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February 2016

Question

We have an ongoing issue in a second floor bathroom. When there is a lot of rain (as recently) and presumably when the wind blows in a certain direction, rain appears to get in through the outside wall extractor-fan vent cover. This is causing damp and water damage in the bathroom. Is there an external extractor-fan vent cover that could be fitted to prevent this from happening?

Answer

Ventilating a bathroom is essential to reduce the propensity for water vapour to condense within a home and is a requirement of the building regulations (Part F – ventilation).

On second floors, mechanical fans are usually provided through ceilings as it is more difficult to install them through walls.

Through-wall vent fans sold in must be CE marked and tested for weather tightness by the manufacturer to avoid the symptoms you describe.

Looking at your photo it’s hard to see what exactly the difficulty is. Could the louvre be upside down?

Your problem is possibly a result of poor installation allowing water to run along the outside of the unit having entered via the seal between the wall and the external louvre flashing which seems to be dislocated.

If the wall is extremely exposed or prone to swirling gusts caused by nearby buildings then the manufacturer’s weathering design may be exceeded by these local conditions or rain could be forced up the wall and past the louvres.

If so then consider fitting a proprietary plastic or metal weather hood sealed to the wall.

These units may also contain a “back draft shutter” to further reduce weather ingress.

These can be noisy in windy conditions so take care in selecting an appropriate unit. Search online, you’ll find there are many types available from just a few euro.

A huge amount of energy is extracted with the stale damp air from bathrooms and kitchens by mechanical extract fans.

In new houses extraction from bathrooms is increasingly specified with “heat recovery ventilation units” such as Nilan or Vent-axiawhole-house systems.

Single room models are also available and are well worthwhile installing if you are considering replacement of your existing extract fan to resolve your problem or as a comfort and energy improving solution. They also cut down on noise problems.

If you still have concerns don’t hesitate to contact a building surveyor: they are trained in building pathology and will study the problem to arrive at a resolution.

Fergus Merriman is a Chartered Building Surveyor and a member of the Society of Chartered Surveyors Ireland.

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