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Fixing Specification
To minimise the increased risk of roof void condensation and additional wind loading, it is essential that these rigid board insulation systems are laid and fixed strictly in
accordance with the manufacturers' instructions and any independent third party assessment. This will include fitting an effective water vapour barrier beneath the
insulation with all joints sealed at all roof details, i.e. hips, valleys, ridges, abutments and around any penetrations through the vapour barrier. This will minimise
the risk of harmful interstitial condensation occurring within the insulation and the system.
The 50mm x 25mm counterbattens laid over the rigid insulation boards must be securely fixed through the insulation into the rafters. Special fixings such as helical
fasteners supported by independent approval (WIM LAS/BBA) are normally recommended.
The Ondutile system is fixed to the counterbattens which now replace the rafters as the primary fixing point to the roof structure.
The Ondutile fixings into these counterbattens must be either ring shank nails or screws of adequate strength, durability and pull out resistance to satisfy the roof dead and
imposed loads and comply with relevant European and British Standards and Codes of Practice.
The standard Type A or Type B Ondutile fixing specification can then be used from this point.
Note
Comprehensive information relating to insulated pitched roofing is included in NFRC Report; Technical Bulletin 21 and BRE Report no. GBG37. |
