January Archive

Carpenter Oak & Woodland’s blogs on timber frames, building, design, architecture and timber craftsmanship.

Frame for a whole house

January 29, 2007 · Posted by Tim Burrell

Over the weekend I was chatting with an architect friend of mine about a conservatory we had built for a neighbour of his. It seems that seeing this, he had been inspired to suggest that it would be really good if there were a way to build a whole house structure in oak! I got the impression that my protestation that we had built literally hundreds over the years was taken as being the beer talking.

Horrified by this event, I called him yesterday to let him know that in fact timber buildings had been made for hundreds of years and that really we were just a modern refinement of that technology, at which he saw my point. Turns out that he had just assumed that these beautiful pieces of work were only used to adorn (otherwise bland and ugly) buildings, and that was the value of oak conservatories, heavy timber roof trusses and the occasional dummy post. If you wanted to build a timber frame, that would be in nasty pressure treated softwood.

Funny really. I had thought that our industry was well established, and our capabilities known. More to the point, I just assumed it was obvious that our frames are in themselves structural and hold the building up rather than having a requirement for the rest of the building to hold it up! So when you read this Steve (well we are friends, and you did give me permission), a fabulous bespoke heavy timber framed home is surprisingly cost effective and in fact needn't cost any more than brick and block place. It should look and feel better, will probably be healthier, will have a higher resale value, be kinder to the environment, and since we can build virtually anything from a square box to a geodesic dome, it will widen your scope to express your architectural flair!

Maybe I'm biased (!) but I find it hard to understand why anyone would build anything else.

More blogs by Tim Burrell

What is 'green' oak?

January 22, 2007 · Posted by Tim Burrell

I've just been asked what 'green' oak means. For such a fundamental material in the timber industry, you'd think that there would be a universal readily understood definition, but surprisingly this doesn't seem to be the case! I've often heard green oak referred to as 'freshly felled', but this isn't really the issue - what is more important is the moisture content. Thinking I'd like to get an 'official view', I called TRADA for their definition, but it seems even they do not yet have one! So, here's my take.

Timber can contain two types of water: 'free' water that sits in the cell cavities, and 'bound' water that is contained within the cell walls. Freshly felled oak is high in both, but will lose water from the time it is felled. At the point where it has lost all its 'free' water, but still retains its 'bound' water, it is at its 'fibre saturation point' - in the case of oak this is at a moisture content of 30%. Below the fibre saturation point, the timber is losing that bound water, and to that extent could be said to be (to some extent) dry. This is when the timber will shrink, and possibly distort. Oak will naturally air dry down to 18%, but below this will need to be kiln dried. Of course, the moisture in the wood will always gravitate to the moisture content around it: drier when the central heating is on full blast and variable and wetter where exposed to the elements. But I digress?

So, my definition of green is "timber that has a moisture content greater than its fibre saturation point". Often, but not necessarily freshly felled, and usually having rested a while 'in the round'.

A last thought. We work with green oak because larger section oak is either extremely expensive or quite possibly unavailable - plus it's easier to work. How that timber will behave when drying is a question for skilled and experienced graders. The shrinkage from green timber need not be a problem with good selection, good detailing and the skill of the craftsmen. Buyers beware, and make sure that your suppliers really know their material!