Insulated Plasterboard

romaderwdcsax

Hi all. A quick query on insulated plasterboard.

I’m getting the heating redone in my house, house was built in 1960. The plumber will be replacing the rads upstairs so now is my chance with internal insulation. I’ll be going with 4” insulated board and fixings. It’s a solid block wall so I’m just wondering if the wall needs something like a moisture barrier between wall and insulation or is it ok to just fix insulated boards to the wall.

nicolasrk

You need some sort of moisture management when installing internal wall insulation as the wall will now be be on the cold side and condensation will occur between the insulation board and the wall. This can be done with a vapour control layer installed between the insulation and the wall, to avoid warm vapour from the inside of the space to travel through the insulation and condensate on the now cold internal face of the wall, mould and all that good stuff will follow. There are also insulation boards that come with an integrated vapour barrier. Care is needed to ensure continuity of the vapour barrier in board joints and in window reveals, etc.

I see now this was posted a few months ago and wondering if you went ahead with the job?

GreeBo

https://www.boards.ie/discussion/comment/122475791#Comment_122475791

You want the VCL on the warm side of the insulation, not the cold side.

If you put it against the exterior wall then the VCL will itself be cold and this is where the condensation will form, run down the VCL and puddle at the bottom.

If the VCL is on the warm side then no condensation forms and you dont have the problem.

You want the wall make up to be:

Cold/Exterior | Insulation | VCL | Plasterboard | Warm

No probleblem,just fix the insulated plasterboard to the wall ,thats perfect

Its just insulated plasterboard,and it is made exactly for fixing to the walls

100% just fix the insulated board to the wall,its not interior wall insultion,its platerboard with insulation already stuck on the back,ready to just fix to the walls

bfclancy2

https://www.boards.ie/discussion/comment/122554115#Comment_122554115

oh lord, please stop talking when you know nothing about it

Sleeper12

https://www.boards.ie/discussion/comment/122555335#Comment_122555335

New account. 5 posts and 3 of them here. Would have to assume a troll with account set up for entertainment purposes rather than trying to help op

custom_build

To be fair, most insulation backed plasterboard is now made with the ability to be directly fixed to an existing external wall.

https://www.kingspan.com/gb/en/knowledge-articles/can-you-fix-insulated-plasterboard-to-existing-plastered-walls/

GreeBo

https://www.boards.ie/discussion/comment/122555833#Comment_122555833

You can, but you shouldnt!

DC999

https://www.boards.ie/discussion/comment/122557390#Comment_122557390

Could I ask why? My knowledge isn't the greatest on it

GreeBo

https://www.boards.ie/discussion/comment/122559032#Comment_122559032

Its near on impossible to get a continuous VCL layer if you are just fixing boards to a wall. The edge of each sheet will not be sealed to anything so warm wet air will pass through these joints, hit the cold external wall and condense. The condensation will be trapped between the wall and the foil on the back of the board, run down and collect on the floor behind skirting and under the floor, potentially causing hidden mold and even rot.

drury..

https://www.boards.ie/discussion/comment/122559519#Comment_122559519

Whats the best method

GreeBo

https://www.boards.ie/discussion/comment/122559600#Comment_122559600

External | Insulation | VCL | Batten for services void | Plasterboard

Insulation against the wall with taped seams/joints.

Then a VCL layer over this, also with taped seams and correct overlapping as per the spec. The VCL should be continuous in the house, i.e. it should be over the ceilings and joining the DPC on under/on the floor for ground level.

Then you just board over that. you could also batten over the insulation, assuming you are using PIR to leave yourself a service void for running electrics etc so that you dont punch a bunch of holes through the VCL.

You can get airtightness membranes that also act as VCL, so you are reducing condensation risk whilst also reducing/eliminating draughts around sockets/switches/skirting etc.

The good boards have foil on the back and behind the plasterboard element. This forms the bulk of your VCL, but it's compromised. You need to use airtightness tape on all the joints and the joints to the ceiling and possibly the floor. This is then good enough. In this situation however you will get mould on the surface if you do not improve your ventilation as the internal air will become supersaturated and find any cold bridges where it will condense.

We foam glued and mushroomed our boards, using the foam glue as a further VC element around the perimeter of each board back.

You should consider insulated board correctly sealed at all seams coupled to MHRV to keep internal humidity low.

This is what we did and after nearly a year no sign of condensation anywhere.

GreeBo

https://www.boards.ie/discussion/comment/122561176#Comment_122561176

The problem with the foil backed board is the joints, you cant do anything to close these joints meaning you have tens of linear meters of space for vapour to pass through to the cold external wall.

Trying to turn a leaky old house into a modern warm/air-tighthouse is fraught with danger. The old houses were "designed" to have many air changes per hour and heated with open fires or radiators running at > 70*C.

If you change this design to reduce the breathability and air changes you need to ensure that you are following all the guidelines. Otherwise you can do bits to try to improve the house but introduce serious condensation/mould/rot issues.

Effectively ending up with a submarine that is 98% watertight…which is actually not a submarine at all :)

I found this the hard way when renovating an old house that had been internally insulated with warmboards. The external walls were damp and mouldy around the edges and at the joints in the boards. There was also evidence of condensation at the skirting level. Now this was in a solid brick house with zero insulation anywhere, but the point is that the house was fine for the first 70 years of its life, then changing the makeup of the walls and upgrading windows introduced serious condensation issues.

Your MHRV is likely the thing that is avoiding any issues, hence why its important that the OP (and others) dont just add insulation or change windows etc.

DC999

https://www.boards.ie/discussion/comment/122561768#Comment_122561768

But if you airtight tape all the joints on the plasterboard side, that solves it. No?

GreeBo

https://www.boards.ie/discussion/comment/122561786#Comment_122561786

I haven't seen an airtight/VLC tape for jointing plasterboard? Regular jointing tape/compound is to stop cracks at joints, its not going to stop vapour.

Also I don't see how you effectively tape the boards to the interior walls and especially the ceiling/floor, most boards wont reach the floor unless you lay horizontally :)

The other issue is that most insulated boards that I have seen have damaged areas, especially the foil, so you would ideally need to be taping all of these up before fixing…

All that said, if the makeup of the rest of the room/house is such that humidity and vapour are not an issue, then just warmboards are likely fine. But if the reason humidity isnt a problem is becuase the house is old and leaky, then as you address each leaky room/window you are increasing the chances of a problem, especiallly behind furniture/wardrobes in seldom used rooms.

https://www.boards.ie/discussion/comment/122561786#Comment_122561786

Its never going to be 100% perfect, but it's going to be 90% if you pay attention to getting it right. That means thing like foaming the gaps, foaming any holes, taping any penetrations and all seams, using 25mm thermal board on all window and door reveals, taping around windows. Don't cheap out on the taping as this is expensive but critical.

The knowledge and materials have come along such a long way that it's possible to avoid the issues people used to inevitably encounter when dry lining.

But here's the thing - you will amplify the damp issues if you don't address ventilation. I would say that adding MVHR is absolutely essential if you are going to dryline. There are single room options - but whole house is going to be the best.

Dont attempt one without the other or you will regret it in the years to come. The solution according to building regs is to insist on 150mm passive vents in each room - but frankly if that your approach why bother.

GreeBo

https://www.boards.ie/discussion/comment/122561858#Comment_122561858

+1

Without MHRV or basically drilling a hole in each room, that final 10% could be the bit that causes black mould behind your walls.