Ventilating a damp cellar

[MacLaverty]

I have got a tanked wall behind plasterboard with insulation in the cavity. However, it seems like I have condensation on the tanked wall and some of the insulation is getting wet so am I better to push the insulation against the tanked wall in the hope it will stop the condensation or best pushing the insulation away from the wall into the plasterboard to stop the condensation being absorbed by the insulation?

 

[robinbanks]

Insulation against the wall. Moist air can reach the cold surface right now. If you insulate the cold surface in a way that moist air can't reach it, condensation won't happen

 

[JohnD]

What steps are you taking to ventilate away the humid air?

 

[MacLaverty]

What steps are you taking to ventilate away the humid air?

Unfortunately little as it's down in a converted cellar. I have an air vent at the bottom of that particular cavity wall but still isn't solving the issue. I have trickle vents in the window down there and dehumidifiers running but condensation is still forming behind the insulation against the tanked wall. At the moment the insulation is neither pressed against the wall or the plasterboard, kinda hovering in the middle so not sure what to do.

 

[wessex101]

We have had a prolonged hot dry spell of weather so condensation is less prevalent at the moment. What does the tanking consist of? Is it possible that the tanking has failed and it is minor penetrating damp rather than condensation?

If it is condensation is there an effective vapour barrier on the warm side of the insulation?

 

[JohnD]

I wonder if moisture is coming through the floor or some other wall.

 

[^woody^]

If the humidity and heating are not sufficiently controlled, then condensation will remain despite and relocation of insulation.

 

[MacLaverty]

We have had a prolonged hot dry spell of weather so condensation is less prevalent at the moment. What does the tanking consist of? Is it possible that the tanking has failed and it is minor penetrating damp rather than condensation?

If it is condensation is there an effective vapour barrier on the warm side of the insulation?

So only some of the wall is ranked and this is the only part getting condensation. The normal wall right next to it is dry so hence presume condensation as no other water entry apart from the tanking. It has happened to other parts of the tanked walls but these were exposed so easy to control.

No vapour barrier which is frustrating but even if there was, there are gaps where air can get into the cavity which are difficult to seal so even with a vapour barrier the warm air would still get behind the wall I reckon. But if the moisture starts to affect the insulation then I think next step would be to take it all down, put a vapour barrier and try again but hopefully won't come to that.

Just not sure whether to press the insulation to the wall to stop the movement of air or just move the insulation away from the wet patch and let it be. Don't think it ever gets to the point of dripping down the wall.

 

[MacLaverty]

If the humidity and heating are not sufficiently controlled, then condensation will remain despite and relocation of insulation.

It's been poorly converted I think so even with a dehumidifier, windows open etc the humidity aways stays high regardless so without spending £30k on having the whole thing ripped out and done properly I think it's just something I am going to have to live with

 

[^woody^]

You can control humidity and heat for less than £30k.

 

[wessex101]

So only some of the wall is ranked and this is the only part getting condensation. The normal wall right next to it is dry so hence presume condensation as no other water entry apart from the tanking. It has happened to other parts of the tanked walls but these were exposed so easy to control.

If only the parts of the wall that are tanked are suffering from condensation don't you think that is suspicious? I suppose it could be a coincidence that the tanked areas are colder and that is why you are getting condensation but I would investigate whether the tanking has failed.

I am working on a property at the moment where the tanking membrane was installed incorrectly and despite the recent dry weather the walls are soaking wet. This has had the added complication of massively increasing the humidity in the building due to all the moisture evaporating out of the wet walls which is causing condensation in other parts of the building. There is condensation streaming down the windows with the temperature outside in the 20's, its crazy.

 

[MacLaverty]

If only the parts of the wall that are tanked are suffering from condensation don't you think that is suspicious? I suppose it could be a coincidence that the tanked areas are colder and that is why you are getting condensation but I would investigate whether the tanking has failed.

I am working on a property at the moment where the tanking membrane was installed incorrectly and despite the recent dry weather the walls are soaking wet. This has had the added complication of massively increasing the humidity in the building due to all the moisture evaporating out of the wet walls which is causing condensation in other parts of the building. There is condensation streaming down the windows with the temperature outside in the 20's, its crazy.

How would I check if the tanking has failed? It is almost all of the tanking in the room so surely not all of it would have failed? The other brick is untreated and bone dry so would it not also be seeping through the normal bricks if it was penetrating damp?

Also, no condensation at all on the window above where the wall is wet which is odd.

 

[MacLaverty]

You can control humidity and heat for less than £30k.

How so? I'm not very good with this sort of thing. The room has no heating and sits around 14 degrees all year round. Only 4m2 converted office space.

 

[MacLaverty]

Also, would a vapour barrier on the warm side of the insulation cause more condensation trapping moisture between the vapour barrier and tanking?

 

[^woody^]

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.