TF House about to start, and last minute pondering... Insulation...

[JohnMo]

OK

[Thorfun]

3 hours ago, JohnMo said:

First the OSB layer has done 90% of your airtightness especially if you use airtight OSB on the joints to worry about.  Or if using a membrane a great flat surface to affix to.

 

Your service cavity will have your plumbing and electric stuff within it,  why would you want then to make loads of holes for light switches etc in the OSB to allow it to be installed?

 

Seems like a double work effort to me for less gain

ok. I understand now and, yes, if using OSB for a VCL then I would 100% do as you said!

 

but as @Nickfromwales says I am putting a VCL membrane on top of the internal PIR and fixing the service cavity battens through that into the TF studs. the OSB will simply be for a more 'solid' feeling wall rather than VCL.

[BartW]

4 hours ago, JohnMo said:

Looking at your wall build with respect your service cavity.  You have plasterboard, OSB, batten for service cavity.

 

Plasterboard on its own is known to have a pull-out strength of paper, and I am likely to have fixtures on the walls, like TV, wall cabinets in the kitchen and so on. To include other things not yet specified. OSB attached to the structural 140mm joists gives no benefit, but just doubles up the bracing role already being taken care of by the external layer of OSB.

 

 

4 hours ago, JohnMo said:

 

 

If you floor has a ventilation within the void it's there for good reason.  If your insulation is above the ventilation why are you worried?

 

I am on about me having a single skin of 140mm block with no cavity to hide telescopic vents, and actively trying to find a solution and hiding them.

 

 

 

 

[Nickfromwales]

9 minutes ago, BartW said:

 

Plasterboard on its own is known to have a pull-out strength of paper, and I am likely to have fixtures on the walls, like TV, wall cabinets in the kitchen and so on. To include other things not yet specified. OSB attached to the structural 140mm joists gives no benefit, but just doubles up the bracing role already being taken care of by the external layer of OSB.

 

 

 

I am on about me having a single skin of 140mm block with no cavity to hide telescopic vents, and actively trying to find a solution and hiding them.

 

 

 

 

Maybe “bell” out the first few courses to give a faux cavity, then rerun in at 45o to the residual depth of just the rain screen? 

[BartW]

26 minutes ago, Nickfromwales said:

Maybe “bell” out the first few courses to give a faux cavity, then rerun in at 45o to the residual depth of just the rain screen? 

 

That's how I had it initially. But it adds unjustifiable labour and material cost of about £5k ...

 

[Nickfromwales]

20 minutes ago, BartW said:

 

That's how I had it initially. But it adds unjustifiable labour and material cost of about £5k ...

 

😳. Ok. Needs something sorting, so you may have to rebate the external EPS. Air is an insulator so it’s not going to sink the ship. 

[Iceverge]

 

 

This part here makes me wonder, if you've just been given an off the shelf solution rather than something proper. 

 

The 15mm air gap created I suspect is for production builders to who only aim for the minimal levels of insulation, thermal bypass or airtightness.

 

It allows them to drop their 140mm panel onto site, the electricians fix a 25mm backbox up against the PIR, the boarders put a 12,5mm plasterboard over the top and hey presto it all matches with a 2.5mm gap to allow the socket cover clamp the socket "firmly" in place onto the plasterboard. 

 

The trouble with that 15mm gap in your case, is that unless it's very well sealed, it'll be able to vent outside air, ( especially in windy weather) making the 125mm of PIR outboard much less effective. 

 

 

 

 

 

 

 

 

 

Solutions. 

 

1. Can you contact the TF company and see if they can either. 

  1. Full fill the studs with 140mm PIR. 

  2. Foam the 15mm gap at regular intervals before fitting the 80mm PIR over the top to ensure that the 15mm air gap behind is trapped in pockets and the air is guaranteed to be stationary (unventilated)  

 

 

 

 

 

As a final touch I would reduce the internal PIR to 50mm,  and boost the service cavity to 45mm and fill with woodfiber or similar high heat capacity and higher density insulant sheepswool or hemp batts. 

 

This would really improve your decrement delay (phase shift) and help prevent overheating. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[BartW]

@Icevergethanks for the detailed response. I will study tonight. Changeplan suggested 0.149u value for my buildup with 50mm PIR.

 

 

[BartW]

11 hours ago, Iceverge said:

As a final touch I would reduce the internal PIR to 50mm,  and boost the service cavity to 45mm and fill with woodfiber or similar high heat capacity and higher density insulant sheepswool or hemp batts. 

I am actually liking this idea. I don't suppose I would get away with a 75mm RWA45 internally, whilst eradicating internal PIR altogether? I appreciate that would re-introduce cold bridges. What about doing 20mm PIR internally, and then 50mm RWA45? I would keep my service void 50mm, but hopefully things like cables and pipes would just squash the insulation a little.

Viable?

[BartW]

18 hours ago, Thorfun said:

can I ask if you have a specific reason for using 2" x 2" battens for your timber cladding?

 

We want to hide all gutter downpipes behind cladding. There may be other ways of achieving this with 1" battens, but I might have to notch / route the back of facade timbers, or create a bespoke downpipe. Sounds like I will be re-evaluating live when at it soon!

[Iceverge]

5 hours ago, BartW said:

I am actually liking this idea. I don't suppose I would get away with a 75mm RWA45 internally, whilst eradicating internal PIR altogether? I appreciate that would re-introduce cold bridges. What about doing 20mm PIR internally, and then 50mm RWA45? I would keep my service void 50mm, but hopefully things like cables and pipes would just squash the insulation a little.

Viable?

 

 

2*2 battens are typically about 45 mm x 45mm, hence that choice for service cavities, filled with 50mm insulation. Going larger brings issues with not being able to use 90mm nails from a nail gun and needing to bang them in by hand or use screws AFAIK. 

 

Screws are probably 10 times the price and ten times slower than nails from a nail gun.

 

I would put a 45mm batten on top of the 140 mm studs. With your 15mm gap to the pir you should be able to add 60 mm batts nicely here, no thermal bypass, 

 

Then a vapour membrane.

 

Then a 45mm batten at 90 deg to the first, this will cancel nearly all thermal bridges with Insulation and service wires + pipes in here.

 

Then osb and then plasterboard. 

 

Rockwool would be fine but again an organic insulant would buy some better heat protection. 

 

 

 

 

 

Edited May 19, 2022 by Iceverge

[Thorfun]

5 hours ago, BartW said:

 

We want to hide all gutter downpipes behind cladding. There may be other ways of achieving this with 1" battens, but I might have to notch / route the back of facade timbers, or create a bespoke downpipe. Sounds like I will be re-evaluating live when at it soon!

then that makes perfect sense. you can fit 68mm guttering and bends behind two 2 x 2 battens. just wouldn't be possible with 1" battens!

 

 

[Nickfromwales]

27 minutes ago, Iceverge said:

 

 

2*2 battens are typically about 45 mm x 45mm, hence that choice for service cavities, filled with 50mm insulation. Going larger brings issues with not being able to use 90mm nails from a nail gun and needing to bang them in by hand or use screws AFAIK. 

 

Screws are probably 10 times the price and ten times slower than nails from a nail gun.

 

I would put a 45mm batten on top of the 140 mm studs. With your 15mm gap to the pir you should be able to add 60 mm batts nicely here, no thermal bypass, 

 

Then a vapour membrane.

 

Then a 45mm batten at 90 deg to the first, this will cancel nearly all thermal bridges with Insulation and service wires + pipes in here.

 

Then osb and then plasterboard. 

 

Rockwool would be fine but again an organic insulant would buy some better heat protection. 

 

 

 

 

 

Great detail, but the con is that all of the electrics would need to be run in conduit due to the insulation filling what was the service cavity. Or the circuits downgraded / cables upsized.

[BartW]

I must admit I am looking at economical factors too. 
 

hence me considering likes of 25mm pir sandwich + rwa45.  Also “horizontal service cavity means services going in that direction or a lot of notching / removing of battens. 
 

What about 2inch vertical battens with 75mm rwa45 (tight!) then blinded with 25mm pir and 25mm service cavity vertically? Then osb and plasterboard?

[Nickfromwales]

5 hours ago, BartW said:

I must admit I am looking at economical factors too. 
 

hence me considering likes of 25mm pir sandwich + rwa45.  Also “horizontal service cavity means services going in that direction or a lot of notching / removing of battens. 
 

What about 2inch vertical battens with 75mm rwa45 (tight!) then blinded with 25mm pir and 25mm service cavity vertically? Then osb and plasterboard?

What about sticking with your original and “moving swiftly on” ? That’s a plenty good enough detail imho. 
I would probably have gone a-la MBC’s higher performing spec of rock wool in the outer, and PIR inner for bridging but that uses a deeper frame iirc to get more wool in. 
Work out what will be the net physical results from all the options / effort and how it will make a difference to your life   

The only main Achilles heel with all PIR only structures is that they’re quite dire in terms of acoustic attenuation. You can rid yourself of some of that by using 15mm SB PB on the exterior walls. 
After that, I’d go and start choosing paint and tiles  

[BartW]

On 19/05/2022 at 13:11, Nickfromwales said:

What about sticking with your original and “moving swiftly on” ? That’s a plenty good enough detail imho. 
I would probably have gone a-la MBC’s higher performing spec of rock wool in the outer, and PIR inner for bridging but that uses a deeper frame iirc to get more wool in. 
Work out what will be the net physical results from all the options / effort and how it will make a difference to your life   

The only main Achilles heel with all PIR only structures is that they’re quite dire in terms of acoustic attenuation. You can rid yourself of some of that by using 15mm SB PB on the exterior walls. 
After that, I’d go and start choosing paint and tiles  

 

 

Yeah, I think I will do just that. Better (worse) things to worry about out there!

 

 

 

B