Sat, 18 Apr 2026 17:43:14 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=717&Focus=7542#Comment_7542 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=717&Focus=7542#Comment_7542 Wed, 03 Oct 2007 13:23:18 +0100 Chris Wardle
Any advice?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=717&Focus=7546#Comment_7546 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=717&Focus=7546#Comment_7546 Wed, 03 Oct 2007 16:24:46 +0100 fostertom https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=717&Focus=7551#Comment_7551 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=717&Focus=7551#Comment_7551 Wed, 03 Oct 2007 19:32:41 +0100 Chris Wardle https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=717&Focus=7555#Comment_7555 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=717&Focus=7555#Comment_7555 Wed, 03 Oct 2007 20:59:30 +0100 fostertom As rafters are so skinny, add minimum 45-50 down-slope battens to deepen the underside of all rafters, 70-75 better. Fit 60 or 80 Cellotex very neatly between the rafters, no gaps, edges bedded or 'pointed' with foam. Cellotex top 25 (diagonally) below rafter top, underside of Cellotex minimum 35 (diagonally) above underside of the deepened rafters.
Spotwelded-type multifoil across the deepened rafters' underside - not the perforated stitched-type multifoil. At present, as far as I know, that means Euroform Xfoil, as manuf'd by my mate Paul Mitton (I'd like to know if others start making non-perforated multifoil). Only the non-perforated type can act as the airtight barrier.
35h x 50w counterbattens across the rafters' underside. Note that the multifoil (nom 30 thk) has 35 up into the rafters' depth and 35 down into the counterbattens' depth - that's the only way to minimise contact - the usually recommended 25h battens are near useless.
Plasterboard soffit. Gives wiring or even pipe space above the plasterboard. Recessed spots - must be cool-running heat-downward (not dichroic) type, or LEDs, can be fitted _ i have a detail/spec to prop the multifoil up locally.
Airtightness - I might consider publishing details of how to join multifoil to multifoil (mechanical clamp only - don't think of using sticky tape), multifoil to Velux frames (requires non-standard trimmed rafter layout), multifoil to wet plastered gable wall, and how to wangle the airtight membrane past the purlins.
As well as airtightness and elimination of solar overheating, this spec should give a whole-heating-season heat loss performance equivalent to about 210mm of Cellotex - but be warned that that's not as good as it sounds - 210mm of Cellotex (or any conventional insulation) will actually lose about 2.5x as much heat as you'd expect from blindly applying its published steady-state k-value.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=717&Focus=7557#Comment_7557 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=717&Focus=7557#Comment_7557 Wed, 03 Oct 2007 22:11:12 +0100 Mike George https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=717&Focus=14836#Comment_14836 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=717&Focus=14836#Comment_14836 Fri, 22 Feb 2008 19:28:45 +0000 woodfire
could you explain that please?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=717&Focus=14839#Comment_14839 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=717&Focus=14839#Comment_14839 Fri, 22 Feb 2008 19:57:56 +0000 Mike George http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=1281&page=1#Item_5

Tom may have a more comlex explanation to do with the accuracy of hot box testing. I've had enough debating of that can of worms for now.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=717&Focus=15041#Comment_15041 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=717&Focus=15041#Comment_15041 Tue, 26 Feb 2008 15:39:27 +0000 Joinerbird