Window Reveal In Cavity Wall

[Onoff]

Another one of my "started not finished" items from eBuild now revisited! Seems easier to address now I've actually got a floor to stand on and ceiling above my head!

 

So.....this is the bathroom window. A generic DG window (Britelite maybe, the house has a mix) set flush with the outside of the outer leaf of the cavity wall. The wall is a mix of  block, breeze and brick. Heavy, uneven, painted render externally.

 

 

As I'm battening, insulating and VCL'ing the walls it's really focusing how draughty it is around this window. It has glued on trim pieces but I can see elsewhere on another window the gaps all round have just been packed here and there with no foam or expanding tape around the edges. I added the blue foam to cut down the fraught along the bottom edge. I have no idea how the cavity is closed here btw but it is rendered. At the moment it's howling up through this cavity:

 

 

So the plan then is to line the reveal with this 27mm insulated plasterboard. 27mm is all I can put on the sides without making it look silly. I can double it up on the sill i.e. two bits of this stuff. I might need to remove the internal side trims or cut the board insulation to suit to get the side bits to sit square. If I removed them I could perhaps also fill the side gaps up a bit with foam then a sealant over the top.

 

 

Do I just "go for it"? Cut my plasterboard then squirt/coat the sill, sides and header with something sticky and gap filling then just push the boards on and weight/wedge in place until dry? Options I see are one of the plasterboard foams or Sikaflex EBT. Whatever I use has to stick to that salmon coloured foam on the back of the plasterboard. The reveal btw will later be tiled.

 

As to the VCL, you can see how I'm attaching it to the face of the battens - the green strip on the right, do I just stop it short of the reveal and rely on the sticky stuff? I could I suppose carry it on in and around the reveal but would need something to stick that to the sill then the pink insulation to the VCL. Maybe I'd be better lining it with the blue DPM material I used to come a metre up the wall? What sticks like the proverbial then to the blue DPM?

 

 

I'm not going for strict air tightness just making the best of a bad base job!

 

Cheers 

Edited November 9, 2016 by Onoff

[Onoff]

In a @daiking esque twist I can't say I'm overly happy at the rendering under the "lintel" in this reveal. It has a rather hollow ring to it. I'm assuming of course that there is a lintel there! Might have to remove and make good before I line it.

[ProDave]

While that cavity is open under the window, is it not a good opportunity to drop some lose fill bead type insulation in there? Keep pouring and pushing it down with a stick until you can get no more in? 
 

[daiking]

2 hours ago, Onoff said:

In a @daiking esque twist I can't say I'm overly happy at the rendering under the "lintel" in this reveal. It has a rather hollow ring to it. I'm assuming of course that there is a lintel there! Might have to remove and make good before I line it.

 

Theres only 1 solution to this, burn it down. Anything else is a fool's errand.

[Onoff]

1 hour ago, ProDave said:

While that cavity is open under the window, is it not a good opportunity to drop some lose fill bead type insulation in there? Keep pouring and pushing it down with a stick until you can get no more in? 
 

That's a good shout. EPS beads I guess you mean? There's not then going to be any damp bridging issues by filling it up?

 

Where to get it locally next.....

Edited November 10, 2016 by Onoff

[Onoff]

8 minutes ago, daiking said:

 

Theres only 1 solution to this, burn it down. Anything else is a fool's errand.

 

I won't use all the matches so I'll send you the rest of the box!

[oranjeboom]

On 11/10/2016 at 09:09, Onoff said:

That's a good shout. EPS beads I guess you mean? There's not then going to be any damp bridging issues by filling it up?

 

Where to get it locally next.....

Did you fill your cavity? I too need to do this for may of my windows. I think with EPS the risk of dampness is minimal.....but best to get the experts on here to confrim.

 

You may find that the cavity 'extends' out along the entirety of the wall down the the footings (likely i think) and that you will need quite a few beads...not just your average bean bag size! And pick a draughtless day....those beads will move like a ferrari if you even fart!

[Onoff]

1 hour ago, oranjeboom said:

Did you fill your cavity? I too need to do this for may of my windows. I think with EPS the risk of dampness is minimal.....but best to get the experts on here to confrim.

 

You may find that the cavity 'extends' out along the entirety of the wall down the the footings (likely i think) and that you will need quite a few beads...not just your average bean bag size! And pick a draughtless day....those beads will move like a ferrari if you even fart!

 

No I didn't fill it in the end. The cavity is so compromised by debris anyway.....

 

I'm just insulating as best as I can that wall with PIR. Even that's grief as to square the room off I'll end up with 50mm in the window corner tapering to over 100mm where the wet room corner is.

Edited December 15, 2016 by Onoff

[Crofter]

Just to add a wee question of my own to this thread...

 

I'm in the process of lining out the inside of the house with 50mm PIR boards. This will then have a vapour barrier placed on top, and battens on top of that to secure it and also to create the service void.

However at the window reveals I am planning on lapping the vapour barrier onto the frame directly, taping it onto the window frame, and then putting the PIR and plasterboard on top, with no battens and no void. The windows are set 150mm into the wall as viewed from inside (measured to finished wall surface). I think I will have to put the vapour barrier directly onto the frame as I need the depth of the PIR and plasterboard to hide the tape on the window frame.

 

Just wanted to check that it's OK to put the plasterboard directly on top of the PIR without any additional support? And, is it best to use plasterboard here or would it be better for any reason to use ply?

Finally- can I use the same method on the internal sill, i.e. it would end up supported on PIR (well the front edge could rest on a batten). My gut feeling is that if someone were to stand on the windowsill for some reason, their weight should be well enough spread so as not to crush the PIR, but then again some people are bigger and heavier than I am...

[Onoff]

I was pleasantly suprised at how solid feeling my lining came out. No apparent "compression" problems at all. It's all as firm as.

 

Mind you I'm using actual insulated plasterboard. The insulation seems denser than that in Celotex. You'll have to bond your plasterboard to the (foil face?) of the PIR, with what I don't know.