Ventiliating a cave in the middle of the house

Property & Home
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Hi all,

Couple of issues about damp to quiz you on but I’ll put the other one on another thread so as to avoid complications.

I have a small cellar which is in the middle of my brick mid-terrace house, ie. it doesnt give on to either the front or the back of the house and is obviously blocked in on both sides so there is not anyway to directly ventilate it.

The cellar was advertised as ‘saine’ when I bought the house and it is indeed dry enough to store items, for the time being. The walls are covered with what looks like cement and over the last few months large amounts of salty deposits have appeared on the walls, suggesting there is significant damp behind them.

I had a couple of different ‘damp experts’ over for free ‘diagnostics’ but quickly learnt that it was just a pretext for them to scaremonger me into purchasing very expensive ‘solutions’ (notably the slathering of the wall with some sort of highly water resistant, pressure resistant material onto the walls).

At the moment the only ventiliation of the cave is into the kitchen extension (before that was built it would have ventilated directly into the garden therefore). There is also a largeish pipe which opens into the cave, travels under the kitchen extension and reappears outside. I havent cleaned this out but I intend to as I suspect this was also an attempt at ventiliation by previous owners.

I have a dehumidifier down there and it usually shows a humidity measurement of 70 when I put it on and it can get down to 50. It gets pretty quickly back up to 70 though when the tank is full and waiting to be emptied. There’s also a pretty manky smell.

I suspect that better ventilation is the way to go, rather than further attempts at sealing out the moisture.

What I want to know is, to what extent this kind of damp is risky for the foundations of the house, how quickly I should act and if you have any suggestions for fixing the situation.

Thank you in advance!

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It’s a cellar…they weren’t ever meant to be dry. Damp and the salts you see are to a degree an unavoidable consequence of wet earth surrounding it.

But ventilation is key - you won’t suck the earth dry with a dehumidifier so your burning electric for no real end result.

A single pipe is better than nothing - and yes that’s to replace the missing vents the extension sealed in. If you can clear that it will help - although your normally looking at two vents so air actually flows.

The obvious damp and heavy salts are avoidable if it’s ventilated - but equally there will be “damp” to a degree.

Cellar walls are cold as well - so prone to condensation if warm or damp air is present.

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How old is the house ?

Is this a year on year problem? Or has it just started this year ?

The reason I ask is that is year has been very humid across France . It happens now and again.

Our cave has become quite damp this winter because of the humidity. I opened up the trap door a month or so back and water run off the back of it like I had turned on a hose. It was wet.

It is just a one off event.

I have heard other stories of similar events this winter.

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Thanks for your replies.

This is the first year in the house so can’t compare with other years yet.

I’ll definitely be clearing out the pipe but I wonder if installing some sort of extractor fan would help? This would use the existing pipe however so it would’t help in creating a through breeze

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It would because of negative pressure, It would draw air through from the house, just as a vmc would do.

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That would be essential.

You need to ensure that air from house can enter the cave. Ventilation grills in the door might be an answer.

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