Underfloor mechanical ventilation/fans

[ianmc]

Hi all - I have run out of ideas as to how to fix a condensation problem. Situation is 1960s bungalow in Cornwall (not great construction and high humidity generally) with a suspended wooden floor. I replaced the floor across one side of the house when we bought it about 5 years ago due to a combination of rot and woodworm, caused I thought by blocked airbricks (botched cavity wall bead insulation). Pretty much all of the underfloor had a thin coating of white mould on it. I cleared and put in additional airbricks on all sides and thought that would cure it. There is still a persistent mould/damp smell in the house, particularly in areas that are carpeted. I have sealed the edges of boards to no avail, and in inspecting under the floor there mould is still there, albeit you can wipe it off easily with your hand. It does seem warm and stagnant down there, even on a windy day.

I can't see how putting any more airbricks in can make much difference (18 at the moment!), and I have knocked through various walls under the floor level in an attempt to get the air moving already. There are no leaks in pipework/drains and I have triple insulated the cold pipe to knock on the head any condensation there.

I am assuming there is moisture getting in somewhere, as in permeating the concrete foundations generally, which is overpowering the passive ventilation I have been able to create. So I either (or as well I suppose) reduce the porosity of the concrete in some way or increase the ventilation rate with a low energy fan.

Any thoughts on either? I have only been able to find radon gas mitigation fans - are these the only option?

Thanks in advance, Ian

 

[foxhole]

What ventilation do you have in the house, airbricks? fans in bathroom and kitchen?

 

[ianmc]

Hi foxhole - 18 airbricks all round, extractors in the bathroom and kitchen. We also have a ceiling mounted PIV on a low setting in the middle of the house. So quite a lot - or at least as far as my experience goes, and also why I am a bit baffled!

 

[foxhole]

You don't dry clothes indoors do you? have trickle vents in the windows? high level vents?

 

[ianmc]

We dry clothes in the box room in winter with a dehumidifier. This is the one room in the house which doesn't smell! Most of the (PVC double glazed) windows are vented - I retro-fitted a few that weren't.

 

[jj4091]

With all those air bricks are you actually getting an air flow under the floor or is it just getting in & circulating? Have you tried ( on a windy day ) checking that the air blowing in the weather side is actually being blown out of other air bricks. Can you try putting a smoke bomb under the floor & see what happens. If you have no damp proof membrane under the sub-floor it is going to be difficult to stop the area under the wood floor being damp. Is the DPC in the walls above outside ground level?