Green oak shrinkage

October 14, 2016

Green oak is a natural, organic material and by its very nature shrinks and moves as it matures and dries, there is no getting away from it. So predicting shrinkage is of paramount importance throughout the design, manufacture and building process. At Welsh Oak Frame, we have made considerable investment to the research and development of a design system which ensures that our frames are well prepared to accommodate the movement and shrinkage which occurs within the oak frames; ensuring that the structure remains structurally sound throughout its lifetime – probably for several hundred years.

The end product of what we build should not be seen as the beautifully tight-jointed green oak frame that has just been erected, but the mature frame after the green timbers have had the chance to dry and shrink.

If the oak is selected and made properly in the first instance, the process should be seen as adding character and quality to the frame, not detracting from it. It is one of the most environmentally friendly and efficient materials to work with and provides a home with a unique character and charm which simply cannot be achieved with other building methods.

So why does green oak shrink and sometimes split?

What’s important to remember is that the splitting and cracking of the oak timbers is not a flaw, they are in fact becoming stronger and harder whilst this natural process occurs. Nine times out of ten, when we take a client to view one of our homes, they are naturally drawn to the imperfect features of the oak and can’t resist feeling the unique ‘fingerprints’ which the oak creates throughout the home.

When a tree is felled it has a high moisture content, in some cases up to 80 per cent, whereas a dry piece of timber inside a building can have a moisture content as low as 8 per cent. Initially in the drying out process the timber loses what is known as ‘free water’ from its cell cavities, and once this has gone the timber is said to have reached it fibre saturation point, which in oak is around 30 per cent.

Most shrinkage occurs within the first twenty-four months and generally the most drastic problem you are likely to encounter is small shrinkage cracks between the oak framework and the plastered infill panels internally, which is easily remedied when routine re-decoration takes place.  Essentially, the oak frame structure is more appealing because of its flaws and cracks which enhance its natural beauty. Our philosophy, which is shared by our clients, is that oak framing is not an exact science it’s a unique and individual craft.