Addendum to the self laying of water mains - Severn Trent Water

Addendum to the self laying 

of water mains and services 

guidance notes 

Introduction 

Severn Trent Water Ltd (STW) is committed to the provision of cost effective self lay mains and 

services to Developers and their self lay organisations whilst ensuring that the standards of the 

installation and water quality are not compromised. Consequently we require all self lay work to 

be carried out in accordance with the UK Water Industry Research (UKWIR) “Self Laying of Water 

Mains and Services, a Code of Practice for England & Wales 2nd Edition” (CoP) and its national 

addendum for the safe Control of Routine Mains Connections (CRMC) published by WRc Plc 

May 2009. This document is an addendum to the Code (‘the Addendum’) and all Developers/Self 

Lay Organisation (SLOs) must agree to the requirements set out in the Code and this Addendum 

prior to undertaking any self lay works. 

Section 1: Contact details 

Severn Trent Water Ltd 

New Connections 

PO Box 5311 

Coventry 

CV3 9FL 

Telephone: 0800 707 6600 

Email: newconnections.selflay@severntrent.co.uk 

Website: www.stwater.co.uk/newconnections 

Section 2: Supplementary clauses 

NOTE: the structure and numbering of these clauses corresponds to the structure and 

numbering of the CoP and CRMC 2009. 

Part 1 – General 

1.5 Competence of self lay organisations 

SLOs are required to have obtained membership of Lloyds Register Water Industry Registration 

Scheme (WIRS) and hold a current approval certificate granting at least partial accreditation 

before they are allowed to proceed with the design and/or construction of any new mains and 

service connections with STW’s operational area. 

1.11 Finances 

1. The Asset Payment is normally paid to the Developer; however this payment can be made to 

the SLO, on receipt of written authorisation from the Developer. 

8. Self laying of mains and services charges are detailed in our New Connections Charges leaflet 

(available on our website). 

Part 2 – Self lay procedures 

2.1 The procedure 

Application forms are available at both the enquiry and application stages. These are available by 

contacting our New Connections Department or are available on our website. 

Guidance notes 

GN5 1

2.1.3 Self lay levels of service 

The current levels of service can either be obtained from OFWAT’s website: www.ofwat.gov.uk or 

are included in the CoP. 

2.2 Initial enquiry 

Where the application is made on behalf of the Developer by the SLO, the Developer is required to 

provide written authorisation to STW that the SLO is acting as an agent on their behalf. The Developer 

will be required to agree in writing to STW’s terms together with the SLO. If the Developer requires 

the Asset Value payment to be made to the SLO, they must also confirm this in writing to STW. 

2.4 Construction stage 

2.4.1 Notification of start 

Before works start on site a pre-construction site meeting must be held between the Developer, 

his accredited SLO and an STW representative. 

The following actions are needed to organise this meeting: 

(i) a minimum of 15 working days notice (in writing) should be given of the proposed 

commencement of the works 

(ii) within the notification a date needs to be incorporated, giving at least five working days notice 

for the pre-construction meeting to take place. 

2.4.3.2 SLOs that have met the Lloyds WIRS requirements for this work are permitted to make 

routine in-line connections subject to the Code of Practice 2nd Edition national addendum for 

Safe Control of Routine Mains Connections. The criteria for routine in-line connections comprise: 

• to a newly laid main (either laid by STW as a spur off an existing main or by themselves or 

another SLO at the end of a previous phase of main laying) 

• to mains which are controlled by a valve or mains that can be squeezed off without affecting 

existing customers; and 

• where there is no interruption to supply to existing customers. 

2.4.4 Service pipe installation 

8. Whilst STW gives installers the flexibility to programme the timing of service connections to 

suit their own construction programme, the activity is subject to each job being performed in 

accordance with an approved programme. This is required to enable us to inspect the work 

when it is being performed. 

9. The programme of service connections must be provided to the STW representative at least 

five working days in advance of the work being performed and any changes to the programme 

must be notified to STW within 48 hours of the planned date. 

10. Where we arrange to inspect the work and find that the activity is not proceeding in 

accordance with the agreed programme, our abortive inspection charges will be recharged and 

the work will be subject to verification before being accepted. 

11. Self lay service connections, which should meet installation requirements specified in Table 

1 and Section 2.4.4. of the code contestable activities in the design and construction of water 

mains and services of the Code, are generally restricted to connections up to and including 

63mm nominal bore. 


GN5 2

12. Details of our requirements and procedures for connecting service pipes directly to existing off 

site mains adjacent to the new development are as published on our website. 

Part 3 – Design and construction guidance 

3.2 Design requirements 

3. Polyethylene should be the default material for all diameters up to 180mm nominal bore 

however, when ground conditions are not suitable for PE80/PE100 the following products are 

approved for use within STW’s operating area: Standard sizes we prefer are 63mm, 90mm, 

125mm, 180mm PE. All other varieties must have approval from STW. 

Mains up to 110mm diameter Puriton, Protectaline 

Mains 180mm diameter Protectaline 

Mains 100mm to 300mm diameter Ductile Iron 

3.4 Design guidance – general 

6. Recommendations for tree and surface planting: 

• Poplar and willow trees should not be planted within 10m of the water main 

• The following trees should not be planted within 6m of the pipeline – ash, beech, birch, 

most conifers, elm, horse chestnut, lime, oak, sycamore, apple and pear 

• No shrubs or bushes should be planted within 1m of the centre line of the pipeline 

• The following shallow rooted shrubs/bushes are suitable for screening purposes in close 

proximity to water mains – blackthorn, broom, cotoneaster, elder, hazel, laurel, privet, quickthorn, 

snowberry and most ornamental flowering shrubs. 

3.5 Design guidance – mains 

3.5.1 Mains design 

2. As a general guide, it should be possible to limit the loss of supply to about 50 properties when 

isolation valves are closed due to operational or emergency situations. 

3. Recommended valve location at road junctions where valves are required to be installed at 

road junctions, the diagram below shows the preferred locations for safer operation. 

Safer operation of valves at junctions 

Footway 

Carriageway 

Footway 

Carriageway 


Traditional 

Valve arrangement for 

valve positions 

safer operation 

GN5 

Not preferred 

Preferred 

3

Valve operation – closing direction of values by STW district 

1 

Shropshire 

and Montgomeryshire 

2 

East 

Shropshire 

15 

Staffordshire 

3 

6 

Worcestershire 

South 

Staffs 

4 

7 

Gloucestershire 

13 

Derbyshire 

14 

Derby 

8 

Warwickshire 

1 West Shropshire and Montgomeryshire Clockwise 

2 East Shropshire Anticlockwise 

3 Wolverhampton Anticlockwise 

4 Birmingham Anticlockwise 

6 Worcestershire Anticlockwise 

7 Gloucestershire Anticlockwise 

8 South Warwickshire Clockwise 

9 Coventry & North Warwickshire Clockwise 

10 Leicestershire Clockwise 

11 Nottinghamshire Anticlockwise 

12 Sherwood Anticlockwise 

13 North Derbyshire Clockwise 

14 Derby Clockwise 

15 Staffordshire Anticlockwise 

12 

Sherwood 

11 

Nottinghamshire 

10 

Leicestershire 


GN5 4 

9

4. Fire hydrants – the types of fitting shall be loose jumper. In built up areas marker posts will only 

be provided where requested by the fire service. 

5. Pressures within the distribution system are maintained as low as possible but should provide 

a minimum pressure of 20m head at the outlet of the stop tap on the boundary for all services. 

6. Maximum flow velocity should be 1m/sec. Minimum velocity should be 0.2m/sec achieved at 

least twice per 24 hour period (not withstanding pipe sizes). 

7. Connections should be designed so that once installed there is no need to disrupt the live 

system again in order to make the final piece through. Piece up lengths should be kept to less 

than 5m in length. 

3.5.2 Depth of cover 

1. All water mains are to be laid to a minimum cover (to finished ground surface) of 900mm. 

The maximum cover should not be greater than 1200mm. In addition: 

• Consideration should be given if mains will be subject to wheel and point loads and especially 

from construction traffic 

• In fields which are likely to be ploughed the minimum cover shall be 1200mm 

• Mains may be laid outside the above specified depths in exceptional circumstances 

(e.g. geological conditions or crossing of existing utilities) with the prior agreement, 

in writing, of STW. 

3.6 Design guidance – services 

3.6.1 Service design 

8. Under normal conditions blue MDPE pipework to BS 6572 shall be used. Where the ground 

is contaminated then metal sheathed MDPE should be used. This is standard MDPE pipe 

factory-sheathed with an aluminium barrier coating protected with an outer layer of blue MDPE 

incorporating 4 brown identification stripes. Various sizes are available between 25 – 110mm 

nominal bore inclusive. 

If copper tube is used as the alternative, it must be to BS 2871 Table Y for underground use 

and be factory coated with blue PE. The pipe must bear a BS Certification Mark which states 

that it has been effectively cleaned internally. 

3.6.3 Sizing of service pipes 

1. The head loss due to friction should not exceed 1m per 10m head at average flow. 

The minimum size for service pipes is 20mm nominal bore. 

3.6.4 Multiple service connections 

4. Where multiple connections (4 and above) are required, manifolds should be installed. 


GN5 5

3.6.5 Meter boxes 

1. All connections to new properties require a boundary box to be fitted, normally on the edge of 

the property boundary to control flows and enable a meter to be fitted. 

For apartments or flats where a single incoming service is provided into the building, internal 

meters shall be fitted to each property in accordance with STW metering specification. 

2. Boundary boxes/stop taps should be situated no more than 300mm from the footway 

boundary. Boundary boxes to comply with WIS 4-37-01 and shall be rigid Type R. The box 

shall provide continuously variable height adjustment up to 150mm. Boxes for installation in 

normal ground conditions shall be Class 2 and in contaminated ground shall be Class 1 sealed 

units with metal union connectors. 

3.7 Construction 

3.7.1 General 

8. Joints in PE pipes – The layout of the pipe system should be designed to minimise the number 

of joints. Butt fusion joints are the preferred method. Electrofusion joints shall only be designed 

into the pipework where site specific circumstances dictate that welding cannot be carried out 

outside the excavation. The design should allow for sufficient room to undertake the process. 

9. Joints in PE barrier pipes (Puriton, Protectaline) – All joints should utilise fluid compression 

fittings in accordance with the pipe manufacturer’s specification. 

10. When installing ductile iron fittings to PE mains, joints should be by stub flange thereby 

maintaining a fully end loaded system. 

3.7.4 Service connections to the water distribution system 

1. The service pipe should be laid at right angles to the main and ferrules. 

2. The minimum spacing between tappings should be 500mm apart. 

3. Service connections to Puriton or Protectaline mains shall only be made using the pipe 

manufacturers self tapping ferrules designed specifically for use with their own barrier pipe system. 

STW standard constructional details are shown on the following pages. 


GN5 6

Main laying typical details 

Sluice valve – installed with new PE: 

5mm to dust 

compacted 

stone backfill 

New PE 

main 

Cover & 

frame 

Sluice valve – installed with new DI: 

5mm to dust 

compacted 


New Dl 

main 

Conc. wall 

sections & 

base unit 

Stub flange 

Cover & 

frame 

Conc. wall 

sections & 

base unit 

Flange 

adapter 

200mm min 300mm max 

from ground level spindle head 

Sluice valve 

Electrofusion coupling 

Note in contaminated 

land where PE barrier 

pipe is laid joints should 

be made using fluid 

compression couplings 

200mm min 300mm max 

from GL to spindle head 

Sluice valve 

Not to scale 


GN5 7


Hydrant washout – installed with new PE: 

Cover & frame 

Cover & frame 

Cover & frame 

Conc. wall 

Conc. wall sections Conc. wall & 

sections base & 

sections unit & 

base unit 

base unit 

Stub flange 

Stub flange 

Stub flange 

5mm to dust compacted 

m to dust stone compacted 

5mm backfill to dust compacted 

ne backfill 


New PE main 

New PE main 

New PE main 

Hydrant washout – installed with new DI: 

Hydrant 

Hydrant 

Hydrant 

Double flanged pipe 



Electrofusion coupling 

Electrofusion Note coupling 

Electrofusion in contaminated coupling 

Note in contaminated 

land Note where in contaminated PE barrier 

land where pipe PE 

land is barrier 

where laid joints PE barrier should 

pipe is laid be joints 

pipe made should 

is laid using joints fluid should 

be made compression using fluid 

be made using couplings fluid 

compression couplings 

All flanged tee compression couplings 

All flanged tee 


Hydrant washout – installed with new PE 

Hydrant 

Hydrant 

washout 

washout 

– installed 

– installed 

with new 

with 

PE 

new PE 

Cover & frame 

Cover & frame 

Cover & frame 

Conc. wall 

Conc. wall sections Conc. wall & 

sections base & 

sections unit & 

base unit 

base unit 

Flange adapter 



New DI main 

New DI main 

New DI main 

Hydrant 

Hydrant 

Hydrant 

NOTE 

NOTE Hydra NOTE n t outle t to be 

Hydra n t outle 200mm t to 

Hydra n min be 

t outle 300mm t to be max 

200mm min from 300mm 

200mm ground max 

min l e 300mm vel max 

from ground l e vel 

from ground l e vel 




5mm to dust compacted 

5mm to dust stone compacted 

5mm backfill to dust compacted 






Hydrant washout – installed with new DI 

Hydrant 

Hydrant 

washout 

washout 

– installed 

– installed 

with new 

with 

DI 

new DI 



GN5 8


End hydrant/washout general arrangement for use on self lay/multi utility sites: 

n 

i 

a 

m 

o 

t 

r 

e 

v 

o 

c 

0 

0 

9 

300 max 

200 

min 

Cover cap over outlet: 

white = loose jumper 

Gun metal not 

plastic or nylon 

400 

Please note the critical dimension of 

300mm from inside face of chamber to 

the centre of the hydrant outlet to allow 

clear access for fitting of standpipe. 

300 

Frame to sit firmly on top 

wall section without shims 


GN5 9 

400 

430 x 280 x 100 deep 

or 75 deep, as required, 

precast concrete chamber 

wall sections 

430 x 280 x 75 deep 

precast concrete chamber 

base section 

Well compacted 

type 1 Stone 5mm 

to dust 

380 x 230 x 125 deep surface box – 

heavy duty grade A. with lid lettered: 

“FH” or “Fire Hydrant” or 

“WO” or “Washout” 

F H 

Not to scale


Marker post and plate details for use on self lay/multi utility sites: 

150 

3 H 

H150 

150 

SV 

3 

Marker post & plate for 

hydrant washout, sluice valve 

3 

150 

WO 

3 

150 

AV 

3 

Marker post 

for field boundary 


GN5 10 

W W 

A A 

T T 

E E 

R R 

Not to scale


Thrust block layout details for ductile iron pipe work used on self lay/multi utility sites: 

Flange 

adapter 

90° double 

flanged bend 

22½° double 

flanged bend 

Flanged bends (ductile iron) 

Thrust block 

45° double 

flanged bend 

11¼° double 

flanged bend 

Flanged bends (ductile iron) 



GN5 11



Thrust block 

90° socket bend 45° socket bend 

22½° socket bend 11¼° socket bend 

Socket bends (ductile iron) 

Socket bends (ductile iron) 



GN5 12



Thrust block details 

Thrust block Bearing area Nominal quantity 

Min. depth (mm) Min. length (mm) Required cubic content (m3 ) 

BLOCK A 300 300 0.10 

BLOCK B 500 600 0.30 

BLOCK C 800 1000 0.80 

BLOCK D 800 2000 1.30 

BLOCK E 1000 3000 3.00 

Thrust block sizes 

Nominal pipe sizes 90º bend End cap & tee 45º bend 22½º bend 11¼º bend 

80 ductile iron B B A A A 

100 ductile iron C B B A A 

150 ductile iron D C C B A 

200 ductile iron D D C C B 

250 ductile iron E E D C C 

300 ductile iron E E E D C 


GN5 13


Service connection general arrangements for use on self lay/multi utility sites: 

¾" BSP x 25mm 

MDPE (pushfit) 

Ductile iron 

Electrofusion 

tapping tee 

(25mm outlet) 

Note *Square sided metal surface 

box to be used in paved areas 

¾" MI x 25mm 

outlet ferrule 

Ductile iron 

25mm x 25mm 

electrofusion 

coupling 

MDPE/HPPE main 

25mm self tapping ferrule 

to suit PE barrier main 

connection to be made to 

Boundary box 

with height and 

slope adjustment 

for plastic lid 

See note* 

25mm MDPE 

service pipe 

25mm MDPE service connection 

25mm PE barrier 

service pipe 

25mm x ¾" MI 

transition 

PE barrier pipe 

Sealed boundary 

box (with ¾" MI 

connectors) 

25mm electrofusion coupling 

¾" x ¾" FI 

double socket 

25mm service connection contaminated sites 

25mm MDPE 

private pipe 

25mm PE 

Barrier pipe 

¾" x ¾" FI 

double socket 

25mm x ¾" MI 

transition 



GN5 14

Addendum to the self laying of water mains - Severn Trent Water

Create successful ePaper yourself

Delete template?

Save as template?