Types of Lintel

A lintel bridges the gap above an opening. The type used will depend on the size of the opening and availability.

To create a doorway or window an opening must be made in the wall. In a loadbearing wall, the top of the opening must carry the structure above. Even cutting a hole in a partition necessitates propping the masonry.

Do it yourself - wall openings

Wooden lintels were commonly built into the brick walls of older houses, often in exterior walls, behind a stone lintel or brick arch. They can suffer from rot due to penetrating damp, but are still used in timber-framed houses.

Brick lintels are used with wood, steel or concrete lintels over external openings, but are not strong. Some are supported by a flat or angled metal bar.

Stone is not strong in tension and cannot be used for wide spans. The stone lintels seen in older houses do not normally support the full thickness of the wall —timber lintels are used behind them.

Concrete lintels are used for interior and exterior openings. Concrete is good in compression but not in tension. To overcome this, metal rods are embedded in the lower portion of the beam to reinforce it. Concrete lintels are made in a range of sizes to match brick and block courses and to suit various wall thicknesses. Though they are capable of spanning large openings, their weight can make handling awkward. Prestressed concrete lintels, reinforced with wire strands set in the concrete under tension, are lighter.

Galvanized pressed-steel lintels are widely used for internal and external openings. They are designed for cavity and solid walls of brick and block or timber-framed construction. The versions for cavity walls include a tray which channels moisture to the outside. Standard sections and lengths are available. They are fairly light in weight and some are perforated so they can be plastered direct.

Heavyweight rolled-steel joists

(RSJs) are mainly used when making two rooms into one. The supplier will cut the I-section beam to length.

Doorframes and window frames are not designed to carry superimposed loads, so the load from floors above must be supported by a rigid beam called a lintel, which transmits the weight to the sides where the bearings are firm. Wider openings call for stronger beams, such as rolled-steel joists (RSJs). There are numerous beams, but all work in the same way.

When a load is placed at the centre of a beam supported at each end, the beam will bend. The lower portion is being stretched and is in ‘tension’; the top portion is being squeezed and is in ‘compression’. The beam is also subjected to ’shear’ forces where the vertical load is trying to sever the beam at the points of support. A beam must be able to resist these forces. This is achieved by the correct choice of material and the depth of the beam in relation to the imposed load and the span of the opening.

The purpose of a lintel is to form a straight bridge across an opening which can carry the load of the structure above it. The load may be relatively light, being no more than a number of brick or block courses, but it is more likely that other loads from upper floors and the roof will also bear on the linte.

The lintel must be of suitable size for the job it has to do. The size should be derived from calculations based on the weight of the materials used in the construction of the building. Calculation for specifying a beam is, strictly speaking, a job for an architect or structural engineer. Tables relating to the weight of the materials are used to establish the figures.

If you are creating a door, window or hatchway which is no wider than 900mm (3ft) across in a non-loadbearing wall, you can cut the hole without having to support the walling above provided the wall is properly bonded and sound. The only area of brickwork that is likely to collapse is roughly in the shape of a 45-degree triangle directly above the opening, leaving a self- supporting stepped arch of brickwork. This effect is known as self-corbelling. Do not rely on the self-corbelling effect to support the wall if you plan to make an opening which is more than 900mm (3ft) wide — provide temporary support for the wall as if it were loadbearing.

Before you make any opening in a loadbearing wall you will need to erect adjustable props as temporary supports, not only for the weight of the masonry but also for the loads that bear on it from floors, walls and roof above.

In practice, for typical situations, a builder can use his experience to help you decide on the required size of lintel. A Building Control Officer may be happy to accept this type of specification, but he can insist that proper calculations are submitted with your application for Building Regulations approval.