Yet Another Condensation on Internal Wall...

creztor

Howdy all. I live in a 1996 house with besser block walls. These walls are rendered over and probably filled with concrete but there is no internal plasterboard wall with insulation. Rooms out the back of the house that get little sun in winter are obviously very cold. The walls are usually 5 degrees warmer than outside. Right now its -1 outside and the wall is about 6 degrees inside. So, if the rooms are kept closed, they are obviously very cold. If heat is turned on then condensation forms on the walls, mainly at the bottom but can form higher up. The back part of the house has higher humidity than the front and this with the cold walls and no internal walls with insulation obviously is the problem. Running a dehumidifier fixed the problem but I'm looking for other solutions. Due to how small the rooms are and built in wardrobes, I can't put up an internal plasterboard wall 15cm thich with insulation as I would lose a lot of space and the builtin wardrobe would have to be majorily altered. Other options I've seen are kv600, thermal wallpaper which at only 3mm thick wont do much more than help the room heat up faster, apparently. Second option is aerogel which goes up to 10mm in thickness and from what I've read it works better than the kv600 but don't expect much. Finally, insulation plasterboard. At best I could go 10mm thick without messing the room up. Any suggestions? Btw I am in Tasmania, Australia. I've posted there asking questions but though I'd try here also. Thanks in advance.

FreeBear

Tasmania explains why you are currently at -1°C - We are basking in 15°C at lunchtime 

Forget the 3mm polystyrene wallpaper - It will do nothing to improve the warmth of the room and will only trap moisture behind it. To be effective and worthwhile, you need at least 50mm of polyurethane foam boards (Celotex & Kingspan are the main brands over here). Using a warm batten method to insulate the walls internally, you'd loose around 90mm overall (25mm battens, 50mm insulation, 12.5mm plasterboard & a 3mm skim). If you are unwilling to give up that amount of space, then external wall insulation would be your only other option. 

creztor

Yes, 90mm is what I expected. My main goalTgoal was to slightly increase wall temperature just enough so condensation is less likely to firm. 50mm boards obviously would need something over them and this would still bring it up to around 90mm or would the foam boards be able to be plastered over or something to be less than 90mm? Yes, external cladding was recommended as best fix but beyond my budget. Thanks.

FreeBear

The way I insulated a wall recently -

Fix 25x50mm battens to the wall vertically at ~600mm centers with a strip of plastic DPC between the wall & wood.

Put up a sheet of 25mm foam board and secure some 25x50mm battens horizontally at ~400mm centres (screw into the vertical battens). Tape the joints with aluminium foil tape.

Fill in the gaps between the horizontal battens with another layer of 25mm foam boards. Again, tape the joints.

Tip - Use a serrated kitchen knife to cut the foam boards, and use a foam gun to squirt expanding foam in to any gaps - With a gun, it is much easier to lay down a thin bead in a controlled manner.

Fix plasterboard to the horizontal battens with screws, not nails. Tape the joints with a mesh scrim tape, and then plaster.

I lost around 70-75mm of floor space even although the insulation/battens/plaster is ~90mm thick. This was down to the original plaster coming off the walls (it fell off in most places). 10m² of wall cost me around £200 ($365 AUD) for materials. Already notice the difference in that room, and I have yet to plumb in a radiator (new one will be half the rating of the old one).

creztor

Thanks. I have just under 10m2 of wall also. I've been quoted around $1800 (£984) for a 40mm batten wall which will consist of 15mm of insulated plasterboard and then another 10mm standard plasterboard on top of that. Anyway, thanks heaps all. Put me on the right track. Once done I'll post an update. I'd rather DIY it or at least some of it to save $$$.

Phil3822

I am no expert but have dealt with a number of condensation issues, if the dehumidifiers work have you considered a PIV unit? Positive input ventilation units. I have used then with great success. Less moisture in the air allows your heating to be more effective and overall more efficient. 

creztor

Phil3822 said:

I am no expert but have dealt with a number of condensation issues, if the dehumidifiers work have you considered a PIV unit? Positive input ventilation units. I have used then with great success. Less moisture in the air allows your heating to be more effective and overall more efficient. 

Hi, yes it will work but the problem remains cold walls which makes the room cold. The PIV would reduce the humidity and thus when heating the room it would obviously reduce the chance of condensation on the walls but the walls would still be cold and it makes the room feel like a freezer. I'd like to insulate the walls even a little to make heating more efficient and the room not so cold.

creztor

FreeBear said:

The way I insulated a wall recently -

So was that essentially two layers of 25mm foam panel insulation?

creztor

Update. I did the room myself. Two walls which included a built in wardrobe and a window. I strongly encourage people who are doubting themselves to just give it a shot. I'm not a tradie. I work behind a computer all day. I watched YouTube, a LOT of YouTube and just tried.

The original walls were block walls that were painted with no insulation. First, I placed a vapour barrier/radiant house wrap over the walls. I then used rondo beta fix clips and screwed them to the walls. The EPs foam panels then slot over these clips. So, foam is flat against the wall with the clips protruding through. Then I used rondo 308 furring channels. These channels clip into the brackets. Then 10mm plasterboard on top which I painted and obviously things like the cornices.

The wardrobe was removed so I could insulate the wall there so I had to cut down/reduce the size so it could fit back in. The window sills I insulated with 10mm foilboard under the plasterboard. Had to use 10mm as obviously 50mm around the window would have resulted in a very small window. I repainted all the walls to match the new colour.  

Total wall thickness 77mm. Total cost around £550. Most expensive part was the 50mm EPs panels. Cost about double what earthwool batts would cost. There is a similar room in the house that is not insulated and the difference in temperature between the two without heating is 4 degrees. With a small 1kw heater on in the room it very quickly gets up to 20 degrees. If you can't tell I'm absolutely over the moon. Is it perfect? No. I hate plastering and you can see some joints when you get very close. 

I'm about to start on the second room and then move onto a third.

Room with cornice pulled down.
The wardrobe yet to be removed.

The clips screwed to the wall. The house wrap went over these before the foam.

The foam slotted onto the clips. No space wasted.

The clips poked through just enough so the channel could clip in flat against the foam.

Channels here clipped in with tape over joints in foam panels and other gaps.

Window was a bit difficult. I had no frame around it. I used a vinyl corner which helped but not having a frame meant plasterboard had to be fixed in limited places. 

Plasterboard up and ready to plaster, which I hate.

Window wall finished.

Second wall with wardrobe done.

FreeBear

creztor said: Total wall thickness 77mm. Total cost around £550. Most expensive part was the 50mm EPs panels. Cost about double what earthwool batts would cost. There is a similar room in the house that is not insulated and the difference in temperature between the two without heating is 4 degrees.

Polyurethane boards (the stuff with foil facing on both sides) has about twice the thermal performance of rockwool/fibreglass. The foil facing will also reflect a small amount of heat back in to the room. If/when you come to do the second room, it may be worthwhile using polyurethane boards and compare the results to EPS sheets.

Did you fill the gap between the furrings with insulation ?

Would have been a shame not to fill the gap...

As you have grounding in IT, have a look at Home Assistant or one of the other open source home automation projects. Put a few temperature & humidity sensors in each room and start logging the data. After a while, you should get a pretty good idea of what works and what doesn't along with some quantifiable numbers to support your findings.

I'm using Home Assistant and Grafana for visualisation with sensors dotted around the house including a couple to record electricity consumption (gas usage is logged purely as boiler on time). Running a smarter heating control has already produced a modest saving on gas, and the data is helping to identify what improvements make the biggest difference.

creztor

FreeBear said:

Polyurethane boards (the stuff with foil facing on both sides) 

Did you fill the gap between the furrings with insulation ?

Would have been a shame not to fill the gap...

As you have grounding in IT, have a look at Home Assistant 

Hi, I looked at EPS and XPS. Settled on EPs due to price but also R difference seemed too little. I just looked up PU panels and they cost 5 times what my EPS cost for same thickness. However, I see the higher R rating for PU. 10mm of PU is what I paid for 50mm of EPS. Id have to do some homework but then due to where I live I doubt anyone selling retail would stock it. After this room I'll definitely look into it. Would 10mm of PU provide sane R rating insulation as 50mm if EPS? I'll look into it. Thanks.

There are no gaps. The foam slotted over the clips and furring channels clip on top. It's essentially one piece of foam against the wall. I taped up all the little gaps I could.

I use Xiaomi home temp sensors and monitor the temp between rooms and also power usage. Without heating and if kept closed the room obviously gets cold. The main difference now is heating it is super quick and the walls no longer radiate cold like they used to. You walk into the uninsulated room and even at the door you can feel the cold hitting you. 

Thanks to everyone here. I've started on the second room and then will look at the third our bedroom (will investigate PU). I'm also looking at better ceiling insulation. We have blown in fluff that at best would be R2 but it's obviously been here since the house was built. However, primary goal is to do these bedroom walls.