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Spray foam under room in roof floorboards - expensive option?


readiescards

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On 25/03/2017 at 09:53, Alexphd1 said:

@readiescards i know you still have to plaster board etc but have you noticed a sound reduction from upstairs with the spray foam in the posi-joists?

 

I can't directly answer that question as the whole spray foam was installed at the same time and sound proofness of the whole house improved substantially - reducing the sound of the wind and rain outside and softening the internal echos. Much better.  Last bit of posijoist installation goes in mid-April and I'm hoping for a reduction of interfloor sound transmission but given there is not much noise around at the moment it will be hard to gauge the amount.

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4 hours ago, Alexphd1 said:

@readiescards& @PeterStarck or anybody else who had had spray insulation. Do you know how much drums the guys went through for a rough m2 and and depth..... Trying a DIY effort...

I'm sorry I can't remember how many drums they used. I do know they under estimated and had to get another one.

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5 hours ago, Renegade105 said:

Hi Guys,

 

I'm in this exact position.....Can I ask are Mortgage providers ok with this, has anyone got any experience with it?

 

also, any good recommended installers?

 

Thanks 

 

Sorry thIs thread has got a few twists and turns. Which position are you in?

 

Spray foam between rafters is definitely problematic in some houses.

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Hi,

 

Roof Truss's aren't in yet but will be soon.

 

Spray foam onto a tight vapour barrier would be the easiest option of speed and air tightness, but this whole time I thought it wasn't BBA approved! Turns out I was wrong.

 

Cant see anything wrong with it...its fast, should get good airtightness, negatives are possible toxins (unlikely) and cold bridging via the actual trusses, and unclear what the heat decrement delay is.

 

Apart from that, seems like a whole lot faster than cutting wood fibre boards etc.

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On 17/01/2023 at 23:12, Renegade105 said:

Spray foam onto a tight vapour barrier would be the easiest option of speed and air tightness, but this whole time I thought it wasn't BBA approved! Turns out I was wrong.

There are different types of spray expanding foam. We used Icynene in our passivhaus which is open cell and with 350mm in the walls and roof we achieved an airtightness value of 0.47ACH without any tapes or membranes. The U value for the walls and roof was 0.095W/m2K and we heated the whole house to 23C with three electric towel rails and warm air from an EASHP in the MVHR system. The house was in East Kent.

Edited by Gone West
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On 22/01/2023 at 08:42, readiescards said:

5 years on, my thoughts are that spray foam insulation is expensive and fairly ineffective as an insulation product (maybe a side effect of it's breathability)

 

 

I would not encourage anyone to use it.

We have a roof over 240m2 all vaulted and have 350mm of icycrene spray foam, behind an airtight vapour control layer.  Heat loss is pretty much as predicted.

 

Agree it is expensive, but compared to spending weeks doing insulation and ripping my hands apart stuffing between the metal webs of posi rafters - a bargain, job done in two days.

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10 hours ago, Renegade105 said:

What's it like being in the attic space then, I assume its habitable...Does it overheat a lot or is it better than the usual PIR stuff.

We only had one area that was an attic, the rest had vaulted ceilings. It didn't overheat a lot but we had reflective film on the windows. Decrement delay wasn't a factor in our area as we were only a couple of miles from the coast and we had sea breezes everyday. We had the Icynene installed in 2015, and we moved in, in 2018. We lived there for over three years and we found it very comfortable.

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On 22/01/2023 at 12:47, Renegade105 said:

Wow really? What do you think is the reason? What U value did you build to and was it open or closed? What’s you’re roof build up like?

 

cheers

200mm between roof trusses - can easily feel draft movement

 

100mm between floor joists between cold garage and heated office - feet get cold in office

 

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