Window board installation cavity

[mkb123]

Hi Everyone,

Attempting first ever DIY projects after having some insulated plasterboard installed. About to install new window board as the old one no longer fit, but it left a hole where it was embedded in the wall. Do I need to fill this for any structural/insulation reasons or can I just cover it with the new board?

If I need to fill what should I use? I’ve seen contradictory info about what to use for external walls ie some say bonding is a no. Would some expanding foam do the trick?

It’s 35-60mm deep as it goes along.

Any help great greatly appreciated!

 

[^woody^]

Your window board should be recessed in to that gap

 

[MrsRenovator]

Just wondering why you haven't removed the plaster reveals and insulated them as well?

I've done quite a bit of experimenting with internal insulation, and I insulate everywhere I can. So I fill every gap I find with expanding foam, and put a layer of left over insulation or even 10mm XPS under the new window boards.

Traditionally window boards are inset under the plaster and have 'horns’ at the sides where they overhang the window reveal. But it's fashion really. You can do what you like. As long as your new boards are fixed down to prevent curling/warping they will look fine with judicious use of caulk.

 

[mkb123]

Just wondering why you haven't removed the plaster reveals and insulated them as well?

I've done quite a bit of experimenting with internal insulation, and I insulate everywhere I can. So I fill every gap I find with expanding foam, and put a layer of left over insulation or even 10mm XPS under the new window boards.

Traditionally window boards are inset under the plaster and have 'horns’ at the sides where they overhang the window reveal. But it's fashion really. You can do what you like. As long as your new boards are fixed down to prevent curling/warping they will look fine with judicious use of caulk.

Thanks so much for your reply.

I haven't really done much myself yet, plaster reveals or otherwise. The plasterers came in, fitted the insulated plasterboard, plastered all 4 walls in the room (didn't do a brilliant job of either, I wouldn't say, took a lot of remedial work). Then it became clear that the old window board didn't fit anymore as the ins. plasterboard came out much further from the wall (obviously would have been 100x better to remove this before the plastering, but sadly I hadn't realised that would be the case). So I pulled the old window board out (was difficult as it was very embedded into the wall) and mist coated the new plaster. That's all I've done so far; please do reply with anything I should be aware of/do next.

I'm feeling pretty confident about being able to install the new board and fitting it neatly. It was just this big cavity I was feeling dubious about. As it's an external wall I wasn't sure if there were damp/insulation or structural issues I needed to consider before just filling it with whatever I had available (in this case bonding or expanding foam). It sound like you think filling the gap with foam and then installing the board in the normal manner would be fine?

Thank you for your help!

 

[DiyNutJob]

Cut notch and insert board.

 

[MrsRenovator]

Or.... don't bother cutting notch, and install board . Here's one I made from oak floorboards.