Wed, 03 Jun 2026 07:48:15 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297553#Comment_297553 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297553#Comment_297553 Mon, 12 Sep 2022 15:26:06 +0100 Newbuild
Essentially we have 500mm of rockwool horizontal loft insulation in an unventilated loft and where this meets the roof at the eves it shrinks down to the available rafter depth, circa 60mm minus 20mm. Unfortunaly there is no hip in the roof to accommodate a deep amount of insulation over the eves.

I have retrofitted ventilators on the wall plate since there is an over eves ventilator but it was blocked by the roof insulation initially - The insulation itself cant be carried over the eves so much since there is a cavity tray running horizontally where a double height lintel protrudes up level with the wall plate. The cavity below is 100mm full fill.

Is there anything I can do to improve this junction? I am just weighing up options, I would mostly like to avoid air infiltration down the cavity or worse down the void behind plasterboards.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297554#Comment_297554 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297554#Comment_297554 Mon, 12 Sep 2022 15:40:33 +0100 fostertom https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297567#Comment_297567 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297567#Comment_297567 Wed, 14 Sep 2022 07:10:28 +0100 tony
http://tonyshouse.readinguk.org/mitigation-of-thermal-bridging/]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297594#Comment_297594 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297594#Comment_297594 Thu, 15 Sep 2022 10:53:39 +0100 jon
In extension, I went for excessively large ceiling rafters, which mean I would wrap around and down into the cavity

For the retrofit, which sounds similar to yours, I used PIR sheets (40mm) going about 200 between joists and continuing only partly over the wall plate. brought the rockwool over that, Just under the joists I then put in 90mm shaped blocks down to the cavity (which was already filled with balls). Very much a compromise.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297602#Comment_297602 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297602#Comment_297602 Thu, 15 Sep 2022 17:42:18 +0100 jon
Have you considered making the architrave massive? (eg 250x250 triangular and done in PIR or maybe poly) It's something I've been looking at but might have to wait until I do a major internal refurb before it gets much more thought.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297604#Comment_297604 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297604#Comment_297604 Thu, 15 Sep 2022 18:15:44 +0100 tony https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297607#Comment_297607 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297607#Comment_297607 Thu, 15 Sep 2022 19:27:27 +0100 Newbuild
Everything so far sounds like great ideas. Don't know if I will be able to get away with selling aesthetically.

Is there a practical way of shoving PIR into the cavity and then sealing it above the wallplate somehow? Is there any reason for there to be a cavity tray present at this location? I think the gap in insulation is because the cavity tray has ended up horizontal.

the window opening has a double height lintel above it, which protrudes up level with the wallplate.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297614#Comment_297614 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297614#Comment_297614 Fri, 16 Sep 2022 07:03:40 +0100 tony
Wind and cold air behind the plasterboard is too big a story to do in this thread, see dot and dab or plasterboard tents!]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297616#Comment_297616 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297616#Comment_297616 Fri, 16 Sep 2022 09:23:10 +0100 jon
Our wall is filled with balls (from a fit done before we bought it). Found the best way to deal with that was to pack the top of the cavity with rockwool: another compromise (but we have lots of weird details so that didn't always work).

First realised there was something seriously wrong with the first poly-ball installation when I opened up the basement area (more of a deep undercroft but basement sounds posher). Found piles of balls next to the front and back walls in the basement. Installers had pumped balls in without realising that the cavity was open to the basement. So some areas had to be closed and then re-filled (used about 70 cubic feet's worth)]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297638#Comment_297638 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297638#Comment_297638 Sat, 17 Sep 2022 10:39:48 +0100 philedge Posted By: Newbuild
Is there a practical way of shoving PIR into the cavity and then sealing it above the wallplate somehow?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297639#Comment_297639 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297639#Comment_297639 Sat, 17 Sep 2022 11:14:37 +0100 philedge
Yep. Buy or borrow an alloy scaffold tower, section at a time strip off the roof covering and add insulation from the comfort of the scaffold. Theres not really any other way to properly retrofit insulation to the eaves.

We did this pre covid and extended the loft insulation to meet the blown fibre cavity fill. Found lots of areas in the cavity with no insulation so that got remedied at the same time. Fitted 500mm lengths of waste pipe to the side of each rafter for ventilation over the wall plate then full filled the area to the underside of the felt. No gap needed with the waste pipe "duct"]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297642#Comment_297642 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297642#Comment_297642 Sat, 17 Sep 2022 13:11:14 +0100 tony https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297726#Comment_297726 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297726#Comment_297726 Thu, 22 Sep 2022 12:54:19 +0100 Newbuild


https://ibb.co/DQDYwgY


Hopefully you can make out 500mm of horizontal insulation meets the pitched roof and retrofitted eves spacer, leaving about 60mm over the wall plate.

Yes the opening does have a double height steel lintel for some reason and the rafter is nibbed to accommodate it, it also makes the lintel height level with the bottom of the wall plate.

Eves spacer was fitted retrospective as the insulation was blocking the over eves vent and all this caused was air from outside to get forced down the wall plate and ceiling plasterboard gap.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297727#Comment_297727 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297727#Comment_297727 Thu, 22 Sep 2022 13:10:04 +0100 philedge https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297729#Comment_297729 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297729#Comment_297729 Thu, 22 Sep 2022 14:22:16 +0100 Newbuild

Would there be any benefit in going from below via the reveal ? Is it likely that insulation between lintel is missing?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297738#Comment_297738 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297738#Comment_297738 Fri, 23 Sep 2022 06:25:19 +0100 philedge https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297739#Comment_297739 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297739#Comment_297739 Fri, 23 Sep 2022 10:32:50 +0100 tony https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297742#Comment_297742 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17564&Focus=297742#Comment_297742 Fri, 23 Sep 2022 13:50:57 +0100 Newbuild