Damp cellar

[charlieh]

Hello to all as I’ve just joined the forum!

We moved into a Georgian house about 5 years ago and I’ve been working on it ever since (and expect to for the rest of our residence!).

The previous owners used kingspan in the cellar ceiling, then covered it with a layer of plastic sheeting and then covered that in plywood.

The plywood is damp and buckling on the ceiling and I was wondering if I should rip it all off?

I was also wondering what advice people have to improve circulation of air anf the use of insulation on floating floors above cellars

Thanks in advance

Charlie

 

[Cubist]

Hi Charlie and Welcome,

As far as the ply-wood is concerned yes, get rid. It will do nothing but attract more damp and continue to fail. Others will have a better view than yours truly regarding Kingspan and and better sheathing materials for it. I'm sure they'll be in touch shortly.

Cheers,
Cubist

 

[charlieh]

Thanks Cubist!

Whole thing just appears to be working as a condensation trap particularly with the plastic sheet.

There are some air bricks in but very high up on the walls, wondering about opening up old coal hole again, or is that just another bad idea?

 

[Cubist]

Hey Charlie,

Get rid of the plastic sheeting too. Cellars are notoriously cold and damp and at any interface between cold and warm air there is the chance/probability of condensation forming. Provided the air bricks are not blocked theres a chance that the previous owner has inadvertently created the damp problem by preventing the flow of air up through the floor above the cellar. I would not bother opening the coal hole if it has been permanently sealed but, if it has not, then it may be interesting to open it temporarily when you've got the ply and plastic out of the way.

Others, I'm sure, will soon be offering much more relavant advice.

 

[charlieh]

Thanks again!

 

[Sam W]

Our house has a cellar which was so damp it was almost unusable. A spray can of builders expanding foam corroded through in about 8 weeks, discovering this had happened was a memorable experience.

Following improvements to ventilation it's now pretty dry. The cellar sits under the middle of the house and didn't have any allowance for airflow. I knocked two airbrick sized holes in walls on opposite ends of the cellar, these went through to (ventilated with air brick) underfloor voids in other parts of the house. For a while I tried leaving it passively ventilated, but it didn't work that wall. I've now installed an inline bathroom extractor (https://www.manrose.co.uk/product/mf150t-mixflo-commercial-induct-fan-timer-150mm/) that discharges directly to one of the vent holes I created. The fan is on a timer, currently running about 4 hours/day.

Last winter this setup was excellent, cardboard could be stored down in the cellar and would stay rigid. Over the summer, it's been a little bit damp, I think the warm temperatures have been pulling lots of moisture from the ground in the underfloor voids, waiting to see whether the problem continues into the winter. Only downside of this system is that now the fan is pulling fresh, external, air in every day, the cellar temperature is less constant than it was.

I found this https://uk.govee.com/collections/thermo-hydrometer/products/wi-fi-temperature-humidity-sensor useful while testing various potential solutions. Constant logging of temperature/humidity so you can see when you're getting on top of the problem.

 

[Feltwell]

We've got a small cellar under our hallway. Like most it's damp - not terribly so, but enough that you wouldn't want to put cardboard down there. The ceiling in our case, the hallway floor, is actually concrete - original to the house. The cellar is vented passively into the sub-floor voids under the adjoining rooms, via air bricks put in when it was built.

I'm presuming in your case you've got timber joists and floorboards above. The adjoining rooms I mention above have a conventional suspended timber floor, but with a big gap underneath, big enough that you can crawl about under there quite easily. There are airbricks to the outside. There was no insulation when we moved in, then about 12 years ago I put rockwool up between the joists - this has worked fine, no condensation problem, I'd say it must be a lot more breathable than Kingspan. You could put rockwool up between the joists then staple breathable roofing membrane across them if you wanted to keep some insulation in there.

 

[a twig]

Or insulation netting does the job of holding in the rock wool and is cheaper than roofing membrane there’s a war on doncha know

 

[Feltwell]

Netting does do the job - but......

I used chicken wire underneath my floor joists, bits of insulation poke through and wisps end up embedded in my hair whenever I go down there! Not really a problem in a sub-floor void but not what I'd want in a cellar.

I think a "solid" but breathable material would keep the cellar cleaner.

 

[charlieh]

Thanks all! Apologies for the delay, been hectic here

 

[Nick England]

Remove everything that you think could attract and retain the damp.

Ventilation is key. If you have anyway to improve through ventilation, you're onto improving the situation.