Cellar ventilation

[davidcoleman]

I will be starting a cellar refurbishment shortly. The cellar has already been tanked (although I'm not sure how well) and boarded and a floor laid.

There doesn't seem to be much damp but there is a little mould here and there. It's currently being used as a store room while refurbishing the rest if the house so it's not really getting much of an airing.

At the moment there is no ventilation which I think may be causing the mould so I was first going to install some proper vents/fans.

My question is exactly what is the best form of ventilation?

I have noticed when passing, on a lot of refurbs around my area, that what look like 2 bathroom extractor fan outlets are installed. Are these just ordinary bathroom extractor fans both venting from the cellar (from the ceiling I imagine) to outside or maybe just just vents with no fans?

Thanks in advance for any info on this.

 

[JohnD]

there will be a slight benefit to having an "air-in" vent from outdoors as well as the extractor. This is because the "outdoor" air will generally be drier than air from inside the house.

If you put a plain vent in the external walls, one on each side of the house, you will get a through-draught that will ventilate your cellar almost all the time without needing a fan. A few air-bricks will do this and need no maintenance (apart from brushing out the dust and cobwebs once a year).

 

[davidcoleman]

Thanks john

So when I see these 2 vents down at ground level at each side of the house or celler they are just vents and not fans? So there is no need to fit a fan? I suppose the fan would need to on all the time to to keep a constant flow of air, but this would occur naturally if they were both just open vents.

Thanks

 

[JohnD]

Vents on opposite sides of the house will almost always have a slight air current between them.

If you have seen houses with two vents next to each other on the same wall it is possible one is trunked down to floor level and one is at cellar ceiling height - there is also a slight airflow from bottom to top, as the moist cellar air will tend to rise (as water vapour is lighter than air).

Otherwise, if there are two vents at the same height on the same wall, they are just to give twice the airflow of a single vent. but vents on the opposite wall are important to give airflow.

 

[davidcoleman]

Thanks again.

That all seems to make sence and ties up with what I've seen.

Bearing all that in mind where would be the best place to position the vents in my situation (below)?

On the outside the vents would have to be at ground level in the ground floor joist space. I was going to use some sort of flexi pipe and vent down out of the cellar ceiling. I'd put one vent at the far left and right of the cellar. Would the vents be best in the ceiling or lower down. I'm building out the wall to cover the consumer unit etc. on this wall so could run the flexi pipe behind this to a lower level or even floor level if it makes any difference, although in the ceiling would be easiest.

Thanks

 

[JohnD]

You can get a sort of Z-shaped duct for air bricks that enables the outside and inside vents to be at different heights. I don't know the correct name for it. You'll just have to take out several inside bricks to fit them. I would be inclined to put them all in just below the ceiling, in the wall.

Make sure you have a mesh to prevent mice and beetles getting in. If the outside brick is near ground level dig out the earth a bit to prevent rain or mud splashing in. If necessary you can make a small pit, lined with bits of slab and with shingle at the bottom.

If you decide to use round duct or soil pipe, I'd hire a core drill to make 110mm round holes through the wall, instead of using rectangular air bricks. This is very quick and easy though a bit dusty.

 

[davidcoleman]

Thanks again.

I'll go the round pipe and core drill route as the front of house is rendered. I'll then run the pipe down behind the stud wall and out of the wall below ceiling height. I'll put some sort of vent covers on to stop insects and rain getting in.

 

[Frederick]

Lack of ventilation is often a problem in cellars and can lead to condesnation problems - in fact the British Standard for basement waterproofing (BS8102) effectively requires ventilation if you are going to use the cellar for habitable space - see http://www.cellars.co.uk/cellar-conversion.php

The humidity controlled fans are the same type as used in bathrooms. However, it pays to buy a good one as the moisture sensor on the cheap ones often packs in after a few years and the fan won't turn off by itself which can get pretty annoying - so people often block it up or switch it off - which defeats the object of having a fan in the first place.

 

[StevenW]

After tanking all the walls in my cellar, using a DPC in the floor and walls, then putting a sub floor, then marine treated flooring, I have a problem. Due to the lack of airflow, the room actually causes shortness of breath as there is not much oxygen down there!

Sounds bizarre, but since I boarded up the ceiling as well, this has gotten worse. I now have to rip some of the wallboards down and take all the building waste out of the coal shute to ensure I get ventilation to the cellar, so don't make it airtight!