What British standards impact tiled roof specification?
The most important British Standards for tile roofs are BS 5534, BS 8000-6 and BS 5250. BS 5534 and 8000-6 relate to design, specification and installation; while 5250 focuses on condensation control.
BS 5534 - design and installation of slated and tiled roofs
BS 5534:2014 is the code of practice for slating and tiling, including shingles, for pitched roofs and vertical tiling.
BS 5534:2014 has recently been significantly updated. An important change is that all single lap tiles must now be mechanically fixed with either a clip or a nail, due to changes to wind load calculations. Mortar can no longer be used as the only means of fixing roof tiles.
Read more on BS 5534 or on the new rules regarding whether mortar can still be used for fixing hip and ridge tiles.
Roofing battens must also meet BS 5534 requirements, and there are a number of batten sizes specified, which depend on type of roof tile and rafter spans. Battens must be appropriately marked and be accompanied by documentation including the name of supplier, origin (i.e. species code), grading, basic size, and type of preservative and method of treatment used. Read more about batten spacing and installation for roof tiles.
Tiled roofs require an underlay that must be specified according to BS 5534:2014 - lightweight underlays in particular are subject to new guidelines to ensure they are securely installed.
BS 8000-6: 2013 - installation of slate and tiled roofs
BS 8000 is the code of practice for workmanship on building sites and Part 6 specifically applies to slating and tiling of roofs and walls.
This standard focuses on installation and often cross reference with BS 5534, which itself is centred on design. In some instances, NFRC* Technical Bulletins are referenced, usually for information. However, references to TB34, Wooden Shingles and Shakes are normative and must be complied with. (*National Federation of Roofing Contractors)
BS 5250 - Ventilation and moisture control
BS 5250:2011+A1:2016 is the code of practice for the control of condensation in buildings.
It describes the causes and effects of surface and interstitial condensation in buildings and gives recommendations for its control, with a specific section for the control of condensation in roofs (pages 152-157).
As the BSI website states, knowledge of the problems that moisture causes in buildings has advanced significantly since it was published in 2011. The 2016 amendment has been published to address some important issues ahead of a full revision of the standard that is due to be published in 2018.
More detailed information on all of the requirements is given in our Roofing specification guide, or in our posts on:
Key design issues for moisture control:
- Considering moisture generated by the construction process, building occupants and weather
- Sealing ceilings to curb the transfer of moist air into roof spaces
- Avoiding construction gaps
- Avoiding roof access doors or hatches in rooms that produce excessive moisture
- Use of sealed loft hatch and frame to be tested for air leakage (BS EN 13141-1)
- Sealing of all services and rooflights
- Use of recessed light fittings rated IP60 to IP65 to BS EN 60529
- Sealing of the head of cavity walls to prevent transferring warm moist air into the loft
Key design issues for thermal insulation:
Suitable insulation should be provided to prevent heat loss and cold bridges in roof construction.
Measures to prevent moisture ingress, condensation and air leakage should be incorporated into the construction details for walls, floors and roofs, with particular attention being given to the junctions of walls to floors and walls to roofs.
As insulation levels increase so does the potential risk of condensation, and so designers should consider the recommendations with regard to the prevention of condensation in ‘cold’ roof voids contained in BS 5250:2011.
BS EN 13859-1 breathable roofing underlay
Breathable underlay should comply with BS EN 13859-1, the standard for flexible sheets for waterproofing and underlays for discontinuous roofing. They may also have Third Party accreditation, such as a BBA certificate.
You can find out more about roofing specification in our guide.