attic insolation

Katz83

We are doing a new build. We have an attic with 9 by 2 joist. We want to comply with building regs but if we put in 12 inches of insolation because of the 9 by 2 joist when we floor the attic (which we want to do becasue we already have all the ploy wood) this will be pushed down and reduced to probably about 11 inches. i am just wondering does anyone have any advise as to what we could do.

We are looking at maybe using an insolated slab for ceiling say of 50mm i think they are called thermal liners and then maybe put 200mm fibreglass insolation rolled out on top of this. Would this meet current building regs does anyone know. I think again reg are .16

Also going putting in recess lights about 22 in the whole house does this have an affect on the insolated slab.

Advise greatly appreciated

Poor Uncle Tom

Instead of compromising the thickness of insulation in the attic space can't you look at ways of actually putting it in?

Put 50 x 50 battens on top of the joists over the area you want to floor out, secure the ply to the top of the battens, thus keeping the insulation as specified.

Katz83

Poor Uncle Tom wrote: »

Instead of compromising the thickness of insulation in the attic space can't you look at ways of actually putting it in?

Put 50 x 50 battens on top of the joists over the area you want to floor out, secure the ply to the top of the battens, thus keeping the insulation as specified.

If we did this could we then just use the 300mm of fiberglass do you know would there be enough room for the insolation to breath

gman2k

Katz83 wrote: »

if we put in 12 inches of insolation because of the 9 by 2 joist when we floor the attic (which we want to do becasue we already have all the ploy wood) this will be pushed down and reduced to probably about 11 inches

Advise greatly appreciated

My advice re your insulation - never compress insulation, as it will no longer fully work as an insulator. It is the air that is trapped in the insulation that actually retains the heat in your building, if you compress the insulation you will remove a lot of this trapped air, and you will be worse off than if you had just put in the 9" (uncompressed insulation in the first place.

Katz83

gman2k wrote: »

My advice re your insulation - never compress insulation, as it will no longer fully work as an insulator. It is the air that is trapped in the insulation that actually retains the heat in your building, if you compress the insulation you will remove a lot of this trapped air, and you will be worse off than if you had just put in the 9" (uncompressed insulation in the first place.

So you think our best bet would be to just do a walkway and shelves and put in say i think if we raise the joists with 2 by 2s we can get about 11 inches of insolation and there is a gap left for air would this be ok to do.

dathi

katz screw 4x2 at right angles to the joists and fill the space with 12" of insulation that way the joists will have some insulation on top of them to help stop thermal bridging ie the timber joists will only penetrate the insulation for the 2"square every time the 4x2 crosses the joist, instead of the full length of the joist if you put the 4x2 parallel with the joist

Poor Uncle Tom

Katz83 wrote: »

If we did this could we then just use the 300mm of fiberglass do you know would there be enough room for the insolation to breath

Pressing 300mm (12") into 275mm (11") space in an attic where the side areas (crawl spaces) are not covered would be acceptable, imo.