Tue, 19 Dec 2023 08:39:47 +0000 http://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=299883#Comment_299883 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=299883#Comment_299883 Wed, 25 Jan 2023 17:29:03 +0000 marsaday
The building control guy is not sure on the new regs and said he will get back to me on what i need to put back.

He is saying i can leave the 50mm rigid foil insulation in between the roof joists and under board with 50mm. So 100mm rigid insulation on the roof.

The flat dorma can have the same, so 100mm.

The dorma sides he wasnt sure, It is 75mm deep here.

On the small eave walls he wants 150mm rigid which doesnt seem right.

Uvalue to achieve is 0.16 on any roof part and 0.3 on walls (i think).

Anyone know about this topic ?]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=299885#Comment_299885 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=299885#Comment_299885 Wed, 25 Jan 2023 19:02:01 +0000 Nick Parsons
Part L kicks in when you 'add or replace a layer'.

100 on the sloping soffits will not achieve 0.16.

Got any pics? Are the 'small eaves walls' for example stud or brick, where the ext wall comes above FF ceil level?]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=299889#Comment_299889 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=299889#Comment_299889 Wed, 25 Jan 2023 23:21:53 +0000 marsaday
The flat height is very low, so me ripping out the current plaster board to now be told i need to fit a deeper level of insulation seems a bit unfair. All i am doing is improving what was there.

So BC says 100mm will be ok, and i thought this didnt make sense to me, but if he is ok'ing it then fair enough.

Insulating the eave walls is another matter. He wants 150mm here. They are studs and behind will be an unused space running the whole way around the flat.

This photo shows the flat roof area, which is a dorma extension done in the 80's. You can see the slopes and the stud eave walls as well.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=299890#Comment_299890 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=299890#Comment_299890 Thu, 26 Jan 2023 08:24:40 +0000 tony
Eaves, across g/f ceiling with 400mm mineral quilt joined to pir but leave gap for ventilation

Dormer cheeks, fully fill and overclad with additional 50 or 80mm pir

Vapour barrier everywhere, plasterboard and plaster]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=299892#Comment_299892 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=299892#Comment_299892 Thu, 26 Jan 2023 09:20:57 +0000 marsaday
These new regs are much stricter but I am learning if on a referb you can you be expected to upgrade what is practical. The head height won’t allow 100mm board under the rafters. 50mm is ok

Can I fill the dorma fully up? I thought we had to allow ventilation?

Having said that, the felt is being redone so I can stick 100mm on the top and add extra in the void to be a warm roof.

bC have said on those eave walls I need 150mm insulation and I think he means rigid, but this is where he is going to check as he isn’t sure.

So this is by biggest query. I wanted to do 50mm between studs and 25mm overboard on these walls.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=299895#Comment_299895 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=299895#Comment_299895 Thu, 26 Jan 2023 10:53:31 +0000 Nick Parsons
Unless he is trying to 'over-do' the stud wall to compensate for the sub-optimal insulation on the slopes then 75 or 100 PIR will do.

If he's talking 150 I think he means mineral wool.

The 'raw calc' for PIR is 0.75(m)/0.022 (lambda value) = 3.409 (R value). 1/R = U, so 1/3.409 = 0.293W/m2K. This is not the full story, though, as your 50mm between studs has 50mm of wood every 400 or so mm, so actually the U value is probably a tad worse than 0.3. As per Tony, I'd always encourage exceeding the requirements of the regs, but if you want to go for the 'minimum minimum' he'll probably accept 75mm.

The calc is easy for mineral wool as the lambda of bog-standard stuff is 0.044, half as good as PIR, so his 150 is (if you forget the studs) correct. If I'm doing 'fat' quilt insulation in stud walls or sloping soffits' I use 'Larsen Trusses' (spaced rafters or cheapskates' I-beams).

Good luck with it. I hope it goes well.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=299896#Comment_299896 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=299896#Comment_299896 Thu, 26 Jan 2023 11:06:25 +0000 marsaday
Do you think it is worth insulating the slopes behind the stud wall as well? So 50 between and 50 underneath?

The eaves will have an access hatch each side, so if I can lower the air flow coming into the eaves this is likely to help the overall space. The hatches are fake ones which seal and have insulation.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=299899#Comment_299899 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=299899#Comment_299899 Thu, 26 Jan 2023 12:20:29 +0000 WillInAberdeen
"Pitched roof constructions (room-in-the-roof
arrangement
Target U value 0.16"

"ceiling to flat
roof area.
Target U value 0.16"

"Dormer window constructions
Renewal of cladding to side
walls
Target U value 0.30"
(They suggest putting the insulation on the outside of the timbers, could you do that while you do the flat roof?)

So for the pitched and flat roof that would be about 50mm PIR insulation between the rafters and another 100mm over/under for U=0.16

For the dormer side walls and eaves walls that's about 50mm between the studs and another 30-50mm outside/inside for U=0.30 (so 80ish mm total like Nick said)

Might be cheaper overall to put all the insulation over/under the timbers, rather than putting some between, as saves faff of cutting to fit, and no thermal bridges so insulation can be slightly thinner.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=299900#Comment_299900 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=299900#Comment_299900 Thu, 26 Jan 2023 12:47:37 +0000 marsaday
Dorma cheeks I can get 75 plus 25. Eaves I can get 50-75 between and 25 over

Roof only can get extra 50 under.

I think there is flexibility in this legislation. Some house just cannot get x amount on the walls if doing it from inside. So people will simply not bother. That’s how I see it.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=299902#Comment_299902 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=299902#Comment_299902 Thu, 26 Jan 2023 13:51:18 +0000 WillInAberdeen
"not technically or functionally feasible"

Examples are given: it's not required to lose more than 5% of the floor space, or to limit the head room, or spend money that wouldn't payback within 15 years. But it would probably come down to what the BCO agrees to.

You could mock up a few square feet of insulation to the regs, to demonstrate that causes a problem, or not?

On our project I worried about this, but it turned out not to be noticeable once the walls were painted. If anything, it made the room "narrower" rather than "lower", but not a problem.

Better insulation means better EPC score so could be helpful.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=299907#Comment_299907 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=299907#Comment_299907 Thu, 26 Jan 2023 15:19:17 +0000 tony http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=299908#Comment_299908 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=299908#Comment_299908 Thu, 26 Jan 2023 16:01:17 +0000 bhommels Posted By: tonyRe dormer flat roof, with the noggins there never was any ventilation so filling it full changes it to a warm roof, odd that it is completely flat. Vapour barrier crucial
Tony, are you always preferring a vapour barrier over a vapour control layer?]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=299909#Comment_299909 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=299909#Comment_299909 Thu, 26 Jan 2023 16:02:23 +0000 marsaday http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=300082#Comment_300082 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=300082#Comment_300082 Thu, 02 Feb 2023 15:40:05 +0000 marsaday
I'm really annoyed by this as I am up dating a terrible flat and to reduce the roof height by so much compromises the space.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=300090#Comment_300090 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=300090#Comment_300090 Thu, 02 Feb 2023 18:52:25 +0000 Dominic Cooney If you want to make it as good as you possibly can, perhaps because you know that it’s the right thing to do, or because it may not be done again for 50 years, or any other reason, have you considered Aerogel for the places with the tightest headroom? With the cheaper PIR in other places where there is a bit more space.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=300093#Comment_300093 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=300093#Comment_300093 Thu, 02 Feb 2023 20:17:39 +0000 marsaday http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=300107#Comment_300107 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=300107#Comment_300107 Fri, 03 Feb 2023 21:06:46 +0000 marsaday
The dorma will be 150mm so a uvalue of 0.5.

I am making it a warm deck as redoing the roof in fibreglass. Do i put the vapour barrier at the plasterboard level ? Or do i lay it over the first deck just below the 100mm insulation ? I am fitting 50mm between the rafters, tight up to the top. Still have about 70mm void space left.

the roof is not flat and has a good pitch on it.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=300108#Comment_300108 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=300108#Comment_300108 Fri, 03 Feb 2023 22:03:51 +0000 djh Posted By: marsadaySpoke to BC today and got the all clear to use 75mm between the rafter and 50mm underneath, giving 0.2 U value.

The dorma will be 150mm so a uvalue of 0.5.
I don't understand that. 75+50 = 125 gives 0.2 U value, but 150 gives significantly WORSE U value for thicker insulation? What do I not understand?]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=300109#Comment_300109 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=300109#Comment_300109 Fri, 03 Feb 2023 22:14:09 +0000 marsaday http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=300111#Comment_300111 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=300111#Comment_300111 Sat, 04 Feb 2023 06:25:25 +0000 Dominic Cooney Posted By: marsadayStill have about 70mm void space left.
.

This strikes me as a wasted opportunity. If you are having 100PIR above to make a warm roof (if I understand correctly?) then I would go 100 in between as well (tight up to the top) leaving a smaller 20mm void at the room ceiling side. The increased material cost would be minimal. That should get you to about 0.13 U Value]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=300112#Comment_300112 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=300112#Comment_300112 Sat, 04 Feb 2023 10:01:17 +0000 marsaday
So can I fill with say 100 above and 100 between, leaving 20mm space?

Would the vapour barrier go just below the joist then? Or would it go over the first osb deck (under the 100mm insulation above). bC have you doing some things which just don’t seem right]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=300113#Comment_300113 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=300113#Comment_300113 Sat, 04 Feb 2023 11:18:49 +0000 WillInAberdeen
Principle of a warm roof is that the insulation goes (mostly) above the deck, so that the deck and rafters are always warm and inboard of the dewpoint. Adding insulation below the deck, makes it colder. There was a rule of thumb that the insulation value above the deck should be at least 2x the insulation below, other people say 3x, it's all a bit rough and ready. Especially for flat roofs which get heated when the sun shines.

If you are thinking to add on more insulation to further increase your 150mm, then maybe add it to the layer above the deck, rather than the layer below, also saves on cutting and thermal bridges? But maybe diminishing returns when other areas have U=0.3.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=300115#Comment_300115 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=300115#Comment_300115 Sat, 04 Feb 2023 14:51:52 +0000 Dominic Cooney Posted By: WillInAberdeenThere was a rule of thumb that the insulation value above the deck should be at least 2x the insulation below,

I haven't heard of this but then I haven't done any research on warm flat roofs - I do need to though with 2 that need sorting on this house.
I wonder what the rationale is for that? when it's okay for a warm pitched roof e.g. 100mm between 100mm over.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=300117#Comment_300117 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=300117#Comment_300117 Sat, 04 Feb 2023 16:30:34 +0000 WillInAberdeen
Cold flat roofs have unbreathable felt or EDPM so they are supposed to have cross ventilation underneath the deck to let moisture escape. Warm flat roofs don't need the ventilation, if the timber is actually warm enough.

TBF there are plenty of cold flat roofs that last for years without ventilation and others that go rotten so it does seem fairly random. Warm flat roofs are mandatory in Scottish building standards.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=300118#Comment_300118 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17714&Focus=300118#Comment_300118 Sat, 04 Feb 2023 16:47:25 +0000 marsaday