Ask the expert

Douglas Kent, technical and research director at the Society for the Protection of Ancient Buildings (SPAB), answers your renovation queries

Q When painting a window, should you paint slightly onto the edge of the glass?

Most definitely. You should paint all coats a couple of millimetres onto the glass beyond the putty line rather than just following it. By coming slightly onto the glazing you fully protect the putty from the weather and prevent rainwater penetration around the glass. The use of precision edge masking tape or a glass scraper can help you to achieve a neat finish.

Qshould I use a dehumidifier to help keep a slightly damp room dry in an old house?

Dehumidifiers are designed to reduce and maintain humidity levels. They can provide an effective way of extracting excessive dampness from old buildings long disused, flooded or recently repaired, but only when they are used in conjunction with air heaters and air movement.

However, where you have condensation problems the permanent use of such devices is a poor substitute for efficient heating coupled with adequate ventilation and air movement. Dehumidifiers are not silent, need a permanent drain and are visually intrusive. Simple lifestyle changes that lower humidity and/or keep surface temperatures above the dew point will usually provide a more practical and less expensive long-term solution than dehumidifiers.

Similarly, whole-house ventilation systems, which can have a role in controlling condensation, should not be seen as the automatic answer in old buildings. Their installation can entail significant harm to the historic fabric of the home.

Q What type of peg should I use when repairing an old timber frame?

Pegs should be cut from oak that is as dry as possible so that they do not shrink and should be ‘baked’ in an oven before use. They must be tapered and rounded at the entry end but left square at the projecting end unless they are to be flush with the surface of the timber they are holding. Firmly tap the pegs in, then do the same on completion and, if possible, again after one to two years. Never use secondhand pegs for repairs.

If you have a renovation question for Douglas, please email periodliving@ futurenet.com *