Super quilt/tri iso insulation

[23vc]

Hi
I've insulated a couple of vaulted ceilings before, and both times did (I think) 100mm celotex between rafters, then another 50mm celotex underneath the rafters, then plasterboarded under that. I've seen the foil stuff (tri iso etc) used recently, looked like it was stapled to the top side of the rafters (under the breather membrane?) and I think it saved space and avoided the need to insulate across the underside of the rafters (prevented cold bridge). Keen to know if anyone's got any views on the tri iso stuff and whether its worth using, and how much celotex you're likely to need alongside it. (Obviously I will speak to BCO about it, just keen to know what the options are)
Cheers

 

[freddiemercurystwin]

There are no advantages of using it, you need an air gap above and below it and an additional layer of about 25mm PIR under the lower air gap.

 

[noseall]

It can be used in conjunction with Celotex etc but it is a faff with having to counter-batten etc. Not much saving regards space, cost or time.

 

[noseall]

There are no advantages of using it, you need an air gap above and below it and an additional layer of about 25mm PIR under the lower air gap.

Bah! Beaten by a pop twin.

 

[freddiemercurystwin]

You snooze you lose!

 

[23vc]

Great thanks. I thought, mistakenly, that it was easier and quicker as could just be stapled to rafters and off you go. I saw a job recently before the PIR had been installed, and you could see the superquilt on top of the rafters from underneath, from what you guys are saying they’d have had to counter batten it. So yeah sounds like a faff.

 

[Notch7]

Although it has approval, there is a touch of snake oil about it.

I believe the space saving is limited because it needs air space both sides.

 

[Notch7]

I know some builders have found this stuff good as its easy to fit

http://hybrid.insulation-actis.com/hybris/

 

[23vc]

I know some builders have found this stuff good as its easy to fit

http://hybrid.insulation-actis.com/hybris/

Cheers I’ll check it out

 

[23vc]

So final question, as I know you guys know it off the top of your head, is the usual method 100mm pir between and 25mm underneath? No vapour barrier? If so that’s what I’ll stick to unless I go for that stuff notch posted a link to

 

[Notch7]

If you 25mm underneath, taping the joints will give you a vapour barrier

 

[freddiemercurystwin]

Prolly get away with 90mm but really you should do some number crunching or get on the celotex u value calculator, as the rafter spacings also affects it. The foil is the VB so tape the joins with foil tape.

 

[23vc]

Ok great will do, cheers