We have an en-suite shower room with no window. We have an extractor fan that lifts vertically through about 2m of a non-insulated ducting through the attic up to a roof-tile vent.
There's no water trap and we have issues with condensation dripping through the extractor fan on cold days. There is also some damp across the bathroom ceiling. What's the best way to increase effective ventilation in the shower room?
Pat McGovern writes: The purpose of the extractor fan is to remove moisture from the space. By removing moisture, condensation is reduced, and the growth of mould is prevented. The extractor fan should therefore extend the life of your en suite fittings and finishes. It should also prevent unpleasant smells and give the room a fresh feel.
Venting it to another area or into the attic, as you have done, simply moves the moisture to another part of the house. Venting out through the nearest side wall is an option: however, the shortest route is the most favourable. If the current 2m-route through the attic is the shortest, there are a number of things you should check to resolve the problem.
1. Make sure the fan is strong enough to do the job. Fans are sized according to the volume of air they can extract – typically 30 l/sec. The standard-issue domestic axial fan will not manage a 2m duct run. For this distance, you will need a more powerful centrifugal fan.
2. Use solid ductwork between the fan and outside air. Avoid cheap flexi ducts as these will buckle and be less effective. Insulate the ductwork by wrapping it in good-quality wool insulation.
3. Check the existing tile vent on the roof for damage and make sure it is properly interlocked with surrounding tiles. Check the connection between the duct and tile vent. You may have to replace it if it is damaged.
4. Make sure there is a 15-minute overrun at a minimum on the extractor fan after the light in the en-suite is switched off.
For improved ventilation, consider fitting a Velux or similar roof light on the rear roof slope and create a light well to the ceiling level to let natural light and air into the en-suite. There is no requirement for planning permission to do this to the rear roof slope.
The dampness to the ceiling may require further investigation to ensure there is no damage to the ceiling structure. If your ceiling is of timber construction, check for decay and replace it as required.
Current house construction is based on airtightness, so it is important that your fan is removing unwanted moist air from the space. If you have a good fan, look to the infrastructure immediately around it for a solution to your problem.
Pat McGovern is a chartered building surveyor and a member of the Society of Chartered Surveyors Ireland, scsi.ie
