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Spray insulation for timber framed new build?


davejura

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On 10/03/2021 at 14:58, Iceverge said:

Have a price up of the below buildup. If you're DIYing it I can't see a cheaper way. 

 

Remember increasing your insulation much beyond building regs isn't worth much unless you're taking care of thermal bridging and airtightness. 

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I'll look into that, thanks. As long as I don't have to go back to the architect again, it shouldn't be a problem! Is the Glasswool 35 cheaper than PIR insulation? And what site did you use for the calculations please? My local supplier of PIR has just quoted me for IKO Enertherm and Recticel boards, and has said there will be a 17% price increase on 1st April!

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1 minute ago, davejura said:

I'll look into that, thanks. As long as I don't have to go back to the architect again, it shouldn't be a problem! Is the Glasswool 35 cheaper than PIR insulation? And what site did you use for the calculations please? My local supplier of PIR has just quoted me for IKO Enertherm and Recticel boards, and has said there will be a 17% price increase on 1st April!

 

Be aware that if you change anything you will have to provide an update SAP calc and amendment to warrant before you get your completion certificate, so you should run any changes to the specifications past your architect asap - you'd be amazed how many times builders "rules of thumb" which get rid of the "expensive, over-specced architects insulation", mean that you no longer comply with the regs!

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7 minutes ago, the_r_sole said:

 

Be aware that if you change anything you will have to provide an update SAP calc and amendment to warrant before you get your completion certificate, so you should run any changes to the specifications past your architect asap - you'd be amazed how many times builders "rules of thumb" which get rid of the "expensive, over-specced architects insulation", mean that you no longer comply with the regs!

Going to have a few amendments to warrant anyway, so that shouldn't be a problem! Yes, architects do tend to over spec things and I'm sure they have shares in Kingspan!

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1 hour ago, davejura said:

I'll look into that, thanks. As long as I don't have to go back to the architect again, it shouldn't be a problem! Is the Glasswool 35 cheaper than PIR insulation? And what site did you use for the calculations please? My local supplier of PIR has just quoted me for IKO Enertherm and Recticel boards, and has said there will be a 17% price increase on 1st April!

I reckon your original buildup had a u value of 0.2 W/mK so the mineralwool 35 betters at 0.19 it albeit with an additional 20mm wall thickness. 

 

A quick Google suggests material only the PIR is £23.65/m2 and dritherm 35 is £8.60 ex vat for the above buildups. This excludes the faf of cutting foaming and fitting the boards. 

 

It's worth getting a handle on the numbers or you risk just doing whatever makes the architects life easiest. 

 

When it comes to insulation architects very rarely overspec the design. Many were educated in the oil era when infinite cheap energy was the solution. They can often outsource SAP calculations with a "just make it pass " requirement. 

 

 

 

 

 

 

Edited by Iceverge
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7 hours ago, Iceverge said:

I reckon your original buildup had a u value of 0.2 W/mK so the mineralwool 35 betters at 0.19 it albeit with an additional 20mm wall thickness. 

 

 

 

 

 

 

 

 

Interesting. Thanks for this. Where do you get the extra 20mm wall thickness? If I put 140mm of mineral wool 35 in instead of 100mm PIR, that could work. Here is the build make up.

image.png.d45d40df79973d9c7c332ffd6727ea72.png

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Looking at your whole wall build up it is actually 5 mm narrower with my suggested buildup as I didn't realise you had a service cavity. 

 

Insulation has little to do with airtightness. It's the vapour control layer that does that in your case. 

 

How much of the work do you intend to do yourself? Do you have anyone with a good knowledge of the main principles to hand?

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9 hours ago, Iceverge said:

Do you have anyone with a good knowledge of the main principles to hand?

I do actually. I'm lucky in that I have secured the services of a local builder on an advisory basis. I'm doing some fencing for him as a trade off! He is also going to mark out and supervise the foundations. 

Thanks for all your advise. I'm just going to email my architect and get her take on it all.

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21 minutes ago, the_r_sole said:

Your architect is going to love being told to change their drawings based on what you've been told on an Internet forum ?

I presume you are talking from experience? ?

Just pinged her now to make her Saturday! Actually, hoping if we don't change the make up, just use the 140mm of ThrameTherm or similar instead of the 100m of PIR, it can just go through as an amendment to warrant at the end. Obviously, will need a new SAP calculation.

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Have you got a load of pv or something to balance out the sap? 

Just doubled checked a recent sap where we looked at similar insulation and needed 50mm pir inside to get to 0.19, even then we needed to add more renewable to get through, ended up being cheaper to rever back to 140 pir between the studs...

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On 13/03/2021 at 14:36, the_r_sole said:

Have you got no windows or something? 

Your spec sounds like what we were doing 10 years ago to get a pass!

I'm not kidding on I have a clue when it comes to this. Just going by what the architect and company that did the SAP calc came up with!

 

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