Numbers from your pdf 1. I would seal before plastering, 3. I cant see the purpose of the ply and it is acting as a thermal bridge and it is not fail safe, 11. I like this, 12. may be fixing foam rather than expanding ma be easier, cause less problems ? 14. there seem to be packers and something else under the window board, what is it and is it necessary or better than more insulation would be?

your numbers 1. you could lift the bottom of the window frame further away from the structure to allow more insulation, remove a course of bricks or smaller window, 2. make good, 3. I cant see why you need ply atall unless you push the window out into the EWI

Important -- you MUST have a drip at the render above the window, I make the render slope upwards towards the window,

Looks like a good detail, shame everyone hasn't got it on their houses we would all be a lot better off them.

I would fix the frame to your brickwork using twin threaded frame fixings three each side, push the window out a bit further too 30mm?

I cant see the window squashing the insulation, how wide are the windows? I did support my wide 2400 ones centrally with a bracket up the outside of the brick wall onto the outside few mm of the front of the frame.

Nice drawings!

Prime principle is to move the frame outboard away from the (now internal) masonry. As it is, you have a v short heat-flow path from outside frame face, thro the frame chambers, reveal insulation, to masonry. V lossy. Move the frame right outboard, into the EWI zone, away from the masonry - that's one of the reasons for using EWI at least 150, pref 200 thick, to fully accomodate frame depth plus a bit of reveal depth.

Depth of insul cover in front of the frame - depth only say 1.3 x the width of cover will be effective. So, if 25mm width of cover, no point in making reveals more than 40 deep (except for visual and weather-shedding reasons). You could increase your width of cover considerably - entirely 'lose' the fixed frames, esp as open-in - no open-out hinges etc to clear.

Yeah, sorry about that. I got busy and forgot to do the model.

Have you got your head around how to actually do the modelling in therm? You need to model a 1m long section of blank wall first and get the U-Value. Then model the detail (excluding the window and frame (see BR496)) and then do a quick sum with the two sets of numbers.

I can post up the calculation, although it is in BR496 anyway.

Update attached based on your comments guys, thanks.

With the window pushed out 30 mm, wouldn't the screw fixings now be too close to the edge of brick?

Another one, would this comply with NHBC requirements? Don't they require two barriers against water ingress or something? Whereas I've only got one seal where the render meets the window frame to the jambs and head, and just the sill flashing to the sill.

3. 20mm is a bit mean for the drip oversail 50mm would be betterer

17. you can angle the fixings a bit towards the middle of the wall.

it is looking like a great detail now though

Posted By: TimberI can post up the calculation, although it is in BR496 anyway.

I'd love to see that - I couldn't understand that bit on the course, not concentrating in fact, struggling with a useless borrowed laptop (got my own (useless) laptop now!).

Posted By: ShevekWith the window pushed out 30 mm, wouldn't the screw fixings now be too close to the edge of brick?

Window fixing straps are available in lengths of up to around 200mm. They are screw fixed to the perimeter of the frame before inserting the window in the opening.

I wouldn't rely on silicone sealant for airtightness. I would seal the perimeter of the frame to the interior face of the insulation with something like illbruck ME500 Duo Flexible Window Membrane:

http://www.tremco-illbruck.co.uk/products/01920_index.html

And then seal the insulation to the inner face of the masonry with something like illbruck ME404 Butyl Fleece Tape:

http://www.tremco-illbruck.co.uk/products/03254_index.html

This can be incorporated into the plaster to maintain the continuity of the air barrier.

David

Thanks again guys.

@David thanks for the tape pointer.

I read through the ME500 literature but couldn't decide whether the W or the E is more appropriate:
http://www.tremco-illbruck.co.uk/celumdb/documents/ME500-E_DS_GB_22553.pdf
http://www.tremco-illbruck.co.uk/celumdb/documents/ME500-W_DS_GB_22554.pdf

I assume then that XPS will be the best insulation for the perimeter because it will be nice and firm to consolidate the tap against with a roller... I'm in two minds whether to use XPS or the same as the external wall insulation (which will probably be PIR or Phenolic).

Updated detail attached using the W product.

I think it is OK though as it has insulation all round it.

Yeah I'm going to try it it Therm. Just need a moment when my head is fresh to get my head around Therm.

Shevek

I modelled the Jamb very quickly using some standard material specs, as I am not sure 100% what materials you are using and got a PSI value of 0.013 W/mK which is very good.

Here is the Heat Flux output. Shows minimal patches of elevated heat flux around the window frame, but they are tiny.

If eliminated by pushing window outboard, what wd the figure be, at a guess?

Awesome, thanks Timber, much appreciated. Must learn Therm!!

Well I had 5 minutes this morning, and curiosity got the better of me. I pushed the window out by 30mm and it has made quite a difference.

We now have a calculated psi value of 0.004 W/mK for the jamb detail. That is excellent. So with EWI on masonry, it seems that pushing the window out improves the calculated PSI values.

Caviat again, I just used some normal material properties etc, so you might come up with a slightly different result when you do the sums for yourself using your own materials. I just used standard values for EPS, brick, plaster and render.