Super quilt & PIR board

[Quilts76]

Hi

after some advise if I may, I’m looking to purchase a house with a very large loft room which has no insulation so the heat loss is unreal and trying to work out project costs.

I have 150mm rafters which have plasterboard on the underside and as I’ve said no insulation....trying to work out my options and was thinking of removing the old plasterboard then applying super quilt stapled onto the rafters (so a large air gap is left to vent the roof void) 25mm batons fitted down the rafters then 50mm insulated plasterboard fixed to the batons.

Is this ok to do or go I need a bigger air gap between the super quilt and insulated plasterboard?

Thanks in advance.

 

[Swwils]

If it has no insulation at all then I wonder how it passed any compliance checks?

Does it have a certificate of completion or do you not mind?

 

[oldbutnotdead]

Are you DIYing or looking for project costs? Be wary of the claims for superquilt, the only one i've looked at in any detail required a static air gap on both sides- obvs the air between the rafters won't be static.
A more conventional approach would be 100mm between rafters (so leaving the required 50mm for ventilation), 50mm fixed to rafters and pb on top. Insulated pb is expensive to buy but cheaper on time to fix. Can you get 8'x 4' sheets up there?
Cheaper on materials but more time would be (if you had the room) add 100mm to the rafters (ripped ply or fence boards), 200mm rockwool between rafters (again 50mm air gap) then 50mm pir and pb fixed to rafters.
EDIT Rockwool also does a better job of reducing any roof noises (rainfall mainly) than PIR

 

[tony1851]

As above, the superquilts do not necessarily give any advantage as they depend largely on reflectivity and can take up considerable thickness.

 

[Quilts76]

If it has no insulation at all then I wonder how it passed any compliance checks?

Does it have a certificate of completion or do you not mind?

The house is 1910 and was constructed over 3 levels with the loft area 8m x 6.2m ( usable space) being existing but over the years Poor work has been completed so doing to strip back to rafters and floorboards and start again.

 

[Quilts76]

Are you DIYing or looking for project costs? Be wary of the claims for superquilt, the only one i've looked at in any detail required a static air gap on both sides- obvs the air between the rafters won't be static.
A more conventional approach would be 100mm between rafters (so leaving the required 50mm for ventilation), 50mm fixed to rafters and pb on top. Insulated pb is expensive to buy but cheaper on time to fix. Can you get 8'x 4' sheets up there?
Cheaper on materials but more time would be (if you had the room) add 100mm to the rafters (ripped ply or fence boards), 200mm rockwool between rafters (again 50mm air gap) then 50mm pir and pb fixed to rafters.
EDIT Rockwool also does a better job of reducing any roof noises (rainfall mainly) than PIR

Whilst I agree with this even the slightest gap on the insulation between the rafters will bridge and cause condensation build up which is why I was thinking superquilt correctly fitted and taped.
My concern is the 25mm between the superquilt and insulated plaster board and i never thought about the static air on both sides.... maybe i need to check with the manufacture regarding this?

 

[Quilts76]

I did also wonder what benefit 100mm celotex on the rafters would give and then plaster board over the top rather than any of the above?

 

[oldbutnotdead]

You mean fix straight to the rafters? Yes that works but think you need 150mm minimum for building regs compliance-you need 0.18 for a refurb. Not sure you can get screws that long....
EDIT You won't get cold bridging with the 100 between/50 over method.

 

[Quilts76]

You mean fix straight to the rafters? Yes that works but think you need 150mm minimum for building regs compliance-you need 0.18 for a refurb. Not sure you can get screws that long....

building regs not involved just trying to insulate as much as possible in the best way, cost being a factor but not causing issues elsewhere.

 

[oldbutnotdead]

Tut tut, technically removing wall finishes back to bare (which is effectively what you're doing if that room is classed as habitable- is it staircase or ladder access) does require the replacement finish to include insulation to modern standards.
If its just going to be storage then throw 300mm wool in the floor & 50mm pir over the rafters.

 

[Quilts76]

Tut tut, technically removing wall finishes back to bare (which is effectively what you're doing if that room is classed as habitable- is it staircase or ladder access) does require the replacement finish to include insulation to modern standards.
If its just going to be storage then throw 300mm wool in the floor & 50mm pir over the rafters.

it’s accessible via an existing staircase built when the house was built.
It’s a large room which I’m possibly looking to convert into 2 bedrooms, hence why I want to get the best insulation properties I can but just trying to think of the best way around this. Hence the original superquilt and 67.5mm insulated board but was worried about air gaps.

 

[oldbutnotdead]

So habitable room so do it right, it'll only come back to bite you later otherwise. Not saying you have to get Building Control involved (though it is a legal requirement) but if you're planning major works you'll end up dealing with them anyway...
EDIT You're getting distracted by details, it takes time and effort to cut pir to the right sizes to fit between rafters (especially on older houses where they tend to be a bit random) but it isn't difficult, the foil tape & 50mm overboarding is what really seals the room.

 

[Quilts76]

V

So habitable room so do it right, it'll only come back to bite you later otherwise. Not saying you have to get Building Control involved (though it is a legal requirement) but if you're planning major works you'll end up dealing with them anyway...

Just seen your edited post above re the 100mm celotex inbetween and 50 over the top. This is what i was thinking but with the superquilt was thinking it would be time saving.

 

[oldbutnotdead]

Check the specs and installation requirements on your superquilt very carefully, there's a lot of snake oil about.

 

[Scarlet Pimpernel]

A couple of comments, if I may.
I understand you can mix the super quilt insulation with other types, and the super quilt insulation should be innermost. So the insulation between rafters, leaving the required airgap, and super quilt fixed under the rafters. That will then include the vpm. But by the time you've counter battened, you've not saved much on space. The total being at least 30mm thick.
Also, avoid the cheap offerings on fleabay, etc. It's seconds, despite being sold as shop-soiled, over-ordered etc,. It's not available for sale in France, (where it is invariably made), and it's horrendous to use. It's stuff that has gone awry with seams etc not matching up. It's impossible to do a tidy job with it. If you think it's worth money saved, be prepared for much cussing and swearing when you're trying to do a decent job, or for a decent bit of wastage.