MAKING HOLES IN WALLS

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Phillips Exeter Academy library carrels (Photo credit: Wikipedia)

Making a small hole in a wall – to fit an air brick, an extractor fan, or to take pipework, for example – is a fairly straightforward job. All you need to do is to chop out the necessary bricks or blocks with a club hammer and cold chisel or to drill the right diameter hole. You won’t weaken the wall in any way by making a hole of this size. But if you’re cutting a much larger opening to install a dcor, window or serving hatch, or if you’re building a new wall that incorporates one or a number of these features, you’ll need to provide support for the wall above. In some cases, such as when you’re removing a wall that divides two rooms, you may also have to support the floor above.

The usual way of spanning an opening is to bridge it with a horizontal beam which will take the load of the wall above, plus any other part of the building that bears upon this section.

Types of wall

Your house is made up of different types of load-bearing or non-load-bearing walls and each requires a particular type of beam to span an opening. External walls are always load-bearing, and may be of solid, cavity or timber-frame construction. Solid walls are built of brickwork or stonework and are either 230 or 330mm (9 or 131/2in) thick: they may support first floor joists, rafters and other roof beams.

A cavity wall has an inner load-bearing leaf or wall of bricks or blocks connected at intervals by means of galvanised wall ‘ties’ to an outer, non-load-bearing leaf, of bricks or stonework. The gap between the two leaves prevents moisture penetrating to the interior. A cavity wall is usually 280mm (11 in) thick with the gap. If you’re spanning an opening in this type of wall you’ll need to fit a special beam that incorporates a damp-proof course, or two separate beams used in tandem; one for each leaf.

Some houses have a timber load-bearing framework clad with a facing skin of bricks, with a gap between them. In this type of structure you’ll have to use the same beams that are used in conventional cavity walls to support openings in the outer leaf; those in the inner leaf should be bridged with timber beams. However, it’s best to consult a builder before removing parts of a load-bearing timber frame.

The internal walls that form the rooms of your house can also be load-bearing or non-load-bearing, and may be built as either solid masonry 110mm (4 V?in) thick, or timber stud frames clad with building boards. Solid walls may be load-bearing; timber-frame walls are always non-load-bearing.

It’s wise to contact your local building inspector for professional advice if you’re not sure whether a wall is load-bearing or not.

Types of beam

Your choice of beam is dictated mainly by the structure of the wall and whether it has to bear a load. When you’re spanning a very wide opening – before removing a load-bearing wall, for example – you’ll need a large heavyweight beam known as a ‘rolled steel joist’ (RSJ) or a ‘British Standard beam’ (BSB). This type of beam has either an H- or an L-section and must rest on stout piers because of the heavy load it carries.

Smaller beams for door and window openings are called ‘lintels’. They’re made from stone, wood, steel or concrete. Stone and timber have now been superseded by other materials, mainly for economic reasons but you may come across them in older houses. Timber is still used for lintels in light-weight internal partition walls.

Lintels made of concrete reinforced with sleel rods can be conveniently pre-cast into a range of shapes and sizes, usually in multiples of 75mm (3in) deep, so that they’ll line up with courses of bricks or blocks. They’re also suitable for spanning wide openings up to about 3m (10ft). The larger ones are heavy and cumbersome to fit, although you can cast them in situ by fixing timber framework to the wall above the opening. Concrete lintels are usually rough-finished for rendering or plastering but ‘fair-faced’ types, which have a smooth finish that can be left bare, are also made. Some concrete lintels have pre-stressed (stretched) reinforcing rods; these are stronger than ordinary reinforced ones, so a thinner pre-stressed beam can perform the same job as a much thicker but unstressed lintel.

Concrete lintels for internal partition walls are usually rectangular in section, although special shapes for various other functions are also cast. The ‘boot’ lintel, so-called because of its unusual cross-section, is designed for use in cavity walls where it also acts as a damp-proof course.

Galvanised steel lintels are probably the most extensively used type for external solid or cavity walls or internal partitions. Their main advantage over the other types of lintel is that they’re lightweight and therefore easier to install. Some steel lintels are used in conjunction with a concrete beam.

They’re rust-proofed and must be handled carefully to avoid damaging the galvanised layer. They come in a range of standard lengths for spanning openings of different widths and wall thicknesses. Like concrete lintels, some steel types also serve as a dpc.

HOW A BEAM WORKS

TYPES OF BEAM

Beams are made of stone, wood, concrete or steel. Your choice depends upon the structure of the wall and whether it has to bear a load.

– stone is no longer used due to quarrying and transport costs

– wood is rarely used except in lightweight internal partitions because of cost. And because it’s prone to insect and fungal attack

In a properly bonded wall, the area that’s most at risk from collapse is roughly in the shape of a triangle directly above the opening. If you cut a square hole in the wall, the unsupported brickwork within this imaginary triangle would tend to fall out, forming a stepped ‘arch’ (A). The brickwork that’s left would be self-supporting -although weaker than it was – up to a span of about 1 m (3ft). So a beam needs to serve two main purposes: to support the walling within the triangle (plus any other parts of the building that bear on this area); and to hold in place the bricks that would otherwise have fallen out. This self-supporting effect doesn’t apply if the walls at each side of the opening are together less than half its span. In this case the load imposed on a beam would extend to ceiling height for the width of the opening in a roughly rectangular shape (B). If only one side of the wall is less than half the opening’s span, the load falls within a rough square shape with sides equal to the span (C).

The purpose of bearings

In either case the load or weight of the walling is distributed to the sides of the beam, which rest on ledges called ‘bearings’. On door or window-sized openings the bearings are recessed into the sides of the opening. The size of the bearing that’s needed depends on the length and width of the beam but should be at least one whole brick or block. For heavy beams you sometimes have to include a stone, slate or concrete slab on the bearing to give additional support. On very large spans the bearings must be substantial ‘piers’ (supporting colums) built at each side, or columns of the original wall left in place.

• concrete is cast in various shapes to span large and small openings in internal and external solid and cavity walls. It’s often reinforced with steel rods.

• steel beams are used for internal and external walls because of their light weight and strength. Special shapes for different wall structures are made.

WHAT TYPE OF WALL?

Before you can decide which beam to use you have to determine what type of wall you’re dealing with. There are two basic types: ‘load-bearing’ or ‘non-load-bearing’. The first is an integral part of the structure of the house, and helps to keep it up; the second offers no support to the building whatsoever.

Non-load-bearing walls usually run parallel to the joists in the floor or ceiling above (A); load-bearing walls (B) run at right angles to the joists.

You can gain a preliminary idea of what type of wall you have from the direction of the floorboards – they always run at right angles to the joists supporting them.

First floor joists, rafters and other roof beams are either recessed into load-bearing walls, attached to them with special ‘hangers’ or seated on a narrow brick ledge.

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