The wood used in building and fitting out your church will have been chosen for two reasons:
1) Availability. It is unusual to find much carpentry and joinery in Scottish churches which has come from local woodland. As supplies of suitable building timber diminished during the Middle Ages and even earlier, imported softwood from the Baltic countries and, later, North America came into common use in Scotland. Scottish-grown hardwoods, such as oak, remained available in places but their use was not widespread. From the late 18th century, more exotic hardwoods were brought in, especially from Britain's imperial possessions.
2) Fitness for Purpose. Structural timber must have inherent strength and be available in the sizes needed to bear the expected loads. As congregations grew in size during the 19th Century, many churches built first and foremost as 'preaching houses' required wider roof spans, uninterrupted by columns preventing direct sight of the pulpit. To achieve these spans with traditional structures and to bear the greater roof loads, more massive beams had to be specified, often from distant sources. Items subject to wear and tear, such as exposed flooring, doors and pews, need durable joinery while decorative woodwork is chosen to be attractive in colour and grain.
Wood is a living material subject in its natural state to eventual decay and disintegration. Prolonging its normal life cycle depends on understanding the strengths and weaknesses of different types of wood, how they react to their (unnatural) role in the built environment and how best to protect them from their three main enemies, rot, insect attack and fire.
A walk through woodland will reveal fallen trees and broken limbs gradually being eaten away by insects and by plant growths such as fungi. The same process will almost certainly take place in your building, given the presence of the following conditions:
1. Moisture. Rot relies firstly on dampness and humidity to form and spread. A bone-dry building will never suffer from rot. Scotland's climate, however, hardly favours such dry conditions and the need to prevent water getting into the fabric has already been emphasised. (see Roofs and Walls).
2) Poor Ventilation. The growth of rot will be further encouraged where the vulnerable timber is boxed in, without access to moving air. Rot attack can be fended off by ensuring good ventilation and air circulation around woodwork enclosed and out of sight, such as under floor spaces and the internal linings of outside walls. Keep built-in vents free of blockage and do not remove or close off roof ventilators without providing another way of keeping air circulating in roof spaces.
3) Timber quality. Sapwood and poor quality timber will be the first to be affected by rot. The heartwood of most softwoods and many hardwoods can resist rot for some time.
4) Temperature. Given the encouragements of wet timber and lack of ventilation, rot may anyway be slow to take hold without the extra incentive of warm surroundings. Dry rot flourishes most at a temperature of 23 degrees centigrade but we should not forget that warmth is also necessary to combat damp.
Look out for two prevalent types of rot. Both take hold when fungal spores start to develop on damp timber which is also warm enough to give them opportunity to grow and spread.
1. Dry Rot which is only 'dry' in its final, most obvious form as a mushroom-like fruiting body, flourishes in moist, airless conditions, commonly in enclosed roof spaces, damp cellars, timber 'safe' lintels and behind wall panelling. It can be sensed through the typical 'foosty' smell it gives off when active and may be recognised by the cube-like disintegration of infected wood.
Given sufficient moisture sources, it will spread very quickly. Its spores and filaments can even travel across other materials, spreading the outbreak well beyond its original source.
It must be quickly dealt with, first by tracing and removing every possible source of moisture, by introducing effective ventilation and then examining the timbers closely to see how far they have been damaged. Where its strength and function has been affected the wood should be replaced with sound material. This will sometimes include cutting back rotten parts of structural beams and joists and splicing in new timber, adding steel or ply strengthening or patching with epoxy resin, all on the same principle followed by a dentist when filling and repairing a decayed tooth.
2. Wet Rot is usually more localised and requires higher levels of moisture than dry rot but it is still capable of causing considerable harm. It typically affects unpainted or poorly sealed joinery where water can gather unnoticed such as the sills and lower frames of windows. It is also common in timbers such as wallplates when in contact with wet masonry in under-ventilated spaces.
The cure is similar. After stopping the ingress of water, cut out and replace with new, well-seasoned wood. Note, however, that while the unaffected but still-damp remaining wood is drying out there remains the potential for dry rot taking over, as it prefers less moisture. Hence the absolute importance of maintaining proper ventilation.
Remember that fungal spores exist everywhere in the atmosphere but that they will never cause problems where the timber is dry and they can find no means of support. Only in damp conditions will they start to flourish.
1. Eliminate the cause of dampness immediately and allow the affected area to dry out as fast as possible
2. Ensure that all rotten timber is examined, replaced as necessary and that all infected material is safely destroyed.
In treating an outbreak, beware of allowing strong and toxic chemical products to be used on nearby woodwork. Any remaining rot spores and filaments will die away and be harmless in dry conditions. When treatment is recommended, effective 'greener' biochemical products are now available and these should be preferred.
We are luckily free from the ravages of timber-loving insects in tropical countries and even from the attentions of the Death Watch beetle which still seems to prefer a more southerly climate.
Woodworm is our most common insect predator. In its adult form it will bore its way into softer types of timber, inside which its larvae will grow and emerge having sucked out the wood's natural humidity and made it brittle and useless. However woodworm, like rot, can only tolerate damp conditions and a dry, well-insulated building will not allow the larvae to survive.
If you spot the small circular holes which give away the presence of woodworm, do not automatically assume that it is still active. Previous careful inspections should have recognised obvious signs and may have recommended no action. It may be that the damage has only affected the outer layers of the more substantial pieces of timber, normally the sapwood, that the worm is now inactive and that the inner core is still sufficient for purpose. The strength of the timber should therefore be tested physically before deciding what should be replaced.
When it appears that it will be necessary to get rid of existing woodwork, do not assume that strong insecticide spraying is called for. Equally effective non-toxic biological methods of interfering with the insect's life cycle are now available.
Regarding its effect on timber it is worth knowing that large beams and columns will withstand fire better over short periods than many other structural materials and that damage may be limited to charring of the outer rings, leaving the main core largely unaffected.
Timber does, however, burn and wooden panelling, lining, sarking, etc. is easily lost in a fire.