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PUBLICATIONS > RCI TECHNICAL NOTE 66

DESIGN AUDITS

The design of roofs in the UK often takes place in a 'piecemeal' fashion, with different parties taking individual design decisions and sometimes working in isolation. This fragmented process was described in an article published in RCI in February/March 1996. For some projects, there is a need for a more co-ordinated approach to roof design to ensure that the completed construction is robust and will last. This is appropriate for projects where there is an unusual roof shape, an exposed site, extreme internal conditions such as pool halls or possibly a prestigious building with a long design life.
To check a proposed construction, perhaps as part of a quality system, design audits are carried out. But what design tasks should this include and is there a systematic approach?

Design Task Check List

For the past couple of years we have used a check list which identifies specific design tasks and the relevant current British Standard. Not every task identified is necessarily appropriate for a given project, although, it is helpful to be reminded of the wider issues. Alternatively on some projects there may be additional specific design requirements since the check list is not exhaustive.
As with most check lists they can soon become outdated, especially with the frequent issue of revised British Standards. Three of the main standards covering the design of roofing systems have been revised in as many years. In the future Eurocodes will be introduced, but currently the timetable for their implementation appears to be several years away. As well as the British Standards given there are many other good authoritative design guides published by Trade Associations and manufacturers, although there are too many to list in this Technical Note.


Design Audits

Design audits should be carried out by competent and experienced people. As a minimum they require a copy of the current version of the British Standard together with a working understanding of its contents. Appropriate time should be allowed for a design audit, recognising that conclusions reached may require changes to the roof to be constructed.

Conclusion

In the increasingly litigious world where the responsibilities of the parties are more clearly defined, those carrying out design work need to have professional indemnity insurance to cover a potential claim in the event of a design error. With the trend to adopt more complex lightweight 'engineered' roofing systems, there is a greater need for a more rigorous approach to the design of roofs in the UK.


References

1. RCI Technical Notes No. 22, 23, 24, Rainwater Goods, January 1992 - May 1992.
2. RCI Technical Note No. 33, Condensation Risk Analysis, October 1993 .
3. IWA Paper 'Working Towards Getting the Roof Right First Time', Reprinted in RCI, February/March 1996.
4. RCI Technical Note No. 49, European Product Standards, April 1996.
5. RCI Technical Notes 55, 56, Wind Loading Codes, January/February 1997 and April 1997.
British Standards can be purchased from BSI, telephone: 0181 996 7000

© Keith Roberts, 1998
First published in Roofing Cladding Insulation, April 1998

 

TABLE 1: ROOF DESIGN TASK CHECK LIST

A Structure - Will the roof collapse or blow away?
- Loading   - Dead
    - Imposed and Snow
    - Wind
BS 6399:Part 1:1984
BS 6399:Part 3:1988
BS 6399:Part 2:1997
- Decking, check flexural strength and deflection  
- Uplift attachment strength (See Table 2)  
- Fasteners  

B Weatherproofing - Will the roof leak?
- Site exposure BS 8104:1992
- Rainfall intensity BS 6367:1983
- Roof slope (See Table 2)
- Rainwater goods BS 6367:1983
- Perimeter details (See Table 2)
- Penetration details (See Table 2)

C Hygrothermal - Will there be condensation?
- Internal operating conditions BS 6229:1982
- Ventilation requirements BS 5925:1991
- U value BS 6993:Part 1:1995
- Condensation risk analysis BS5250:1989
- Cold bridge details  
- Thermal movement  

D Durability - Will the roof last?
- Local environment and pollutants BS 7543:1992
- Lifespan of surface coatings BS 5427:1996
- Fire resistance BS 476:Part 20:1987
- Smoke release system or rooflights  

E Serviceability - Will the roof meet the owner's needs?
- Appearance
- Daylighting BS 8206:Part 2:1992
- Acoustic BS 7643:Part 3:1993
- Cleaning BS 6270:Parts 1, 2 and 3
- Access BS6037:1990
- Safety provisions for future maintenance BS 8213:Part1:1991
BS EN 363:1993


TABLE 2: MAIN BRITISH STANDARDS FOR ROOFING SYSTEMS
APPLICABLE IN APRIL 1998

Slating and Tiling - BS5534:Part 1:1997
Profiled Sheet Roof and Wall Cladding - BS5427:Part 1:1996
Fully Supported Metal Zinc
- CP143:Part 5:1964
  Copper
- CP143:Part 12:1982
  Aluminium
- CP143:Part 15:1986
Flat Roofing - BS6229:1982
Built-up Felt - BS8217:1994
Mastic Asphalt - BS8218:1998


Important Note: Readers should check that they are using the latest version of the relevant Standard

RCI Technical Notes

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