Period character guide: Timber frames

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My first close encounter with timber framing was as a teenager. It was unpleasant; I started banging my head on beams. The ceilings had not become lower, instead the inevitable had happened and I had grown taller. Although low beams might cause some of us to adopt a permanent stoop, they are an intrinsic part of an old building’s character so are worth caring for.

Timber framing flourished in the Middle Ages and the many wonderful examples that still exist, in places such as the Wealden villages of Kent, Sussex and Surrey and towns like Lavenham, in Suffolk, pay tribute to the carpenters’ art. Timber framing is the skeleton of many houses and cottages, forming the walls, floors and roof. Oak cut and shaped soon after felling when it was still ‘green’ – and so easiest to work – tended to be the timber of choice because of its durability.

Trees were selected specifically for individual parts of the frame depending on their height, girth and shape. For example, ‘cruck’ construction consists of pairs of curved posts inclined inwards and meeting at the top, producing a distinctive triangular appearance. Other timber buildings are constructed so that the entire roof weight is supported on the ‘box’ frame of the walls. The frames themselves were prefabricated on the ground and, when erected, the joints were held together with wooden pegs.

In higher status buildings, beams were sometimes finished with mouldings or chamfers. If a ceiling is taken down and these are revealed, it indicates that the floorboards and joists above would originally have been left exposed. Regular nail holes in beams are a sign that, at some point, a lath and plaster ceiling existed.

New green oak frames
The tradition of building timber frames continues today at Carpenter Oak & Woodland’s yards in Wiltshire and Scotland. The process starts with the selection of good quality timber. Andy Parker, commercial director for Carpenter Oak & Woodland, explained to me that, for each component, the framer must check the size and position of knots, the angle at which the grain meets the edge of the timber and a number of other strength reducing characteristics.

Unlike the timber that a joiner would normally use, green oak has natural twists and deflections (bends). Andy told me that it is accommodated by using a method called ‘scribe framing’. This necessitates working from datum lines struck on the timber using a piece of inked string, rather than from the timber’s edges. Because the datum is straight, deflection can be accounted for in the position and depth of the joints.

In the framing yard, the individual timbers are set out as they will relate to one another in the finished frame. Once the framer is sure he has all the critical dimensions established, he starts to mark out each joint from the datum lines. The joints are then cut, mostly using power tools, and the air is infused with the aroma of fresh oak.

According to Andy, another characteristic of traditional framing is draw boring. This involves joining timbers using oak pegs in offset holes to ensure tight joints. Typically, with a mortise and tenon joint, the hole in the mortise is offset to the hole in the tenon by about 3mm rather than drilled straight through. It is marked before drilling using a tool called an offset pricker. When the tapered oak peg is driven home during erection it acts as a wedge and pulls the joint tightly together.

Poise and balance
Just as with a skeleton, the elements that make up a timber frame are vital to its stability. Damage through rot, overloading or the cutting away of timbers can change the way the frame works. It may not always be apparent what is going on so, when consulting ‘experts’, be sure to employ those who are familiar with such intricacies.

‘Reading’ a frame can be fascinating as it often holds clues to the building’s history and original layout. Joints, peg holes and carpenters’ marks may indicate where beams were once fixed and the position of walls, door and window openings that no longer exist.

A timber frame is a good way of extending an old house, although it is important to employ an experienced framing company. About 60% of the cost will be for the fabrication and this will be influenced by the style of the frame, with the number of joints, rather than the amount of timber, pushing the price up. Some manufacturers are now using computer-controlled machines but these result in a more regularised frame than one made using scribe framing.

Care and repair
Repairs should be approached with caution; always try to replace as little timber as possible. Work may consist simply of strengthening a failing joint with a purpose-made metal strap. Alternatively traditional repairs may be needed, by a skilled carpenter who is used to working with timber frames.

One of the most common questions I get asked is how to clean beams. There is no magic formula and it is worth remembering that ‘cleaning’ can destroy the patina of age that has accumulated over hundreds of years.

Most methods of cleaning or stripping need patience and are invariably time consuming and labour intensive. If you do proceed, make tests on an inconspicuous area first. Never shot blast beams as this will remove the surface of the wood and may reveal a mass of worm eaten timber that will be hard to consolidate. Removing beetle-affected timber by hacking back to sound wood is a destructive process which radically alters the appearance of the timber and destroys the historic surface.

Dust and dirt may be removed with a damp cloth or a soft brush and, if a light sheen is required, apply a thin coat of beeswax polish. When new timber is used it will look stark against the old but, rather than staining it, give it time and it will take on a colour that blends in.

ABOVE (clockwise from top): Freshly cut timber laid out for inspection at Carpenter Oak & Woodland’s yard; A timber beam is being prepared. First a datum line – in this case an inked piece of string held taut – is struck on the timber so that the deflection can be accounted for in the position and depth of the joints; A mortiser is used to cut the joints; Mortises are finished by hand.
BELOW (clockwise from top left): The ‘shoulders’ of the tenons are finished by hand; The frame is assembled to check the joints at Carpenter Oak & Woodland; Embellishments to the timber frame are skilfully carved by hand; The timber ‘skeleton’ emerges as it is erected on site; One of Carpenter Oak & Woodland’s completed frames.

Word for word: A glossary of timber frame terms
CARPENTERS’ MARKS A modified form of Roman numerals scribed on the timbers at joints to ensure that the frame can be assembled correctly when the building is erected.
INFILL PANELS These fill the spaces between the timber frame. Originally they were wattle and daub – a lattice panel of hazel or willow covered in a mixture of clay, dung and straw – but many have been replaced with lath and plaster, brick or stone.
JETTY An upper wall projecting beyond the wall below to form an overhang and provide a greater floor area to an upper storey.
MORTISE AND TENON JOINT A traditional way of joining two pieces of wood together – the mortise is the hole, the tenon is the piece of wood that slots into it to hold timbers together.
SOLEPLATE Timber that sits on the brick or stone plinth of the house, forming the bottom rail of the frame. The posts of the frame are mortised and tenoned into the soleplate, distributing the load across the base of the building.

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WORDS ROGER HUNT PHOTOGRAPHS ROGER HUNT; CARPENTER OAK & WOODLAND
Featured in the August 2009 issue of Period Living