Extending use of wood fibre insulation

March 11, 2022

At Barefoot Architects we are determined to reduce the environmental impact of our projects as much as possible. One way of addressing this aim is the use of natural materials, and timber in particular.

Timber is a natural and renewable building material, it acts as a carbon sink and has low embodied energy. The energy needed to convert trees into structural timber is significantly lower than that required by other structural materials such as steel and concrete.

Wood fibre insulation is made from timber, so it has the same ecological properties. It has many other benefits too; acoustic comfort, protection from summer overheating due to its high thermal mass, non-toxicity for the occupants (and site operating staff). Further details are well covered by this article.

Cost is often a main reason for reverting to more commonly used insulation materials such as PIR, XPS, EPS or mineral wool. We have recently undertaken a cost exercise comparing the cost of insulation for one of our typical extension projects:

Based on this basic cost exercise we have developed a typical wall and roof buildup which has so far been suitable for all our current Exciting Extension projects (see below).

Oversizing the wall timber studs means that we can keep the buildup consistent for walls and roofs and hence reduce site waste and simplify the building process. It also reduces the cost of insulation, as in order to achieve the required U-value, we can use more of the flexible wood fibre insulation which is significantly cheaper than the rigid external insulation board. This said, we assume that the additional cost of the timber will not overly exceed the saving, given the relatively small area of external wall and roof needed for an extension. As the majority of our extension projects are for terraced houses in Bristol, our typical wall buildup includes a 9mm Magply board to provide 60 minutes fire resistance to the structure, as required by AD part B.

We worked closely with the technical team at Mike Wye who have been great at providing technical advice and U-value calculations. There are currently three extension projects being tendered using this buildup and we are awaiting the contractor's feedback.