The experts at NAPIT discuss site preparation and resistance to both contaminants and moisture.
BS 7671 and Building Regulations
The sealing of wiring systems is detailed in Regulation 527.2.1, which specifies the requirements for wiring systems that pass through building construction, such as floors, walls, roofs, ceilings, partitions and cavity barriers.
Although this regulation is located in a section that is concerned with minimising the spread of fire, it is detailed further in Regulation 527.2.4, which discusses resisting external influences, such as water and moisture.
In Appendix 2, references are provided to the Statutory Regulations, particularly bullet (ii) Buildings, which lists the Building Regulations in England, Wales, Scotland and Northern Ireland.
Building Regulations have documents and handbooks to further explain the requirements:
โขย Approved Document C โ England 2004, including 2010 and 2013 amendments
โขย Approved Document C โ Wales 2004, including 2010 and 2017 amendments
โขย Technical Handbook โ Scotland June 2023 Edition
โขย Technical Booklet C โ Northern Ireland 2012.
These documents are sometimes overlooked by electricians when undertaking installations in domestic properties and you may be caught out by your astute local building control officer who may bring the relevant statutory documentation to your notice.
Approved Document C has Item 6.12 which states:
To avoid excessive moisture transfer to roof voids, gaps and penetrations for pipes and electrical wiring should be filled and sealed; this is particularly important in areas of high humidity, e.g., bathrooms, shower rooms and kitchens.
An effective draught seal should be provided to loft hatches to reduce inflow of warm air and moisture.
The Technical Handbook states in 3.15.5:
A floor, wall, roof or other building element should minimise the risk of interstitial condensation in any part of a dwelling that it could damage.
Walls, roofs and floors should be assessed and/or constructed in accordance with Section 8 and Annex D of BS 5250: 2002.
Although it isnโt as detailed as the Technical Handbook, the Technical Booklet C states in 8.2:
A dwelling should meet the requirement to avoid any harmful effects caused by interstitial condensation if it is designed and constructed in accordance with BS 5250.
It is the Building Regulations that provide information regarding the building materials and workmanship required to satisfy both conditions:
โขย Materials are of a suitable nature and quality in relation to the purposes and conditions of their use.
โขย Workmanship is such that, where relevant, materials are adequately mixed or prepared and applied, used or fixed so as to perform adequately the functions for which they are intended.
If downlights are installed in bathrooms, shower rooms, or other areas of high humidity, an open backed downlight, even if there is no living accommodation above, or even a fire-rated downlight, would not be the first choice, see Fig 1.
In areas of high moisture content, electricians and specifiers should consider a moisture resistant downlight. An IP65 rated fitting with an adequate intumescent seal would be adequate, see Fig 2.
This applies even if the ceiling below which they are installed is outside of zones 1 and 2 and is at a height exceeding 2.25 metres in locations containing a bath or a shower.
The light fittings that meet these requirements are widely available from a range of suppliers.
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