I was planning on doing a similar DIY window move. I was going to box them out with a plywood frame right into the insulation zone. I am going for 200mm and if your drawing is scale then it looks like you might not have room for this. I was also thinking of making them removable from the inside only. On the outside there would be an EWI overlap. I would put the windows in with some squirty foam and then attach through this int the ply. I would fit some insulation internally to make the reveals fit right and cover with thin ply, painted. Hope this makes sense. I would be slightly worried about the increased thermal bridge your way but I am being picky.

I was trying to make a CAD drawing but it is a bit tricky to get the 3d effect of it. I will try and post it next week when I am back home.

Hi fostertom,

I think that it was your comment about moving out the windows that set me off on this so thanks for the comment.

So given that I only have 100mm to play with would you recommend:

Some very rigid insulation underneath the timber support (i.e. 25mm of celotex/PU)?
or
pmagowan's approach of carrying the external insulation up over part of the outside the surface of the window frame...

This will only effect one window so I could just splash out and buy a fancy new window to remove the 'ease of window removal' design constraint.

Thanks

John

Posted By: arnyjcan U tell me just how you fix window,,,to the insulation edge.

There are two main options.

One is to form a plywood box fixed to the internal reveal of the window and protruding out into the insulation layer. Fix the windows into this box. See http://www.building.co.uk/passivhaus-diary-part-13-windows-and-doors/3152373.article for an example.

The second option is to use metal straps or brackets fixed to the edge of the frame and then fixed back to the solid wall, either the inner reveal, or L-shaped brackets connecting to the outside face of the wall. They will need to be spaced appropriately to support the weight of the windows.

Posted By: fostertomThe ply box idea seems like a mighty continuous thermal bridge to me - or is it OK Mark?

In principle I agree with you, although clearly the heat transfer has to travel along the length of the plywood, which is generally only 18mm thick so has some thermal resistance. Furthermore, this box is on the outside edge of the frame, so would be well wrapped in insulation and any heat would need to travel along the length of the plywood and then across the frame. It's almost certainly better than just bolting the window frame direct to the internal structure.

There's a PassivHaus certified detail available so it must work reasonably well.

At some point in the near future I plan to fit EWI to the renovation/extension that I'm working on. I'm happy with how you can mount the window out into the insulation envelope to reduce the thermal bridge but I'm more interested in the detail of the DPC that has to be fitted around the window to keep building control happy.

Does anyone have any drawings/details of this so I know how to keep building control happy?

Where can I find the documentation/BBA cert to give prove this to building control to keep them happy? As when they came round today to inspect my foundations and I brought up how I wanted to fit the window’s all he kept going about was how I was going to fit the DPC if I fitted the windows out into the Insulation.

Posted By: fostertomthe patent EWI system is warranted fully waterproof and the render skin just has to be weather sealed to the window frame

Posted By: MarkBennettwaterproofing is a non-issue with an external render system

EWI is wonderful! All existing weatherproofing problems sidestepped at a stroke! Even problem render can be just left in place, any looseness secured forever by the EWI's mechanical fixings. New or altered openings can be crudely bashed through and made good without need for careful DPC work or external finish. The existing structure becomes dumb internal 'furniture' covered up by the plaster and EWI (but immensely valuable as thermal mass in the right place).

Both!
Do the latter anyway - it's easy and has a great effect on reducing edge bridging loss.
Do the former if you have space. With window frames about 100 deep (inside to outside depth) set withn EWI about 200 thick plus render finish, and external reveal depth about 100, then the inside face of the frame comes close (but not quite touching) the extg. external wall face. If your EWI is 250 thick then there's 50 gap between frame and wall, which you can insulate.

I will be adding EWI (some timber clad, some rendered) to my renovation cottage. I've therefore detailed my new windows to generally be slightly narrower than the openings, and to sit flush with the front face of the existing wall (cement rendered) with bent straps (maxiband) turned back to sit on the inside face as the fixings. This leaves a returned space between the frame and the existing reveal of the wall. Where the space is large, we've inserted 50mm celotex; where smaller, filled it with squirty foam. (probably the latter is actually more scalable/buildable on balance, because inserting a separate element means more cutting, and doubled airpaths at the join that have to be filled/taped later.) Where the window head is below the lintel, we've filled that gap with foam as well. The EWI insulating layer will overlap these new insulated surrounds. So on 3 sides the window sits entirely in the insulating layer, apart from a little bridging by the straps. If I had had space below the window cill/board, then I might have inserted celotex there as well, as suggested by others, but my builder would have definitely sucked his teeth at that one - windows are heavy things that need solid support, so the wood cill does sit on the masonry bridge at that point. I'm not sure a foam board would ever seem stable enough to us. And losing/changing window height is much more problematic than losing a bit of width, I'd say.
It is rare to be able to specify windows smaller than their openings to allow my solution, I suppose - normally the width is governed by the existing lintel. But we've made a couple of openings bigger where new lintels had to go in anyway, and elsewhere I deliberately specced windows to be smaller than the maximum in order to surround them with insulation. I do cringe when Grand Designs type shows proselyse about having huge glazing - do they not know even the best windows have always been 5 or even 10 times worse for heat loss than walls, even allowing for some useful solar gain...? So being prepared to sacrifice a little glazed area (which is a lot more expensive than insulation anyway) does I suggest allow a practical simple and cheap solution to bridging around windows, certainly where EWI is involved (Cavity walls may be a bit different?).
Incidentally, the earlier point about DPCs; wooden windows still should have vertical DPCs at their sides - we have used extra wide ones (easily available) pinned to the inner face of the frame ("damping up" it's called) before insertion, which will be trapped behind the final cladding frame or rendered finish, thus making sure the window is fully weathered (outside) as well as insulated (in the middle) and taped/Orcon glued for airtightness (on the inside) - these are I gather the 3 principles of the RAL European standard for how we are supposed to deal with windows joining walls - although not yet adopted here...

If your EWI was as thick as it should be (200mm) you'd be able to move your windows completely outboard of the existing wall, so not have to come inside the reveals. In fact that way, glass area can increase a little bit, or at least not diminish because of prob bulkier new frames.

Hello,
Urban West is the UK distributor for Stomix EWI systems, in my experience it is always best to change the windows first prior to installing EWI, this will ensure that arounf the windows the EWI looks perfect rather than patched in, as taking the windows out post EWI installation will cause some interference with the render.
if this cannot be done then we have a hydrophbic tape which can be placed between the window and teh edge of the system stopping any moisture penetration and creating a barrier between the EWI and the window frame.
the tape is not expensive and can be sent in the post.
if anyone is interested we have some standard detail drawings which I can email out

Posted By: michaelcarringtonin my experience it is always best to change the windows first prior to installing EWI

Why not install the windows outboard - within the EWI thickness? Unless you're not thinking in terms of 200 (!50 minimum) EWI, which is thick enough to achieve that.

If installing new windows, there's no justification, nowadays, for leaving the windows deep-set, with skimpy EWI to the old masonry reveals. That's really obsolete.

If you spam commercially like this, expect to be criticised. What you've said here shows little understanding of modern-spec EWI practice - looks like still the old 50 thick mentality, as applied by the hectare to tower blocks etc.

Michael carrington - we have the internets these days - in fact we're on it right now - why not just post your standard details here for discussion rather than offer to mail them to selected individuals?

(yes we are interested).

Fostertom - Sorry, it's actually now called marmox thermoblock (some competition for foamglass perinsul):
http://www.marmox.com/en/index.php?page=products&proid=61

michaelcarrington I'm sure you have much valuable experience to offer - why don't you join in as a respected contributor, like many other trades people on here, without overtly plugging your wares - and let trade come your way naturally by virtue of reputation. 'Be a farmer not a hunter'.