Best Drylining method for concrete house

Weepsie

We're in the process of redoing rooms in our house.

1940s poured concrete house. We're dryling exterior walls. 2-3 rooms were done before we moved in. Looks like they're stuck directly to wall with mushrooms. We're going for a mix of 50mm, 37.5 mm and 26mm depending on the wall and room.

Were debating whether to go that route for the others or if dot and dab with a small air gap or using timbers and again a small air gap would be better.

We've been advised to try and have the airgap by neighbours who don't and have had some damp.

The Continental Op

I'd be interested to hear having lived in a mass concrete house if the airgap makes any difference. IMO I doubt it will. The old house we lived in was cold and damp but most if not all the moisture was due to condensation on the cold wall. There was no DPC of any kind but the walls weren't particularly damp at the bottom and perfectly dry on the outside.

You still have a lot of concrete to heat up if you do external insulation and of course heat rises and the lowest part of the walls will be the last to get warm and possibly get condensation on them.

You need to get a proper test to see if you have damp check out the Peter Ward videos on youtube for more good info.

https://www.youtube.com/watch?v=KuoKhF31hL8

GreeBo

I'm in a solid brick house and would echo what @The Continental Op says, any moisture is coming from within and condensing on the cold wall. (Assuming of course you don't have a leaky gutter etc outside!)

So I would say the airgap makes no difference other than concealing any damp/mould behind the board rather than allowing it though.

Ideally you would batten the walls and insulated between the battens, vapour barrier over that and then board over with insulated board, making sure the insulated plasterboard has lower u value than the insulation between the battens to avoid any condensation between the two layers.

The vapour barrier will stop any moisture from the room condensing onto the cold wall and possibly forming mold. If you just use the insulated boards directly then you are relying on the foil backing as your vapour barrier but it has untaped joins and also is on the cold side rather than the warm side.

Really the foil backing is to stop a wet wall from soaking up into your finished internal wall, but a wet wall is a problem if it has no way to dry out.

Solid walls dry both to the inside and the outside of the home depending on the weather conditions, you are removing one option by drylining the wall...

Weepsie

Cheers for the input.

We don't actually have any damp issues, at least none I can see anywhere or feel. Condensation the odd time from clothes drying.

Goal is to get the house as warm as possible. We might dot and dab the partey wall, batton the exterior walls, insulate,.vapor barrier and insulated plasterboard.

Seems to be whomever I speak to they just have their own idea and want to do what's easiest for them rather than what's the best for the building

GreeBo

The easiest by far is to just dot and dab them onto the wall, but when you have to redo it in a year or so it wont seem so easy! :)

The best for the building is to glue 2 layers of 25mm PIR boards directly to the wall, staggering your joints, attach a vapour layer and then fix regular plasterboard with mushrooms, skim and paint. For your upstairs rooms you should do the same to the ceiling so you get a continuous vapour barrier (but you probably wont need the 2 layers assuming you have attic insulation.)

This will give you the warmest result, however might be a pain in the backside if you ever want to fix heavy things to the walls.

Battening the wall is probably next best as it gives you fixing points at the cost of thermal bridging and reduced insulation levels, but you can offset that by using something like 27mm insulated plasterboard sheets.

Weepsie

I'm waiting for a few call backs anyway to get some input anyway from people who do this daily.

Hoping to get External insulation down the line but it's not on the cards yet as we have to solve an issue with a shite extension that in an ideal (and cash rich) world would be gone or could be reconfigured heavily.

GreeBo

Doing EWI on top of IWI is going to be a waste of money and may end up causing random interstitial condensation issues, id probably save my money and spend the money on ditching the extension and putting in the EWI (via a grant) tbh.

Weepsie

We would if we could, but we also can't afford to wait a couple of years to live in a house that's looked like shite internally for years.

Previous owners had some very questionable approaches to diy

Shoog

https://www.boards.ie/discussion/comment/119705361#Comment_119705361

Consider that external insulation does nothing for the top of the wall and behind the facias. In our case this represents about 20% of the total surface. This will represent a huge thermal leak and make external insulation all but useless.

The solution I came to was internal dry lining and dropped ceilings with loads of insulation in the void. I mostly avoided using battens because over extended time they are a potential source of mould and rot. This arrangement totally avoids cold bridges which will be condensation points and cause black mould.

TimHorton

https://www.boards.ie/discussion/comment/119719984#Comment_119719984

Also does little for the bottom, Also heat has to penetrate all the way out to the EWI , Think Internal option if viable (Space Loss) is better.

loyatemu

https://www.boards.ie/discussion/comment/119719984#Comment_119719984

Can't envisage how you have 20% of your wall surface behind the fascia?

done properly, EWI is supposed to be brought behind the fascia and over the top of the wall to meet the attic insulation, and also down below floor level at the bottom. From observing some of our neighbours getting it done, I get the impression that most installers don't bother with any of this though.

How did you manage at 1st floor level (that would still be a gap in your insulation), or is it just a single storey house?

Shoog

https://www.boards.ie/discussion/comment/119730540#Comment_119730540

Mine is a single story massed concrete house. The fascia and roof profile mean that 30cm of the top of the wall are behind the fascia, then at the top of the wall is about 50cm deep which is all but impossible to access effetively and if you did you would be cutting off any air circulation at the eaves. Since we have 3 1/2 m tall walls this accounts for 20% of the above floor level surface which is inaccessible.

My son lives in an old council house with external insulation and it is very effective been a two story terrace, but certain house would need very significant structural modification to benefit such as our which would need the roof reprofiling or replacing altogether.