Wall isolation with cork

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horsewoman
Posts: 378
Joined: Fri Jun 07, 2019 4:11 am

Wall isolation with cork

Post by horsewoman »

Our tenant complains that it is too cold in his flat. Which is totally true, we have lived in this flat as well and I can attest that it is very chilly in winter no matter how much on heats it up - there are way too much outer walls (it is a long rectangular buliding).
We have been warned by multiple (and credible) sources to put insulation on the outside because of getting mold, so we stumbled upon the idea of putting sheets of cork on the inside. There is not much information to be got online for how effective it could be. So I'm wondering if any of the DIYers here has some experience with it, since it is quite an investment to buy the cork.

Lucky C
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Re: Wall isolation with cork

Post by Lucky C »

If it feels cold (drafty?) and mold is a concern, first check for good air sealing because that may be just as much a concern as lack of insulation. Feel around the windows to see if there is a strong draft which you can seal for just a few dollars. Either pry off the framing around the windows and use spray foam designed for windows and doors, or caulk around where the framing meets the walls. Also check outside around window and door framing to check for rot or any gaps.

In the U.S. the standard practice for wall insulation retrofit is to drill a hole in each cavity (16" spaced wall studs), blow in cellulose (treated with mold and termite resistant stuff), and patch up the hole. Pros can do this quickly so it's not very expensive compared to the energy savings you will get. If you add insulation on the inside you still have to be careful about warm moist air condensing on a cold surface. If you add cork then that would probably be a good surface for mold to grow on (on the dark cool wall side), unless there is some air sealing to prevent the moist air from getting there. I would also wonder about an entire cork wall being a fire hazard / against building codes?

Instead if you really need to add insulation on the inside, you could add mineral wool insulation (Rock Wool, or Owens Corning Thermafiber which is much cheaper if available where you are), which is moisture and mold resistant, fire resistant, and likely a better insulator than cork. But there are tons of considerations and pitfalls in doing this. You would want to put in 3.5" thick framing to hold it in, but going horizontally to minimize thermal bridging (see "Mooney wall"), you would want to put up drywall or boards or some type of material to box it in, and you would want to air seal it to avoid draftiness and again more importantly to prevent moisture from getting through which could lead to mold (not on the mineral wool but on the framing for example). That's a lot of work to get it done right and your tenant will likely not want to give up 4" or so of living space along the walls. There are probably other things in the way too like outlets, light switches, plumbing, radiators...

So as you can see it will be much easier to focus on windows and doors and any other building penetrations like vents, before trying to go the insulation route. If you do go with insulation, contact someone who does the blown in cellulose to see if that's possible and tell them your concerns about mold to see what they say.

rube
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Re: Wall isolation with cork

Post by rube »

Do you know and can you explain the construction of the wall?
I guess it might be a brick wall with plastering on the outside? Do you know if it is cavity wall?

The structure makes a huge difference in what you can do. As lucky C said, you need to be careful and know what you can doas otherwise you can create great condition to grow mold.

And agree with Lucky C, getting rid of draft might help also (though make sure there is still ventilation!)

horsewoman
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Re: Wall isolation with cork

Post by horsewoman »

I never heard about the he drilling method, I will investigate if this is done here in Germany.

The problem with any kind of framing is that the door is pretty close to the wall, so there is not much leeway.

The flat is (or was) not drafty, we put those insulation strips in when we lived there. But it might be good to check it the are still in good condition.
The problem seems to be that the large living room has 3 outer walls, above is an uninsulated attic, below are unheated garages. So there is cold pressing in from all directions, and the only heating source is a wood stove.

The building is made of regular red bricks with air compartments (I don't know the proper word in English).

Jean
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Re: Wall isolation with cork

Post by Jean »

The best solution is completly dépendant on the actual construction. Outsider insulation is great, can bé diyed, but it's a lot of work. Sealing air draft coukd go a long way. Cork is a decent insulator. Adding 1 cm of Cork over 10 cm of brick would about divide wall heat loss by two. But again, it depends on what you have now.
How insulated is it from thé attic and garage? That's usualy easier.

rube
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Re: Wall isolation with cork

Post by rube »

I believe the word is 'cavity wall' (according Google translate).
The drilling method with cellulose Lucky C explained does not work for brick cavity wall building. But there might be somewhat similar insulation methods possible (drill holes on the outside and fill the cavity with insulation material, not cellulose though). You'll need to ask a specialist what would be possible for your specific situation. Also to find out if cork can be placed in the inside.

On this page you can compare some insulation values of different materials including cork:
https://www.energuide.be/en/questions-a ... lation/62/

tonyedgecombe
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Re: Wall isolation with cork

Post by tonyedgecombe »

horsewoman wrote:
Sat Dec 21, 2019 12:41 pm
The flat is (or was) not drafty, we put those insulation strips in when we lived there. But it might be good to check it the are still in good condition.
The problem seems to be that the large living room has 3 outer walls, above is an uninsulated attic, below are unheated garages. So there is cold pressing in from all directions, and the only heating source is a wood stove.
Insulating the attic is a relatively cheap thing to do and is like putting a blanket on top of the house.

Campitor
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Re: Wall isolation with cork

Post by Campitor »

Insulating the attic floor would help as well as insulating the ceiling of the unheated garage underneath. Also are the windows insulated? Glass is a good conductor of temperature and will wick away heat and also create cold drafts - the air next to the cold window will drop in temperature and make the lower half of the flat very cold. Interior storm windows can help: https://youtu.be/B-tKaWghWOQ.

You can insulate the interior using polystyrene panels which is only 1.5 inches thick: https://youtu.be/BoXGHtOCBDw. Also don't get caught up in a perfect solution - perhaps insulating 2 out of the 3 walls or insulating the attic and basement above/below the flat may be enough to minimize the cold.

Gilberto de Piento
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Re: Wall isolation with cork

Post by Gilberto de Piento »

What about curtains for the windows?

Lucky C
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Re: Wall isolation with cork

Post by Lucky C »

Blown in cellulose is sometimes done from the inside as well, so that might be possible if the construction is brick | air cavity | drywall? It's not ideal since you would have to move everything out of the way and it can be messy, but if using contractors they will take care of the dirty work. They would drill holes a few cm wide to fit in the hose that blows in the cellulose, then the holes will need to be plugged, patched, and painted.

Checking weatherstripping around doors and windows is a good idea. If a draft isn't obvious you can light an incense stick and see where the smoke goes. You can also check that any switch plates or outlet covers on the exterior wall are blocking air. The hardware store has pre-cut pieces of foam for outlets/switches that will work like a gasket to stop air from leaking out that way.

horsewoman
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Re: Wall isolation with cork

Post by horsewoman »

What I think from living there (with the caveat that this was 14 years ago, so my memory might be not absolutely reliable) is that the long outer wall (4,5 m in the living room and 6 m in the corridor) feels very cold. My husband and our tenant say the same thing.

There are no windows in this wall in the living room, and all other windows are double glazed isolation glass. This is kind of a standard in Germany - I was aghast when I learned that all the windows in our cousins house in Boston are singe pane! This is more or less unheard of in Germany, unless you live in a listed building.

I've talked to DH and he said that both the garages and the attic are isolated with sheets of styrofoam.
He is pretty much fixated on the cork thing, particularly because the doors are so close to the wall. There simply is no room for a decent lattice wall/dry wall.

He thinks that the hole drilling method is not done here in Germany, at least he has never heard of such a thing. The bricks look like this:
Image

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