Cloakroom ventilation

[abelliott]

Hi, I’m looking for some advice or even opinions on something.

We are currently in the process of changing our under stairs cupboard to a toilet & sink cloakroom. It’s a semi detached & our stairs are next to adjoining properly so no window.

The electrician wants to duct it with a 4 inch pipe and box it in, which will need to be ducted with rigid pipe approx 5m under the floor to get access to outside.

The plumber things I shouldn’t really bother as there won’t be much moisture at all.

I happened to be talking to a diy guy I know who suggested (as it’s just for “bad smells”) to simply run the vent down under the floor joists.

I know it wouldn’t pass building control regulations etc but we aren’t planning on moving/ selling the house.

My question is has anyone else done this and what the turn out has been? Clever idea or terrible?

I know if moisture was involved (ie a shower etc) it would be a massive no no but just for the changing of air?

Any advice or tips would massively be appreciated

 

[freddiemercurystwin]

We had a terraced house where the previous occupants had squeezed a loo under the stairs, that 'extractor fan' merely diverted into the floor void, I just disconnected it and we never used it all the time we lived there, it was never a problem, occasionally the sprogs would do something unearthly in there but an extractor only does so much in any case, 99% of the time we and any visitors used an upstairs loo for no2's, I think that's pretty normal.

 

[stem]

I had a similar situation with a totally internal WC and didn't fancy the underfloor route, so I ran the duct from the cloakroom above the ceiling and between the joists under the bathroom floor to outside. It was a nuisance at the time, but it's been there 17 years and I'm glad I went to the trouble now.

With an underfloor duct, if condensation were created it could sit in the bottom of it. However, I tend to agree that if it's just for a WC then it's unlikely that condensation would be an issue, especially if the duct is insulated. I would be concerned though if there were ever a shower, tumble dryer etc in there.

Also to be considered is the length of the duct from the fan to outside. The resistance created by an extended duct can seriously effect the fans performance, especially if there are also several bends. For the route you describe a centrifugal fan which generates a higher pressure than a standard axial fan would be better. I would also look for one that gives at least double the extraction rate required to make sure it was achieved the required minimum by the end.

The extract below is from the Building Regulations 2010 Approved Document Part F

There's also a post here, from someone with an underfloor duct.

 

[JohnD]

Presumably you are running a 4 inch soil pipe under the floor? Or are you using a mincer?

Why is it too much effort to run a similar duct at the same time for ventilation?

Householders often complain they don't like to use downstairs WCs due to noise and odours. Both should be dealt with at original planning and construction.