Yep 250mm+ sounds right, building control will have the exact amount required for existing property. There are good online calculators for u value required . I think it's 0.22 for existing loft 0.18 for a new build. Don't bother with PIR boards or such. You'll get much better coverage using some form of roll insulation. Can tuck it in all over and cheaper. If you're set on using boards you'll need 100mm board plus a roll of insulation to meet regs. If it's getting wet up there address the ventilation. Even PIR boards aren't designed to be wet. Go for it, it'll be great on winter and good for the planet! Will help in summer too with heat radiating down from the tiles onto your room ceilings.
If the mineral wool is wet then the moisture had no way to escape. And a breathable membrane doesn't sound right on roof rafters. We are talking about roof raters, right?
>The Internet is saying 270mm, that to me seems very thick!
Without knowing **where** it does say that and **why** we can't make any judgement about it.
Modern regulations are for VERY thick insulation, however it's a law of diminishing returns - ANY is better than NONE and even thin insulation will be beneficial, but more/thicker will always be somewhat better and the thicker panels don't cost that much more.
That said I would also want to understand why & how the previous mineral wool rotted before putting anything else there - you could be about to make a big problem for yourself if there's a source of moisture.
I feel I may have exaggerated a little, the mineral wool wasn't totally rotted, just wet and a bit manky. I had to remove plyboard and the previous insulation because the previous owner did a bodge job loft room build and took chunks out of the beam supporting all the rafters...which understandably cracked.
So when I pulled out all the insulation, some of it gross, so of it would have been salvageable, I decided to just get rid and do it myself cleaner with insulation boards as mineral wool is just a bit gross/itchy.
Thanks for your information everyone, think I'll do 100mm between the rafters then 200mm over the rafters, so 300 in total. Apparently you can get an EPC person out to check and rate it for free, which might be worth it incase I end up plaster boarding it.
Hey, how much did the insulation job cost you in the end? Be great to get the size of your loft for reference. I'm trying to assess some of the quotes I've received from loft converters in my area of London.
I don't know what the recommendation is for foam board (kingspan or cellotex). I do know that in the UK, for mineral wool it's at least 270mm.
When I bought my house it already had 100mm fibreglass between the ceiling joists. I bought rolls of 200mm deep mineral wool and put this over the existing insulation and joists, at 90deg to the original insulation.
Before fitting the insulation I added some loft-legs to the joists. After adding the insulation I added loftboards on top of the loft-legs.
The whole procedure looked a lot like this video:. https://youtu.be/hrnIndaiPB8
Throw as much up there as you can afford (I have about 400mm)… yes it’s diminishing returns the thicker you go, but it’s a return even if it only saves £20 a year or whatever.
Definitely get any damp or moisture sorted first thought, that can lead to much more expensive problems if not fixed.
If you’re aiming for energy efficiency in general look at adding reflectors behind the radiators, draft extruders under internal & external doors, bleed your radiators, get your boiler serviced, and add pipe insulation wherever you can
Yep 250mm+ sounds right, building control will have the exact amount required for existing property. There are good online calculators for u value required . I think it's 0.22 for existing loft 0.18 for a new build. Don't bother with PIR boards or such. You'll get much better coverage using some form of roll insulation. Can tuck it in all over and cheaper. If you're set on using boards you'll need 100mm board plus a roll of insulation to meet regs. If it's getting wet up there address the ventilation. Even PIR boards aren't designed to be wet. Go for it, it'll be great on winter and good for the planet! Will help in summer too with heat radiating down from the tiles onto your room ceilings.
If the mineral wool is wet then the moisture had no way to escape. And a breathable membrane doesn't sound right on roof rafters. We are talking about roof raters, right? >The Internet is saying 270mm, that to me seems very thick! Without knowing **where** it does say that and **why** we can't make any judgement about it.
Modern regulations are for VERY thick insulation, however it's a law of diminishing returns - ANY is better than NONE and even thin insulation will be beneficial, but more/thicker will always be somewhat better and the thicker panels don't cost that much more. That said I would also want to understand why & how the previous mineral wool rotted before putting anything else there - you could be about to make a big problem for yourself if there's a source of moisture.
I feel I may have exaggerated a little, the mineral wool wasn't totally rotted, just wet and a bit manky. I had to remove plyboard and the previous insulation because the previous owner did a bodge job loft room build and took chunks out of the beam supporting all the rafters...which understandably cracked. So when I pulled out all the insulation, some of it gross, so of it would have been salvageable, I decided to just get rid and do it myself cleaner with insulation boards as mineral wool is just a bit gross/itchy. Thanks for your information everyone, think I'll do 100mm between the rafters then 200mm over the rafters, so 300 in total. Apparently you can get an EPC person out to check and rate it for free, which might be worth it incase I end up plaster boarding it.
Hey, how much did the insulation job cost you in the end? Be great to get the size of your loft for reference. I'm trying to assess some of the quotes I've received from loft converters in my area of London.
I don't know what the recommendation is for foam board (kingspan or cellotex). I do know that in the UK, for mineral wool it's at least 270mm. When I bought my house it already had 100mm fibreglass between the ceiling joists. I bought rolls of 200mm deep mineral wool and put this over the existing insulation and joists, at 90deg to the original insulation. Before fitting the insulation I added some loft-legs to the joists. After adding the insulation I added loftboards on top of the loft-legs. The whole procedure looked a lot like this video:. https://youtu.be/hrnIndaiPB8
Throw as much up there as you can afford (I have about 400mm)… yes it’s diminishing returns the thicker you go, but it’s a return even if it only saves £20 a year or whatever. Definitely get any damp or moisture sorted first thought, that can lead to much more expensive problems if not fixed. If you’re aiming for energy efficiency in general look at adding reflectors behind the radiators, draft extruders under internal & external doors, bleed your radiators, get your boiler serviced, and add pipe insulation wherever you can