Preparing openings ...

[syne]

After reading, lots. im still unsure whats a good idea and whats not.

 

 My new openings are bare at the moment.

Block inner skin,

150mm cavity -full fill eps bead-

Block outer skin -to be rendered-

Brick window detail on/below sill.

Cavity closers still to go in

 

Current windows are set back varying amounts and im looking to replace these later and equalise the setback at the full brick depth. 

 

What should i be doing before measuring And ordering?

 

Is there a good way to suppurt windows that are essentially going to be sat above/ within the cavity?

 

 

 

[DannyT]

With regards to your last question. Some people build a plywood liner on the inside, blocking off the cavity and maybe giving the window something to fix too.

something like the link below.

 

https://forum.buildhub.org.uk/topic/19031-200mm-cavity-some-questions/

 

If your windows sit against the back of outer skin then they should be slightly bigger than opening in my opinion but the inner skin should also have larger opening than the outer to allow windows to be fitted from inside.

 

Windows fitted into the opening should have maybe 4mm a side for allowance. 
a 1200mm window opening, 1192mm window.

 

Edited November 8 by DannyT

[joe90]

44 minutes ago, DannyT said:

If your windows sit against the back of outer skin then they should be slightly bigger than opening in my opinion but the inner skin should also have larger opening than the outer to allow windows to be fitted from inside.

I did this and it’s called check reveals, made the fixing of windows easy to the back of the outside wall, windows are within the insulation area (my reveals were angled as well to give better light penetration).

[bmj1]

On 08/11/2024 at 19:50, joe90 said:

I did this and it’s called check reveals, made the fixing of windows easy to the back of the outside wall, windows are within the insulation area (my reveals were angled as well to give better light penetration).

 

I also did checked and splayed reveals at the front of our house, gives a nicer visual externally by hiding some of the window frame, and it's a nice detail internally with the angled reveals.

[syne]

 

Thanks all, so with an arrangement as above, the window isnt on the osb?

Is the osb just to give a soilid fixing for plasterboard?

 

Im planning on setting my windows in the cavity but they're going to have to sit on the outer leaf a little bit; 20mm or so, as the brick work isnt neat or square enough.

 

If i've got this wrong let me know but my plan of work is;

 

Cavity closers,

Windows on straps from inner leaf,

Compriband on the edges,

Ply box that butts up to inner frame,

Airtightness tape on frame to ply,

+Airtight on ply reveal to walls?

Plasterboard the reveals 

Then later..

Full fill eps beads,plaster

Window board, sealant ect..

 

 

[Iceverge]

21 minutes ago, syne said:

Thanks all, so with an arrangement as above, the window isnt on the osb?

 

Window bolted to the external leaf and resting on the concrete window sill. The windows is set behind the external leaf. 

 

OSB is to close the cavity, and provide Airtightness. It's a completely independent box to the window. Just joined by AT tape. 

 

It's foamed and AT painted to the inner leaf and the cavity is completely filled with EPS blown beads. 

 

I would alter the method I use the next time by screwing J beads to the windows. 

 

Do you have any pics of the openings as they are today? 

[Iceverge]

Also from a thermals perspective I would add EPS to the exterior of the frames sandwiched between the external leaf and the frame. 

[crispy_wafer]

23 hours ago, Iceverge said:

I would alter the method I use the next time by screwing J beads to the windows.

With the OSB/Ply being used to close the cavity and it only being fixed to the internal leaf, would this allow any flex in the board at the window frame, or is the OSB rigid enough over the width of cavity?  What would the J bead be used for?