Tue, 19 Dec 2023 06:47:36 +0000 http://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275396#Comment_275396 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275396#Comment_275396 Thu, 05 Sep 2019 21:36:22 +0100 debbiel
The rafters are 400mm centres and are 190mm deep. What is the best way to insulate between rafters? Best insulation to use? Do I need to leave any air gaps, or full fill? Breather membrane/vcl? External insulation not an option, so what would be best for an internal thin layer to stop thermal bridging? The work will be done by volunteers, so I'm thinking Kingspan or similar for ease of use, but all ideas welcome.
It will be finished with plasterboard internally - unless anyone has a better alternative?
Thanks in advance.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275430#Comment_275430 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275430#Comment_275430 Mon, 09 Sep 2019 08:50:50 +0100 GreenPaddy
I try to avoid Kingspan being the default, but it's what people tend to know a wee bit about, so it's a good benchmark. No idea what insulation you have in floor or walls, or what Uvalue you're trying to achieve, so a little guesswork, and pragmatism, and recognising "volunteer labour"...assume you might think of 100mm kingspan:

Option 1. polystyrene in 100mm and 50mm sheets, to give 150mm. That's about the same as Uvalue 100mm Kingspan, but not as expensive or dusty to work with (yes it "snows" but sawing kingspan is horrible). Push it so it against the roof sheet, to give some space below for cables, recessed lights, what ever. Squirt in expanding foam around the edges to hold it in place and stop air blowing around. Using expanding foam - less is more!!

Option 2. Knauf earthwool loft roll 40. Either two layers of 100mm or one of 200mm (comes in both these thicknesses). That again will give about same Uvalue as 100mm kingspan. Easy to fit, not itchy, though a bit fluffy. Much cheaper than kingspan.

Either way (I'd personally go for option 2), I'd add a VCL, just some cheap polythene, installed in the same direction as the ceiling joists, so the overlaps land on a joist. Staple it in place, and tape over the joints. Actually, if you run double sided tape onto the already fitted edge, it makes fitting the next run much easier, and gives the seal in one go. When the plasterboard goes up, it will nip the VCL sheets and keep them together anyway.

Good luck.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275461#Comment_275461 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275461#Comment_275461 Tue, 10 Sep 2019 09:34:44 +0100 debbiel http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275464#Comment_275464 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275464#Comment_275464 Tue, 10 Sep 2019 12:09:29 +0100 GreenPaddy
You can beef up the Uvalue by going for the earthwool frametherm 35 or even 32. About 20% better thermally, but quite a lot more expensive. Using loftroll40, Uvalue of around 0.23W/m2K. With FT32 around 0.19W/m2K

By the way, earthwool has a vapour resistivity of about the same as wood fibre and better than sheeps wool. Appears to be "relatively" green, but I haven't researched the reality behind headlines.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275469#Comment_275469 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275469#Comment_275469 Tue, 10 Sep 2019 18:23:42 +0100 Nick Parsons http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275518#Comment_275518 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275518#Comment_275518 Wed, 11 Sep 2019 20:12:26 +0100 debbiel http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275524#Comment_275524 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275524#Comment_275524 Thu, 12 Sep 2019 07:59:22 +0100 GreenPaddy
What depth are the wall studs, I'm guessing 140mm? It might be worth investing in the FT32, as it's the last chance you have to insulate the place. If the labour's free, put some of that saving into the materials.

I would add a foil faced VCl over the studs/wool (foil facing into the room), then nail 25x50mm battens onto the studs, to give you a service void. A classroom is likely to have sockets, switches added over time. Make life easy for yourself, and also the void stops electricians ripping huge holes in the VCL, to fit a little cable through it. Plus it improves the Uvalue with the foil/void lowE unvented cavity. Actually, you might want to use 25x100mm for the service battens on every other stud, so that the plaster board edges have a bigger landing area for fixing. Volunteers, might not be quite as accurate with the batten locations, so gives a bit more leeway.

Also add plenty of fixing pads, for shelves, cabinets, wall mount TV's, coat racks, etc. You can do this easily by nailing 25x100mm horizontally across the wall studs, in the service void zone before fixing the vertical battens. Doesn't add to cold bridging like noggins would.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275546#Comment_275546 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275546#Comment_275546 Fri, 13 Sep 2019 18:24:16 +0100 debbiel http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275554#Comment_275554 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275554#Comment_275554 Sat, 14 Sep 2019 18:42:20 +0100 GreenPaddy

No, the foil VCL doesn't really do anything for cold bridging itself, it's just a slight improvement due to the cavity, and low emissivity surface.

Do you mean 25mm Kingspan? Not sure it's avail at 20mm, at least not readily?

According to Part L (I use Scottish Regs, so maybe double check this), for non-Dom...

Roof = 0.18
Walls = 0.28
Floor = 0.22

Roof- 190mm loftroll40 between roof joists does not meet BRegs at only 0.22. Under draw it with 25mm kingspan takes you to 0.17, so a pass. Under draw with 50mm kingspan gives 0.142. If you do under draw, then consider battening the ceiling as per the walls (we call that brandering), so again you have a service void for lighting cables, and an easy fix for the plasterboard. Of course you could just whack up some kingspan backed plasterboard, but then lights/cables will end up penetrating the VCL, hence my pref for service battens/branders. Again if you use 25x100mm every other joist, (as mentioned previously for walls) you'll have a big target for the plasterboard edges to land on, and get fixings in.

Walls - you'll just scrape BRegs with 140mm studs filled with loftroll40, foil VCL, service void, at around 0.26. If you add a layer of 25mm kingspan, that takes you to 0.2. Add 50mm takes you to 0.16. Note, if you add the foil faced kingspan, then the VCL onto the studs need only be a polythene, since the the foil face of the kingspan will give you the low E surface.

Floor - don't know what the build up is?

Look at flat LED panels for lighting?]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275561#Comment_275561 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275561#Comment_275561 Sat, 14 Sep 2019 21:17:43 +0100 WillInAberdeen
There's exemption for certain buildings (historic, small, unheated, ...)]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275576#Comment_275576 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275576#Comment_275576 Sun, 15 Sep 2019 22:47:30 +0100 debbiel http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275583#Comment_275583 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275583#Comment_275583 Mon, 16 Sep 2019 16:42:50 +0100 GreenPaddy
I would also have assumed you would have agreed with building control office, what you would be building, and to what values, but since I've only built large commercial buildings in England, and since all the drawings, specs, and regulations must be signed off in Scotland before you make a start, I'm not familiar with the vagaries of domestic building control down south...get the impression it can be a voyage of discovery.

Anyway, I suggest you confirm with your BC person what Uvalues he/she is expecting as a minimum (should be as I noted above), and then you're not taking any risk, and the BC officer knows what they're going to see when they get to site to inspect, at the pre-plasterboarding inspection point.]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275584#Comment_275584 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275584#Comment_275584 Mon, 16 Sep 2019 22:04:59 +0100 debbiel http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275594#Comment_275594 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275594#Comment_275594 Tue, 17 Sep 2019 16:50:38 +0100 debbiel So that means I can go ahead with the earthwool / Kingspan combo as suggested by you GreenPaddy, thanks for all your help. One final question before I leave you in peace, on this set up would the polythene VCL go between the studs and the 25mm Kingspan, or on the internal side of the Kingspan?]]> http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275604#Comment_275604 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16233&Focus=275604#Comment_275604 Wed, 18 Sep 2019 09:03:44 +0100 GreenPaddy
The other point is that you get the benefit of the foil face of the insulation board, as it will face into the batten service void, not covered by the VCL.]]>