Insulating wall on inside

quattros

Hi all I have a room in the North section of the house and it’s a cold room the Gable wall side on the inside is cold to touch , wall is cavity type . so was thinking about applying insulated plasterboard which has (Foam/ polystyrene attached to the plasterboard type )on to the inside wall on top of the plastered wall to help with this. Is it just a case attaching to the wall and getting it plastered or is a small air gap required? 

Or any other thoughts? 

The wall also suffers from mould in places but I have a feeling it’s due to poor circulation due to bed and cupboards close to wall but not 100% sure.

grumbler

I don't think it's required if it's a cavity wall, but I'd remove the existing plasterboard first.

quattros

grumbler said:

I don't think it's required if it's a cavity wall, but I'd remove the existing plasterboard first.

Ok thanks for your reply looking at the pic the solid wall construction guess would cause bridging  if there was damp issues.
my wall on inside is Bonding onto brick and then plastered would I need to remove that or apply on top with the insulated plasterboard?

FreeBear

I'd also remove any existing plaster. Stick the boards to the walls with a foam adhesive - https://www.screwfix.com/p/dow-insta-stik-expanding-foam-grab-adhesive-gun-grade-750ml/72793

Add some mechanical fixings at regular intervals (600mm spacing as I recall), then plaster.

quattros

FreeBear said:

I'd also remove any existing plaster. Stick the boards to the walls with a foam adhesive - https://www.screwfix.com/p/dow-insta-stik-expanding-foam-grab-adhesive-gun-grade-750ml/72793

Add some mechanical fixings at regular intervals (600mm spacing as I recall), then plaster.

Ok why would the plaster currently on the wall need removing?  sorry not my specialist area 😬

Jeepers_Creepers

quattros said:

Ok why would the plaster currently on the wall need removing?  sorry not my specialist area 😬

You don't need to. It'll gain you - ooh - what would have been a lost half-inch of space...

If the existing plater is solidly attached, then simply adhere the insulated boards straight on. You can use pretty much any adhesive including drywall 'dot and dab' adhesive. The spray-foam adhesive mentioned above will probably be easier, and even stuff from cartridges - StixAll, GripFill etc - will go (as long as any solvent content won't attack the insulation...)

ANY thickness of this board will TRANSFORM your room, even the lowliest 35mm stuff. Go a bit thicker if you can (if you can afford to lose the space) but the 3"+ layers I've seen folk on here add is nuts.

Imo  

Are you DIYing this? Don't forget to do the window reveals, and trim the boards so's the insulation layer butts neatly, and the p'board skin overlaps to complete the corners - you'll know when you come to do this

An aerosol of spray foam/adhesive carefully run along all the butting insulation edges will also help to both bond the sheets and prevent cold gaps.

FreeBear

Jeepers_Creepers said:

quattros said:

Ok why would the plaster currently on the wall need removing?  sorry not my specialist area 😬

You don't need to. It'll gain you - ooh - what would have been a lost half-inch of space...

Could be 12mm of floor space saved, or it could be 25mm - Depends on how thick the original plaster was slapped on. If there are any blown, cracked, or loose areas, these need to be fixed first - If it is anything like the plaster here, knock of a blown section, and the rest ends up falling off... But if the original plaster is firm and in good condition, it doesn't have to be removed.

As above, do pay attention to the detailing around window reveals and corner junctions.

quattros

Jeepers_Creepers said:

quattros said:

Ok why would the plaster currently on the wall need removing?  sorry not my specialist area 😬

You don't need to. It'll gain you - ooh - what would have been a lost half-inch of space...

If the existing plater is solidly attached, then simply adhere the insulated boards straight on. You can use pretty much any adhesive including drywall 'dot and dab' adhesive. The spray-foam adhesive mentioned above will probably be easier, and even stuff from cartridges - StixAll, GripFill etc - will go (as long as any solvent content won't attack the insulation...)

ANY thickness of this board will TRANSFORM your room, even the lowliest 35mm stuff. Go a bit thicker if you can (if you can afford to lose the space) but the 3"+ layers I've seen folk on here add is nuts.

Imo  

Are you DIYing this? Don't forget to do the window reveals, and trim the boards so's the insulation layer butts neatly, and the p'board skin overlaps to complete the corners - you'll know when you come to do this

An aerosol of spray foam/adhesive carefully run along all the butting insulation edges will also help to both bond the sheets and prevent cold gaps.

Hi yes going to be DIY’ing it, I will keep your advise in mind when coming to do this job , The Boards I have seen is plasterboard with polystyrene stuck on to the the back but think they was 22mm . 

Also seen the other type which is foam like PIR material onto the plasterboard too.

FreeBear

quattros said: The Boards I have seen is plasterboard with polystyrene stuck on to the the back but think they was 22mm . 

Also seen the other type which is foam like PIR material onto the plasterboard too.

Polystyrene has a u-value of 0.035-0.040 W/m²K compared to 0.022-0.025 W/m²K for PIR type boards. When trying to squeeze the most out of limited space, the numbers can soon add up. I would recommend using the PIR type boards and go for the thickest you can get away with. At a minimum, 35mm (that is 25mm of insulation and 12mm of plasterboard). 65mm would be better.

Jeepers_Creepers

quattros said:

Hi yes going to be DIY’ing it, I will keep your advise in mind when coming to do this job , The Boards I have seen is plasterboard with polystyrene stuck on to the the back but think they was 22mm . 

Also seen the other type which is foam like PIR material onto the plasterboard too.

It's an excellent DIY job since at least half the cost - actually probably a lot more than - would be labour.

As FB says, worth going for high-insulation value stuff, especially if you are going to keep it 'thin'.

The room I'm sitting in now is an attached single-skin garage which I converted into a multi-purpose room 15 years ago. It's long - nearly 20' - but narrow at around 8', so minimising space loss was important. I strapped the walls out with treated 2x1 and fitted 1" Jablite (cheap expanded polystyrene foam - the 'snow beads' type) insulation in between, and overboarded this with 35mm Knauf or similar, which was 9.5mm p'board with a high-value polyurethane (I think?) bonded to it. This room is the easiest in my whole house to heat - the warmth from the plasma TV I use as a PC monitor is more than enough to heat it! In retrospect, I wish I'd simply adhered 2" Knauf straight to the wall as this would have been far less work and a better U value, but I wasn't clued-up on D&D techniques back then, so assumed it needed strapping first! 

Just to confirm - your existing plaster & bonding coat needs to be fully solid and secure if you aren't going to remove it. I hope it is, because taking this layer off would be the worst job of the lot (unless it really is on the verge of falling off by itself)... If space is a premium, then be happy knowing that even the 35mm stuff (1" insulation) will make a HUGE and NOTICEABLE difference, but that 2" would obviously be a lot better (tho' nowhere near twice as much). My personal view on this insulation malarkey is that going more than 2" is not worth the extra cost and hassle, and starts to introduce undesirable issues like making rad mounting and stuff difficult.

If your floor is draughty - eg T&G floorboards - then sort that too, especially around the perimeter under the skirting boards. Eg - seal under the new wall boards with a bead of foam before fitting the new skirting boards.

quattros

Jeepers_Creepers said:

quattros said:

Hi yes going to be DIY’ing it, I will keep your advise in mind when coming to do this job , The Boards I have seen is plasterboard with polystyrene stuck on to the the back but think they was 22mm . 

Also seen the other type which is foam like PIR material onto the plasterboard too.

It's an excellent DIY job since at least half the cost - actually probably a lot more than - would be labour.

As FB says, worth going for high-insulation value stuff, especially if you are going to keep it 'thin'.

The room I'm sitting in now is an attached single-skin garage which I converted into a multi-purpose room 15 years ago. It's long - nearly 20' - but narrow at around 8', so minimising space loss was important. I strapped the walls out with treated 2x1 and fitted 1" Jablite (cheap expanded polystyrene foam - the 'snow beads' type) insulation in between, and overboarded this with 35mm Knauf or similar, which was 9.5mm p'board with a high-value polyurethane (I think?) bonded to it. This room is the easiest in my whole house to heat - the warmth from the plasma TV I use as a PC monitor is more than enough to heat it! In retrospect, I wish I'd simply adhered 2" Knauf straight to the wall as this would have been far less work and a better U value, but I wasn't clued-up on D&D techniques back then, so assumed it needed strapping first! 

Just to confirm - your existing plaster & bonding coat needs to be fully solid and secure if you aren't going to remove it. I hope it is, because taking this layer off would be the worst job of the lot (unless it really is on the verge of falling off by itself)... If space is a premium, then be happy knowing that even the 35mm stuff (1" insulation) will make a HUGE and NOTICEABLE difference, but that 2" would obviously be a lot better (tho' nowhere near twice as much). My personal view on this insulation malarkey is that going more than 2" is not worth the extra cost and hassle, and starts to introduce undesirable issues like making rad mounting and stuff difficult.

If your floor is draughty - eg T&G floorboards - then sort that too, especially around the perimeter under the skirting boards. Eg - seal under the new wall boards with a bead of foam before fitting the new skirting boards.

Thanks i will definitely be looking Into doing this and will look at the 35mm boards and see how much i will loose space wise, The room under the bedroom is a garage and there carpet near the front 3/4 of the bedroom is cold and draughty so will have to look into that too . Will have to empty the room and go from there and see where the drought is coming from .