External Wall Build Ups Explained

timber frame external wall detail

Timber frame external walls are constructed in various ways, but mostly you will find that they follow the same theory of detailing. Being aware of this theory will give you a head start on understanding how your timber frame external wall will be constructed and ensure you can follow the specification list included with your timber frame quotation.

The theory

Starting outside and working in, the general theory works like this…

An external breathable membrane is laid over a layer of structural sheathing. Voids between structural studs (which will form the external walls) are insulated with a primary layer of insulation. Secondary insulation layers are set over the panel studs and sheathed with an air-tight vapour control barrier. An internal service cavity is created by adding battens. Internal boarding and skirting are fixed over the service cavity.

In practice

In more detail, the illustration above is constructed as follows (again starting outside and working in). The outer layer consists of a TF-200 reflective breather membrane which minimises the risk of condensation forming and enhances thermal performance. This external breather membrane is laid over 9mm OSB structural sheathing. 140 x 38mm structural studs are constructed at 600mm centres creating panels that are factory-fitted with 120mm PIR (polyisocyanurate, which is a type of rigid foam insulation) between the studs. 50mm PIR insulation is set over the panel studs. The panel is then sheathed with reflective VC foil to enhance the wall’s thermal performance, and deliver air tightness and a vapour control barrier. 45mm battens are used to create the internal service cavity, fixed over the studs at 600mm centres. 12.5mm plasterboard is fitted over the service cavity. 145mm skirting finishes the detail.

The pre-fabricated external wall detail shown above is typical; however, it’s important to note that while it represents a high-performing option, our self-build clients can specify different wall detail configurations. You can choose from a wide variety of insulating materials to achieve specific U-values and wall thicknesses or meet specific project budgets. For more information on flexible wall options read more here


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