How to Span an Opening in Walls

A doorway, window or hatchway requires an opening to be created in the wall. In a loadbearing wall, the top of the opening must be built to carry the structure above – even cutting a hole in a partition means propping the masonry.

Where supports are needed

Door or window frames aren’t designed to carry superimposed loads, so the load from floors above – even the brickwork above the opening-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.

Span  Opening  Walls

The forces on a beam

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.

Calculating lintel size

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. It is more likely that other loads from upper floors and the roof will also bear on the lintel.

The size of the lintel must be suitable 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 a job for an architect or structural engineer. Tables relating to the weight of the materials are used on which to base the figures.

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

When to support a wall

If you are creating a door, window or hatchway which is no wider than 1 m (3ft) across in a non-loadbearing wall you can cut the hole without having to support the walling above providing 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 1 m (3ft) wide. In that case, temporarily support 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.

Filed Under: Home & Maintenance


About the Author: Jason Prickett loves to write about home maintenance and stuff you can do yourself instead of hiring any professional. His step by step guides will assist you in completing your home maintenance tasks.

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