Many load-bearing walls are made from concrete blocks. A lintel, which is a horizontal slab of concrete or steel-reinforced concrete, can be inserted above the proposed opening of a new doorway or window to give the support necessary for removing part of the original wall. The lintel must be of sufficient strength to support the wall above it and prevent collapse.
Temporary Steel Props
To install a lintel in a concrete block wall you need temporary steel props, which are also called "acrows" and several pieces of 6-inch-by-2-inch timber no longer than 9 feet in length. Timber used in this way is referred to as a "needle" structure. A simpler replacement for the needles, if you are not experienced in the process, is to use strong boy attachments which require fewer props and no drilling. Strong boys fit between the concrete block work when the mortar layer is removed with a chisel. Boys should be no farther apart than 3 feet.
A concrete floor takes the weight of a new lintel and side props, but a wooden floor will not usually suffice. Wooden floorboards must be lifted up and replaced with a thick, concrete base onto which the heavy props and lintel can rest without risk of damage or even collapse. Joists beneath the proposed location of the new lintel-supported wall should also be checked for rigidity and wood worm, since any joist which appears old and worn or infested with dry rot, will not withstand the pressures put upon it by a modern lintel set-up. Always use a large, horizontal plank of strong wood between the floor joists and the prop work to extra support, weight distribution and balancing.
Any new lintel installed above an intended opening in a structurally supportive wall must extend at least 6 inches outwards from the outer edge of the opening you are planning to make, on either side, as described by DIY Doctor. The process of ensuring the lintel is wide enough to rest in a stable position on top of the props is called "projection" and can be the difference between an unstable wall and one which lasts for years in its intended position, so it is worth getting projection rules right to begin with. Replacing a damaged or badly fitting lintel is difficult when the wall's stability has been compromised and requires expensive scaffolding and engineering fixes.
As with any construction project involving masonry or concrete blocks, the joints between the blocks, the lintel and the door or window frame are as important as the components themselves. A solid, properly mixed mortar using high-quality cement powder, sand and gravel, laid neatly and professionally using the correct tools is essential in creating a sound structure. Apply a bed of consistently mixed mortar to the lintel, the top edges of each prop and the lintel end projections using a trowel. Make sure the lintel is checked for position using a spirit level, or the project will fail.
As with many DIY projects that involve structural repairs or major alterations to brick work or concrete block walls, it is advisable to contact your local planning or building regulations department to find out if you need to apply for official permission. To some extent, it does depend on your area, the age of your home and the importance of the wall in terms of its structure and what it supports, such as a neighbouring party wall, but in most cases, the council does need to know your plans. All lintels must comply with Part L legislation, British, European or U.S. guidelines, NHBC standards and building consent, according to Planning Approval.