7.2 Pitched roofs

Also see:

6.8

7.2.20 Weathering 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. raking 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 22: Suitable materials for flashings

MaterialStandardAdditional information
Rolled lead sheet(2) BS EN 12588 Apron and cover flashings(1), saddles(1) and soakers should:
• be a minimum Code 4 (blue) and soakers minimum Code 3 (green)
• not exceed 1.5m in length
Aluminium and aluminium alloys BS EN 485 and BS EN 573 0.7 - 0.9 mm thick and protected on both sides by a coating of bituminous paint where built into brick, stone or concrete
Zinc alloyBS EN 988Minimum of 0.8 mm thick
CopperBS EN 1172Flashings, soakers and saddles should be:
• fully annealed
• 0.55mm thick (0.7 mm thick for inclined valleys)
Proprietary products eg lead replacement products, GRP flashings etc Technical Requirement R3(3)

Notes

1. Lead thickness may need to increase in line with the severity of exposure. Thicknesses quoted are for sheltered to moderate exposure zones.

2. Where lead flashings are turned into joints by more than 50mm, they will require bitumen paint protection on both sides.

3. Propriety products should hold a satisfactory assessment by an appropriate independent technical approval’s authority acceptable to NHBC.

Abutments#

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.

At abutments:

  • flashings, soakers and gutters should be provided as necessary
  • lead flashings should have a minimum upstand of 75mm and minimum lap of 100mm
  • flashings should be tucked 25mm into a bed 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
  • free edges of lead flashings should be clipped to prevent lifting, in accordance with the Lead Sheet Training Academy ‘The complete manual’.

Where a pitched roof abuts the wall at an angle:

  • a preformed 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.

Roof side abutment details should be correctly formed, dependent upon the chosen tile or slate.

When using double-lap clay and concrete plain tiles, side abutments should be formed:

  • using soakers and step flashings or
  • an abutment gutter including a single step flashing, detailed in accordance with manufacturers recommendations (where there is a risk of blockage by debris, a step and cover flashing should be provided).

When using single-lap clay and concrete interlocking tiles, side abutments should be formed:

  • for profiled tiles, a flashing detail conforming to the tile manufacturer’s recommendations or an abutment gutter including a single step flashing, detailed in accordance with manufacturers recommendations (where there is a risk of blockage by debris, a step and cover flashing should be provided)
  • for flat or substantially flat tiles, an abutment gutter including a single step flashing, detailed in accordance with manufacturers recommendations (where there is a risk of blockage by debris, a step and cover flashing should be provided).

When using natural or artificial slates, side abutments should be formed:

  • using soakers and step flashings or
  • an abutment gutter including single step flashing, detailed in accordance with manufacturers recommendations (where there is a risk of blockage by debris, a step and cover flashing should be provided).

Where abutment gutters are constructed using sheet metal they should be detailed in accordance with the relevant sheet metal technical recommendations.

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 (eg at mansards and sprockets), flashings or soakers should be used
  • 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.

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 (eg 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. Where lead slates are used they should be supported (eg using exterior grade plywood) to prevent sagging.

Raking Copings#

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 each stone coping to the head of the wall.

The brackets should:

  • have dowel bars that fit into restraint holes in the copings
  • be adequately durable and manufactured from stainless steel (such as grade 304/316 to BS EN 10088-2)
  • be fixed to a solid piece of masonry, with fixings of a suitable length, gauge and durability.

DPCs should prevent the downward passage of moisture and be installed under the coping to ensure that the wall is weathertight. The DPC should:

  • be bitumen-based material to BS 6398, BS EN 14967 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.

Copings should have an overhang with throatings a minimum of 30mm clear of the wall, 40mm where the wall is rendered.

Where GRP copings are used, they should:

  • be fixed in accordance with the manufacturer’s instructions
  • include a DPC beneath
  • be sealed using an appropriate sealant
  • allow for normal differential movement in the timber or LSF structure
  • hold a satisfactory assessment from an appropriate independent technical approvals authority acceptable to NHBC.

Further guidance can be found in Chapter 6.2 ‘External timber framed walls’ and Chapter 6.10 ‘Light steel framing’.

Last updated: 2nd January 2024

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