What is Timber Frame Construction?
Most timber frame buildings in the UK are constructed using prefabricated wall panels, made up of softwood vertical studs and horizintal rails, a wood-based panel sheathing and a plasterboard lining. The studs carry vertical loads through the structure and transfer them to the foundations. The sheathing provides resistance to lateral wind loads (known as racking resistance). At openings, such as doors and windows, the vertical loads are carried by timber lintels over the opening and through additional supports, known as cripple studs at each end of the lintel. The outer cladding provides decoration and weather protection.
Thermal insulation is usually incorporated in the spaces between the studs of external walls and various protective membrane materials may also be required, depending on the design of the wall.
Wall panels in the UK are usually factory-produced. Their size and degree of prefabrication varies between:
Open panels comprising studs, rails, sheathing and an external breather membrane. The thermal insulation, internal vapour control membrane (where needed) and lining are all installed on site
and
Closed panels as above but with insulation, protective membranes, linings, external joinery and sometimes even services, already installed.
Additional layers of insulation and board materials are added to provide higher levels of sound insulation and additional fire protection where required, eg party walls between houses and party walls between flats.
The choice of floor and roof construction for timber frame is the same as for other building types. Ground floors can be of concrete or timber. Intermediate floors are of timber joists or prefabricated panels. The joists or prefabricated panels are usually installed on top of the wall panels and provide a platform from which to build subsequent storeys – hence the term ‘platform frame’.
Roofs are frequently trussed rafters, but other types are also suitable, including prefabricated panel types.
Completion of a weatherproof shell for a two-storey house using manual erection with a team of four men typically can be achieved within a working week and using crane erection, in one or two days. Once the timber frame shell is completed, work can continue inside the building regardless of weather conditions. Depending upon the degree of prefabrication of the timber frame panels, this may comprise installation of:
insulation, vapour control layer and wall linings in external walls
internal non-loadbearing walls
floor decking and ceilings
internal joinery
services and and fittings
Externally, the cladding is applied. Brick cladding is erected as a separate skin, linked to the timber frame studs by stainless steel wall ties. Differential movement is likely to occur between the timber frame and brick or block cladding and the design detailing must make allowance for this. Tile and timber cladding is fixed on timber battens fixed through to the studs of the wall panels.
External joinery is fixed into openings in the timber frame, not into the cladding.
Roof slates or tiles are fixed to tiling battens and external works completed.
