In this guide
3. Load-bearing walls
A load bearing wall is one which supports other elements of the building, such as (and most commonly) the:
- roof - part of the roof structure which would include the ceiling joists within the loft area are sometimes supported from internal walls
- wall above - there is possibility that if another wall sits directly above then it could be supporting that wall
- floor Joists - floor joists are sometimes built into or sitting on top of an internal wall.
These are the most common parts of a building an internal wall could be helping to support, however there are other things to look for. An example could be where the chimney stack has been removed on the ground floor. A beam has been placed across the underside of this stack to support it, which then sits on an internal wall to transfer the load down to the foundation.
A structural engineer or surveyor can be employed to determine if the wall is load bearing and then design a beam to cater for these loads.
The beam should be designed to cater for the loads that the wall was originally taking. This beam then needs to be supported on two other supports (typically walls) that are capable of taking the loads to foundations. Any new beam should normally have at least 150mm bearing (overlap onto the existing wall) on each side of the opening and the existing wall beneath the bearings are likely to need to be strengthened to prevent crushing of them. This may require the installation of an area of dense concrete (cast in-situ or pre-cast), known as a padstones to spread the load. The size of padstones will vary depending on the circumstances of the case in hand it is advisable to speak to a structural engineer or surveyor before starting any works.
If the beam is steel then it should normally be protected against fire so that it will have 30 minutes resistance to fire (if measured in a standard test). There are different ways that this may be achieved, but most common is the use of two or more layers of properly fixed plasterboard - the thickness of which will depend on the manufacturer's specification.
If an exposed timber beam is preferred then a calculation is generally required to demonstrate how much inherent fire resistance it has - dependent on it's size and species of timber. A concrete beam, which would normally have steel reinforcement inside it, would generally has adequate fire resistance properties, providing the steel inside is adequately covered by the concrete.