NHBC’s overarching purpose is to raise the standards of new homes to protect homeowners.
We do this in a variety of ways and an initiative for the organisation during the downturn has been to provide free training to the industry, focused on key areas where our claims data would suggest that practices on site could be improved. I have told you about some of these previously including fire safety, which was provided to nearly 500 site managers across the country. A further area where it was suggested improvements could be made was in respect of roofs, so over the last six months we have worked with the roofi ng industry to train over a thousand builders across the country in some of the key failures identified through claims on roofs and how they can be avoided.
As a warranty body, NHBC has its own set of standards which customers are required to meet in order for the homes they are building to be offered the protection of the 10 year warranty cover. The starting point for meeting the standards is the minimum standards set by the Building Regulations, these are then added to with additional guidance based on claims data and also advances in construction technology and the standards are updated regularly.
Following on from the seminars on roofs, the standards in relation to pitched roofs will be updated in January 2012 to address some of the issues identified with roofing failures. What has this got to do with building control? Well as I said, the starting point for our standards is the minimum standards of the Building Regulations, which in respect of roofs (amongst others) would be to ensure the weather tightness of the building. Therefore, the changes highlighted in the standards, whilst not necessarily Building Regulation requirements make good sense and should worth thinking about on your next job even if you are not going to require a warranty.
MECHANICAL FIXING OF RIDGE AND HIP TILES
For many years, it has been traditional to bed ridge and hip tiles in mortar to secure them to the roof. Experience shows that pitched roofs will be subject to some movement during the early life of the property. Mortar is generally not tolerant of that movement and can easily crack or de-bond, making ridge and hip tiles vulnerable when subjected to high winds.
The revised standards will require mechanical fixing for all ridge and hip tiles (including tiles to hips on low level bays), which will greatly reduce the risk of tile de-bonding failure.
DENTIL TILES IN RIDGES AND HIPS
In addition to mechanical fixing, a further requirement has been added to the standards to align with BS 5534 requirements and address failure to deep sections of mortar bedding. Where ridge and hip tiles are bedded on mortar to rolled tiles, concealed or decorative dentil tiles should be fully bedded into all joints in excess of 25mm thick.
INTERLOCKING TILES
Some roofs can be complex in design, (dormers, integral solar panels, roof lights and steps in levels etc.). Traditionally, large interlocking tiles have not had the flexibility to prevent very small or inappropriate cuts to some of these details. To address this problem, manufacturers have introduced ½, ¾ or 1½ tiles within some of their current interlocking tile ranges. The revisions highlight the importance the design team/specifiers can play in ensuring that the selected product provides sufficient alternative tile sizes to suit the roof complexity. Where verge cuts are unavoidable to interlocking tiled roofs, the tile should be at least ½ tile width, mechanically fixed and preferably located on the more secure right-hand verge (where the adjacent tile interlock helps to hold down the cut tile) rather than the weaker left-hand verge.
VERGE ARRANGEMENTS
The revisions provide more detailed guidance regarding verge arrangements, including the suitability of tiles and the acceptable overhang, positioning of the undercloak and tile batten, together with revised guidance for tile fixing, including bedding, nailing and clipping. The revised standards now explicitly require verge tiles and slates to be bedded on a minimum 100mm width of mortar, placed in one operation. The allowable tile overhang at the verge has also been revised for interlocking tiles. Finally, where specified, clips need to be installed correctly, taking account of the tile profiles to ensure clips correctly engage with the top of the tile.
INFORMATION
Full details of the changes as well as copies of the revised standards can be downloaded for free from www.nhbc.co.uk.
