Pitched roofs

7.2.21Valleys and hidden gutters

Valleys shall have suitable weathering details, including flashings, to resist the passage of moisture to the inside of the building.

Valleys, and the components used, should:

  • be in accordance with the design
  • have a finished pitch which complies with the minimum recommended for the roof
  • be fixed in accordance with the manufacturer’s recommendations
  • small cut tiles should be avoided
  • have a lead flashing (minimum code 4) or other suitable saddle flashing, at the head of each valley
  • be formed using either preformed GRP, valley coursing tiles (plain tiles), valley trough tiles (interlocking tiles), non-ferrous metal or a proprietary system to Technical Requirement R3.

Where the roof covering is slate or plain tiles, the following may be used:

  • A laced valley
  • A swept valley
  • A mitred valley with soakers.

Valleys using valley tiles

Where valleys are formed using valley tiles:

  • purpose-made valley coursing tiles should be used where the roof uses plain tiles
  • purpose-made valley trough tiles should be supported by gutter boards where the roof uses single lap interlocking tiles
  • they should be mechanically cut to the correct rake
  • adjacent coverings should be neatly cut to form a smooth junction, and preferably be cut from tile-and-a-half tiles
  • they should be bedded in mortar with a minimum 100mm wide channel (minimum 125mm for pitches below 30°).

Lead-lined valleys

For lead-lined valleys, the tiles should be cut and bedded as for valley tiles, except that the mortar should be bedded on an undercloak (to prevent direct contact between the lead and the mortar). Mortar should not bridge the welt detail.

Lead should be:

  • either code 4 (colour-coded blue) or code 5 (colour-coded red)
  • supported on gutter boards of 19mm exterior grade ply, or as specified in the design
  • laid in strips no longer than 1.5m
  • lapped by a minimum of 150mm, where pitches are above 30°.

Proprietary gutter or valley systems

Proprietary gutter or valley systems should be in accordance with the manufacturer’s recommendations, and securely fixed to suitable supports (exterior grade materials should be used).