Sub-Floor Ventilation

[Kingpinrich84]

Hello People,

What are peoples opinions on fitting active ventilation in sub-floors?

I have an old victorian suspended wooden floor with which I have just finished laying new boards and replacing rotten joist ends.

Airbricks are present at the front of the property but on investigation only ventilate into the wall cavity! There is a single unobstructed airbrick at the rear. To encourage ventilation i am playing with the idea of fitting a shower type extracter van under the floor or at the airbrick ....any thoughts? My immediate worry is a potantial electrical/fire hazard.

Thanks.

Ps.This is my first post on this site...new home owner !

 

[freddiemercurystwin]

Add some more air ricks to the rear and ensure the ones at the from vent into the void beneath the floor. There shouldn't be any need for mechanical ventilation if enough air bricks are present.

 

[Kingpinrich84]

At the front a dwarf wall supporting the floor makes access with a drill very difficult, unless i temporarly remove it. I think it would also badly impead the flow of air, this combined with The sub floor being below ground level inside, i'm not convinced it would make very effective ventilation.

For considerbly less hassle (famous last words) maybe a low voltage van, or extracter placed at the rear air brick, then some grills in the floorbooards so air can be pulled down into the void and expelled out?


What about a solor powered fan?

 

[Static]

Would only effectively work if you put a fan to blow air in one side of the house and suck out the other.. with the cost of running two fans 24/7 you could probably get in 3 builders to knock a few air bricks in..

 

[Kingpinrich84]

The dwarf wall and wall plates make access very diffuclut to the front inside wall, i'd have to remove them temporaly to be able to get a drill in.

How about having the fan(s) on a timer? or solar power?

One thing that puzzels me, airbricks allow cold air from the outside into the floor void, when this mixes with the warm air from the room above would this not create ideal conditions for condensation?

 

[freddiemercurystwin]

No because its dragging the air through, its not staying there. Effectively its open to the atmosphere.

It may be worth investigating Radon Fans if you're dead set on avoiding the simplest most effective methods albeit troublesome to install.

 

[ajrobb]

A conventional suspended floor has air bricks front and back with like an open lattice brickwork for walls in between. In the winter, cold air from outside is very dry, even at 100% RH (e.g. overnight with dew forming). When it gets under the floor it warms up and the RH drops.

I think you should aim to keep the underfloor above dew point at all times to prevent condensation and maybe at least 5°C above dew point for much of the day to allow dampness from other sources to dry out.

I like the look of the Silent 100 CHZ bathroom fan. It is supposed to be efficient, very quiet and has a humidistat control. Put it under the floor at the end with the dwarf wall and run 4" drain pipe from the fan to a new opening at the other end of the building. You then have forced ventilation drawing air across the building.

As an aside, ventilation becomes even more important if you insulate the floor.

 

[Kingpinrich84]

I'd be pretty chuffed if i could control my sub-floor temperature to within 5°C of the dew point!

Thats the sort of thing i was thinking.
I've seen fairly cheap in-line fans that come with ducting, originaly meant for showers/bathrooms, but I can see why they could be used for this applicaiton. My concern would be noise and how to wire it in.

How about a low voltage fan?