Internal window reveal details

[Barnboy]

My barn conversion is basically a timber frame inside of a thick stone wall.

I'm now looking at how I'm going to finish my plasterboard and insulation back to the windows.

I decided and purchased a long time ago some Spacetherm blanket to insulate the reveals with but can't come up with any solutions that I'm happy with for fixing everything in place nicely. 

Most of the reveals are splayed to some degree which isn't helping.

I originally thought of screwing a small angle to the edge of the frame to fix the outer edge of the plasterboard to and then nothing else until it met the timber frame, but the gap is a minimum of  400mm and I'm not sure the angle on the window would be that strong as the back of the plasterboard would only sit around 12mm into the frame, not giving much for screwing the angle into the frame with.

The original stone reveals were very uneven so with the original idea, I decided to lime plaster these to build them up to an even surface but this doesn't really give me anything solid to fix into either.

My other thought is to build an 18mm marine ply box, maybe pocket screwing the corners and trying to slide this in ontop of the breather membrane and insulation before wrapping the vcl over the front of it and fixing the plasterboard into the ply.

I'm not sure how well this idea would work, especially as I've got the reveals to do on 2 doors which are about 2.2mtrs tall and another glazed door surround  that goes up into the 1st floor, so is around 2.8mtrs tall. 

Has anyone any solution or ideas please ?

[markc]

As you don’t have a lot of window frame to play with how about PB onto adhesive foam on the masonry to give you more support, or even something like aqua panel instead of PB to minimise moisture creep from the solid wall 

[Barnboy]

47 minutes ago, markc said:

As you don’t have a lot of window frame to play with how about PB onto adhesive foam on the masonry to give you more support, or even something like aqua panel instead of PB to minimise moisture creep from the solid wall 

I'd thought about trying foam, but have never used it before.

I've got to get the breather membrane, Insulation and vcl in behind the plasterboard or whatever I use. I'm not sure that foam will bond to the membranes, or if it does will it stay held or will each layer gradually fall away from the next?

[jayc89]

Tape your breather membrane to the window frame, stick your insulation to that, run your VCL and tape that to the frame too, like you did the breather membrane, then PB. The thickness of the PB should hide the tape on the frame. 

[Dave Jones]

window is really set too far to the front, its way outside the insulation envelope. Prior to building the internal stud, i would have cut 100/150mm both sides and bottom of the reveal and put 100mm celotex and a ply box to frame the window. Then refit the window so its sitting in that insulated box you have now made. This leaves the lintel which you cant easily add depth to accommodate celotex and is the worst cold bridge of the lot. Aerogel make the best performing insulation for thickness that you can add to the lintel.

 

Lastly strap the window when refitting don't screw through the frame. 

[jayc89]

4 minutes ago, Dave Jones said:

window is really set too far to the front, its way outside the insulation envelope. Prior to building the internal stud, i would have cut 100/150mm both sides and bottom of the reveal and put 100mm celotex and a ply box to frame the window. Then refit the window so its sitting in that insulated box you have now made. This leaves the lintel which you cant easily add depth to accommodate celotex and is the worst cold bridge of the lot. Aerogel make the best performing insulation for thickness that you can add to the lintel.

 

Lastly strap the window when refitting don't screw through the frame. 

 

How would that work on the outside? Wouldn't you see the ply box, so would only work if it was being rendered etc?

[Dave Jones]

you cut the reveal enough to accommodate 80% of the frame so you  still have an external weatherproof surface to trim/seal the frame externally. 20mm is enough and really impoves the performance a lot. Compriband can be easily put all around the frame using the box method as well, lastly make sure to remove any packers used to level the window once its been securely strapped as these are a really good cold bridge as well.

 

It's all a bit anal I know, but there is little material cost and a lot of  manual labour but I consider it time well invested. 

[jayc89]

8 minutes ago, Dave Jones said:

you cut the reveal enough to accommodate 80% of the frame so you  still have an external weatherproof surface to trim/seal the frame externally. 20mm is enough and really impoves the performance a lot. Compriband can be easily put all around the frame using the box method as well, lastly make sure to remove any packers used to level the window once its been securely strapped as these are a really good cold bridge as well.

 

It's all a bit anal I know, but there is little material cost and a lot of  manual labour but I consider it time well invested. 

 

So, if I've understand correctly, in a 9" solid brick wall, you would remove the inner brick all the way around the reveal, fit your insulation/boxing back level with out outer brick, and site the frame half on the brick, half on the box (or whatever ratio you like)? Presumably the lintel would need extending 150mm beyond the boxing for structural support.

[Dave Jones]

pretty much but obviously not the header/lintel as its structural.  depending on the frame of course but as much as you can inside the now insulated box.

 

wouldn't worry about extending the lintel for a single brick as its still sitting on 2 more personally but you can if you want.

Edited February 3, 2023 by Dave Jones

[eandg]

35 minutes ago, Dave Jones said:

you cut the reveal enough to accommodate 80% of the frame so you  still have an external weatherproof surface to trim/seal the frame externally. 20mm is enough and really impoves the performance a lot. Compriband can be easily put all around the frame using the box method as well, lastly make sure to remove any packers used to level the window once its been securely strapped as these are a really good cold bridge as well.

 

It's all a bit anal I know, but there is little material cost and a lot of  manual labour but I consider it time well invested. 

How do you remove packers? There's one left on one or our doors on the external side of the airtight membrane but hadn't thought of removing it. 

[Barnboy]

3 hours ago, jayc89 said:

Tape your breather membrane to the window frame, stick your insulation to that, run your VCL and tape that to the frame too, like you did the breather membrane, then PB. The thickness of the PB should hide the tape on the frame. 

This is the layering I'm planning on, the problem I have is on how to secure the plasterboard .

[Barnboy]

2 hours ago, Dave Jones said:

window is really set too far to the front, its way outside the insulation envelope. Prior to building the internal stud, i would have cut 100/150mm both sides and bottom of the reveal and put 100mm celotex and a ply box to frame the window. Then refit the window so its sitting in that insulated box you have now made. This leaves the lintel which you cant easily add depth to accommodate celotex and is the worst cold bridge of the lot. Aerogel make the best performing insulation for thickness that you can add to the lintel.

 

Lastly strap the window when refitting don't screw through the frame. 

I like this idea, and if I wouldn't be so far into things I'd have done this, but as it is the windows have been in for a while and it would be major reworking of everything around them to be able to do this.

They can't come further in as any further in and the clay/straw filled cavity of the wall would be open and also our heritage people wouldn't have been happy as the appearance of the building would have changed.

[Dave Jones]

12 hours ago, Barnboy said:

This is the layering I'm planning on, the problem I have is on how to secure the plasterboard .

 

use megastick adhesive foam, really good stuff.

[Dave Jones]

14 hours ago, eandg said:

How do you remove packers? There's one left on one or our doors on the external side of the airtight membrane but hadn't thought of removing it. 

 

as long as the installer hasnt screwed through them and the frame is otherwise foamed/fixed in place just knock them out with a screwdriver and hammer.

[Iceverge]

How about woodfiber or phenolic board fixed direct on to the reveal. Then taped to the window and membrane and render or plasterboard over the top. 

 

[ETC]

Insulated plasterboard.

[jayc89]

On 03/02/2023 at 18:57, Dave Jones said:

pretty much but obviously not the header/lintel as its structural.  depending on the frame of course but as much as you can inside the now insulated box.

 

wouldn't worry about extending the lintel for a single brick as its still sitting on 2 more personally but you can if you want.

 

Along the lines of this;

 

 

Darker bricks being the outer face, lighter bricks the inner face. Inner face having been chopped out by approx half a brick's width.

 

Then insulate, and cover with OSB, to bring the inner face back flush with the outer, concrete screws through to secure the insulation and OSB, before installing the window, overlapping the outer facing bricks and the OSB and fixing the window to the OSB using fixing lugs?

 

 

Then insulate over the lintel once the window is fitted?

 

[Dave Jones]

that's it, i also cover the face of the lintel with insulation (100mm celtox same as i am putting on all our internal walls - solid 9") and then aerogel to the reveal of the lintel as its thin.