Dealing with condensation

Every time we breathe, cook and heat water for baths and showers, the air in the house takes up more water. In warm weather the air is able to hold onto this moisture, but when the weather cools, this moisture condenses on cool surfaces such as glass or an external wall.

Misted windows
A misted window is one of the most common forms of condensation. Wet windows can soon rot the lower edge of timber window frames.

The only effective answer is to add secondary glazing or replace with double-glazed units that form a more effective barrier between the cold outside temperatures and a warm house.

Condensation in the loft space
The moisture may gather in the loft space and rot the roof timbers, and this can be damaging to the structure of the house if left untreated. It's usually caused by a lack of ventilation, especially in modern houses with felted roofs.

Check that the soffit boards around the edge of the roof have air vents at regular intervals to allow fresh air to circulate, and you may also need vents within the roof.

Tip: If you already have vents in the soffit boards, check that new loft insulation hasn't been pushed right to the edge of the eaves and blocked the openings. If so, clear the vents and check if the area dries up.

Chimney breasts

If a chimney has been blocked up but not properly vented at the fireplace opening, air is trapped and may cause condensation. Although rare, this can still be a problem.

All blocked chimneys should have a plastic or metal ventilation grille in the middle of the fireplace. If yours doesn't have one, fit a grille, let the chimney breast dry out and then paint with an anti-damp paint before redecorating.

Damp rooms
Walls in a particular room can also form surfaces for condensation if the temperature is slightly lower than the rest of the house. This often happens in an unheated spare bedroom as warm moist air is drawn into that part of the house.

The best option is to even out the heating in the house, so try to make sure the radiator in that room is regularly left on though the winter. Condensation may also occur if the room is badly insulated. Make sure the roof space above a bedroom has at least 100mm (4in) of insulation.

You can also fit insulated plasterboard as a thermal on the walls, but this does make the room slightly smaller - so try treating the affected wall with an anti-condensation paint and keeping the room slightly warmer first.

For more information, log on to the British Wood Preserving and Damp-Proofing Association.