insulating a roof

[doctor Bob]

Hi,
My garage has a loft space, ideally the overhead roof rafters should be insulated with celotex or something similar.
However to do it on the cheap can i do the following,
(outside to inside)... Pan tile / breathable membrane / earth wool insulation (85mm) / breathable menbrane.

The trusses are 75mm. The final membrane is just to hold it all in place.

Do you reckon it's OK, any issues with the wool possibly pushing external membrane up causing damp issues, can this happen.

Should I bite the bullet and just use celotex

 

[skipdiver]

You can use earhwool if you leave a 50mm gap above, so at 75mm, you haven't got sufficient room. I have 100mm rafters in mine and used 50mm earthwoll with 11mm OSB lining.

 

[doctor Bob]

You can use earhwool if you leave a 50mm gap above, so at 75mm, you haven't got sufficient room. I have 100mm rafters in mine and used 50mm earthwoll with 11mm OSB lining.

so it needs to be something like celotex then, no other option?

 

[skipdiver]

Read this. Page 86 explains.

http://www.knaufinsulation.co.uk/sites/ ... evel_1.pdf

You could put timbers on the rafters to widen them and then use earthwool. Still cheaper than Celotex.

 

[No skills]

I thought you only needed a 25mm air gap, or is it 50mm specifically for that product?

 

[wide74]

I've done my workshop and quite a bit of my house with celotex so have experience of both. Simply for your own sanity bite the bullet and use celotex. It's cleaner, quicker, won't hold moisture and is a less attractive home for small fury things! I know the cost is off putting but it's a crappy job so the quicker and easier it gets done the better IMO. Have fun!

Sent from my SM-G935F using Tapatalk

 

[Myfordman]

You could save money by using cellotex seconds?

 

[Beau]

You could save money by using cellotex seconds?

Yes was going to say the same. Seconds and Co have some good deals from time to time. Celotex/Kingspan offers better levels of insulation per cm than earthwool will. Easy to instal and and to make it a really good fit and airtight use a foam gun to fill any gaps.

 

[Jake]

Whatever you use, the internal face should be vapour impermeable (dpm or the like, not breather membrane).

 

[skipdiver]

I thought you only needed a 25mm air gap, or is it 50mm specifically for that product?

I just followed the guidelines for earthwool, which i used in my roof. 25mm is probably ok for some products.

 

[Doug B]

You could try Xtratherm sometimes cheaper than the others
http://www.insulation4less.co.uk/xtrath ... e-r-floor/

Also check on the air gap if using breathable membrane under the tiles, you may not have to leave one, quick phone call to building control would sort it & it might mean you could fit in an extra bit of insulation.

Personally I'd just use a ridged foil faced insulation & forget any covering as the foil will reflect light.

 

[skipdiver]

I used celotex type board for my walls and found that if you shop around, the prices are not that much different to seconds an co, whose stuff looks like any old tat to me. I found that with 25mm celotex on the walls and 50mm earthwool in the rafters topped off by 11mm OSB. the workshop is well warm enough for me and on a really cold day, 30 mins with a with a hot air blower soon warms it up to a level that is comfortable for working. All in, my 5mt x 3mt workshop cost about £600 to do and it has made a huge difference to comfort levels and was money well spent.

 

[stuartpaul]

You could save money by using cellotex seconds?

Yes was going to say the same. Seconds and Co have some good deals from time to time. Celotex/Kingspan offers better levels of insulation per cm than earthwool will. Easy to instal and and to make it a really good fit and airtight use a foam gun to fill any gaps.

I'm in the process of insulating my garage and have found (currently) that Seconds and Co are only pennies cheaper but then charge £35 for delivery and this effectively makes them more expensive.

I understand that celetex (and all the other makes) are broadly twice as effective cm for cm than wool so it depends what you're planning to do in the garage afterwards?

 

[Jake]

it depends what you're planning to do in the garage afterwards?

You do not want to know.

 

[Beau]

You could save money by using cellotex seconds?

Yes was going to say the same. Seconds and Co have some good deals from time to time. Celotex/Kingspan offers better levels of insulation per cm than earthwool will. Easy to instal and and to make it a really good fit and airtight use a foam gun to fill any gaps.

I'm in the process of insulating my garage and have found (currently) that Seconds and Co are only pennies cheaper but then charge £35 for delivery and this effectively makes them more expensive.

Thats a shame. Admittedly it was some years ago I used them but they were 20% cheaper due to slight variations in the thickness of the sheets.