Learning Outcome Lesson Objective Understand the techniques used in the construction of superstructures for low-rise domestic and commercial buildings Lesson Objective To be able to explain the techniques used for construction of external walls in domestic timber frame construction

Wall construction Knowledge check? Where in modern houses are dense blocks used? How can cavity walls be insulated? What is a cold bridge? How can cavities be closed at the jambs and how is damp penetration avoided?

Timber framed construction The timber frame building offers several potential advantages over more traditional forms of building: What are they? Fast construction Good quality control On site construction is reduced because of prefabrication Less dependence on traditional ‘wet’ skills Reduced dead-load. Good thermal insulation

Timber framed construction

Timber framed construction With timber frame construction external and internal load bearing walls are formed out of timber frames that have vertical timber studs nailed to top and bottom timber plates. The studding will be covered on the outside by a sheet material called sheathing, which will usually be plywood. What is the purpose of this sheathing? To stiffen the frame and to help prevent deformation from wind loads.

Timber framed construction The studding will be covered on the inside by plasterboard to provide an acceptable finish. Weather protection can be provided by external timber cladding or tiling or more commonly in this country by an outer leaf of brick work. The frames are usually pre-fabricated in storey high panels not more than 3.6 metres in height allowing easier handling on site. Larger panels would need the use of a crane on site.

Timber framed construction Breather membrane A waterproof, but vapour permeable, layer protects the timber from any water, such as wind driven rain, which finds its way across the cavity, whilst also allowing any moisture vapour in the panels to escape.

Timber framed construction Vapour Control Layer To prevent condensation occurring within the external wall panels some form of vapour control layer is required in between the insulation and the plasterboard. The most common material is polythene sheet

Timber framed construction Cladding In the UK, brick is by far the most common type of cladding to timber framed houses. Unlike a traditional brick and block house the brickwork can be built (and usually is) after the roof has been completed.

Timber framed construction Cladding Brickwork, however, is not necessarily the most practical cladding - for three main reasons. What are they? its weight means it cannot be supported by the timber frame and therefore requires a foundation a free standing wall would soon buckle and bulge in high winds so it must be restrained by the timber frame the method of restraint (wall ties) must allow for differential movement between the brickwork and timber.

Timber framed construction Brick Cladding

Timber framed construction Wall ties Wall ties must be fixed to the studs and not just the sheathing. The flexible wall ties should be laid to a slight gradient (i.e. sloping outwards) to ensure that shrinkage in the frame does not create a back fall in the ties when the frame shrinks.

Timber framed construction Fire and Acoustic Protection If the house is semi-detached, the separating walls must provide fire protection and adequate resistance to airborne sound.

Timber framed construction Openings The panels are 'trimmed' to form openings

Timber framed construction A lightweight lintel normally requires a timber cavity barrier. The need for a separate cavity tray again depends on location and lintel finish (galvanised, stainless steel, special coatings etc). Most lintels for timber framing require lintel restraint clips which must be screwed or nailed to the timber frame. These help restrain the lintel but must, at the same time, allow for differential movement between the timber structure and the brick facing.  

Steel frame housing The principles of modern steel frame construction are similar to timber frame construction. Use is made of a platform frame but the panels are made of galvanized steel sections rather than timber. In the factory the sections are welded or riveted together but on site self tapping screws or bolts would be used.

Steel frame housing The positioning of the required insulation in the external wall is slightly different for steel frame construction compared to timber frame construction. Rather than being positioned between the frame members, foil backed insulation boards are fixed to the outside face of the frame members, keeping them warm so that there is usually no need for a vapour check.