Tim Burrell

Tim is Carpenter Oak & Woodland’s managing director. Tim has extensive experience of managing companies of all sizes, in many business sectors, including construction and building. Tim’s no-nonsense hands-on approach, coupled with his outstanding management experience and commercial acumen, make him the ideal complement to the craft-based skills of the rest of the team.

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Previous posts

• Revised Part L
• Engineered timber
• Past project revisited
• Directory of Oak Frame Architects
• Whisky brings warmth to timber framed homes

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By Tim Burrell

We were looking at a frame last week (not one of ours I hasten to add), where a considerable number of posts and studs had twisted, and we got to discussing why this was. 

Trees are both geotropic and phototropic – that is, they generally grow straight down by default, but also grow to the light. While this might imply that the obvious way for a tree to grow is straight up, and that therefore the grain in it should be straight, in reality this is rarely true.

To a greater or lesser extent, all trees have tension built in. As soon as we cut a tree down, the tension will try to dissipate. This means that spiralled grain will try to straighten out, causing twisting along its length. (It is this same principle that makes boards of timber distort and cup – the rings are effectively straightening out with nothing restrain it.) None of this affects the structural strength of the timber, but can, of course look unsightly.

For the purposes of timber framing, our specification does not allow for markedly sloping or spiralling grain, so problematic pieces will be rejected. However, even a small twist can become relevant over a long period, so that a beam of good quality which is perfectly square when it comes off the sawmill, is unlikely to be perfectly square by the time the joints are cut in it.

This twisting effect is why we use the manufacturing methods that we do. We physically lay out the timbers and mark them up in relation to the others so we can take this movement into account, rather than assume the whole beam is square and take the edges or centres at the separate end as datum points.

So, like shrinkage, which we seem so keen to keep talking about, twisting shouldn’t be an issue provided that the milling process and the manufacturing process take it into account.