The external wall insulation timber frame of timber frame walls is a key aspect of the overall thermal performance of the structure, whether new build or renovation/extension. It should be installed to achieve U-values that meet Building Regulations and provide a home that is comfortable for its occupants.

It’s important to note that the thermal performance of a timber framed wall is largely controlled by its materials, construction methods, location and orientation. In order to improve its performance there are several options for insulating existing timber framed walls; externally, internally or a hybrid system that uses mineral wool or PIR board between the studs.

External Wall Insulation for Timber Frame Houses: A Practical Guide

External wall insulation (EWI) is the most common method of insulating timber frame walls. It is generally installed over sheathing boards that form the base of the wall and the interior finish. Sheathing is usually 2 x 6 tongue & groove, V-jointed pine planking. Typically vertical strapping in the form of 1×3’s are fastened to this sheathing at 16”o.c.

Rigid foam insulation is then attached to the strapping with a commercial grade mastic. The sheathing boards and mastic are then covered with an appropriate facing material to protect it from the elements.

ISOVER Metac is a high-performance mineral wool ’slab on roll’ that can be fitted either internally or externally of a timber frame, it is able to achieve low U values and can help reduce energy consumption. Alternatively, ISOVER SuperQuilt can be fitted on the internal face of the timber frame, it is a vapour open insulation and works as a high-performance moisture barrier reducing the risk of interstitial condensation and preventing wood rot.

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