Timber framed buildings and internal beams are often admired for their pristine beauty and perfection but it is easy to forget that they are vulnerable to decay and damage if not properly maintained and repaired. Sadly, poorly thought out alterations and the use of inappropriate materials have frequently wrought havoc with the timbers, not only causing damage aesthetically but structurally, with the result that they are no longer adequate to bear the loads placed upon them.
Even where no timber is visible, it is worth remembering that it is likely to be present. As well as being used for complete frames, timber was employed for lintels above doors and windows, joists and other elements. In some cases, changes in fashion, or the need to make timber framed buildings more weatherproof, meant that they were rendered over externally or were clad in tile hanging, while some were ‘re-fronted’ in brick or stone.
Understanding the way timber has been used and its structural importance is vital when assessing its condition, carrying out repairs or making alterations. For these reasons it is advisable to employ a surveyor or structural engineer with experience of buildings of the same type and age when problems are suspected or major work is to be done.
Check for damage - Decay is the biggest enemy of timber and results from moisture, which leads to rot and beetle infestation. Always try to identify the source of dampness, such as blocked gutters or downpipes, inappropriate external cement renders or high ground levels and deal with these issues rather than just tackling the symptoms. Ensure the problem cannot occur again through repair and regular maintenance and monitor the affected areas after the issue appears to have been rectified. Test suspect timber by prodding with a penknife: sound timber will resist penetration. Most old buildings have evidence of beetle attack but much of this is historic and unlikely to be of concern. Active beetle infestation is often revealed by fine dust or ‘frass’ where the insects have emerged through ‘exit’ holes. Where holes are present, look carefully to see if their walls are dark and dirty. If they are, the attack is likely to be historic rather than live. Clean, light coloured holes are probably more recent. In the past, timber was often assessed and tidied up by ‘defrassing’ – slicing off the affected timber. This is a highly destructive process that radically alters its appearance and results in the loss of the original surface.
Where an assessment is required to ascertain the structural integrity of a beam, non-destructive techniques are now available. At its simplest, this involves drilling into the timber with a fine drill bit but specialist companies can undertake more accurate testing. Bear in mind that timber treatment relying on the use of chemicals will only deal with the symptoms of the problem, not the cause. Chemical treatment is generally unnecessary if the source of the dampness has been removed and the timber has dried out because further decay will be limited if not halted completely.
Many beams have been painted or have darkened with age but think hard before attempting to clean or strip them: in a few moments ‘cleaning’ can destroy the patina of age that has accumulated over hundreds of years. Dirt and dust can usually be removed with a soft brush or damp cloth. Avoid using linseed oil on beams as it stays sticky and attracts dirt. If a finish is desired, apply a thin coat of beeswax polish. Removing paint from beams requires patience, time and effort. Never use shot blasting or other abrasive methods – the surface of the timber may be removed and worm eaten wood underneath revealed. In addition, the original shape and texture of the beam will be lost. Liquid paint strippers, poultice systems or hot air guns may remove paint. Beware of the risk of fire and never use a blowtorch, protect surrounding areas and understand the dangers associated with removing lead paint. With any method, always test a small area first.
Appropriate solutions - Approach repairs with caution and consider the structural issues involved but never assume that timber needs replacing. Medieval beams were frequently much larger than were necessary so even where there is rot, the timber may still be capable of carrying the structural load. Where damp problems exist, rafter feet and the ends of timbers built into brick or stonework often become saturated and rotten. Wherever possible avoid replacing timbers and instead make repairs so the least possible amount of original wood is lost.
One of the simplest, most honest and cost effective repair methods to rotten timbers is to use a metal strap. A strap can be made up by a local blacksmith and is simply bolted into place to hold decayed elements together. The strap method has the added benefit of being reversible and causing the least possible disturbance to the surrounding fabric of the building. Where it is necessary to cut out timber and make repairs, a good carpenter with an understanding of old buildings should be able to scarf in new sections using traditional jointing methods.
A major problem with timbers is that electricians and plumbers ‘notch’ into the top of joists in order to lay cables or pipes, dramatically weakening them. Where this has happened, joists can usually be strengthened with metal straps or by fitting additional joists alongside.