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How would you insulate in and around a structural oak timber frame?

Chris Brookman
Member Admin

With traditional Oak or Douglas fir frames the frame does all of the structural work and so the infill panels are largely just that, infill. However, this doesn't materially change the way in which they would be built up from our standard suggestions, which you can see below. The main difference is that you need to wrap the structural frame with the VCL membrane so that as this frame shrinks you do not open up huge air gaps. This takes time as there is a lot of cutting and taping of the membrane around the timbers and junctions, etc. and this should be brought round to finish flush with the internal faces of the timber frame.

Once the membrane is installed, the softwood panels and rafters can be installed in the appropriate positions and the membrane lapped on to the inside faces of these panels/rafters. This can then be taped to the air tightness layer on the inside of each section.

In terms of minimum build-ups for the panels in the walls I'd suggest the following:-

This will achieve a U-value of 0.177 W/m2K which would be required by building control.

For the roof I’d suggest the following:-

This will achieve a U-value of 0.134 W/m2K which will just pass through building regs.

Hope that helps.

Topic starter Posted : 11/03/2021 11:59 am
Dave Matthews



I note that you use a breather membrane here. I was under the impression that the sarking board was an alternative to the breather membrane?

Posted : 19/01/2022 11:45 am
Chris Brookman
Member Admin

Hi Dave

Breather membranes are just an easy addition to the build-up to satisfy building control without lots of justification. However, if you have bats you will need to omit the breather membrane and rely on the boards. Either is fine from a functional point of view, it just depends on the requirements of the roof. The boards are designed to cope without being covered by a membrane.

Hope that helps.

Topic starter Posted : 19/01/2022 12:45 pm

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