7.2 Pitched roofs

7.2.21 Valleys 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 and BS 5534
  • have a finished pitch which complies with the minimum recommended for the roof
  • be fixed in accordance with the manufacturer’s recommendations
  • have a suitable saddle flashing (see Figure 70) or appropriately detailed lead flashing (minimum code 4) at the head of each valley
  • be formed using: valley coursing tiles (plain tiles), valley trough tiles (interlocking tiles), non-ferrous metal or proprietary products which hold a satisfactory assessment from an appropriate independent technical approvals authority acceptable to NHBC.

Tiles either side of an open valley should:

  • be cut from double tiles, tile-and-a-half or half tiles where available from the manufacturer
  • where small pieces (less than half tile width) of cut single lap tiles are used, these should be bonded to the adjoining full width tile, in accordance with manufacturers recommendations.

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.

Horizontal valley gutters, where positioned over a compartment wall, should achieve the roof classification as required by the Building Regulations ie, BROOF(t4) and be appropriately fire-stopped.

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
  • have a minimum 100mm wide channel (minimum 125mm for pitches below 30°)
  • they should be fixed in accordance with manufacturers recommendations.

Lead-lined valleys

For lead-lined valleys, the tiles should be cut and bedded on mortar over 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 (blue) or code 5 (red)
  • supported on gutter boards of a minimum 19mm exterior grade plywood to BS EN 636-3, 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°
  • used in accordance with the Lead Sheet Training Academy ‘The complete manual’.

Proprietary valley or gutter systems

Proprietary valley systems should:

  • be used in accordance with manufacturers recommendations and securely fixed to suitable supports (exterior grade materials should be used)
  • be assessed in accordance with Technical Requirement R3.

Proprietary gutter systems should:

  • be used in accordance with manufacturers recommendations and securely fixed to suitable supports (exterior grade materials should be used)
  • be assessed in accordance with Technical Requirement R3.

Last updated: 2nd January 2024

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