Externally mounted extractor fan

[simonski1]

We have a first floor property which we let out in a 1960s concrete floored, double-glazed building.

There is a humidity-driven fan in the kitchen and bathroom. During both winters which we've let the property ( different tenants), black mould has appeared during the particularly cold snap on the outside walls of one bedroom, lounge and bathroom,and bathroom ceiling.

Both tenants have told us that water is streaming down the walls at times. Clearly this is condensation, and appears because of "life-style", ie bathing, showering, cooking, washing on radiators and breathing in a warm flat which has cold uninsulated walls.

The mould appears at the top of the outside wall and bathroom ceiling and just above the skirting in the lounge and bedroom - I believe it's above the skirting because it has run down the walls. I think the best solution would be to dry-line the outside walls but that's too expensive and fiddly.

More practical is to introduce a fan into the hallway to "dribble" air movement through the property and put 1 or 2 air vents into each room - currently there is only one in the hallway. Because there already is a grill in the hall ceiling which (presumably) heads through a cavity and appears as an air brick on the side of the building,

I would ideally sit a fan instead of this air brick to suck the air through and out of the flat because this is a) less noisy than having a fan in the hallway and b) I can put it on a timer so that the tenants cannot switch it off. Does anyone know of such an externally mounted extractor fan? Thanks.

 

[swbjackson]

You need this airbrick. Extractor fans don't work unless fresh air is available to replace the air extracted. There are trickle extract fans with heat exchangers built in that warm the incoming air available to fit a 5" core drilled hole. This would be a better solution.

Dry lining the outside walls would just move the condensation somewhere else.

 

[bengasman]

This also happens when rads are used to dry laundry

 

[simonski1]

swbjackson, point taken, I'll leave the airbrick situation as is, and likewise I understand what you're saying about dry-lining. Bearing in mind what I've said about ventilation in the property, ie there is only one air-vent, in the hallway in the centre of the property, my other thought is to core-drill a 3-4" hole and fit a vent behind each radiator on the outside walls. My logic in this is that these vents would be in the lounge, both bedrooms and the bathroom and would not be accessible to tenants and therefore they couldn't block them up. Do you think this would give enough ventilation to work? My concern about the internal trickle vent is the possible noise, cost and tenants being able to switch it off.

bengasman, I'm aware about the radiators being to used to dry laundry problem, but I cannot force tenants not to do this - they always will!

Thanks again.

 

[tryitandsee]

It's an impossible scenario to cure. Putting in holes to the outside will only make the rooms colder than they already are. People/tenants are not daft, any draught coming in will soon be found and blocked.

I have installed bathroom vents on timers, on delays when bathroom light comes on, all an improvement, but with this very cold winter we've just had, mould has come back with vengeance.

The only thing I have managed to do (semi successfully) is buy a portable dehumidifier and paid the tenant for the running costs of it. Also, bleached, aired and then painted the problem walls with proper bathroom emulsion paint (three times as expensive as normal emulsion). Again this helped.

Ventilation and warmer rooms is the only cure, but when times are hard, heating is the first to go.