External masonry walls

6.1
Also See:
Chapter 6.5
BRE Report ‘Thermal insulation: avoiding risks’

6.1.12Lintels

Lintels, and supporting beams, shall be installed correctly, safely support the applied loads and be of the type and dimensions appropriate to their position within the structure. Issues to be taken into account include:

  1. thermal insulation and condensation
  2. durability and resistance to water entering the home
  3. placing lintels.

Concrete, steel and reinforced brickwork are acceptable materials for use as lintels. Timber lintels should not be used, unless:

  • protected from weather
  • they do not support masonry or other rigid or brittle materials.

Lintels should:

  • comply with BS EN 845-2 ‘Specification for ancillary components for masonry’, where steel or concrete
  • be designed in accordance either with Technical Requirement R5 or the manufacturer’s recommendations
  • be provided where frames are not designed to support superimposed loads
  • be wide enough to provide adequate support to the walling above
  • not have brickwork or masonry which overhangs more than 25mm
  • have cavity trays where they are specified in the design
  • have padstones and spreaders provided under the bearings, where necessary
  • not have point loads applied before the manufacturer’s requirement of fully bedded brickwork is met (this is to avoid overstressing).

Lintels should extend beyond the opening (at each end) by the minimum lengths shown in Table 5.

Table 5: Lintel bearing

Minimum bearing length (mm)
Span (m)Simple lintelLintel combined with cavity tray
Up to 1.2100150
Over 1.2150150

Where steel lintels are used:

  • the manufacturer’s recommendations for providing adequate fire resistance should be followed, particularly to the lower steel flange
  • the inner and outer leaf should be built up together to avoid twisting the lintel flange
  • the difference in height between the leaves should not exceed 225mm.

Thermal insulation and condensation

The risk of condensation at potential cold bridges, such as reveals and soffits, increases as the level of wall insulation increases. To avoid cold bridging:

  • wall insulation should abut the head of the window frame
  • insulation should be provided at the underside of the lintel, unless the manufacturer produces an alternative.

In England and Wales, account should be taken of Accredited Details.

Durability and resistance to water entering the homes

Cavity tray/damp proof protection should be provided:

  • over all openings, either combined as part of the lintel or separate
  • where the outer leaf is fairfaced masonry or where full-fill insulation is used, all cavity trays (separate or combined) should have stop ends.

Separate cavity tray protection should be provided when corrosion protection to the lintel is inadequate, or the shape of the lintel is unsuitable, such as when:

  • the profile of the lintel does not form a cavity tray
  • steel lintels in external walls have material/coating in accordance with L11, L14 and L16.1, see Table 4.

In Scotland, Northern Ireland, the Isle of Man and areas of severe or very severe exposure to driving rain, a separate cavity tray should be provided over all lintels.

Lintels should be:

  • austenitic stainless steel where used in aggressive environments, e.g. coastal sites
  • located and sized so that the external edge of the lintel projects beyond, and therefore offers protection to, the window head.

Placing lintels

The design should be checked and lintels should:

  • be an appropriate size for the opening and the end bearings (at each end)
  • have padstones where required, e.g. for long spans
  • be installed level on a solid bed of mortar (not soft or non-durable packing)
  • be set out to ensure that lintels bear on a full block
  • not have brickwork or masonry which overhangs more than 25mm.

Concrete floor units or other heavy components which bear on lintels should be positioned carefully to avoid damage or shock load.