Pitched roofs

Also see:

7.2.20Weathering details

Weatherproofing shall be provided at abutments, flat roof intersections, changes in slopes and projections to resist the passage of moisture to the inside of the building. Issues to be taken into account include:

  1. abutments
  2. flat roof intersection or changes in slope
  3. projections through the roof
  4. copings.

Flashing details should be appropriate for the roof and the type of roof covering used, in accordance with BS 5534. Where flashings come into contact with metal, they should be formed using non-ferrous material.

Table 13: Suitable materials for flashings

MaterialStandardAdditional information
Aluminium and alloysBS EN 5150.6-0.9mm thick, and protected from contact with mortar by a coating of bituminous paint
CopperBS EN 1172Flashings, soakers and saddles should be:
■ fully annealed
■ 0.55mm thick (0.7mm thick is suitable for gutters)
Rolled lead sheetBS EN 12588 Flashings, gutter linings etc. should:
■ be a minimum of code 4, and soakers a minimum of code 3
■ sections should not exceed 1.5m in length
Zinc alloyBS EN 988Should be a minimum of 0.6mm thick
Proprietary productsTechnical Requirement R3Should be securely fixed in accordance with the manufacturer’s recommendations


At abutments:

  • flashings, soakers and gutters should be provided as necessary
  • lead flashings should have a minimum lap of 100mm
  • flashings should be tucked 25mm into a brick joint and wedged in place at not more than 450mm centres, or a minimum of one per step for stepped flashings
  • joints between the masonry and flashing should be pointed with cement mortar or suitable exterior grade sealant in accordance with the manufacturer’s recommendations.

Where a flat or pitched roof over an enclosed area abuts a wall, or a balcony abuts a wall, cavity trays should be linked to the flashing to prevent water penetrating into an enclosed area. Horizontal flashings should provide weathering to a minimum of 75mm above the intersection with the roof.

Where a pitched roof abuts the wall at an angle:

  • a stepped cavity tray linked to a stepped flashing should be used
  • stepped flashings should be cut from a strip a minimum of 150mm wide
  • stepped flashings should be a minimum of 65mm wide
  • where slates, flat interlocking tiles or plain tiles are used, soakers (or a secret gutter) should be installed.

Flat roof intersection or changes in slope

Where there is a change in the slope, or an intersection with a flat roof and:

  • the change is 5° or more (e.g. at mansards and sprockets), flashings or soakers should be used
  • a ridge meets the main roof, a saddle flashing should be used where a ridge meets the main roof.

Where a flat roof adjoins a pitched roof:

  • the waterproof membrane should be carried up under the tiling to a height of 150mm above the flat roof, and lapped by the roofing underlay
  • the lowest course of tiles or slates should not touch the roof membrane
  • where the flat roof is over a dormer, the flat roof should have a fall to the front or sides.

Projections through the roof

Where there is a projection through the roof:

  • components should be installed according to the manufacturer’s recommendations
  • flashings should be provided (e.g. at chimneys)
  • where pipes penetrate tiling, a weathertight joint should be formed using a lead slate flashing and upstand or a purpose-made one-piece accessory (supplied by the roof covering manufacturer); where lead slates are used they should be supported (e.g. using exterior grade plywood) to prevent sagging.


Copings, including those manufactured from natural stone reconstituted stone, and GRP, should be securely fixed to gable walls using suitably durable fixings, and be weathertight.

To resist wind uplift and gravitational forces, L-shaped brackets should be used to secure stone copings to masonry walls. The brackets should:

  • have dowel bars that fit into restraint holes in the copings
  • be manufactured from stainless steel (such as type 304 to BS EN 10088-2)
  • be fixed to a solid piece of masonry, with fixings of a suitable length, gauge and durability.

DPCs should be installed under the coping to ensure that the wall is weathertight. The DPC should:

  • be bitumen-based material to BS 6398, or other material assessed in accordance with Technical Requirement R3
  • extend the full width of the wall
  • be fully bedded in mortar
  • be supported over the cavity.

Fixing methods that penetrate the DPC should be designed to ensure weathertightness. This can be achieved by extending the lower DPC under the bracket, and installing the next section of the DPC over it to create a lap that covers the fixing point.

Where GRP copings are used, they should:

  • be fixed in accordance with the manufacturer’s instructions
  • include a DPC
  • allow for normal downward movement in the timber frame.

Further guidance can be found in Chapter 6.2 ‘External timber framed walls’.