In my (not new) anymore new build we have a detail in the eves that I am trying to improve / weighing up options.

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.

See what Tony’s house did, false skeiling ceilings to overcome the problem.

http://tonyshouse.readinguk.org/mitigation-of-thermal-bridging/

One thing I forgot:

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.

I will work on a section sketch but it's been awhile since I have been up there and took some images.

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.

Coving. Sorry Tony!

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)

My comment doesnt seem to be displaying even though its there if I go to edit it, so heres what I said-

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"

Here is my attempt at the section.



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.

Sounds like a summer job!

Would there be any benefit in going from below via the reveal ? Is it likely that insulation between lintel is missing?

+1