Venting!!

[chapel]

Hi all,

So we've been preparing our cellar for use as a lounge (it used to be one, but has suffered years of neglect). It has a window at one end to which i've fitted x2 trickle vents.
We've been leaving the door to it open for the last year or so and there is no damp down there really.
Last week i had a newton membrane fitted to one wall which was ragstone and mud (earth retaining) and dry lined. there is also a little bit of membrane on the floor lapping up this wall.
The room has been decorated.

However, just short of sorting the underlay and carpet i've notice some moisture on top of the membrane on the floor and in one corner at the bottom of stairs down. I think this must be condesation - its been around 95%RH down there at 20c the last few days and the floor/walls are cold.

Obviously the trickle vents and leaving the door open cant cope with these extremes, so i'm thinking about mechanical ventilation.

I've seen/heard of vents with humidity sensors used in bathrooms and kitchens- and just wonder if anyone has any experience of such application.

thanks all,
Paul

 

[Lime]

Cellars are usually high-humidity but stable-temperature places at the best of times.
At worst they flood.
I would expect a humidity fan to be operating most of the time in a cellar.
Also I would be very reluctant to place a carpet and underlay down and expect no problems myself even over a membrane.

My experience of cellars is that they are subterranean and that usually means damp at some time or another.

 

[chapel]

thanks Lime...

Does anyone have experience of using a mechanical vent in a cellar?

thanks, Paul

 

[Penners]

I've seen/heard of vents with humidity sensors used in bathrooms and kitchens- and just wonder if anyone has any experience of such application.

Some friends of ours have a town house in Cambridge, with a shower-room in the cellar. This is equipped with a ventilation fan controlled by a humidistat. All I can really tell you is that it appears to work satisfactorily. If you have a shower in there (which I have done) the fan quickly comes on and is quite effective at ridding the room of its steam in short order. They haven't apparently suffered any mould down there. I'm not sure of the volume rating of the fan, but judging by its size I'd say that it's rather bigger than the normal 100mm dia. 50 litre/sec axial type that you find in most toilets or bathrooms.

On the humidistat you can, of course, adjust the RH setting at which the fan cuts in.

I'm not surprised if you've suffered condensation over the past few days. As you mentioned, the heat and relative humidity have been extremely high, and against a cold cellar wall there's bound to be considerable precipitation.

 

[MatthewC]

Some friends of ours have a town house in Cambridge, with a shower-room in the cellar. This is equipped with a ventilation fan controlled by a humidistat. All I can really tell you is that it appears to work satisfactorily.

Given the small altitude of Cambridge above sea level, and the proximity of the rather damp fens, I think that's amazing! Having lived nearby (in Huntingdon ), it always seemed that there was water everywhere locally, and even a small amount of rained caused floods.

 

[JoceAndChris]

We have one of those humidity sensing vents in our London bathroom - it's a basement flat. It works fine. No damp.

The last few days are unbelievable in their effects on my elderly pamment floor in the basement kitchen here. Returned home from a few days away to find it covered in puddles! it often sweats in summer but this is the worst I've seen it.

 

[Penners]

it often sweats in summer

But then so so I. I vent sometimes, too.

 

[JoceAndChris]

Me too! :lol: That's why I forgive the floor.

 

[Keithj]

It fits the rules of physics really, doesn't it.

On a hot day - it was 30°C and 90% humidity here last week - the hot soggy air percolates down through the open door into the cellar and cools. It therefore increases in humidity, so the water will condense out. If it's very hot and humid outside, and cool in your cellar, you will get damp and puddles.

An RH sensor and fan will run until the RH falls below the threshold set. If the humidity outside at ambient temperature is above your RH setting, the fan will just keep running. You certainly need the fan, or a dehumidifier, or both.

 

[JoceAndChris]

Thanks Keith. I shall tell that to Chris, who persists in believing the water is seeping up from the ground through the pamments. I think it's condensation.

 

[Penners]

I suppose it's not impossible that both explanations could be correct. Perhaps the acid test is to wait until you get hot, humid weather that doesn't follow a period of heavy rain (however meteorologically unlikely that may be!), and see what happens.

But I still tend towards your condensation theory.

 

[Keithj]

... or a period of heavy rain without hot and humid. Winter cometh!