SIP wall thickness vs u value

[JohnMo]

@cheekmonkey

All good info above.

[G and J]

4 hours ago, cheekmonkey said:

My advice is don't over think it. You're on the right lines.

We didn't use Kingspan, we used a system from SBS via our installer NewForest SIP, but have 170 walls & 200 roof. Essentially same as your make up here but only have internal void if req. I deliberately designed service runs to avoid battening all the internal walls so just picked a few. ultimately to just save time & money & also have walls i can fix things direct to OSB like kitchen units.

We also have batten & counter externally with 20mm half lap larch over glidevale membrane

We didnt bother with vapour barrier or any special taping, i did externally tape the glidevale membrane with their recommended tape but TBH i think it was probably a waste of time.  all panel joints were foamed on install & mastic around roof joint.

we've achieved an air test of 2.56 (that's even with 14m of leaky sliding doors), an epc of A & the place is toasty warm with no heating on at all. it's very stable temperature, we also have MVHR. 

That’s really good to hear, thank you.

 

Whilst I readily accept that I shouldn’t ‘over think it’ it’s actually hard to turn the ‘CPU’ off.    😕

[G and J]

4 hours ago, cheekmonkey said:

Edited June 4 by G and J
Removal of duplicate post!

[Bournbrook]

Can I ask a technical question regarding battons that cladding is fixed to externally. What difference is there using 25mm vs 50mm? Does it make a big difference to u value?

I know for using a brick skin a 50mm is needed, but we are trying to minimise wall thickness so ideally use a 25mm with an insulated board and brick slips. Would save an inch!

[Alan Ambrose]

Little difference to theoretical u-value as it’s assumed that the cavity between the cladding and SIP is ventilated at outside temperature. Try ubakus.de if you want to play around with different set-ups. Some cladding suppliers recommend 50 rather than 25mm to get max ventilation, but I’ve always read this as ‘would be nice’ and probably depends a lot on your local environment (wind, rain etc) a lot. W coast of Scotland, probably 50mm, some sheltered place in Suffolk, probably 25mm.

 

Of course, horizontal cladding will save you 25mm too.

[saveasteading]

50 minutes ago, Bournbrook said:

for using a brick skin a 50mm is needed

25mm would work better as insulation but 50mm is the norm for other reasons.

A smaller gap has less air circulation so will lose less heat.

25mm batten is fine.

[SteamyTea]

Run the numbers on the different thicknesses, it is the only way to work out the best solutions.

[eandg]

We looked at various sips kits but found going with 142mm Kingspan and augmenting it with our own led to best u-values. (We put 60mm in walls and 100mm in roof). Obviously not the only part of the story but our as built SAP rating is 101 and it's a very warm house. Do the additional insulation and the airtightness yourself to make sure there's no shortcuts and voids. 

[Bournbrook]

17 hours ago, SteamyTea said:

Run the numbers on the different thicknesses, it is the only way to work out the best solutions.

Is there a tool for running the numbers? I’ve found the Kingspan u value calculator but I can’t seem to see SIPs panels as an option 

[Bournbrook]

16 hours ago, eandg said:

We looked at various sips kits but found going with 142mm Kingspan and augmenting it with our own led to best u-values. (We put 60mm in walls and 100mm in roof). Obviously not the only part of the story but our as built SAP rating is 101 and it's a very warm house. Do the additional insulation and the airtightness yourself to make sure there's no shortcuts and voids. 

Thanks for this. Yes have read that having a 142 with separate insulation is better than a 172. What are your wall thicknesses in total?

[SteamyTea]

5 hours ago, Bournbrook said:

Is there a tool for running the numbers

I just use a spreadsheet. Easy enough to get the thermal properties of the materials.

Then you can do side by side comparisons easily.

[G and J]

On 06/06/2024 at 12:51, Bournbrook said:

Can I ask a technical question regarding battons that cladding is fixed to externally. What difference is there using 25mm vs 50mm? Does it make a big difference to u value?

I know for using a brick skin a 50mm is needed, but we are trying to minimise wall thickness so ideally use a 25mm with an insulated board and brick slips. Would save an inch!

Our cladding is vertical, therefore we have to batten and counter batten. That’s why we have 50mm in our wall build up.

[eandg]

On 07/06/2024 at 08:58, Bournbrook said:

Thanks for this. Yes have read that having a 142 with separate insulation is better than a 172. What are your wall thicknesses in total?

65mm facing brick

50mm cavity 

142mm sips kit

60mm PIR

25mm typical service void

12.5mm plasterboard

355mm total