External Walls Carl James

Here we look at the external walls of a typical modern dwelling – often known as a ‘domestic construction’. While this form of construction is very traditional, modern materials are now widely used to improve the performance of the wall. In particular, there has been a vast improvement in the insulation incorporated into new buildings.

Functions of an external wall Structural In most domestic construction, cellular techniques are used – your own home is likely to be of this type. (see next Slide) Here the walls act structurally to transfer loads to the foundations from the floors and the roof, as well as the superimposed loads from the users of the building. The diagram below shows how loads are distributed through a building down to the foundations.

Weather protection A major function of the external wall is to provide protection from wind, rain and snow. This is achieved in three ways:

Thermal insulation The Building Regulations require all buildings to be well insulated: for example, external walls should have a U-Value of 0.35 W/m²/°C. This is normally achieved by fitting insulation into the wall cavity, either as a partial fill (where an air space is maintained) or a full fill (where the entire cavity is filled with insulation). An alternative, or additional, method is to use insulation blocks. These have insulating properties, through the use of a lightweight aggregate, aeration (where air bubbles are introduced into the concrete) or by the inclusion of insulation such as polystyrene or fibreglass.

Sound insulation The wall must prevent excessive transfer of sound from the outside of the building, e.g. traffic noise from a busy road. The most effective way do to this is by using dense materials, such as concrete blocks.

Security The external walls of a building provide security against burglary and unwanted intruders.

Lighting Most walls in traditional construction do not allow the transfer of light. However, in modern construction, glazing systems and curtain walling mean that, in some buildings, the external wall can have the function of providing natural light.

Superimposed loads – the load applied to a structure: for example, the weight of furniture or items stored in the building, or the load imposed by snow on the roof Curtain walling Job – a glazed cladding system used on some high rise structures

Openings in external walls Head The head is the part of the opening, such as a door or window, that has the task of supporting the load of brickwork above it. As well as carrying the load, the head has to transmit the load to the jambs at the sides. Lintels or beams are used for the construction of such heads. Different types of material are used depending on the type of opening involved.

Jamb This is the vertical part of the wall opening. On a single door or window opening, one side is known as the hanging jamb, and the other is the closing or shutting jamb. There are several different types of jamb treatment, depending on the type of wall. On a solid wall, the jambs are bonded to give them their shape and strength; in cavity walls, the area where the opening is can be closed by a timber frame, incorporating a damp-proof course (DPC) (PTO)

as required by the Building Regulations as required by the Building Regulations. The detailing of the vertical DPC, cavity closure and insulation is particularly important. If this is not done correctly, ‘cold bridges’ could be created, and moisture or damp could penetrate. On the next slide are some examples of what jamb treatments to openings might look like.

Arches An arch is made from special types of brick called voussoirs. These bricks are wedge-shaped, designed to support each other and carry a load over an opening. However arches can also be constructed from standard bricks where the radius of the curvature is quite loose. When an arch is being constructed, it is important that the arch is given a temporary support until the mortar is set and arch is able to carry its own weight.

Sills Look at any window or door, and you will see that it has a piece of material below it – plastic, concrete or timber. This material is shaped to allow rainwater to run off, away from the opening. This is called a sill or threshold. It does not have to carry any load, but is simply there to get rid of the rainwater that runs down the surface of the door or window.