Damp cellar conundrum

[Sploing]

My house is an 1950’s, stone built cottage with a cellar.

The cellar has been tanked (Not very well) at some point and has an air brick in one corner just above the outside ground level, a radiator, a door separating it from the rest of the house and a variable speed axial fan fitted by a previous owner extracting air into a riser pipe on the outside of the building (he made models and I assume the fan was for fume extraction)

The cellar is always damp, anything I put down there becomes either rusty or mouldy or both. Hygrometer readings generally show 100% RH.

This dampness is the case all year round, even during the 2 month heatwave we’ve just enjoyed.

I’ve tried a variety of things to correct the situation such as turning on the fan (no change even after days of running), opening/closing the door (nothing)

The only thing which seems to dry things out is turning on the radiator which I generally only do in winter.

The dampness is particularly concentrated near to the air brick, the ceiling timbers there are always damp and mouldy and none of the others are.

Can anybody suggest what might be the cause of the problem?

Would blocking up the air brick help?

Thanks,

Sploing

 

[Feltwell]

Blocking up the air brick will make it worse!

Your cellar was never designed to be a habitable room, which is the root cause of the problem. Tanking is effectively just trying to build a sealed box inside that original damp structure - no matter what you do with it that original outer structure will remain damp. OK, you can tank successfully and achieve that dry inner box, but the gamble then is that you're stopping that original outer box from breathing and losing it's moisture into the air in your cellar - so what can happen is that damp is then pushed further into the upper structure of your house. It's only a possibility, but it is a very real one.

You can put a dehumidifier down there or ventilate it more and you'll reduce the humidity in the air, but you're fighting a losing battle I think to use it as a habitable room. As a straight storage room I'd say ventilate it more to the outside, introduce more air bricks if you can to get a cross-flow of air, and accept that it will always be damp and you are limited in what you can keep down there.

In my cellar I have a freezer - which the damp atmosphere doesn't seem to bother - plus stuff that the damp won't affect - such as plastic tins of paint, ideal in a cellar as it never freezes.

 

[Flyfisher]

I agree. Cellars and damp go together like Morecambe & Wise.

Unless they are constructed from a hermetically sealed box sunk into the ground they are basically a permeable structure sunk into an effectively infinite source of moisture. Improving the ventilation will help to reduce the humidity but it will never cure it completely. Likewise, a dehumidifier will help reduce humidity but it will need to be left running continuously.

I use a dehumidifier in our small cellar during the warmer months, mainly to help keep the humidity in the ceiling beams at a reasonable level and not dripping with moisture as used to happen (warm summer air mixing with cold cellar surfaces etc) and this seems to work fairly well, though it’s far from being a habitable room . . . and therein lies the problem - trying to use a cellar for something it was not designed for. They are perfect for storing things unaffected by humidity such as wine, other bottled foods, coal etc, but not really that great for things like soft furnishings or any valued books.

 

[Sploing]

Thanks for the replies.

I’m not looking so live down there, I just don’t want my tools to keep going rusty.

I know cellars ought to be damp to a certain degree buta couple of things which bother me are:

- Why does it seem to be wettest near the air brick (incidentally close to the bottom of the stairs leading to the rest of the house), does this suggest the damp air is somehow being drawn in?

- If it’s just a ventilation issue why does turning on the extractor fan (a large, high capacity unit) not improve matters?

Is it possible that knocking off the old tanking slurry might help?

Thanks,

Sploing

 

[Abi Cott]

All the stone has been at least partially sealed with an impermeable layer. The only stone that has the ability to breathe is in the vicinity of the air brick. That does at least sound logical even if I've got no proof it's actually true.

Is the air brick and the flue on the same wall? Are you getting a stagnation of air rather than a circulation that is altered by the radiator because of its convection currents?

I have a very damp cellar. It's marginally less damp since I tackled the probable leak in one of the external drains (probable because it was the one damn area the camera couldn't get to) I blocked it and it's drier down there which is probably a good sign.

I'm leaning towards the Newton membrane option. It seems to be a viable option for an airtight cube.

 

[Flyfisher]

- Why does it seem to be wettest near the air brick (incidentally close to the bottom of the stairs leading to the rest of the house), does this suggest the damp air is somehow being drawn in?

Warm air laden with moisture (the warmer the air, the more moisture it can carry) finds its way to the cool air brick, which cools the air causing the moisture to condense. It accumulates around the airbrick because this is where the warm air is cooled first when entering the cellar.

Under the stairs is probably a better place to help prevent rusty tools.

 

[Sploing]

Thanks again for the replies so far.

Is it possible that using some kind of fraught excluder on the door leading to the rest of the house might help?

I’m wondering if then, when I fire up the fan, it’ll draw air through the air brick which is likely to be closer in temperature to the cellar rather than from the house?

 

[Cubist]

Hi Sploing,

I read your thread this morning but did not have a ready contribution to make at the time but after mulling it over I can at least offer the following.

Air bricks are typically used either to allow air to circulate beneath suspended wooden floors to help prevent Wet/Dry Rot in the timbers or to allow ingress of fresh air to replace oxygen consumed by open fires. In the latter case the air brick would be mounted high up on an external wall whilst those intended to prevent Wet/Dry Rot would be placed at roughly the same height as the joists for each suspended floor.

The air brick in your cellar will be intended, I'm sure, to prevent Wet/Dry Rot that may affect the wooden joists and floor forming the roof of the cellar. Used for this purpose air bricks depend on internal and external temperature variances to create the necessary convection flow of air to protect the timber - its the movement of the air rather than its temperature that provides the protection. Typically the temperature variance between the outside atmosphere and that below a floor, or in a cellar, is not large and the speed of the convection current is therefore quite small and, as a consequence, the relative moisture content at floor and ceiling height will also be quite small. This can change dramatically if a heat source, like the radiator installed by the previous owner of your property, is introduced into the equation.

I would be happy to gamble that heat from the radiator is the root cause of the excessive damp you are seeing around the air brick and nearby timbers. My best advice would therefore be to permanently switch off the radiator, fit the draught excluder and find a new home for your tools. It would not hurt to run the fan for a while to accelerate the air flow within the cellar which may help to dry out some/all of the damp mentioned above - could be worth an experiment but I would guess several days or even weeks may be needed to see any improvement.

Hope this helps.

Cheers,

Cubist

 

[Cubist]

Hi Again Sploing,

You will have to forgive me but I have been a life-long victim of a Obsessive Compulsive Disorder that presents when I encounter an intriguing problem - mine or anyone else's.

So another contribution - welcome or not - concerning your damp cellar problem.

Could I ask when you first found more significant damp around and in close proximity to the air brick? Was this perhaps a little time into the recent heatwave? If so, then the excessive damp in that area may well result from the fact that the high external temperatures and lack of outdoor air movement have contributed to the problem by in effect trapping the colder air in the cellar. At the interface between the cold cellar air and the much warmer air outside - in other words the air brick - moisture would be shed from the cold air. This process, because the cold air is trapped, would continue until the ambient temperature variance is effectively eliminated.

It could therefore be that the excessive and localised damp you're seeing is restricted to periods of high external temperatures. None of this changes my earlier suggestions of course but the use of the fan during such periods would help by forcing the cold air out thus allowing the warmer air in. However, the performance of this approach may be limited by the location of the extractor fan in relation to the air brick.

Again, I hope this is of some help.

Cheers,

Cubist

 

[Sploing]

Cubist,

Thanks for the detailed reply, sorry it's taken me a long while to respond.

The air brick is directly underneath the front door of the house and so is level with the floor joists supporting the hall (See below, apologise for crudeness)

I noticed the dampness as soon as I moved into the house approximately 2 years ago, the seasons don' seem to have an effect on the dampness.

I did find it interesting though that the joists which are regularly damp, being the ones at the bottom of the stairs closest to the air brick, were wet even during the recent heatwave.

The only time I have known them to dry out is during winter when the radiator is on.

For around three weeks now I've had the extractor fan running at a low speed constantly, the net result is a reduction in the RH from a typical 100% (ish) to around 90%

I found myself wondering today whether using the extractor fan with the cellar door closed in order to increase air flow and encourage air from outside was less effective then it might be since my house is close to the bottom of a valley and the outside air is generally quite humid (90% today, but its raining)

I've decided today to try leaving the fan running but with the cellar door open so that drier air from the rest of the house is encouraged to pass through the cellar instead


---Door----------------------------------------------------------
I I I I
I I I Extractor fan
I Stairs I Alcove I I
I I I I
I I I I
I ------------- I I I
I I I
I I
I I
-----------Air brick-------------------Radiator---------------

 

[Sploing]

---Door----------------------------------------------------------
I...............I............I........................................ I
I.............. I........... I......................................... Extractor fan
I ....Stairs ..I... Alcove I ........................................I
I.............. I........... I........................................ I
I.............. I........... I....................................... .I
I ------------- I............ I....................................... I
I........................... I....................................... I
I.................................................................... I
I................................................................... I
-----------Air brick-------------------Radiator------------------I

 

[CliffordPope]

I don't know the answer, but would observe that all the replies have concentrated on the circulation, or not, of damp air drawn in from somewhere.

Might the cause simply be that the water table is higher than the cellar floor, so whatever you do, there is an infinite supply of moisture rising from the floor and coming through the lower walls? I've read that in such circumstances the only answer is to excavate a collection sump below the floor and continuously pump the water out.

 

[Feltwell]

Might the cause simply be that the water table is higher than the cellar floor, so whatever you do, there is an infinite supply of moisture rising from the floor and coming through the lower walls? I've read that in such circumstances the only answer is to excavate a collection sump below the floor and continuously pump the water out.

If the water table was higher than the cellar floor I'd expect the cellar to flood. Mine has, but only once - about 11 years ago when we had an extremely wet period, lots of local flooding, even though I live on a high spot the cellar flooded by about 6" so I don't think the water table can be that far below the cellar floor normally. The water came and went surprisingly quickly, I didn't need to pump it out, it just disappeared back through the quarry tile floor.

Sploing, your "fan plan" is OK for now but sounds a bit expensive once your heating is on! I think you may be battling against the tide here - if it's like my cellar and the moisture is coming in through the floor and lower walls, which is how most are, there's pretty much an infinite supply of moisture and by drying the air in the cellar I'm just pulling it in even faster. Any drying will be superficial, the brick walls will be well saturated.

 

[Cubist]

---Door----------------------------------------------------------
I...............I............I........................................ I
I.............. I........... I......................................... Extractor fan
I ....Stairs ..I... Alcove I ........................................I
I.............. I........... I........................................ I
I.............. I........... I....................................... .I
I ------------- I............ I....................................... I
I........................... I....................................... I
I.................................................................... I
I................................................................... I
-----------Air brick-------------------Radiator------------------I

I'm baffled Sploing, but thats not unusual. What is the above trying to communicate?

Cliffords thoughts, in conjunction with your comment about the air-brick being beneath the front door, has got me thinking that perhaps the problem may be rain water being driven in through the air-brick. Is there any evidence that the external ground level is is higher than it may need to be?

 

[88v8]

I'm baffled Sploing, but thats not unusual. What is the above trying to communicate?

It's a plan view of the room, as one might have created on a telex. A real period piece. I think it's a first on the forum.
Our telex operator used to while away the empty hours creating pictures of Marylin Monroe.

As to the problem, I would have put the fan there, where it is. It draws air through the airbrick, across the cellar. As feeble attempts at drying go, it's about as good as can be done.
Why the timbers are damp by the air brick, I've no idea. What's nearby outside? Drain? Gutter downpipe?

Timbers that damp will rot.

Tools need to be elsewhere. If I had that cellar, I'd use it to grow mushrooms.

Otherwise, yes close off the airbrick, create a vent from the house, and put a dehumidifier down there. It will run continuously, but heyho.
The Ebac 2650 is quiet and long-lived, and cheap to buy https://www.ebac.com/dehumidifiers. Ours reduces the rh by about ten points, but it's not a closed system, the cellar stairs are open to the kitchen. In a closed cellar it would do better. It pulls out maybe a gallon a day.

Ivor

 

[Flyfisher]

I think you may be battling against the tide here - if it's like my cellar and the moisture is coming in through the floor and lower walls, which is how most are, there's pretty much an infinite supply of moisture and by drying the air in the cellar I'm just pulling it in even faster. Any drying will be superficial, the brick walls will be well saturated.

That’s my feeling too. Damp and cellars go together like Morecambe and Wise. I use a dehumidifier in the summer to prevent dripping condensation from the floor joists above but it’s still a very damp room and I have no plans to attempt making it inhabitable. It’s a good place to store wine though

 

[Cubist]

It's a plan view of the room, as one might have created on a telex. A real period piece. I think it's a first on the forum.
Our telex operator used to while away the empty hours creating pictures of Marylin Monroe.

Coo, I was a sprog the last time I saw a Telex machine but do have some fond memories of the Marylin Monroe, and other, pictures they could reproduce. Thanks Ivor for the context, I had grasped it was a map but beyond a rough layout I was at a bit of a loss - I've clearly been spoiled by more modern technologies.

That aside Sploing's damp cellar has kicked off my OCD problem solving with a vengeance and right now the diversion is too tempting - I was finalising my decision on Home Insurer offerings which is about as dull as watching nails rust.

Rain water penetration through the air-brick, or perhaps from beneath the front door - which I note is immediately above the air-brick - may be one cause. These should be easy to check by simple observation during the next heavy rain-fall.

The more likely suspect, I think everyone would agree, is moisture transfer from the cellar walls/floor to the atmosphere which is then condensing out at the air-brick where the warmer air meets cooler air. As soil temperature at 1 metre below ground can vary by two or three degrees above or below the outdoor temperature, in winter and summer respectively, there will always be a temperature variance even without any form of extra heating. If my memories of schoolboy physics are reliable then condensation at the air-brick is unavoidable and will occur almost continuously irrespective of whether its warmer or colder outside.

All of which goes to say that the problem is probably insurmountable - but that just goes against my personal grain.

Two possible solutions come to mind one expensive and difficult the other very cheap and easy. The former is to get the cellar thoroughly tanked to prevent moisture leaching into the cellar atmosphere but I have no idea how much that may cost or how successful it could possibly be - others may be able to offer an opinion and guidance on this option. My second offering is the strategic placement of a Moisture Trap (about £5 from Amazon) which may significantly improve the situation.

To my mind though one thing is for sure - do not light up the radiator, this can only add to the problem.

 

[Cubist]

My OCD problem solving keeps bringing me back to this conundrum - can't help myself - so an additional thought that could provide another cause.

A couple of years back I was considering alternative heating solutions and, among other systems, gave some consideration to Ground Source Heat Pumps. While looking at these I came across some data comparing air and soil temperature (at one metre below ground level) which suggested these varied by as much as 3-4 degrees plus or minus depending on the season. The obvious conclusion being that the walls of any cellar will absorb and radiate heat transferred from the surrounding soil. So during the winter months the ambient temperature in the cellar may be 3-4 degrees (perhaps less) higher than outside and vice-versa in the summer. As a consequence, even without any other form of heating being present, a warm air and cool air interface will occur at the air-brick and moisture will condense out.

Now for a solution.......I don't think there is one. Leaving the radiator off may/will reduce the extent of the damp problem but short of filling the cellar in I cannot think of anything that will stop it completely. However, I would suggest you try an experiment using a strategically placed Moisture Trap (Amazon £5-10) near the air-brick to see if the there is any net gain/improvement - could be a lot cheaper than running a De-humidifier.