Mon, 12 Oct 2026 22:13:42 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214712#Comment_214712 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214712#Comment_214712 Fri, 05 Dec 2014 12:07:53 +0000 Triassic
Slates
Batters
Vapour open roofing membrane draped by 8mm over rafters
Rafters
30mm air gap
Foam insulation between rafters
Foam insulation below rafters
Plaster board.

Target U-value of 0.11W/m2k

The question is, does this leave the Timber on the cold side of the insulation and would it be better to have the Timber on the warm side by putting the insulation aboutve the Timber?

Also would you go for OSB sarking over the whole roof?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214713#Comment_214713 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214713#Comment_214713 Fri, 05 Dec 2014 12:35:07 +0000 owlman If tiling, you'll need vertical counter battens before the actual tile batten, which together with the OSB thickness and insul. may affect the overall finished roof height, which may impinge on other aspects like flashings, design, and the interior too if you're working to an overall planning height restriction etc..]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214714#Comment_214714 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214714#Comment_214714 Fri, 05 Dec 2014 12:35:37 +0000 ringi https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214716#Comment_214716 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214716#Comment_214716 Fri, 05 Dec 2014 12:53:59 +0000 Triassic
Would you place the insulation just below the sarking, rather than where it is now?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214717#Comment_214717 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214717#Comment_214717 Fri, 05 Dec 2014 13:09:46 +0000 Jamster
We went for in between in the end as we wanted to get the roof on before the weather completely got on top of us, but it did seem to take a while to fit and we used a lot of squirty foam!

Another very good point that was made to me on here was that if you aren't using the space for a room in the roof, you are considerably increasing the volume of space in the house that you are committed t heating...

My thoughts only as a self-build project manager mainly - some real hands-on experience will be along soon I a sure...!]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214718#Comment_214718 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214718#Comment_214718 Fri, 05 Dec 2014 13:22:17 +0000 bot de paille https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214719#Comment_214719 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214719#Comment_214719 Fri, 05 Dec 2014 13:48:06 +0000 CWatters https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214721#Comment_214721 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214721#Comment_214721 Fri, 05 Dec 2014 14:12:31 +0000 Ed Davies https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214728#Comment_214728 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214728#Comment_214728 Fri, 05 Dec 2014 16:23:47 +0000 Triassic https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214731#Comment_214731 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214731#Comment_214731 Fri, 05 Dec 2014 16:45:15 +0000 PaulJ https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214734#Comment_214734 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214734#Comment_214734 Fri, 05 Dec 2014 17:35:51 +0000 Triassic Posted By: PaulJIf you go for above and between rafters, you need at least the same thickness above as between. looking at a previous email from the architect he suggested 1/3 above and 2/3 between the rafters. What is the logic for having the same thickness above and between?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214735#Comment_214735 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214735#Comment_214735 Fri, 05 Dec 2014 18:04:55 +0000 Ed Davies https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214737#Comment_214737 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214737#Comment_214737 Fri, 05 Dec 2014 18:22:20 +0000 Triassic https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214738#Comment_214738 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214738#Comment_214738 Fri, 05 Dec 2014 18:32:23 +0000 Ed Davies
“Foam” (I'm assuming PUR sheets rather than something sprayed as you don't distinguish from the stuff inboard of the rafters) between rafters with essentially no wind protection outboard of it would worry me as it's not obvious there won't be thermal bypass due to air blowing down the gaps between the foam and the rafters. It'd need tricky sealing which would be difficult to inspect.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214739#Comment_214739 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214739#Comment_214739 Fri, 05 Dec 2014 18:40:25 +0000 Triassic
The whole roof is rather thin, so I'm not sure if the insulation between the rafters (150 deep) could be changed to rockwood or similar.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214740#Comment_214740 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214740#Comment_214740 Fri, 05 Dec 2014 18:43:39 +0000 ringi https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214742#Comment_214742 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214742#Comment_214742 Fri, 05 Dec 2014 19:28:19 +0000 woodgnome Slates
Batten
Counter batten
Non tenting membrane sealed at laps
Wood fibre sarking
Rafters
Mineral wool full fill between rafters
Polyurethane insulation
OSB
Vapour Barrier
Battens/counter battens/plasterboard/plaster.

Edit..Thanks to David Freeborough.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214745#Comment_214745 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214745#Comment_214745 Fri, 05 Dec 2014 21:07:46 +0000 Ed Davies
- metal instead of slates,
- timber boards instead of wood fibre sarking (with more membrane inside for additional wind protection),
- rafters as timber I-beams,
- vapour/air barrier outboard of the PUR (for protection from service fixings and compression/mechanical fixing of the laps)
- not plasterboard in most parts of the house.

235 mm I-beams with full-fill mineral wool between, 90 mm PUR inboard.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214749#Comment_214749 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214749#Comment_214749 Fri, 05 Dec 2014 22:56:51 +0000 willie.macleod Posted By: TriassicI had in mind OSB sarking to the exterior (silicone sealed to the rafters as per Viking House) to stop the wind.


If you do OSB then I wouldn't recommend silicone sealing to rafters. Get T&G OSB and use a polyurethane D4 adhesive like Caberfix designed for the job.

I found silicone sealing doesn't work well in practice, it invariably is VERY messy, a decent sized roof uses a huge amount of tubes of silicone and you have the problem of how you deal with the unsupported long edges.

I'd pay the few quid extra for the T&G OSB 3 and save hours and do a neater job.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214758#Comment_214758 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12862&Focus=214758#Comment_214758 Sat, 06 Dec 2014 10:15:57 +0000 woodgnome