By John Mercer, Pitched Roofing Consultant.
As the construction industry returns to work, it seems an ideal time to just refresh ourselves on some of the relevant Standards and practices roofers need to be aware of; from workmanship, to design, through to installation.
Goods to site: handling and storage
Starting when goods arrive on site, it is important to check materials and products to ensure that they conform to the project specification. There could potentially be a serious financial risk to the roofer if materials are installed without having been checked, only to find out later that the wrong products have been used or there is a quality issue.
Similarly, handling and storage on site prior to installation is important to prevent damage from passing traffic or soiling from ground conditions or mortar preparation. Product manufacturers’ storage instructions should also be adhered to avoid damage from, for example, exposure to direct sunlight whilst in plastic wrapping, or from water saturation if exposed to excessive rain.
Roof tiles and fittings should be stored as close as possible to the roof to avoid excessive handling, in compact and stable stacks on a firm, even base free from soiling and away from the risk of damage from passing traffic. Stacking of tiles on the roof prior to installation must be done in such a way to avoid slippage, and they must be distributed evenly to avoid overloading a part of the roof structure.
Before commencing work, the roofer should check that the roof is square and with no uneven junctions, for example at party walls or gable walls. Fascias should be set at the correct height to maintain the general tile pitch at eaves and cavity trays checked for the correct height for the tiling and weathering flashings. At hips and valleys there should be noggins or boards to support the ends of the tiling battens. Whilst it is also the responsibility of the designer, the roofer should check that the pitch of the roof is suitable for the tiles and fittings being installed.
When stripping and re-tiling old roofs, timbers should be checked to ensure they are sound and free from insect attack and dry or wet rot. All metal fixings should be checked for signs of corrosion, movement, or breakage. It must be established that the roof structure can support the new roof covering with an adequate safety factor. Building Regulation Approved Document A stipulates that if a new roof covering is more than 15% heavier than the original, then the structure should be checked by a competent person to establish if it can safely support the increased load, and whether any extra strengthening work is required. Similarly, if a new roof covering is to be 15% or more lighter than the original, then the structure must be checked for adequate anchorage against wind uplift.
Roof tiles are regarded as a fragile roof covering, both in terms of safety of the operatives and risk of damage to the materials. Therefore, tiling works should be planned so that battens are used as footholds where they pass over the rafters, to avoid walking directly on laid tiles. Where access or working directly over tiling is unavoidable, this should be done from crawling boards or access ladders, suitably packed with foam or other compressible material so as to spread the load and avoiding point contact on the tiles, and properly supported and anchored to prevent slipping or tipping.
Tiling battens on old roofs deteriorate with age. They should not be used as footholds unless they have been inspected by a competent person who has confirmed that they are strong enough. If in doubt, they should be regarded as fragile.
It is unsafe to work or handle materials in windy conditions. HSE recommends that tiling work should cease if the mean wind speed reaches 23 mph (gusting to 35mph or over) and if handling rolls of underlay, the limit reduces to 17 mph (gusting to 26 mph or over).
Always follow the manufacturer’s recommendations for roof pitch, headlap and tile gauge. Be aware of any special factors such as long rafter lengths. It is not always apparent that the stated minimum roof pitch may be caveated with a maximum rafter length, therefore, if in doubt, contact the manufacturer for advice.
When installing single lapped tiles, every tile on every roof must be mechanically fixed. Mechanically fixed means a secure fixing to the structure, such as nailing, clipping, screwing or some form of dry fix system. All tiles at perimeters, i.e at verges, eaves, ridge, abutments and adjacent to hips and valleys must be twice fixed. At verges, a dry fix verge system usually counts as one of the tile fixings, provided it complies with BS 8612: British Standard for dry fix ridge, hip, and verge systems; the manufacturer will confirm this. Cut tiles at hip and valley should be large enough to twice fix. Where small cuts are unavoidable, one of the fixings can be a suitable adhesive securing the cut tile to an adjacent tile.
Remember to always obtain a roof tile fixing specification from the roof tile manufacturer. This will determine the appropriate fixings required to resist predicted wind pressures for the location and building design.
It is equally important to choose a suitable underlay. The underlay bears a significant proportion of the wind pressure; therefore, it must be strong enough for the location. In general, underlay packaging includes a zonal classification system indicating its suitability for given UK zones. However, be aware that there are restrictions such as the height of a building, site altitude and local topography. Therefore, if in any doubt, contact the tile or underlay manufacturer.
- Always check materials arriving on site for quality and compliance with the specification. Store with care and to avoid any possible damage.
- Check the roof for suitability for the chosen materials.
- Always regard laid roof tiles as a fragile roof and access accordingly.
- Comply with the underlay and roof tile manufacturer’s technical data and always obtain a fixing specification for the underlay and roof tiles.