Timber may decay if it is exposed to persistently damp conditions for a long time months rather than weeks. Any temporary wetting, from water spilt on a wood floor say, will not set up decay if it is dried out quickly.

Rot usually develops where timber is in contact with damp brickwork or concrete. It is not the moisture itself that causes decay but rather wood-rotting fungi which can grow in the damp wood.

The areas of a house most susceptible to rot are:

• cellars

• bathrooms and lavatories

• floor timbers and skirting boards in contact with wet masonry

• conservatories and porches

• window frames, door frames and garage doors

• roof timbers.

Inspection should begin with a careful examination of the walls outside to see if there are any indications of leaking gutters and downpipes, such as green staining from growths of algae and mosses. Then have another look during a heavy shower of rain to pinpoint the problem areas. If damp is dis¬covered, any internal woodwork in contact with these areas should be carefully inspected.

Rot usually begins in wood that is in direct contact with the outside walls, and it may remain undetected until it has reached an advanced stage. Only by taking up the floorboards alongside an external wall is it possible to find out whether the ends of joists in the walls are sound. Leaks from gutters also frequently cause decay in lintels over the windows.

Unsound wood is fairly easy to recognise as it is usually warped and shows signs of its surface collapsing. This becomes more obvious after any damp problems have been solved and the wood has dried out the decayed areas shrink much more than the sound wood. Any areas of woodwork under suspicion should be prodded with a sharp pointed tool, such as a bradawl or a small screwdriver. The point will slip in easily if the wood is rotten, whereas sound woodwork will resist both insertion and withdrawal.

If decay is suspected in a floor, take up the floorboard which runs alongside the outside wall and prod the ends of the joist below. Prod all around the ends and pay particular attention to the areas where the joists enter the outside wall. In old buildings with cellars, the ground-floor joists can often be con¬conveniently inspected from below.

Rot should also be suspected in a floor if wide gaps appear between the skirling and the floorboards. The suspicion is con¬firmed by the development of fungal growths on the surface. Suspect decay in wood block flooring if the blocks tend to become loose or to curl up at the sides.

Rot in window frames and external doors usually occurs at the joints between the lower rails and the upright pieces. It is particularly prevalent when glazing beads (the small strips of wood that fix the glass) have been fixed without external putty or where putty has failed.