Loft Bedroom Insulation

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Hi all, hoping for some advice on the below: -


Suggested kingspan/Celotex/Recticel thickness for a loft conversion (I was thinking 100mm)?

Do I need to tape joints between sheets (where the timber is) with aluminium tape?

Do I need to fill any gaps between joists and sheets with expanding foam?

Thanks!
 
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Thanks for reply. Any advice for insulation thickness for a loft bedroom.......up in NE Scotland? 100mm suffice? Got a quote for 100mm Recticel for £36 per 2400x1200 sheet from a local supplier, dropping to £33 if I buy 20 sheets or more!
 
100mm wouldnt be passed in my area
most lofts i do are 100 between 40 under rafter to meet 0.18
 
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Normally it's put a 25mm batten on top of the joist, and then 100mm celotex in the joist, then fill any gaps with foam. then you want 50mm insulated plasterboard running across the joists, then use Alli tape to close the gaps.
 
90mm between with 50mm over the rafters will meet regs also, and as Doggit says you may need to build the rafters out to maintain your airgap behind the insulation. Shouldn't be any gaps but if you have some small ones then yes fill with expanding foam.
 
Thanks, so the kingspan I fit between the joists should this be left a certain distance away from the back of the plasterboard or should it be up as close as possible?
 
As close as possible, otherwise heat gets lost into the gap before the kingspan stops it. What you want is a gap between the kingspan and the tiles.

90mm between with 50mm over the rafters will meet regs

I could be wrong Chappers, and please correct me if I am, but I though it was 135mm of PIR required. Actually, now I look at it, the confusion could be coming from me. When I quoted 50mm insulated plasterboard, I was working on 35mm PIR, and 15mm plasterboard.
 
probably about right which means that the nearest size is 40 mm laminated to 12.5mm as std off the shelf.
 
Sorry Doggit, what do you mean by "What you want is a gap between the kingspan and the tiles." The walls I`m doing aren`t near the external walls, so for simplicity let`s say they are in the middle of a loft area away from the roof or any external walls.
 
Are you saying this is for an internal partition, if so then no regs on that, just use 100mm insulation on a roll, for sound deadening, celotex will transmit sound, not to mention the unnecessary expense and effort .
Incidently completely different regs/specs for walls
 
Yes sorry, internal partitions. Sh*t, already ordered the Celotex. Understand what your saying, thanks.
Will the 100mm Celotex provide better insulation than the 100mm insulating wool? If so, how much better? I`ve had a thermometer up there for the last week, highest it`s reached is 10C.......lowest was 0.8C :O
 
yes the insulation properties will be far superior but the sound deadening will be far inferior.
Our loft is insulated to regs as described above never have the radiator on up there, heat from the rest of the house and a small towel rail on very low in the en-suite is plenty
 
Perfect thanks for your help. I`ll stick with the Celotex, the point about sound deadening won`t really be an issue up there for me.
I`m actually planning on having an electric blanket with a smart socket which I can put on just before coming home from nightshift, hopefully no heating. If it does end up being too cold I`ll use an electric heater with the smart plug.

One last question - my joists are 600mm apart (centre to centre) and 72mm deep, the Celotox is 100mm. Do I :-

1. Cut the Celotex (circa.) 550mm and fit them inbetween the joists, which essentially would leave a 25mm gap at either side between the Celotex.
2. Cut the Celotex at 600mm (meaning no gaps between Celotex) but I`d need to cut notches out of both sides of every sheet (28mm).

Hope this makes sense. If not I`ll try and attach a drawing from paint!

Cheers.
 
Sorry Shavey, but this is what I was referring to (as I assumed you were referring to insulating the roof) in the previous post you queried. You want to keep the cellotex away from the room tiles, so subtract 25mm from the 72, and your left with 47mm, which we'll round to 50, so you screw a 50x50 batten to the joists, and then fit the cellotex between the joists so that everything ends up flush; then you fit insulated plasterboard that gives you 35mmPIR+12.5mm plasterboard across the joists.
 

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