Insulating bungalow roof

[dagoof]

I've recently moved into a bungalow, with an attic conversion, there's a little mineral wool scattered among the ceiling joists (of the ground floor) but nothing on the pitched roof.

I'd like to put in kingspan (or similar) to improve insulation but, having done the job of friction fitting the kingspan to the pitched roof in a previous house (it was a nightmare job), I'm wondering if I'm better to kingspan between the joists (I.e. The ceilings of the ground floor), rather than the pitched part? I could then insulate the smaller pitched part of the roof, that sits above the attic room.

It seems to me that this way, we're preventing the heat from travelling through the ground floor ceilings and heating the eaves (which would essentially be heating a 'dead zone')?

 

[RandomGrinch]

It seems to me that this way, we're preventing the heat from travelling through the ground floor ceilings and heating the eaves (which would essentially be heating a 'dead zone')?

That's why lofts are normally insulated between (and over) the joists!
If there isn't the possibility of converting the loft to a habitable space, there is no reason to use kingspan.
Rockwool/fibreglass/etc. is still cheaper per unit area and will be far less hassle to lay.
It may be thicker than PIR, but no-one's going to see it up there!

 

[dagoof]

Ah ok Grinch, I know it's relative (to depth) but I just thought the r-value of PIR was still far superior to fibre wool. It'd been a while since I researched but on checking again, it's seems only twice as effective (I.e. 50mm PIR = 100m wool).

I think there's 50mm wool in much of it currently, so I should be ok to whack more on top (I'm guessing to any depth I like)?

 

[RandomGrinch]

I think there's 50mm wool in much of it currently, so I should be ok to whack more on top (I'm guessing to any depth I like)?

Yup!
As long as you don't block any ventilation that's up there, it should be fine.