Reveal extension for secondary window

[Timberrrr]

Hi We're currently replacing the plasterboard on the inside of a hardiplank weatherboard external wall with a soundproofing system (acoustic insulation batts, resilient mounts, furring channel and 2 layers of soundshield or fireshield plasterboard).

Once we do that, the wall will stick out more than the window reveal. Is it okay to add an extended reveal onto the current reveal and then install a secondary aluminium window inside that? Are there any safety issues with this method?

We're trying to save time and money where we can, so we'd prefer not to take the current window out to construct a whole new deeper reveal.

The current reveal is maranti. Should we use the same timber or something else? One final question, is the reveal work done before the new plaster work or after? thanks

[Ronaldo451]

hi,

What's a 'secondary aluminium window'. Are you just making the walls thicker and so need to increase the width of the reveals?

If so, I had a similar situation when I relined rendered walls with gyprock and replaced the existing windows with others that had a narrower reveal than the originals - would have left a gap of 40-50 mm from the edge of new reveal to the outside edge of the new gyprock. I trimmed some timber to the width of the gap and screwed this to the sides of the reveal to give the window architrave something to be fixed to. This doesn't need to be a continuous length, just bits of scrap as they are going to be covered anyway.

I then got a piece of 3mm ply and cut into 4 sections to cover the four inside reveals, painted them to save getting paint on the window frames later and just glued them in place. Fixed architraves and its finished!

[Timberrrr]

hi,

What's a 'secondary aluminium window'. Are you just making the walls thicker and so need to increase the width of the reveals?

A secondary window is a noise reduction window with laminated glass. It sits, ideally, 100mm behind the existing window but inside the window frame. The air gap improves the noise reduction. At the moment there is only 70mm of reveal available, so I figured that as the wall will end up thicker, might as well extend the reveal and at the same time and get the 100mm air gap.

As I'm not sure how much the secondary window weighs, I thought it would be safer to nail an extended reveal onto the existing reveal on the inside rather than around the edge.

[echnidna]

Use a thin layer of silicon between the reveal and the extension

[Timberrrr]

Use a thin layer of silicon between the reveal and the extension

Good idea! For gaps, here and there, we were going to use a fire and acoustic rated sealant like Bostik Fireban One which is a polyurethane sealant or Fuller Firesound acrylic sealant. Would these be as good as the silicon?

[echnidna]

Sorry, don't know