Attic Insulation

LA2016

Started our two-story self-build this year. House is build and roofed with windows and doors on. We are stuck on attic insulation. We need to insulate our rafters before applying plasterboard in our attic and vaulted ceiling in our kitchen. We were thinking of using spray foam. We have got mixed opinions on this as some suppliers spray directly to the felt and some use a filler piece to keep foam away from the felt. The person spraying foam directly onto felt say that the foam is breathable, therefore the roof can breath. The other person who keeps the foam away from the felt says you need the space because the foam isn't breathable and without the space there will be condensation, causing the rafters to rot down the lime. There doesn't seem to be a definate answer to this. I have asked builders and even my engineer isn't sure. Is there any handier way of doing this or is rock wool a better option? I know people who have cut insulation sheets and placed between rafters but getting this fitted properly is almost impossible and it won't be close to being airtight whereas the spray foam pretty much is. Also I have been quoted in the region of €4-5000 for the spray foam option. Any suggestions or ideas would be welcome. Thanks

BryanF

LA2016 wrote: »

. There doesn't seem to be a definate answer to this.

Simply google the data sheet for the foam product.
Give it to you engineer and he should be able decipher the requirements.
Without knowing the specific of the products I would suggest you need vent cards, unless you double battened outside the breathable membrane.

LA2016

Thanks for the reply.
Our engineer is happy for us to go with either option - he said it's a personal preference.
I can't see how this is the case, so has anyone completed this work recently. What did you do?

BryanF

LA2016 wrote: »

Thanks for the reply.
Our engineer is happy for us to go with either option - he said it's a personal preference.
I can't see how this is the case, so has anyone completed this work recently. What did you do?

Ask your engineer if he is signing of on part A of the building regs or all the building regs?

I just told you in my previous post what route to go - which would help to avoid excessive condensation?

Put up a link to the Iab or bba 'data sheet' - nothing else, please

Shefwedfan

Why use foam? Why not buy insulation boards, cut them to size and push them between the rafters......

lolliedog

You could get cellulose insulation pumped in. This will depend if you have the rafter depth to achieve u- values.

tedimc

For what it's worth, I got my roof sprayed and very happy with it.

The guys doing it stapled special cardboard inserts onto the rafters, which kept the spray down about 50mm from felt. I have heard that even with breathable foam you should not spray directly onto felt. If you do, you may cause the felt/membrane to push out towards the tiles/slates as the foam expands. If this happens, any moisture that gets under your slates will flow down the membrane and be channeled on top of the rafters, where it slowly rot it around the nail holes in the felt, etc.

The felt naturally sags between the rafters usually, so any water will stream down the valley away from the rafters.

chillit

hi tedimc

can you give a rough cost for the spray. per m2 or something similar. I guessential it depends on depth as well as area

were they quick doing it

Gumbo

chillit wrote: »

hi tedimc

can you give a rough cost for the spray. per m2 or something similar. I guessential it depends on depth as well as area

were they quick doing it

I got a price for my attic to be done during the build.
58 Sq. M. Open cell with vent card to keep the 500mm required ventilation gap. Price was €1382 inclusive of VAT.

tedimc

It cost approx. 7.5k inc VAT for a 2500+ square foot bungalow.

Where it is shaved, it's approx. 100mm deep; but in the attic spaces it's not shaved probably averages 150mm deep.

The foam wouldn't be as good an insulation as say 100mm of PIR board, but you would struggle to get that cut tightly between the rafters. The foam is excellent at stopping drafts and I noticed a huge difference straight away even without any wall insulation or heat on.

chillit

thanks for the feedback. was if a pretty quick process

tedimc

chillit wrote: »

thanks for the feedback. was if a pretty quick process

3 days from what I recall. But our roof is in different sections, and half of it had to be shaved which is a slow process. One long straight attic the same size would probably be done in 2 days easily enough.

mfceiling

sirwin357 wrote: »

Eskimos use ice. Now if you have a big enough freezer and leave all heating off this winter, a few tons of solid ice in the rafters will have you and the family snug as a bug.

Useful...

bikenut

tedimc wrote: »

The foam wouldn't be as good an insulation as say 100mm of PIR board, but you would struggle to get that cut tightly between the rafters. The foam is excellent at stopping drafts and I noticed a huge difference straight away even without any wall insulation or heat on.

I'm thinking of cutting 100mm of PIR and fitting between ceiling joists with expandable foam to fill any small gaps. Very time consuming I know but DIY job.

Then cover with Xtratherm walkR boards

Any issues with the above? Most concerned about insulation - can't stop draughts up there

tedimc

bikenut wrote: »

I'm thinking of cutting 100mm of PIR and fitting between ceiling joists with expandable foam to fill any small gaps. Very time consuming I know but DIY job.

Then cover with Xtratherm walkR boards

Any issues with the above? Most concerned about insulation - can't stop draughts up there

Would be a good job if you do it yourself, as you'll take the time and be fairly methodical. Is this a flat ceiling you are insulating from above? You will need to be carful around light cables, down lighters, etc.

Would a pumped cellulose or recycled newspaper be a better option?

I think you can get PIR in sheets pre-cut like an accordion which compress to fit between rafters:

http://www.kingspaninsulation.ie/Products/Therma/Thermafit/Overview.aspx