Timber framed buildings

Timber Framed Buildings
It is seldom possible to make a conclusive inspection of the timbers in a timber framed building because the greater part of the surfaces of the “exposed timbers” are usually hidden by the surrounding or in-filling fabric. Careful comparison of a completely stripped timber framed building with such a building which is occupied or fit for occupation illustrates this clearly. Nobody can express an accurate opinion of timbers which cannot be seen.

The main structural members of the frame, the corner posts and horizontal plates which carry the roof and the first floors, are often completely hidden, particularly at their bearing ends which are the most important and the most vulnerable parts of them. At ground floor level, the main sole plate on which the whole building rests may be partly visible from the outside and inside, but the condition of it internally cannot be discovered without extensive drilling. This cannot be done during a normal survey. The sole plate is seldom protected by a damp proof course, unless one has been inserted in recent years, and it is therefore likely to be subject to decay. It may be necessary in some cases to cut it out in short sections at a time, and replace it together with new brickwork incorporating a damp proof course.

The construction of the upper floors in this type of building frequently prevents access to the underside of the floorboards. If the joists or “beams” are exposed in the ceilings below, “ceiling” material is often fixed directly to the underside of the floorboards. In other cases, wear in the original floorboards may have been covered up by a second complete layer of floorboards on top of the original. It is common to find insulating material under the floorboards in between the joists. The use of wooden ground floors was unusual before the 19th century. Originally, timber framed houses had earth and later brick built ground floors. Buildings were not, therefore, designed for wooden floors and where these have been added later, ventilation has been impossible and the joists have usually been laid directly on to the earth. They are, therefore, prone to fungal decay. If extensive renovation has been carried out in the past, it is even more difficult to give an opinion of the condition of the timbers, because the more obvious defects may have been removed and others covered up by elaborate and often expensive decorations. Timbers exposed internally may have been covered by a sealing decorative finish, which makes penetrative treatment with effective insecticides impossible unless this finish is first removed.

What then can be done? Firstly, such buildings do have some advantages over modern buildings. They are not prone to extensive outbreaks of dry rot (Serpula lacrymans). They do not suffer from rising damp in the walls (apart from the rising moisture that may affect the sole plate). The oak or elm of which they are constructed is resistant to fungal decay and is not likely to be structurally weakened by the Common Furniture Beetle, which will only cause serious damage in the sapwood of the timbers. In any case, there is usually a large margin of safety because the timbers are frequently bigger than they need be for the loads they have to carry. Generally then the biggest danger is from attack by the Death Watch Beetle (which is associated with fungal decay) and pockets of fungal decay which have occurred if moisture had been allowed to enter the fabric of the building for any length of time. It is, therefore, essential to ensure that the building is made weatherproof and is maintained in a watertight condition.

Specific areas where necessary can be chemically treated to preserve the timbers, but it should be understood that the extent and effectiveness of such treatment will be limited by the extent to which opening up and full exposure of the timber is economically practicable. This cannot be determined during an initial inspection just as a doctor could not undertake a general examination of a patient who is fully dressed in winter clothes. Any general opinion given in such circumstances must be without prejudice.