Loft insulation
Discussion
For obvious reasons I am looking at our loft insulation which is a bit lacking. Half of the loft isn’t easily accessible so I’ll just use the normal insulation.
The other half is used for storage down the middle, so I am thinking of using celotex/kingspan type PIR board between the joists, so I can then put boards over the top. Then keep the normal wool type along the sides.
Any draw backs to this? Thinking PIR board under storage boarding as it has higher R rating for a given thickness so easier to maintain under the boards.
Will the PIR boards need air gaps? Between the ceiling below and or the boards on top?
The other half is used for storage down the middle, so I am thinking of using celotex/kingspan type PIR board between the joists, so I can then put boards over the top. Then keep the normal wool type along the sides.
Any draw backs to this? Thinking PIR board under storage boarding as it has higher R rating for a given thickness so easier to maintain under the boards.
Will the PIR boards need air gaps? Between the ceiling below and or the boards on top?
Evoluzione said:
Trustmeimadoctor said:
just raise the boarding and use loft roll over it all. you need to cover the joists too not just pir between them otherwise the joists bridge the insulation and you will end up removing alot of the benefit
Have you got a thermal image to back that up?
s off 
yes i do
Edited by Trustmeimadoctor on Monday 24th October 12:00
Trustmeimadoctor said:
Evoluzione said:
Trustmeimadoctor said:
just raise the boarding and use loft roll over it all. you need to cover the joists too not just pir between them otherwise the joists bridge the insulation and you will end up removing alot of the benefit
Have you got a thermal image to back that up?s off yes i do
What are we looking at there, a window with ceiling above? Are the joists the blue bits some way above the window then?
Evoluzione said:
Trustmeimadoctor said:
Evoluzione said:
Trustmeimadoctor said:
just raise the boarding and use loft roll over it all. you need to cover the joists too not just pir between them otherwise the joists bridge the insulation and you will end up removing alot of the benefit
Have you got a thermal image to back that up?s off yes i do
What are we looking at there, a window with ceiling above? Are the joists the blue bits some way above the window then?
That bit in the loft
Edited by Trustmeimadoctor on Monday 24th October 13:58
RizzoTheRat said:
In my parents loft we used the usual rockwool between the existing joists, then laid new joists at 90 degrees in the area they wanted to use as storage, with rockwool laid between those, and the boarded over the top. Quite an easy job.
That's my intention. Don't fancy the legs solutions often recommended. We put too much crap for storage in the loft.Rockwool is (probably) a good UK made product in South Wales and has decent fire resistance (so say all their logistics trucks, unsurprisingly).
Trustmeimadoctor said:
Evoluzione said:
Trustmeimadoctor said:
Evoluzione said:
Trustmeimadoctor said:
just raise the boarding and use loft roll over it all. you need to cover the joists too not just pir between them otherwise the joists bridge the insulation and you will end up removing alot of the benefit
Have you got a thermal image to back that up?s off yes i do
What are we looking at there, a window with ceiling above? Are the joists the blue bits some way above the window then?
That bit in the loft
I'm just procrastinating before going up there and doing mine....
Evoluzione said:
Trustmeimadoctor said:
Evoluzione said:
Trustmeimadoctor said:
Evoluzione said:
Trustmeimadoctor said:
just raise the boarding and use loft roll over it all. you need to cover the joists too not just pir between them otherwise the joists bridge the insulation and you will end up removing alot of the benefit
Have you got a thermal image to back that up?s off yes i do
What are we looking at there, a window with ceiling above? Are the joists the blue bits some way above the window then?
That bit in the loft
I'm just procrastinating before going up there and doing mine....
Evanivitch said:
RizzoTheRat said:
In my parents loft we used the usual rockwool between the existing joists, then laid new joists at 90 degrees in the area they wanted to use as storage, with rockwool laid between those, and the boarded over the top. Quite an easy job.
That's my intention. Don't fancy the legs solutions often recommended. We put too much crap for storage in the loft.Rockwool is (probably) a good UK made product in South Wales and has decent fire resistance (so say all their logistics trucks, unsurprisingly).
B'stard Child said:
That's really bloody useful because I was intending to do same with PIR between the joists in an area that is really bloody awkward to get to - I guess I'll take the compromise of doing between the joists and accept that the joists with have a relatively small impact over the whole of the ceiling
Indeed, it's fine if you have the space. I replaced the old wool stuffed in between joists and hten boarded over running down the centre of my loft to give me 100mm PIR down the centre, and I still bang my head on my hands and knees! But it has massively helped, chucked 350mm+ into the rafters although this slowly drops to 100mm at the eaves, but so far this winter the house is much much warmer, yes it's been mild, but we've still got the windows open on the latch as the rooms are getting too warm at night!Evoluzione said:
No air gaps needed. It'll be very time consuming.
You may want to Google 'electric cable near pir insulation' and have a good read.
I'd consider elevating the deck up permanently and using glasswool.
Ah I’d not considered that…. You may want to Google 'electric cable near pir insulation' and have a good read.
I'd consider elevating the deck up permanently and using glasswool.
On the time consuming, I hadn’t realised how important a tight fit is with PIR…. All things considered it does sound like it’s better all round to raise the floor and stick with the woolly stuff.
When I did my loft, I extended the joists with 3x2" on 3x2" spacers, which with the existing 4x2" joists gave 10inches from ceiling (plasterboard) to flooring (8x2' chipboard) . The glasswool was then rolled out (I think rockwool is similar performance) between the joists and spacers, aiming to minimalise air in the gaps between joist and 3x2 timbers.
This basically worked well. However I did get issues with condensation on the underside of the attic boards. I solved this by adding a vapour barrier into the bedroom ceilings, one room which had already been skimmed was treated with paint on barrier paint, the other two where sheeted with polythene and over boarded with plasterboard and skimmed. I was plastering the bedroom ceilings anyway to cover artex, but if I had my time again I would thing about raising the attic boards another 2" to give an air space to ventilate. Bathroom wasnt board due to downlighters and not needing the space.
As the house then also had sloping skelling sections, which at this point where still just plasterboard to outside, these then also got awful condensation on the inside of the rooms. So room by room I removed the plasterboard, cut foam board to between the 3x2 timber, leaving an 1" air space to the felt, and extending them up into the loft space ass much as i could to hold the glass wool back too, and then a second 2" sheet over the the lot to give 4" (about the same performance as 10" glass wool) and then plasterboard over that, and roll it in with skimming the rest of the ceiling. Wasnt a ten min job, but I could do each room at a time, in a couple of evenings after work, when I was ten years younger (25 at time) and didnt have kids!
This was a med-size 3 bed with a simple roof that I could stand up in and walk around, but if you have smaller loft space an extended cottage or the like, then raising the attic boards becomes more and more of an issue. I also had the cavity walls filled with carbon roller eps balls at the same time, if you have solid walls, condensation on those also becomes an consideration I am sure.
This basically worked well. However I did get issues with condensation on the underside of the attic boards. I solved this by adding a vapour barrier into the bedroom ceilings, one room which had already been skimmed was treated with paint on barrier paint, the other two where sheeted with polythene and over boarded with plasterboard and skimmed. I was plastering the bedroom ceilings anyway to cover artex, but if I had my time again I would thing about raising the attic boards another 2" to give an air space to ventilate. Bathroom wasnt board due to downlighters and not needing the space.
As the house then also had sloping skelling sections, which at this point where still just plasterboard to outside, these then also got awful condensation on the inside of the rooms. So room by room I removed the plasterboard, cut foam board to between the 3x2 timber, leaving an 1" air space to the felt, and extending them up into the loft space ass much as i could to hold the glass wool back too, and then a second 2" sheet over the the lot to give 4" (about the same performance as 10" glass wool) and then plasterboard over that, and roll it in with skimming the rest of the ceiling. Wasnt a ten min job, but I could do each room at a time, in a couple of evenings after work, when I was ten years younger (25 at time) and didnt have kids!
This was a med-size 3 bed with a simple roof that I could stand up in and walk around, but if you have smaller loft space an extended cottage or the like, then raising the attic boards becomes more and more of an issue. I also had the cavity walls filled with carbon roller eps balls at the same time, if you have solid walls, condensation on those also becomes an consideration I am sure.
RizzoTheRat said:
Yeah, we looked at legs but worried they were a bit fiddly, and would need to be well secured to ensure they didn't collapse sideways while we were working on it. With crossways joists we only needed a couple of 90 degree brackets on each one as the screws down through the boards we put on top made it really solid.
I also thought individual legs could be a bit fiddly to line up and lay boards across especially given our joists aren't particularly evenly spaced, so as mentioned above I used the Loftzone system. I've never used individual legs to compare but this was really easy to install, just run a plumb/laser line to get the triangular legs aligned then screw into place every 2-3 joists at roughly 1.2m gaps (the span of the rails). Once in place the steel rails slot into place and they're held with a screw into the top of the leg with the straight legs then slotted in as additional support between the spans.
The good thing about with rails is other than working in straight lines you don't need to worry too much where the legs themselves go, the only dimension between rails you need to be accurate with is the distance between the two rails that will support the ends of your 1.2m or 2.4m long loft board so you can support the edge of another board next to it. Rails can also bridge obstructions and oddly spaced joists more easily so if there's an electrical junction box or wiring in the way you just put the legs on the joists either side and bridge over it. The only real faff is when the joists are significantly under or over 40cm/60cm spacing and you need to cut the rails down to fit which I had to do in about 3 places (meaning 18 rails to cut). A multi material mitre saw blade made short work of that job but would have been a nause to hacksaw them all! Once that's in you obviously lay the extra insulation in the same orientation then slide boards across the rails and screw straight down into the steel.
The end result is a really stable and strong platform that can probably take more weight than the 4" joists it's sitting on is designed to take.
Edited by LocoBlade on Monday 24th October 18:15
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