Corodrain Valley Troughs

A Type Valley

A Type Universal Valley Trough

The Corodrain A Type Valley Trough is a narrow valley trough for use with single lap tiles in limited applications. There is a standard (type:HA) and heavy duty (type:AX) option. The valleys incorporate a 35mm sanded strip for the mortar adhesion.



  • BBA Approved Cert No. 89/2153
  • At least durable as lead
  • Similar in appearance to lead
  • Less prone to theft
  • Quick to install
  • UV light and acid rain resistant
  • Smooth surface inhibits the growth of moss & lichen and build-up of debris
  • Fire resistance to SAB to BS476 part 3 and Class 3 BS476 part 7

ideal for

  • Suitable for use on roofs with pitches from 22.5° to 49°
  • Can accommodate a maximum difference between two rafter pitches of 10°
  • Designed for use with interlocking tiles, can also be used with natural and manufactured slate


Please contact our Technical Department who will be happy to advise on installation instructions.

 Valley Selection Table 


 Roof Area (less than 25m²)  Roof Area (25-100m²)  
Rafter Pitch  Valley Type  Max Valley Length   Valley Type Max Valley Length  Min Lap Length 
 17.5°-22° B/D  7.0m - - 350mm
 22.5°-29° A/B/D  7.0m B/D 14.5m 300mm
 30°-34° A/B/D 7.5m B/D 15.0m 200mm
 35°-39° A/B/D  7.5m B/D 15.5m 150mm
 40°-44° A/B/D  8.0m B/D 16.5m 150mm
 45°-49° A/B/D  8.5m B/D 17.0m 150mm
 50°-55° B/D 9.0m B/D 18.5m  150mm


Universal Valley HA/HX 


  1. Valley boards should be fitted of sufficient width to provide support for the roofing battens, either: min.12mm ply lay boards set between 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 th 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 appropriate centre line 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 to the counter battens at max: 500mm centres.

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.


GRP lasts as long as lead, is tougher, cheaper, more resistant to accidental damage, and is less prone to theft or vandalism. Using preformed GRP valley troughs saves significant installation time over traditional methods. Roofers report elimination of many problems with valley troughs when changing from lead to CORODRAIN GRP. Coloured lead grey as standard (other colours available on request). 

Made with high quality un-filled polyester resin with glass fibre reinforcement for maximum strength. A tough bonded melinex film gives excellent weathering performance. Minimum life of 30 years. 

Manufactured to BS EN ISO 9001:2008 quality standard, our automated continuous pultrusion plant in Coventry. All available from stock for rapid delivery to site.

The inherent qualities of the materials make the valleys UV light and acid rain resistant, and the smooth surface finish inhibits the growth of moss, lichen and the build up of debris.

Valley Weights  
Standard valley troughs: 1.64kg/m²

Heavy Duty valley troughs: 2.10kg/m²

Valley Thicknesses

Standard valley troughs: 1.3mm

Heavy Duty troughs: 1.6mm



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