Will this create a cold spot

[Lostdog]

I have a brick wall house with no cavity, this is on the first floor, I've stripped the walls back to brick and I'm going to put 3" by 2" cls on edge, probably braced here and there but not properly fixed back to the brickwork with 75mm celotex in between the stud work, then insulated backed pksterboard over the top to finish.

Will there be a cold spot between the brick and the celotex layer?

 

[phatboy]

Im confused, the brick will be outside of the insulation, so will be cold, surely?

Also 3x2 on edge will be more like 70mm finished, so you wont get 75mm solid insulation in.

Can you avoid all fixings to the wall, by fixing to the ceiling and floor?

 

[Notch7]

You could fit the insulation direct to the wall, tape all the joints, then screw 50 X 25 battens flat, then vcl and plasterboard.

That gives you a continuous layer of insulation and a 25mm service void for cables.

If you want to do studwork direct to the wall with insulation in between, there will be Some thermal bridging -which you are mitigating somewhat with insulated plasterboard.

 

[Lostdog]

the brickwork is no where near flat and my concern is I'm going to end up with condensation between the brick and cellotex,
This is the design from the architect to get r values, yes I can fix top and bottom, I've made ceiling height 2.4 so i think the 3by2 will be fine over that height and because the brickwork is all over, old house, then the gaps behind will be minimum of 5mm because of the cellotex but will be 25mm in places, I can expanding foam behind the studs to lose that gap, but will condensation ocur behind the cellotex that would cause a problem?

 

[Lostdog]

I know it's a little different cause there's no cavity but I would have thought building paper then something like the green earthwool batts of insulation would be better because you can squeeze that into where it needs to go loosing any gaps at the back?

 

[phatboy]

I know it's a little different cause there's no cavity but I would have thought building paper then something like the green earthwool batts of insulation would be better because you can squeeze that into where it needs to go loosing any gaps at the back?

Soft thermal insulation doesn't want squeezing in, it needs the free air in it to retain heat.

 

[Mr Chibs]

I recently spoke to Kingspan regarding old lime based, solid wall, internal insulation.

This is the answer I was given.

25x50mm roofing batten, sat on top of length of dpc, screw this lot the wall... pack to get plumb.

Insulation screwed to batten, tape it up, try to ensure its fully taped.

Plasterboard over the lot.

Kingspan, said you should leave 25mm air gap, so condensation (if there is any) will not be transferred into battens and rot them.

 

[Mr Chibs]

Soft thermal insulation doesn't want squeezing in, it needs the free air in it to retain heat.

I think he may be using this to fill any voids from uneven brickwork. Not needed if there is an air gap.

I realise that there is a train of thought about insulation direct to wall and batten on top to hold it to the wall.

I'd be curious to hear others views.

I have done the batten first method, and it's been successful for me, two years down the line.

 

[Lostdog]

Soft thermal insulation doesn't want squeezing in, it needs the free air in it to retain heat.

I agree, with the 70mm cls and gap behind the 100mm batts would just be touching in some places but compressed by 30mm in others,
so i would have gone for that but theres already to much difference in r value, 2.86 for the Knauf green slabs 100mm and 3.4 for the 75mm celotex/kingspan
I cant say i know a great deal about R values but that sounds like enough to make a differance.

I recently spoke to Kingspan regarding old lime based, solid wall, internal insulation.

Kingspan, said you should leave 25mm air gap, so condensation (if there is any) will not be transferred into battens and rot them.

the mortar is probably lime based but the bricks aren't, so this is why im trying to stay away from having an air gap or the need to have vents top and bottom on the walls

maybe im over thinking this to much because done properly the chances of the condensation transferring into the room are slim, my concern is if theres a lot condensation over time it could affect the floor joists which sit in pockets in the brick work.

 

[Mr Chibs]

Yes probably overthinking, but I know it's a concern.

I will be doing a room within the next month, similar to your description, and the brickwork is very old and very uneven.
I had thought of 50mm rockwool behind the foam board, and mechanically fixed straight to the wall, not sure I will be able to get it plumb though.

So I will revert back to battens I think, only thing you have to mindful of, is when you want to hang shelves and heavy items, as you need longer fixings etc. I will probably use 400mm spacings, perhaps less if I know something heavy is going on a certain wall.

The lime mortar, is the thing that allows the moisture to escape, as it won't dissipate through bricks quickly.
Unless you have a damp problem, you should only have increased moisture through the autumn/winter months.

AS for R values, the higher the better.