Fixing insulated plasterboard - general advice

[JP_]

This makes me feel a bit better about being tight with the budget:

"There are some in the industry who say that we should therefore set our target U value considerably less than current building regulations and go for something like 0.6 U value, when retrofitting IWI. Ideally, each property should be assessed according to its own situation. For example, where you have a brick façade which has a northerly orientation, you would be more concerned to keep some heat going into the wall from inside."
https://www.greenregister.org.uk/blog/pitfalls-and-solutions-for-internal-wall-insulation

No idea what my U value will be, but certainly nowhere near the latest recommendations!

 

[tomfe]

2.2 W/m2K to about 1.0 W/m2K,Not a dramatic difference

I'd say halving the (theoretical) cost to heat the room is dramatic

For £25, you could have got 25mm of PIR but for small quantities, delivery costs dominate.

+ vat + delivery + they are seconds so you might end up with rubbish (you normally don't but you've got to factor that in)

MKM I find really expensive have you tried a local BM or anyone else?

But you do pay a premium for them to stick the pb to the insulation if you buy the pd and insulation separately you'd easily get it under £10 a sheet.

 

[JP_]

Yeah, maybe I should have done that - stick the two together. But, first time DIYer and want to make it easy for myself.

Anyway, another issue, although hopefully not a serious one!

I just took off the PIR (foiled covered) I put against the wall last Sunday (just pushed against and held in place with some tape around the edges) and the wall was wet behind. Will adhesive provide a big enough air gap to prevent that condensation touching the insulation? The wall was dry before doing this, no sign of water getting in from the outside, so I assume and hope it is just internal moisture that was already in the wall and then having nowhere to go once the PIR board was there. The insulation board I bought has no foil, so I assume moisture can travel through etc.?

New boards arrive and leaning against wall, supported by bed, until the weekend (and my adhesive) comes.

Old, wet behind (was only there since Sunday, 4 days):

new, that will be stuck to wall

This whole thing started because the bottom of the wall, floorboards and joists were rotten. I made 2 new airbricks in the subfloor, so hopefully that will stop the moisture below floor problems - do I need to do something to deal with moisture on the wall, or will that be OK once the new boards are in and everything balanced?

 

[Doggit]

Careful with the PIR boards that are foil back both sided, as they can't be D&D to the wall; you'd need to peel the foil off first. Now if the wall is still wet, then you can't fix them yet, as it can weaken the adhesive. If there's excess moisture in the room, then you can't let that get through the wall, so you'd need to use ali tape to seal the joints, and then fix the plasterboard to the PIR. Normally, you'd batten the wall with a DPM under the battens, fit the PIR in between the battens, add a VCL, and then screw the plasterboard to the battens.

 

[JP_]

Hmmm, now, I thought the adhesive / dot&dab route was to help avoid putting wooden battens on a wall that might become damp at times?

But the insulation board I have bought is not PIR, its polystyrene with plasterboard attached - https://www.mkmbs.co.uk/prodb001892...terboard-2400mm-x-1200mm-x-30mm-tapered-edge/

Maybe I will run the dehumidifier constantly. But now starting to wonder ... if what I have bought won't stop moisture ... it will just stay wet behind?

 

[motorbiking]

Personally, I'd have taken the existing plaster off and then used these https://www.toolstation.com/shop/p43718 to fix to the wall perhaps with dot n dab. You don't take the foil off.
see :

 

[Doggit]

I suspect the threads got a bit confused. Jonbey was going to use polystyrene, but it looks like cellotex behind his bed, which normally has foil both sides, and can be glued to plasterboard. PL4000 is already glued, and doesn't have foil on the back of it, so can be D&D to the wall.

 

[JP_]

OK, spoke to MKM and Siniat and sounds like I need to change my boards.

So, should I just get something like a foil backed PIR, mechanically fix this to the wall, and then glue plasterboard to that?
Siniat suggested shallow wall channels for fixing plasterboard to external wall, as any moisture could result in the adhesive failing.

Suggestions? (i see a new message just arrived, so will post & refresh)!

 

[mwatsonxx]

For fire protection, it should also have mechanical fixings, nine per board.

what sort of fixings are those? something specific, or just screws into masonry rawl plugs?

Hammer fixings/Frame fixers/nail screws, total length = thickness of sheet + thickness of wall finish (if any) + 50mm.

https://www.screwfix.com/p/fischer-nylon-hammerfix-8-x-100mm-50-pack/33940

 

[JP_]

Thanks. Although I am now thinking that this is all a bad idea, due to condensation / damp/ mould risk behind these boards?

 

[JP_]

Daft question - if the probably with sticking my plasterboard with EPS to the wall is moisture making it fall down, and the problem with just fixing direct with mechanical fixing is that condensation will form on the wall and get into the insulation, causing mould, rot etc. could I use some sort of non-permeable batten to leave an air gap behind the boards?

edit - could these work?
https://www.recycledplasticbuilding...d-plastic-wood-38-x-22mm-battengate-stop.html

Batten the wall, attach boards to this?

 

[endecotp]

I just took off the PIR (foiled covered) I put against the wall last Sunday (just pushed against and held in place with some tape around the edges) and the wall was wet behind. Will adhesive provide a big enough air gap to prevent that condensation touching the insulation?

That's not how it works; no moisture is supposed to get through the insulation from the room, so there is nothing to condense when it reaches the colder brick behind. The foil layer, plus foil taping at the joints, is supposed to achieve this - or you add an additional impermeable layer.

But your description of finding condensation behind the temporary board sounds quite worrying. Have you measured the humidity in the room? I recommend getting a cheapo digital temperature/humidity gauge from ebay and seeing what it says.

 

[endecotp]

I'd say halving the (theoretical) cost to heat the room is dramatic

It's nothing like that much - there is still all the heat loss theough the ceiling, windows, ventilation and so on.

 

[JP_]

the temporary insulation was just shoved against the wall (see photo). But, the product I bought has no vapour barrier, and no way to add one (eps stuck to plasterboard).

I think I need to return that I get something completely different, such as foil covered PIR plus plasterboard. But then I still have the issue of fixing it to the wall - I guess I can glue just to get it in place, and then mechanically fix when everything is where I want it to be?

 

[JP_]

can I use this board? https://www.mkmbs.co.uk/prodb001449-kingspan-thermapitch-tp10-tf70-tw55-2400mm-x-1200mm-x-50mm/
it says " Thermapitch TP10 can be used for pitched roofs and under tiling or slates, Thermafloor TF70 may be used for insulating solid concrete floors, and Thermawall TW55 can be used with timber frame or steel frame wall constructions. " - no mention of against brick wall .... does that matter? How does it know??!?