A roof valley is formed where two roof slopes come together. It can be one of the most vulnerable parts of a roof’s weatherproofing, as it is prone to debris build-ups and poor drainage, which can lead to water infiltration.
GRP dry valley troughs help to mitigate these problems, providing a clear and continuous path for efficient rainwater discharge.
Marley’s GRP dry valley troughs are compatible with our entire range of clay and concrete roofing tiles and give the appearance of a closed-cut roof. They provide a lightweight and reliable alternative to traditional zinc valleys and are suitable for dry-fix installation. GRP dry valley troughs are also easy to install, as they are simply nailed in place.
Two GRP valley trough options are available: high profile and low profile. Both are provided in lengths of 3,000mm and are easy to cut to size.
Provides weathertight ventilation in the roof slope
Provides up to 10,000mm² free area of ventilation
For natural, mechanical or soil pipe ventilation
For use with all concrete plain and interlocking tiles
Accommodates up to a 20° pitch variation either side of the valley
Continuous support for the valley through must be provided using ply boards
Rafter pitch |
Max. valley length |
Min. lap length |
15 to 17° |
10.0m |
400mm |
17.5 to 22.5° |
12.0m |
350mm |
22.5 to 29° |
14.5m |
300mm |
30 to 34° |
15.0m |
250mm |
35 to 39° |
15.5m |
200mm |
40 to 44° |
16.5m |
150mm |
45 to 49° |
17.5m |
150mm |
50 to 55° |
18.5m |
150mm |
This table is a guide to the recommended application criteria. It assumes a standard roof intersection of 90° and a roof drainage area of 100m². For applications other than this, specific advice should be sought from our technical department.
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