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 Technical Guide

Installation DetailsInstallation Details

Installation Instructions:
NFRC technical bulletin 28: ‘Use of Inclined Preformed GRP Valley Troughs’ installation recommendations are summarised as follows:
1. Valley boards must be fitted of sufficient width to provide support for the roofing battens, either: min.12mm ply lay boards set between the rafters, or 6mm continuous ply boards laid over the rafters.
2. A single strip of roofing underlay should be laid up the centre of the valley.
3. Counter battens the same depth as the roofing battens should be fitted onto the valley boards.
4. The main roofing underlay should be laid over the counter batten. Roofing battens should be fitted with the ends firmly located onto the valley boards, positioned close to the counter batten, with care taken to avoid damaging the underlay.
5. The fascia board should be cut to allow the GRP valley trough to pass through and discharge into the gutter without flattening out. The end of the GRP valley trough should be trimmed using a fine toothed hacksaw to the approximate centreline of the gutter – which normally entails a ‘V shaped’ cut.
6. The GRP valley trough should be fitted with care taken to ensure it is centrally located between the valley boards: the sides should be nailed into the counter battens at max. 500mm centres.
Valley Trough Installation
Warning:
Concealed water troughs behind the mortar bonding strip MUST be kept clear and not blocked with mortar.
Take care to maintain correct width between cut edges.
NFRC recommend that tiles should not be cut in situ and should not be laid dry and then back fill pointed.
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