Roof Insulation

martincodd

Building at the monmet. Will be pumping the cavity with ecobead or similar and wondered if i can use it for the roof also. Would save a lot of labour compared to trying to fit rafterlock between the rafters. I've got breathable felt on and want to use my attic space for storage...

sydthebeat

martincodd wrote: »

Building at the monmet. Will be pumping the cavity with ecobead or similar and wondered if i can use it for the roof also. Would save a lot of labour compared to trying to fit rafterlock between the rafters. I've got breathable felt on and want to use my attic space for storage...

just be aware that you will be required to fit a much larger thickness of a blowin-in material than a rafterloc material... probably 300mm (1')

check teh certification of that material to check its uses...

sinnerboy

You may be better to consider blown in cellulose - it is intended for that application .

martincodd

I'll fit plaster slabs to the underside of the rafters then get the insulation blown in - I think that thickness of insulation (150mm) would be ample insulation in any roof.
Cellulose is expensive...

Jimbo

If the insulation is installed at rafter level, the maximum U value allowed for the roof is 0.2.

Your constuction will only give a U value of about 0.3.

sydthebeat

martincodd wrote: »

I'll fit plaster slabs to the underside of the rafters then get the insulation blown in - I think that thickness of insulation (150mm) would be ample insulation in any roof.
Cellulose is expensive...

in all respect... "thinking" thickness complies is not good enough...

you, or your certifier, must KNOW the thickesses are good enough to comply...

miss indecisive

Just about to start a build also. Planning to pump the cavity with ecobead, the company also supply blown rock wool for the attic. U values seem pretty good but need to look into it more

Carlow52

sydthebeat wrote: »

in all respect... "thinking" thickness complies is not good enough...

you, or your certifier, must KNOW the thickesses are good enough to comply...

+1

MacTheKnife1

martincodd wrote: »

Building at the monmet. Will be pumping the cavity with ecobead or similar and wondered if i can use it for the roof also. Would save a lot of labour compared to trying to fit rafterlock between the rafters. I've got breathable felt on and want to use my attic space for storage...

Why not add insulated plasterboard 42.5mm (or greater) on ceiling. That should help get you where you need to go.

martincodd

sydthebeat wrote: »

in all respect... "thinking" thickness complies is not good enough...

you, or your certifier, must KNOW the thickesses are good enough to comply...

Compliance is my own business... I'm just asking if something can be done or has been done before by anybody. Taking advice from the boards to heart without propper backup would be a bad idea...!
Thanks for the replies...

sydthebeat

miss indecisive wrote: »

Just about to start a build also. Planning to pump the cavity with ecobead, the company also supply blown rock wool for the attic. U values seem pretty good but need to look into it more

do not believe sales reps u values....

get them checked by a competent professional...

sydthebeat

martincodd wrote: »

Compliance is my own business... I'm just asking if something can be done or has been done before by anybody. Taking advice from the boards to heart without propper backup would be a bad idea...!
Thanks for the replies...

no its not.... especially if you are borrowing money to pay for the build... compliance is most definitely the financial institutions business as well...

anyway, on polystyrene beads in the attic..... all electrical services would need to be contained within protective conduits in the attic.... this alone could make the whole endeavour not viable...

but the fact youd need nearly 300mm of depth makes it impractical...

KingPuck

martincodd wrote: »

I'll fit plaster slabs to the underside of the rafters then get the insulation blown in - I think that thickness of insulation (150mm) would be ample insulation in any roof.
Cellulose is expensive...

I know you said the felt is breathable but be careful of condensation. Rafterloc allows the roof to breath from underneath also. If you fit a slab and blow the insulation in you will completely fill the cavity. This will probably lead to a big condensation/ rot problem. Came across a guy who did something like this and had to trow out thousands of euros worth of insulation.

CJhaughey

Do you have sarking on the trusses or is the felt directly onto the truss?

If you have sarking fitted you can use hardboard and battens on the inside to create an airspace, then if you slab directly onto the inside of the truss you can blow insulation in.

damienfitzp

like most people i was just planning 1 roll of rockwool with joists and 1 opposite way in my attic , but now have decided to plywood my attic floor for storage so would anybody have any ideas how to get a dood u value between floors now? joists are 7 inches deep maybe blow up that yellow foam stuff , or thick slabs?

thanks

BERmad

damienfitzp wrote: »

like most people i was just planning 1 roll of rockwool with joists and 1 opposite way in my attic , but now have decided to plywood my attic floor for storage so would anybody have any ideas how to get a dood u value between floors now? joists are 7 inches deep maybe blow up that yellow foam stuff , or thick slabs?

thanks

There is an insulation company that do a boarded walkway with insulation stuck onto the bottom of ply-wood.

This link should solve your problem, but it will probably be very expensive to do your whole attic in it but would be handy if you only wanted to put up a few sheets. A fairly good U-Value as well.
http://www.xtratherm.com/products/literature/thinrwalkrirl.pdf

mailburner

would it be worth my while paying 1000 to get the wall cavity done?
theres flooring in the attic so thats ruled out
would there be a noticeable difference in the house just by
getting this done given there isnt a grant for this alone

clint_eastman

I've a relatively straightforward query I think.....btw my build is only at early stages with no roof so assumptions are being made for specifications/costs comparisons only.

For a pitched roof with insulation at ceiling joist level, AFAIK I need 250mm of rock wool (with Thermal Cond of 0.04) to meet regs u-value of 0.16.

Is it a case so that whatever size joists are fitted will dictate the insulation thickness if I want to floor out the attic with ply? For example, if I have 9” (225mm joists) and I need to fit 250mm of rock wool, do I need to batten out with 25mm studs along the length of the joists to allow me rest the ply on? Is there a need for an air gap between insulation and ply i.e. would I add 50mm battens instead of 25mm?

or do I have this methodology messed up?

Quiksilver

Hey martincodd, i would be very careful with pumping anything into the rafter of your house. Firstly ecobead isn't designed to be installed into roofs or timber frames, only cavity walls. If you get someone to install this for you and some problems occur you won't have any come back. As someone already mentioned all electrical cables would need to be covered anyways. As for rockwool/paper/fiberglass pumping i wouldn't go pumping into the rafters of a new build. There can be very homogenous materials and even with breathable felt it is still good to leave some breading space in the rafters. Also the rockwool/paper/fiberglass could sag over time and you could end up with voids in the insulation. If it is only going to be used for storage i would say it would be cheaper to use Fiberglass in the joists 150mm between joists and 150mm across joists and place 6"x2" 's on the joists for your flooring so it is above the insulation. This = Best U-Value with your storage. If you plan on converting to a Room to live in then it would be best to stick with something like rafter loc and an insulated slab.