Timber Frame Consultancy

• SIPs (structural insulated panels) consist of a layer of oriented strand board (OSB) bonded onto each side of an insulating foam core. These composite engineered products can be used as a structural loadbearing element.
• CLT (cross-laminated timber) uses wood panels in which the thickness is made up of a number of narrow widths of timber laid together with each layer at right angles to the previous layer. These panels can be pre-cut in the factory to form wall, roof and floor elements.
• Engineered stud is a simple way to allow a large depth of insulation to be installed between the loadbearing timber studs used for timber frame wall panels. A number of different types of engineered stud are available, using either I-joist or metal web joist designs.
• Twin stud is two timber frame stud walls in parallel, separated by a cavity, but only one of these carries the vertical load of the building.

The BM TRADA publication Innovative timber construction: New ways to achieve energy efficiency gives comprehensive information on each of these timber building methods.

All forms of construction need to comply with the fire performance requirements laid down by national building regulations. Timber frame dwellings have no difficulty in meeting the required levels, given correct design, standards of manufacture and workmanship. The following are important considerations:

• Internal linings, usually plasterboard, limit the potential for a fire to develop and provide the period of fire resistance required by the building regulation.
• Cavity barriers prevent a fire from entering a cavity and prevent a fire from escaping to an adjacent cavity zone. Their correct installation on a timber frame site is of paramount importance.

Further guidance

• The BM TRADA publication Timber frame construction: Designing for high performance 5th edition
• Fire performance of timber frame dwellings – part of our series of Wood Information Sheets
• UKTFA advice on construction sites and fire safety.

Sole plates are a very important element in a timber frame building. As the first timber frame components installed on site, their installation has a direct effect on the building’s service life, line, level and plumb, as well as contributing to the speed of construction. Sole plates are an accurate jig for setting out the timber structure, and transfer loads to the foundations through bearing and with the aid of fixings.

Requirements

• They must be level and correctly laid out to the sole plate drawing, installed to the structural engineer’s specifications.
• They should be preservative treated.
• All timber, including sole plates, must be at least 150mm above external finished ground level.

Further requirements and information can be found in the BM TRADA Wood Information Sheet Sole plates in timber frame construction.

Current timber frame construction incorporates high levels of insulation within structural elements, but clients are now seeking designs that can deliver improved thermal performance. This can be achieved by using:

• deeper solid timber studs
• deep engineered timber studs (typically timber I-joists or open web joists)
• additional layers of insulation material (internally or externally)
• novel construction methods such as SIPs.

Options for improving the thermal performance of existing timber frame buildings include:

• improving airtightness
• increasing roof insulation
• upgrading windows
• adding floor insulation
• upgrading wall insulation.

See the BM TRADA publication Timber frame construction: Designing for high performance 5th edition and the Wood Information Sheet Improving the thermal performance of existing timber frame buildings for detailed information on the options available and how to implement them.