Timber Frame Building Companies in the UK

All about Timber

Timber is perhaps one of the oldest known building materials used in the British Isles since the Stone Age. A recently discovered timber structure in London (See 1) dates back 6000 years, which is 500 years before Stonehenge. Many species are suitable for exterior use because of their natural resistance to decay.

Profiles available range from very traditional feather edge as you would see on historic barns, to machined shiplap. Profiles to choose from include:

• Sawn: square edge, feather edge, waney edge
• Machined: shiplap, halflap, tongue and grooved, splayed

Careful selection of species is required taking into account not least of all, appearance, durability and finish:

• Green or Dry Oak; English or French
• Elm
• Sweet Chestnut
• Western Red cedar

Oak (Quercus)

Oak grows widely across the whole of the British Isles and continental Europe.

Locally grown oak has many environmental benefits, including a reduction in carbon emissions from transport and the contributing of funds to our native forest management. Dry oak is normally used for profiled cladding sections and is either naturally dried or kiln dried to a moisture level of 15 – 25%.

A wide range of colours is common in newly machined British oak; as the cladding weathers, the colour variation between the boards will decrease and they will turn natural silver. One feature of oak that must be considered is the high tannin content. During the first few years after the cladding has been attached, tannin will exude from the boards, resulting in streaks down the cladding and stains on masonry.

Relative to green oak this problem will not be as severe. Tannin also corrodes ferrous metal, so it is therefore important to use either stainless-steel or at least good galvanized fixings.

The working properties vary widely; oak cuts well and takes fixings satisfactorily, but can be brittle. The tannins in oak can corrode tools if not cleaned properly after use and will corrode ferrous fixings. However problems associated with tannins will be less severe than for green oak. Fixings should always be pre-drilled.

Sweet Chestnut (Castanea sativa)

Sweet chestnut grows widely across Britain and the rest of Europe. British sweet chestnut has a similar golden colour to oak, but with stronger grain and occasional dark brown mineral streaks. Chestnut will weather to a natural silver colouring if left untreated. British sweet chestnut is hard-wearing, strong and durable, and relatively light when compared to other hardwoods, making it ideal for cladding. Additionally, sweet chestnut is known to be a very stable timber, resulting in less movement, distortion or splitting.

General Fixing Advice

When using species such as oak and sweet chestnut with high tannin or corrosive oil content, it is important to use stainless steel nails and screws to avoid corrosion of fixings and blue staining of the wood. Ring shank nails are preferable to normal wire nails because of their extra grip; hardwoods, and dense softwoods such as Siberian larch, will need pre-drilling.

Further reading:

TRADA Publication: External Timber Cladding (ISBN 1900510308.)

BS 1186-3; Quality Grading of Cladding Boards & BS EN350-2; Durability of Timber Species

Notes: 1. River Thames, adjacent Belmarsh Prison, Greenwich, London