Minimum Reasonable wall width for good U values?

[ProDave]

34 minutes ago, Moonshine said:

 

Do you know what a typical U value of that build up would be with 50mm pir on the inside of the timber.

 

How do you fix the pir to the timber frame? I would have thought any screws for battens will need to go all the way through the pir and create a cold bridge?

No I don't know the U value but it should not be too hard to work out.

 

The modern method would be hold the PIR in place with the battens that form the service void. The fixings are so few I don't think cold bridging is much of an issue.

[A_L]

1 hour ago, Moonshine said:

Do you know what a typical U value of that build up would be with 50mm pir on the inside of the timber.

 

U=0.124

 

 

[Moonshine]

5 minutes ago, A_L said:

 

U=0.124

 

 

Thanks, but the build up I am thinking of has mineral / glass insulation in the timber cavity not pir.

 

Is that a software to do the calc?

[Moonshine]

1 hour ago, ProDave said:

The modern method would be hold the PIR in place with the battens that form the service void. The fixings are so few I don't think cold bridging is much of an issue.

 

Ah I see, that makes sense and the plasterboard only fixed to to battens rather all the way through to studs.

 

I presume that if something heavy was fixed to the wall (e.g kitchen wall cabinets) they would have to penetrate all the way through the pir though to the studs.

[ProDave]

15 minutes ago, Moonshine said:

 

Ah I see, that makes sense and the plasterboard only fixed to to battens rather all the way through to studs.

 

I presume that if something heavy was fixed to the wall (e.g kitchen wall cabinets) they would have to penetrate all the way through the pir though to the studs.

Where you are expecting your kitchen cabinets, put horizontal battens across at top of cabinet height so you have something to fix to, otherwise it is unlikely the cabinet fixings will line up with the studs.

[A_L]

48 minutes ago, Moonshine said:

Thanks, but the build up I am thinking of has mineral / glass insulation in the timber cavity not pir.

 

Is that a software to do the calc?

 

With 150mm of 0.035 mineral wool instead of PIR in timber frame U=0.147. It is software but not currently available. 

[pudding]

Here you go - https://www.changeplan.co.uk/u_value_calculator.php

[puntloos]

On 16/01/2020 at 11:58, Carrerahill said:

I am not too keen on that, over your OSB you would have a membrane like Protect TF200 or Dupont Reflex and if you stuff PIR board of the same thickness as the depth of the cavity then you have removed the ventilation over the face of the membrane and this would as I see it create a perfect moisture trap at the OSB layer. 

 

We went for render, block, 50mm cavity, breather reflective membrane over 11mm OSB (I wouldn't use anything less than 11 for the cost of it - even 11mm is fairly flimsy), onto 6x2 studs, 100mm of QuinnTherm PIR in-between studs, then plaster and skim - we could have gone for the same makeup but a layer of QuinnTherm over the studs too but we didn't need it, we did however do that on the ceiling. We could have also use 125mm QuinnTherm but that would have reduced our service void too much and to be honest, as it stands the rooms take only the warmth of Henry the hoover running to take the chill of it! 

 

 

 

Getting back onto this discussion! (hi)

 

@epsilonGreedy - being an amateur I don't read your list super-well - in particular "PIR in-between studs" - does that mean I have to count the studs as well?

What's your final wall buildup thickness and U, decrment etc values achieved? I take it you are standard masonry here, and I am counting:
 

inside

20 - Render

100 - Block

50 - Cavity

11 - OSB

100 - PIR

20 - Plaster

outside

 

-> 300mm? 

 

We've decided to go for masonry, and for now our bog standard (and therefore presumably fairly cheap?) 400mm looks like this, but happy to be informed of better buildups 

 

 

Composite material properties:

 

0.18 is higher than most people have here, but not terrible, I'd say?

 

[epsilonGreedy]

14 minutes ago, puntloos said:

 

@epsilonGreedy - being an amateur I don't read your list super-well - in particular "PIR in-between studs"

 

 

Hi I don;t think I have posted in this thread, you quoted @Carrerahillin your post.

 

A few years ago I was involved with a discussion here about how to top up the U-value of a masonry wall with internal insulation. Options in that discussion were (1) battens with a rockwool layer sandwiched between block and plasterboard (2) as 1 but with say 2" of pir sheet or (3) PIR backed plasterboard.

 

I am leaning towards PIR backed plasterboard now having watched Charliediyty use it however @PeterWreckons it requires a skilled trademan to fit it with a pro end result.

 

 

[A_L]

25 minutes ago, puntloos said:

does that mean I have to count the studs as well?

 

you have to assume that 15% of the tf/insulation layer is timber and calculate the U value accordingly, see my 2nd last post above.

[Mr Punter]

32 minutes ago, puntloos said:

We've decided to go for masonry, and for now our bog standard (and therefore presumably fairly cheap?) 400mm looks like this, but happy to be informed of better buildups 

 

Yes you could fully fill your 200mm with Platinum EPS beads.

[puntloos]

18 minutes ago, epsilonGreedy said:

 

Hi I don;t think I have posted in this thread, you quoted @Carrerahillin your post.

Ha apologies, somehow you both look the same to me, apparently!

 

18 minutes ago, epsilonGreedy said:

 

A few years ago I was involved with a discussion here about how to top up the U-value of a masonry wall with internal insulation. Options in that discussion were (1) battens with a rockwool layer sandwiched between block and plasterboard

 

Yes, that's the buildup that I listed, right? "HP Rockwool partial fill"

 

18 minutes ago, epsilonGreedy said:

(2) as 1 but with say 2" of pir sheet or (3) PIR backed plasterboard.

 

"with" - you mean replacing 50mm of the rockwool with PIR? - so 100-ish Rockwool, 50-PIR assuming we're using my 400mm one

 

18 minutes ago, epsilonGreedy said:

 

I am leaning towards PIR backed plasterboard now having watched Charliediyty use it however @PeterWreckons it requires a skilled trademan to fit it with a pro end result.

 

Might not be a crazy idea, but then heh I'm coming back to the 'how to find a skilled tradesman' - perhaps by smell!

 

18 minutes ago, epsilonGreedy said:

 

 

 

[puntloos]

14 minutes ago, Mr Punter said:

 

Yes you could fully fill your 200mm with Platinum EPS beads.

My current design is 150mm but either way.. 

 

I wonder how much those beads are, compared to equivalent PIR or RockwoolHP...

[PeterW]

You don’t have a partial fill - you can’t partial fill with rockwool, it has to be retained both sides with masonry. 
 

400mm build up seems to be 15mm plasterboard and skim, 100mm block, 170mm cavity, 100mm block and 15mm render ..?

 

If so, 170mm rockwool and 170mm EPS are pretty much equal, 120mm PIR with 50mm cavity is probably 25% better but more difficult to detail and will cost more. 

[puntloos]

2 minutes ago, PeterW said:

You don’t have a partial fill - you can’t partial fill with rockwool, it has to be retained both sides with masonry. 
 

400mm build up seems to be 15mm plasterboard and skim, 100mm block, 170mm cavity, 100mm block and 15mm render ..?

 

If so, 170mm rockwool and 170mm EPS are pretty much equal, 120mm PIR with 50mm cavity is probably 25% better but more difficult to detail and will cost more. 

 

@PeterW Dumb question but wouldn't this build up need some way to make it airtight? Some membrane somewhere perhaps?

[PeterW]

Sand cement slurry on the inner blockwork. 

[puntloos]

27 minutes ago, PeterW said:

If so, 170mm rockwool and 170mm EPS are pretty much equal, 120mm PIR with 50mm cavity is probably 25% better but more difficult to detail and will cost more. 

 

"50mm cavity" - meaning "empty air"?

or 120 PIR and 50 EPS perhaps?

 

[PeterW]

You can’t full fill with rigid insulation. It has to have a cavity on the external side. Some of the “full fill” rigid boards have a 10mm spacer system built into the front to keep a cavity. 
 

I would always go beads these days and where possible up the cavity to 200mm. 300mm wall ties aren’t much more expensive and as you’re using block and render then split lintels are easy. 

[Buzz]

@puntloos just going to jump in on your thread ,  @PeterW i have 150mm cavities block and brick have asked for full fill 32 think this will give me .17 ? any benefit going to blown beads ?

[PeterW]

Quicker and easier as the brickies don’t need to install insulation. But you need to keep the cavities clean so may need to use snot boards. Beads get everywhere - that is a good and a bad thing ..! 

[Buzz]

2 minutes ago, PeterW said:

Quicker and easier as the brickies don’t need to install insulation. But you need to keep the cavities clean so may need to use snot boards. Beads get everywhere - that is a good and a bad thing ..! 

  only just started to price 32 but looking like £15m2 for 150mm how does that compare with the best beads ? 

[puntloos]

26 minutes ago, PeterW said:

You can’t full fill with rigid insulation. It has to have a cavity on the external side. Some of the “full fill” rigid boards have a 10mm spacer system built into the front to keep a cavity. 
 

I would always go beads these days and where possible up the cavity to 200mm. 300mm wall ties aren’t much more expensive and as you’re using block and render then split lintels are easy. 

 

@PeterW So.. summarizing one more time:

15mm plasterboard and skim, 

100mm block with sand cement slurry (for airtight) 

120mm PIR (maybe 150 if I'm feeling frisky)

50mm Cavity - filled with ecobead platinum or whatnot and some spacer system

100mm block 

15mm render

 

 

Edited March 20, 2021 by puntloos

[PeterW]

From memory the EPS graphite beads were £12/m at 150mm cavity. 

[puntloos]

7 minutes ago, Buzz said:

  only just started to price 32 but looking like £15m2 for 150mm how does that compare with the best beads ? 

 

"price 32"?

 

But yeah I'd love to figure out the price per m2 of my buildup I listed above versus the price per m2 of "20 render 100 block, 150 rockwool, 100 block 20 plasterboard"

[PeterW]

2 minutes ago, puntloos said:

, 

120mm PIR (maybe 150 if I'm feeling frisky)

50mm Cavity - filled with ecobead platinum or whatnot and some spacer system

 

 

 

you cannot fill the cavity when using PIR. 
 

Either use 120mm PIR with a cavity OR

Use 150mm blown bead or rockwool.