Find me a wreck

As with a classic car, many prospective purchasers fear an old house will collapse at every corner or require unobtainable spares. Most parts of an old building do not, however, have a definite lifespan: their durability will depend on how they have been looked after. Timber, for example, should suffer decay only if the building is damp or poorly ventilated, in which case it is more likely to result from poor maintenance or bad modernising than original design defects.

Specialist advice will determine whether an old house is essentially sound or an accident waiting to happen. Many architects will be unfamiliar with older methods of construction and materials such as roofing stone, earth walling and wattle and daub. The Royal Institution of Chartered Surveyors has an accreditation scheme in conservation for its surveyor-members, and the Society for the Protection of Ancient Buildings can suggest specialist advisers and contractors.

Old buildings are generally built with soft materials that need to "breathe". Hard cement mortars and renders or impervious modern paints are incompatible with older structures and lead to dampness and decay. Choosing appropriate traditional materials, such as lime mortars for pointing or render, should help prevent problems. It is vital, too, to check regularly that gutters, downpipes and drains are working, and that underfloor ventilators are clear.

About half a million old buildings in England are now listed, ranging from mansions to hovels and if they are in reasonable condition listing often increases their value. The downside is that you will need consent for any alterations, although if these are modest and sympathetic it should not be difficult to obtain.

The SPAB has a property list, available to members, that identifies old buildings for sale but in need of repair, ranging in price from £10,000 to £10 million. In addition, many councils now produce information on listed buildings that are "at risk" and SAVE Britain's Heritage (020 7253 3500) sells a countrywide list. Many of these buildings will not be on the market but, with negotiation, sometimes they are available to buy. Where a council cannot secure repair of a listed building, it occasionally resorts to compulsory purchase and may then need to find a buyer. Building Preservation Trusts (020 7930 1629) often take on listed houses that councils have been forced to acquire, and sometimes they will sell these after completing basic structural works.

The internet is a valuable tool for hunting independently for old houses needing work, though few sites as yet allow searches based on terms such as "listed" or "in need of renovation". Disused farmhouses and cottages are usually sold by estate agents that specialise in the agricultural market. Auctions often include old buildings needing work and may yield a bargain.

Matthew Slocombe is deputy secretary at SPAB (020 7377 1644).