What EWI for 1930s solid brick (215mm) wall home

[Russell griffiths]

If your budget is stretched then I would re think Internorm, dearest quotes I had, and I have yet to hear from anybody who was happy with the fitters. 

 

If you look look at the third fitting option the windows are completely fixed to the brickwork. 

 

We used norsken they are in poole, 

[tanneja]

@Russell griffiths to be honest internorm with alu clad UPVC looks spectacular, and prices same or less than all other quotes we have had from Norsken / Rational / Schucco.  I'm sure its the concession to UPVC which brings it in below everyone else, but its a change we were comfortable to make. I managed to get myself mixed up on the diagrams, indeed 3 is inside the blockwork.  WHat relative thickness of EPS would be helpful on those returns?  One of the EWI guys said he could do that in 10mm, then have near 20mm render.  My concerns with that were whether 10mm would be worthwhile, and whether losing 30mm on the top and sides would then make the window look strange given the bottom would be larger by some degree (please note the walls will be in white render, window likely anthracite grey).

[Russell griffiths]

@tanneja we where looking at the alu clad upvc and had a couple of visits to the showroom, it wasn’t until the second visit that we noticed that the coloured wrap on the upvc does not extend into the open areas of the window, so in effect it was grey on the outside but when open you could see the white upvc in all the openings. 

 

If you know this cool bananas. 

[MikeGrahamT21]

13 hours ago, tanneja said:

@Russell griffiths Do you have the contacts of any suppliers/installers who might consider the south east?  Logically, if the heavy windows (triple glazed Internorm) can be held robustly and it doesn't threaten the airtightness over time of repeated opening and closing, the second and third options are clearly thermally best.  Neither EWI installer today would entertain anything other than the windows being entirely in the brick walls.  My builder likewise thinks I am crazy, I showed him pictures of the steel brackets used on some of the projects here, again thinks I am bananas.

 

@MikeGrahamT21 I must say I don't want to be worrying about the rigidity of any of the windows in their place, and the airtightness being compromised by any movement in the EPS.  I can't seem to find any brackets online.  Would you recommend them over a wood frame or a compact foam frame?  Did I forget to say, budget already stretched!

 

I don't think there will be many brackets available online for this, majority are custom made and welded on-site, or by a steel fabricator.

 

There is also as you mention the compactfoam, i've never seen this product but there are videos on youtube showing it being used for windows, so it must be pretty strong.

 

With regards to airtightness, as long as you have a flexible airtight tape from window frame to masonry, there shouldn't be any issues with slight movement.

 

If you don't hang the window right out, there will always be a thermal bridge, as you say will have 30mm EPS on it, but still a lot less than the rest of the building. Personally I'm keeping my windows where they are, and doing a return, and then using insulated plasterboard on the reveals internally to compensate.

[tanneja]

@MikeGrahamT21 This is likely the only option builders, EWI installers and window installers will tolerate, so seems like the compromise I will settle on.  I offer my sincere thanks for your opinion.

[Ferdinand]

30 minutes ago, tanneja said:

@MikeGrahamT21 This is likely the only option builders, EWI installers and window installers will tolerate, so seems like the compromise I will settle on.  I offer my sincere thanks for your opinion.

 

Another approach is to build a plywood box out into the insulation layer mounted on the wall, like a deep picture frame and mounting the windows in those.

 

F

[MarkyP]

my 60% outboard method also included going over the face of the window frame slightly with EPS. The windows are fine and included a monster 1200 x 2400 3g picture window which is very heavy (I recall installing only too well!) The brackets were/are rock solid, the EWI hasnt moved at all (nor did I expect it to). There are lots of ways to skin this cat, it's a quesiton of what you and your builder feel comfortable with. I've seen the compac foam method - looked neat - battens of compac foam securely bolted to the wall face in line with reveal to provide an insulated outboard structure to fix to and window sits in this. You could also fit a 50mm x 100mm timber batten to the bottom of the reveal to extend the structural sill out 50mm and sit the window partially on that, and use angle brackets to the side. You have to weigh up the stress and complexity of the solution with the gain, Therm models show that the cold bridge is reduced significantly by partially outboarding and even more by fully outboarding. But your renderer will also want a bit of reveal to play with to render in and up to your frame faces so if you have 90mm EWI then you might not get away with going much more than 50mm outboard. remember at this distance you should still be able to sit your window on the structural blockwork and just angle bracket the sides. You can also run metal flat from the side of the window to the side of the internal reveal. I'd also consider running strips of marine ply (12mm) as straight strap from side of window to inside of reveal as well, much reduced cold bridge. If I had my time again I'd use ply strips over metal brackets but my windows were a shade tight to allow a reasonable thickness of ply. Dont lose too much sleep over this detail - the EWI will be a huge improvement, this is marginal gains stuff now though always do what you can where you can do it, and within reasonable cost.

[joth]

On 30/07/2020 at 22:14, Russell griffiths said:

I would re think Internorm, dearest quotes I had, and I have yet to hear from anybody who was happy with the fitters. 

 

Fwiw, while not entirely ecstatic I've found a few people that weren't unhappy with their install: (these are all via ecohaus. I'll give my own feedback in a few days....... ?)

 

https://forum.buildhub.org.uk/topic/1529-connecting-window-frames-how/?tab=comments#comment-20728

 

 

 

https://forum.buildhub.org.uk/topic/3238-passive-window-recommendations-please/?tab=comments#comment-50364

[tanneja]

My sincere thanks all.  We are still asking some other companies too, but struggling to get prices back, or beat out Internorm quote.

 

It seems that a 50mm wood frame approach would bring the U value around the window opening to 1.0, where if we made a frame with 50mm of compacfoam (cf200, not done any calcs to confirm it is capable of supporting half of the near 100mm deep windows) then the U value goes down to 0.6.  Not sure what low conductivity fixings you can use to attach a compacfoam frame to the masonary.  I see the cost of the compac foam to be about £1200.

 

Alternatively we have the EPS overlap the 110mm frame by 20mm, then have 20mm render (so 40mm in total) which brings the outer perimeter to around 0.84, with the window entirely held in the masonary.

 

I understand these are likely very minimal gains thermally due to the small surface area involved, my main reason for still investigating this is one comment saying i could be inviting window consensation unless bringing up the U value where the window juntions with the wall.  Is condensation a real concern if the U value is 1.8 for the line around the window perimeter?  Would the 20mm EPS over the frame be the most pratical?

[Ferdinand]

If you are well ventilated that should help control your risk of condensation, which is water vapour condensing from a wet atmosphere on a cold surface.

[Ferdinand]

1 hour ago, Ferdinand said:

If you are well ventilated that should help control your risk of condensation, which is water vapour condensing from a wet atmosphere on a cold surface.

 

In practice a lot of people with MVHR find that their washing dries so well inside that washing lines outside are redundant.

 

Control condensation *THAT* well for many.

Edited August 2, 2020 by Ferdinand

[Russell griffiths]

Are you sure you will have 20mm of render, I was under the impression that the render used on eps was just a thin coat with mesh imbedded, probably ending at about 7-8mm. 

[tanneja]

Thanks very much @Ferdinand, if condensation isnt an issue, that is great to know. I'm looking back at a CF200 external cill option to have the window set 40-50mm proud, going to call internorm fitters tomorrow to ask what their install method would be (velfac have metal window mounts that attach on each edge of the window).

 

This is the online Velfac install video, they say render finish of the reveals should be complete before install, where my builder and ewi installer said the opposite. Watching the Velfac videos, once installed you see all the frame, no render over the top or sides as was suggested to me was the way all windows go in.  If Velfac videos are the standard procedure, would that mean having EWI done prior to window installer survey / measurements? What is the praticality of that happening while we are living in the orginial (not extended but having EWI and windows), will we need to have plywood window coverings in the phase between the EWI and window installs?

[tanneja]

2 minutes ago, Russell griffiths said:

Are you sure you will have 20mm of render, I was under the impression that the render used on eps was just a thin coat with mesh imbedded, probably ending at about 7-8mm. 

You are right of course @Russell griffithsit is a thin coat. Looking at the velfac install thought I dont think the ewi would want to go over the frame and impact the window aesthetics.

 

If the metal fixing elements are the same as used by velfac, where they protrude back into the house to be attached to the masonary, then as long as there is a structual cill capable of holding some of the weight of the window (like a structured foam maybe CF200 that comes up on forums), it feels quite simple to have the window sit partially in the EWI layer and the attachments all will marry up with masonary.  It seems like the best practice would be do EWI first, window install second.  Complication is us living on site during this.  What would you advise? 

[Mr Punter]

If you are having Velfac outward opening windows where the sashes are the same size as the frame you need to render first and fit the window within the render - normally 10mm gap all round that is sealed with Compriband.  Otherwise they would not open.  Many other windows you render up to the frame or a render bead that butts to the frame as the sash is smaller than the frame.

[tanneja]

@Mr Punter ok, so if one were ordering tilt and turn (inward opening), would standard install be to render partially over the outer aluminium frame?  The internorm we have been considering is the KF520 which is sash-less externally, the glazing is the sash.  While you could overlap the external frame with render, I was curious whether this is the done thing, perhaps this velfac install was the preferred method regardless of opening system.  My apologies for being so green with this.

[tanneja]

For what it is worth, the best solution feels like the wood frame approach, probably 50mm deep (planned 100mm deep EPS), with then having the EPS overlap the sides and top of the frame by 20mm (you can ask for the Internorm window to have XL sides and top which are 20mm wider frames than the bottom, meaning when you then bury that 20mm of those sections, the exposed frame amount looks the same both sides, top and bottom).  If the windows can be fit to the front of the wood frame in this way, I see that gets the perimeter U value down to about 0.77 which is close to the internorm window itself.

 

Speaking with various internorm sellers, seems they can fix the windows either by direct fixing screws through the frame, and / or using anchor straps that can be attached to the inside window reveal using screws and packers as per the Velfac video I linked, I would probably request both to ensure a robust attachment.  Only small concern is that the internal frame fixing position for the Internorm is around the middle of the frame, so about 50mm from the front of the frame, and so could line up with the intersection of the wood frame with the masonry, which presumably isn't an ideal fixing position for the through frame mounting screws.  I guess for now I would make the 50mm boxes and the fitters can micro adjust the depth of the window relative to the front of the box, based on what they are presented with.

 

For anyone with experience, I would use marine or structural ply for the boxes?  Layer up 2 thickness of 25mm I assume to get to 50mm depth?  Would we use metal fixing screws to attach to the masonary?