on 0800 88 22 12. 

For information regarding : 

• Factors Affecting Floor Performance 

• Permanent Loads 

• Serviceability 

• Floor Openings 

• Ducts for Mechanical Services 

• Cantilevers 

• Strongbacks 

Refer to : 

“Pryda Floor Truss and Rafter Truss Systems : Guide to Specification” 

Available from www.pryda.co.nz or contact the Pryda Engineering Design 

Office on 0800 88 22 44. 

15

16 

S8: Support and Connection Details 

S8(a): End Support Details - Diagrams 

The following is a sample of “typical” end support details for Flexus Modular Floor units using PrydaSpan 

trusses. End support details for other Module types are available upon request.

S8(a): End Support Details – Fixings Notes 

Fixing Notes 

Unless specified otherwise fixings shall be as follows: 

(A) - When supporting trusses via Bottom chords 

each Truss Bottom Chord shall be held onto its 

supporting plate/bearer by a minimum of 2/75 x 3.15 

mm dia. nails. If preferred, a better fixing may be 

achieved by using on Pryda Multigrip Long with 3/35 

x 3.15mm dia. Pryda nails per tab. 

(B) PrydaSpan truss boundary stringer to; 

a) stringer attached to supporting steel beam or 

b) continuous timber bearer fix using a minimum 90 x 

M8 Coach Screw @ 500mm centres. 

(C) Upper wall Bottom Plate (BPL) to PrydaSpan truss 

Top Chord (TC) - use 1/100mm washered Drive Pin 

@ 600mm centres. 

(D) For continuous floor over load bearing wall - 

stringer to stringer - use minimum 90 x M8 Coach 

Screw @ 500mm centres between edge truss or joist 

and top chord of adjoining truss. 

(E) Module to Module Edge Fixing - use minimum 90 

x M8 coach Screw @ 500mm centres between edge 

truss or joist and top chord of adjoining truss. 

(F) Fixing for diaphragm action not included. 

Diaphragm action fixings and details need to be 

specifically designed. 

“Fixings Notes” above are for Residential Application i.e. Floor Load = 1.5kPa / 1.8kN). 

For other applications contact the “Reid Construction Systems” Engineering Design office on 0800 88 22 12. 

17

18 

S8(b):Edge Connection Details 

Adjoining Flexus Modular Floor units should be connected together – ideally Top Chord to Top Chord. 

For other floor loadings contact the Reid Construction Systems Engineering Design office on 0800 88 22 12. 

S9: Stability Bracing 

“Stability Bracing” shown above is for Residential Application i.e. Floor Load = 1.5kPa / 1.8kN). 

For other applications contact the “Reid Construction Systems” Engineering Design office on 0800 88 22 12.

S10: Flexus Modular Flooring – Design Request Form 

Project Description: 

Project Address: 

Client: PH: 

Builder: PH: 

Architect: PH: 

Engineer: PH: 

Information Required 

Project covered by NZS3604 – refer NZS3604 Table 1.1 Y / N 

What are Imposed Floor Live Loads - refer NZS3604 Table 1.2 ? 1.5 / 2.0 / 3.0 kPa 

Are Floor Load Areas Identified on plans supplied ? Y / N 

Project SED (Specific Engineering Design) 

What are Imposed Floor Live Loads - refer AS/NZS1170 Table 3.1 ? 

Y / N 

UDL ? ( ) 

Point Load ? ( ) 

Are Engineer’s plans supplied ? Y / N 

Are Floor Load Areas Identified on plans supplied ? 

Does the floor area contain a Diaphragm ? 

Y / N 

If Y- is area identified on plans supplied ? Y / N 

If Y – what is shear flow value ? Y / N 

Are shear walls identified on plans supplied ? ( )kN/m 

If Y - then shear blocks must be included in module design 

If Y – contact Reid’s Engineering Design office 

Y / N 

Additional Ceiling Loads e.g. services, bulkheads ? Y / N 

Do module joins need to be grouted for Fire Rating ? Y / N 

PS1 compiled (Pryda and Reid) and passed to owner ? Y / N 

19

Recently Finished Projects 

Middlemore Hospital 

Ryman Health - Gisborne REX Apartments 

Flexus is a brand marketed by Reid Construction Systems. 

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Flexus Modular Floor Authorised Manufacturer: 

Version 5 May 2012. All information is © Reid Construction Systems, a division of ITW New Zealand Ltd. All rights reserved. Moral rights asserted. 

Reid reserves the right to change information without notification. For current information, please refer to www.flexus.co.nz. 

20

guide to specification - Reid Construction Systems

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