Ventilating a damp cellar

[MacLaverty]

Wessex makes a good point on checking if the tanking has failed.

Typically, tanking fails at joints, corners, abutments and penetrations. If nothing visually obvious, then it may need instruments and someone experienced to determine.

Excess humidity can be dealt with via ventilation - trickle and boost mechanical extract fan which could be a heat recovery unit, or a positive pressure fan.

Great, thank you. I was thinking about a humidity controlled extractor fan so will look into it. Window already has a trickle vent and dehumidifier runs a fair few hours but humidity always stays high. Got a look of books down here and still staying strong after 15 months so hopefully something is working well!

 

[MacLaverty]

I have a converted cellar that suffers from relatively high humidity. Am I best keeping the window on a latch, it's small so even when open no-one can climb through it, permanently to allow ventilation or am I best off shutting it and opening it for an hour a day? I don't have trickle vents on the window but concerned that if I leave it open 24/7 I may be causing humid air to enter the cellar rather than get rid of it, especially when it's particularly humid outside.

I do also have a dehumidifier which is on for about 4hrs a day to try and control the humidity but guessing having a window on a latch won't cause the dehumidifier to try and dehumidify the world.

 

[mattylad]

While you think a window is small, thieves are often very thin or use children to get through small windows.

 

[robinbanks]

I'd install a mechanical, heat recovering ventilation system

 

[JohnD]

Fit a steel grill. You need ventilation on at least two sides or ends to get through flow of air.

 

[MacLaverty]

Than you all. I may price up a humidity controlled extractor fan but due to the layout of the cellar there isn't a great deal of places I can put it if any. The cellar was converted before we moved in but it is a DIY job so not waterproofed properly. However, in most cases the cellar is bone dry apart from 1 tanked wall which I think is caused by summer condensation as that particular wall only gets wet when its warm and has been raining which leads me to think its condensation and not anything more. Had absolutely no issues over winter and hardly had the dehumidifiers on!

I'm trying to ventilate the area as much as possible but was concerned having the window open in Summer was just drawing in warm, moist air so will close the window for now and see if that does anything to the condensation issue.

I have an air brick on one side of the wall and a window on the other so my theory was if I have the window open on a latch then that will create air flow but just concerned I am dragging in warm, moist air into the space causing the condensation.

 

[ericmark]

What heating is there? If out side is warmer than the celler then air flow will make it damper, and if out side is cooler even in pouring rain air flow will remove mosture.

 

[MacLaverty]

Absolutely none, tends to sit around 15/16 degrees in the summer and 12 in winter so not massively cold. I don't use the room that much so I don't really want to be heating it 24/7 to keep it a good temperature.

Would getting a humidity controlled fan in there help the situation?

 

[foxhole]

Absolutely none, tends to sit around 15/16 degrees in the summer and 12 in winter so not massively cold. I don't use the room that much so I don't really want to be heating it 24/7 to keep it a good temperature.

Would getting a humidity controlled fan in there help the situation?

A conventional low wattage bathroom extractor fan with run 24/7 for modest cost .

 

[MacLaverty]

I have a converted cellar, was done in 2020 well before we bought the house but a bit of a DIY job so hasn't had the full waterproof treatment etc. Unfortunately when we moved in July 2022 we had our washing machine leak in the cellar which required me to cut a small hole in the drywall, as seen below, to dry the internal wall and replace the wet insulation. I never got round to skimming the wall to make the cut piece blend in and sort out the rest of the wall as it was behind a cabinet so was not visible.

I got round to starting this week and took the panel and insulation out and noticed the tanked wall behind was moist. Think it is condensation and not a leak or penetrating damp as does not happen further up or lower down the wall and does not seem to drip. I don't think it will ever get to the point it gets so wet it drips down the wall and may just be summer condensation that is causing the issue but how best can I deal with the issue or if it is not causing an issue do I just leave it and keep and eye on the wall for signs of damp/ moisture? At the moment there is no other signs of mold/ dampness in the cellar and don't really want to get an extractor put in as worried that this may cause more issues than it solves. There is a very small window in the cellar and an air brick on the opposite wall.

I have tried to push insulation onto the wall to stop warm air contacting the cold wall. It did slow down how quickly the wall got wet but the wall was still getting wet and insulation becoming wet so I removed the insulation off the wall today.

I cannot seal off the wall fully to try and stop air circulation as the cavity wall ends in a small utility room in the cellar which has an open side, as seen in the pictures, as I need access to the water stop tap etc. It does not have a vapour barrier on the other side of the dry wall and without removing the entire wall I wouldn't be able to put one in.

Would adding an air vent onto the cut out section directly in front of the wet part help dry the wall out or would that just introduce further warm air and cause further condensation?

 

[Swwils]

ventilation

 

[MacLaverty]

Agreed but how do I ventilate an insulated cavity wall? I can't put air bricks in as the entire cellar is under the ground apart from 1 very small window. I could put an air vent at the bottom and top of the plasterboard where the wall is wet but it would only vent into the main room and not outside so not sure if it would solve the issue or not?

 

[MacLaverty]

The rest of the wall is bone dry, probably because most of it is not tanked, but I am unable to ventilate the area sufficiently due to the layout to help stop this condensation. As the area in question is only small, just bigger than the cut out piece, would spraying insulation foam directly onto the affected part stop this condensation forming on this small area?

 

[MacLaverty]

I have one part of an original wall behind plasterboard which is becoming wet due to condensation as you can see by the below picture. The rest of the wall is bone dry, probably because most of it is not tanked, but I am unable to ventilate the area sufficiently due to the layout to help stop this condensation. As the area in question is only small, just bigger than the cut out piece, would spraying insulation foam directly onto the affected part stop this condensation forming on this small area?

 

[MacLaverty]

I have one part of an original wall behind plasterboard in a converted cellar which is becoming wet due to condensation as you can see by the below picture, the wall had just been wiped so not currently wet. The rest of the wall is bone dry, probably because most of it is not tanked, but I am unable to ventilate the area sufficiently due to the layout to help stop this condensation. As the area in question is only small, just bigger than the cut out piece, would spraying insulation foam directly onto the affected part stop this condensation forming on this small area by stopping air flow to that part of the wall?

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