Insulating between bay windows, behind stone mullions?

[GlanMenai]

Hello! 

 

We are renovating our 1890 Victorian house. We have three bay windows (each with three windows) on each floor that we've recently replaced with wooden sash windows. 

 

Between the windows we have stone mullions that form the bay, and where the window meets the stone mullions there's a fist sized gap between each windows, which most definitely results in both heat loss and sound coming into the house. Apart from expanding foam, can anyone suggest anything for me to put into this vertical gap between each window, before I put the wooden trim on around the windows and then the paneling?

 

It's also fairly deep, the size of the sash boxing, so might something like rockwool work for this? Or is there anything that some can suggest that will do the trick to tackle both heat loss and sound insulation?

 

Many thanks!

[GlanMenai]

Just incase this is useful for anyone else, I decided to go with some SuperFOIL multifoil, as it seems I can do everything from; cutting it down, staple it to the window boxes, and stuff it into crevasses with ease - and I can even double it up if I've got leftovers. 

[NSS]

59 minutes ago, GlanMenai said:

Just incase this is useful for anyone else, I decided to go with some SuperFOIL multifoil, as it seems I can do everything from; cutting it down, staple it to the window boxes, and stuff it into crevasses with ease - and I can even double it up if I've got leftovers. 

 

My whole house is insulated with multifoil but please be aware that it relies on the air pockets between layers to be effective as insulation. Stuffing it into crevices may reduce drafts but it won't do a lot of insulating. It's also not the best sound insulation, which it not an issue for us (as we're in a very quiet spot) but may be for you. 

[GlanMenai]

Hey - thanks for that NSS - that's great, I can make sure that there's some air pocket between the SuperFoil and the stone mullions, and thanks for the heads up regarding the sound insulation. I can maybe combine the Foil with some Mineral Wool to stop that maybe?

[NSS]

2 minutes ago, GlanMenai said:

Hey - thanks for that NSS - that's great, I can make sure that there's some air pocket between the SuperFoil and the stone mullions, and thanks for the heads up regarding the sound insulation. I can maybe combine the Foil with some Mineral Wool to stop that maybe?

You may have misunderstood, the air pockets need to be between layers of the foil, not at its edges - see image below 

 

 

[GlanMenai]

But doesn't the product already come like that? The Multi-layer Foil Insulation SF19+ by SuperFOIL for example? I've got a sample pack from them and it has multi-layers that has air pockets? 

[NSS]

7 minutes ago, GlanMenai said:

But doesn't the product already come like that? The Multi-layer Foil Insulation SF19+ by SuperFOIL for example? I've got a sample pack from them and it has multi-layers that has air pockets? 

 

Multifoil generally arrives as a compressed roll that has to have room to expand to its effective state. If you cram it into uneven gaps will unlikely do so.

[GlanMenai]

Ahhh, I see what you mean - if kept compressed then it's not going to perform as it should. Fortunately, I think there will be plenty of space for it to expand to its final form - 'crammed' might have been the wrong word to use in my post, but I think it should be ok. And thanks again for the acoustic note, I'll try and get a combo of both foil and wool in there to dampen then outdoor noises.

[Mr Punter]

I think that mineral wool may be better.  Some of the foil stuff is flammable the sellers can make dubious claims about their insulative properties.