insulating ubder old loft ceiling

M

marsaday

i dont need to meet bld regs for my loft roof as i am only upgrading what is already there. i was planning on doing 50mm between the rafters and 50mm underneath them.

however could i just add some insulation (probably just 50mm) underneath the current old ceiling and then plaster board over this ?

this would be loads easier and i would still be improving the insulation of the room.
 
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You could but wouldn't it be easier to insulate above the ceiling though? Cheaper too. Not much point in reality if you're using polystyrene though as its cr*p. What size/spacings are the ceiling joists? Really can't see how it would be easier though as you'll need to get it plastered and painted too! Is this a wind-up?
 
M

marsaday

this is a usable attic room at the moment

i want to insulate UNDER the rafters so i dont need to rip down the old lathe and plaster ceiling.

i will then plaster board onto the insulation, screwing through this, the old ceiling and into the rafter.

the rafters are 75mm at 400mm centres
 
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Oh I thought you meant under the loft ceiling! :rolleyes: You can stick your insul under the existing ceiling at roof level no problem, the roof is probably unlikely to collapse.
 
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@Freddy

Don't really understand your comment on polystyrene. It's as good as glass-fibre and in 7 years when the insulating gassing-agents have leaked out, all the closed-cell foams i.e. PIR, PUR and extruded polystyrene will also only have the same U value.
 
M

marsaday

whats the difference between using Kcooltherm k18 50mm and plasterboard and 50mm normal kingspan?

are they the same? you just do more work yourself
 
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@Freddy

Don't really understand your comment on polystyrene. It's as good as glass-fibre and in 7 years when the insulating gassing-agents have leaked out, all the closed-cell foams i.e. PIR, PUR and extruded polystyrene will also only have the same U value.

You're right, its a conspiracy. :rolleyes:
 
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@Freddy

Don't really understand your comment on polystyrene. It's as good as glass-fibre and in 7 years when the insulating gassing-agents have leaked out, all the closed-cell foams i.e. PIR, PUR and extruded polystyrene will also only have the same U value.

Has this actually been proven yet?
 
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whats the difference between using Kcooltherm k18 50mm and plasterboard and 50mm normal kingspan?

are they the same? you just do more work yourself

Yep obviously cheaper to do the work yourself. Probably not much diff U value wise, although IIRC the K18 foam is slightly different. Possibly denser, possibly pink.
 
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@Deluks

It's something I have now read on several "scientific-type" web-sites but can't remember any links.

Have also read that some official body is pushing for insulation materials to be rated at their 7-year old measured values to give a better indication of what benefits you are actually going to get over total installed life.
 
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@hotrod

1) Can't remember. Will try looking back to see if I saved it in favourites.

2) Because they wrote that by this time the closed-cell foams were
gassed-out and therefore stable.
 
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Haven't yet found sites I was indirectly referring to, but looking in Wiki there is a comment about the loss of insulation property over time and an incomplete article about LTTR ( Long Term Thermal Reduction ) which is a method/proposal to give a weighted-average value over 15 years.
 

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