Timber frame buildings: what is your surveyor looking for?25/04/22
A case of the shakes?
Oak timber frame buildings are built from green oak, using trees that were felled 12-18 months earlier. Green oak is usually cheaper and is easier to work with, hence its popularity. As the wood is still ‘green’, it has a high level of moisture content. While it dries out over time, natural ‘shakes’ may occur and some shrinkage will take place. As it will take between seven and ten years for the timber to fully dry out, it is usual to see small shrinkage gaps appearing between the oak frame and plastered infill panels. It is of course important during construction that joints are pegged to help keep the joints tight to allow for drying out while ensuring that the building remains structurally sound.
Oak beams are pretty much maintenance free and do not need treatment. Over many years, natural tannins in the timber react with the surrounding air and it changes gradually from a light honey colour to a more silvery shade. It can be treated or sealed but be warned, once you start this process, you have to carry on with it, as weather erodes the treatment off.
Modern paints and sealants can spell trouble for timber frames
Very often, it is actually the homeowners desire to seal, protect and preserve their oak framed buildings that leads to trouble.
Modern paints and sealants, such as silicone, acrylic caulk, mastic, foam and putty, seal water against the timber. This can cause catastrophic rotting. Similarly, cement and putty are often used to fill holes and cracking in the timber, especially where joints have eroded over time. This traps water against the timber and again can make the wood rot.
When the original wattle and daub, or lath and lime plaster panels deteriorate and fall out, they are often replaced by brick, with cement mortar. This can have horrendous implications for a timber frame house. Increased weight on the frame can cause distortion, which may lead to collapse. Brick and cement also hold moisture, which will rot the timber frame too. Using cement render on panels traps water into the panel, causing the timer frame members to rot.
Proper conservation and restoration of infill panels often involves removal of cement render and careful caulking around the edge of the panel before conserving with lime mortar and re-rendering the panel in lime render too. Modern paints on infill panels also spell trouble. We often see daub panels painted with white acrylic, or even worse, white gloss paint. This traps moisture into the panel and cause the staves, withies and oak surrounding the panel to rot.
Another issue that we come across is the commonplace use of galvanised mesh under supposedly lime rendered finishes on panels. This often turns out to be only cement with a shovelful of builders’ lime. The lime then reacts with the galvanising in the mesh and the render cracks and falls off. Conservation work usually involves the removal of all these materials and replacement with traditional materials, such as lime render, although alternative meshes, such as fibreglass, can be used.
If you have any concerns about the condition of the timber frame at your property – or at one you’re thinking of purchasing – get in touch with our expert surveyors. They will be able to advise you on your best course of action.