LINTEL
A lintel is a type of beam (a horizontal structural element) that spans openings such as portals, doors, windows and fireplaces. It can be a decorative architectural element, or a combined ornamented structural item. In the case of windows, the bottom span is instead referred to as a sill, but, unlike a lintel, does not serve to bear a load to ensure the integrity of the wall. Modern day lintels are made using prestressed concrete and are also referred to as beams in beam and block slabs or ribs in rib and block slabs. These prestressed concrete lintels and blocks are components that are packed together and propped to form a suspended floor concrete slab.
The most common materials for lintels are timber, steel and concrete.
Timber is low cost, readily available and can be easily cut to size on site. However, it is generally only suited to small openings with low loadings.
Precast concrete lintels are economical and provide robust support for structures such as masonry over door and window openings. They are able to accept a wide range of surface finishes.
Steel lintels are generally made from pre-galvanised steel which is cut and either roll-formed or pressed into the required shape. Steel has the advantage over concrete in that the lintels are usually lighter and are easier to handle on site. The lintel can be shaped so that it is not visible above the opening. Steel is also versatile and can be custom-produced according to the specific building requirement, whether arched, in a corner, forming a bay window, and so on.
In order to specify the type of lintel required, the nature of the load to be supported must be calculated. This includes both dead and imposed loads. Dead loads refer to the static mass of the building components such as floor coverings, roof tiles, masonry, and so on, whereas, imposed loads refer to the weight of furniture, fittings, people and so on.
Lintels must have adequate support at each end, and typically, the length of lintel for a masonry wall is calculated by measuring the total width of the structural opening, and adding 150 mm for end-bearings at each end. If lintels or end-bearings are inadequate specified, they can cause cracking in decorations, or in the structure itself, and ultimately can cause structural failure and collapse.
Lintels are also important in terms of their role in reducing heat loss from a building and the occurrence of damp and condensation. Lintels must be designed and constructed carefully to avoid thermal bridging (a direct connection between the inside and outside through elements that are more thermally conductive than the rest of the building envelope). This may include the creation of a cavity within the wall above the lintel, and the insertion of insulation.
Lintels may also need to incorporate a cavity tray or damp proof membrane to direct water within the wall or cavity to the outside through weep holes. Stop ends at either end of lintels prevent water flowing off the end of the lintel back into the cavity where it may dampen the inside wall.
