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I live in an apartment on the 4th floor. My bedroom has the misfortune of being in the very corner of the building - it has two outer walls. On top of that, the corner between these two walls is facing north (where the sun don't shine) and there are no obstacles for the cold winds coming from that direction. The only insulation that the building has is about 30cm of concrete.

As a result, the corner tends to be substantially cooler than the rest of the walls and lots of condensation gathers on the wallpaper. Since I cannot do anything to the outside of the building, is there anything I can do on the inside? Some material that I can place beneath the wallpapers? (I have enough spare wallpaper to fix the corner, but not the entire wall)

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4 Answers 4

Insulation is certainly the best long term solution. A measure that may decrease the problem is to re-balance the heating so the bedroom isn't as cold. Warm air tends to be drier air. The condensation should diminish if the room is properly heated. Depending on the heating system, this can be simple or impossible. The general idea is to either increase the heat going into the bedroom, or decrease the amount of heat going everywhere else in the apartment.

Duct systems often have balancing dampers behind the register, or the registers themselves can be adjusted to lessen the flow. Radiator systems often have a balancing (locksheild) valve on the outlet pipe, or other valves can sometimes be adjusted.

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It depends on ownership and what you're allowed to do under your rental agreement, but this was the solution on our house. It's stick built 2x4 construction, you didn't say what wall construction is used, so it may not apply. Same situation, north facing, cold corner, black mold growing in the plasterboard surface and paint about 4 inches back from the corner on both walls, looked like someone used a paint roller to apply it.

I stripped the plasterboard off the wall to the stud closest to four feet from the corner. The 70's insulation was mouse power R-6 pretending to be something like R-13 but which didn't completely fill the air space.

After clearing everything out of the stud bays and bleaching the minor surface mold that was on the exterior sheeting, I examined what I had to deal with.

The most egregious problem was the empty box created where the two walls came together. We're talking about uninsulated dead air space that is open to the outside atmosphere and sealed by the exterior trim. It was a source for both draft and cold. You could feel the air flowing into and out of the room. I took a wood knife I had and opened up the spaces between the 2x4s that enclose this empty space so I could get a nozzle straw in from floor to ceiling so I could fill it with Urethane foam. You don't want to do the whole space all at once, urethane foam in quantity develops a skin, massive internal voids and blows itself out of the containing space in massive mushrooms that waste the material. This is why you want a slot that gives freedom of movement for the nozzle straw. After about six passes and a couple days for full expansion and cure of each foam application, the void was completely filled with minimum waste. No more cold vented dead air space or drafts!

I got R-15 which was the highest R rating available for 2x4 studded walls (R-19 is standard for 2x6) and filled the stud bays completely with no voids. Over the top of this went 6 mil plastic for vapor barrier so no internal moisture would intrude. Put the plasterboard back, taped the joins, copied the simple skim coat, primed and repainted the two walls to match.

After the project, the corner is actually warmer than the rest of the wall because it has working insulation with no empty, uninsulated and unsealed air spaces. No more mold!!! My only regret is I probably should have done the whole whole room on the reinsulation.

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A short term fix may be to hang insulated drapes on the wall. Ever wonder why they hung tapestries on the interiors of castle walls? It was to stop the drafts and make the room feel warmer.

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A serious flaw with this solution, even as a short term fix, is the warm humid air will still be touching the cold surface, so you will still have condensation. Worse, is with drapes there, you will get no air flow. This will quickly cause mold to grow. And with drapes there, it will hide the problem, so you will tend not to think about it. So please don't try this solution. Fix the problem, don't just hide it. –  user558 Nov 17 '12 at 19:29

Ideally you should insulate the whole length of both walls.

You will need to strip the wall paper off the walls to make sure that there's no moisture trapped underneath, then line the length with insulated plasterboard (sheet rock). Finally skim and finish with a coat of paint or wall paper.

You will have to remove and replace the skirting boards and the trim around and windows.

Skimming and painting solves the problem of not having enough wallpaper to redo the whole of both walls.

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The problem is - I just (3 months ago) renovated the room and put fresh wallpaper on it. I don't want to redo it all again. :P I thought that the problems with the cold would disappear after I plugged all the holes in the panel joints. :P –  Vilx- Nov 17 '12 at 16:18
    
Does sheetrock act as insulation? I might think about it. –  Vilx- Nov 17 '12 at 16:19
    
@Vilx- - not in and of itself, but you can get it with an insulating layer. –  ChrisF Nov 17 '12 at 21:24

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