Insulating rooms in roof space

[ajstoneservices]

We have just bought this bungalow and it needs updating throughout. One of the first jobs that needs doing is the insulation as it's pitiful at the moment.
How should we go about insulating the knee walls and roof slope to the attic rooms? Would it be better to remove the plasterboard and use something like Kingspan Thermapitch on the knee walls and roof slope with mineral wool elsewhere.

I was wandering whether it might be better to re-tile and insulate from the outside.

Untitled

• ajstoneservices
• 16 Apr 2013
• 1

Untitled

• ajstoneservices
• 16 Apr 2013
• 1

Untitled

• ajstoneservices
• 16 Apr 2013
• 1

Untitled

• ajstoneservices
• 16 Apr 2013
• 1

 

[mointainwalker]

Removing the plasterboard has to be what you do. Having done that though, why would you be looking at fibre-wool "elsewhere " ? Why not everywhere ?

Fibre-wool pros:

Very cheap, flexible so easy to fit

Cons:

Holds water if gets wet, slumps if not fixed in place

.....................................................

PIR Board Pros:

Easy to fix in place as rigid, better insulation values so more suited if space limited

Cons:

Expensive - probably 4-5 times more than fibre-wool per m2 .


PIR has 60% better insulating qualities than fibre-wool for same thickness.

 

[ajstoneservices]

Thanks MW, we're going to remove the plasterboard from the knee walls and ceiling slope and insulate with kingspan and re-board.

We've decided to re-wire it at the same time so removing the boards will make that a little easier.

 

[tony1851]

Granted the glassfibre is a lot cheaper, but in the sloping (raftered) part of the roof, it may not be effective.
If the rafters are, say 4" deep, and the felting is the old bitumen-based stuff, you would need an air gap of 2" above the insulant to maintain some form of ventilation and prevent condensation. Two inches of glasswool is next to useless insulation-wise. This is why PIR/PUR boards score best when thickness is limited, though yes, they are expensive.

 

[geraldthehamster]

We have just bought this bungalow and it needs updating throughout. One of the first jobs that needs doing is the insulation as it's pitiful at the moment.
How should we go about insulating the knee walls and roof slope to the attic rooms? Would it be better to remove the plasterboard and use something like Kingspan Thermapitch on the knee walls and roof slope with mineral wool elsewhere.

I was wandering whether it might be better to re-tile and insulate from the outside.

I did this with my bungalow. We were having dormers installed at the time but the principle is the same. First I made the mistake of wondering how little I could get away with removing. Then I did what I should have done in the first place, and removed all the plasterboard from side walls, sloping walls and flat ceiling.

On the sloping bits, my rafters were only 3x2, so I added 3x2 battens to make them 6x2. This enabled me to insulate to the satisfaction of Building Control. That is, a 2 inch air gap beneath the felt, 4 inches of Kingspan between the rafters, and one inch of foil-backed Kingspan over the lot, to provide a vapour barrier. I did this up to just above ceiling level.

The flat ceiling I replaced and put rock wool insulation above. The standard is 300mm (or it was 3 or so years ago when I did this).

The dwarf walls you can just insulate behind with rock wool. Alternatively you can take the Kingspan right down to eaves level, in which case you don't need to insulate behind the dwarf walls as they are on the warm side. Whichever you do, ensure that you don't prevent the air gap behind the insulation on the slopy bit being ventilated from the soffits (if no ventilation at the soffits, insert soffit vents).

Pulling everything out also enables you to consider room layout, wiring etc., in case you want to change any of that.

Being a fuddy duddy, when I had removed the ceilings I belt-sanded the ceiling joists and put the new plasterboard above them, giving me a "beamed" ceiling and a few extra inches of perceived ceiling height.

Even if you aren't involving Building Control (which technically you should), it's worth doing the insulation to regs as it makes a *huge* difference to the warmth of the house.

The Kingspan wasn't cheap, but you can get second quality stuff from various firms you can find on the Internet, which keeps the cost down. The odd dint and scrape isn't going to affect its function.


Cheers
Richard

 

[Alastairreid]

Good post Gerald.