Minimising Thermal Bridge - Bay Window

[IGP]

Hello,

 

I’m looking to insulate my bay window which I’ve take back to brick to find a stone curved cill. The bay window is double brick, no cavities unlike the rest of the house. 

I’m planning to have triple glazing throughout the house, but I’m unsure of how to tackle insulating the bay window, especially when it comes to the stone cill as that’s surely a massive cold bridge. 
 

Any suggestions?

 

[SteamyTea]

10 minutes ago, IGP said:

Any suggestions

Can you get rid of it when you get the triple glazing put in?failing that, can you get insulation on the outside, basically box it in.

[Redbeard]

Insulate the lot with rigid wood-fibre. You can probably wrangle (3-4) layers of 20mm round that curve. Finish in lime. I find the Baumit products very easy to use if you are not used to lime.

[Radian]

If you wish to retain the cill, how about making a window seat but instead of using it to store the usual clutter, fill the void with EPS beads. The top edge of the cill will need to be lapped with rigid insulation to break it from the window frame and inside face.

[Dave Jones]

If the adjoining walls aren't insulated to the same level not sure theres any point ?

 

Same with triple glazed, save the money you will never get a return from it.

[IGP]

The all other walls are cavity walls filled with EPS beads, and I’m going for triple glazing as I intend to live here for a very long time, not for a a financial return. 
 

I like the window seat idea @Radian, thanks! 

[SteamyTea]

The problem seems to the that the window frames will be sitting on the cold concrete surface.

The inside part of the cill has a relatively small surface area, but the outside part is massive, and cold.

That means the frame will also be cold.

The frame will have a relatively large area when combined with the cold cill.

I am not sure how low a window frame can get thermal transmittance, but will have to be good in both the vertical and horizontal planes.

[Radian]

14 minutes ago, SteamyTea said:

The problem seems to the that the window frames will be sitting on the cold concrete surface.

The inside part of the cill has a relatively small surface area, but the outside part is massive, and cold.

That means the frame will also be cold.

The frame will have a relatively large area when combined with the cold cill.

I am not sure how low a window frame can get thermal transmittance, but will have to be good in both the vertical and horizontal planes.

That's why I suggested creating a deliberate thermal break for the frame to sit on. Most frames will have a break that requires the frame to be located such that the inner section is stat back on an insulated part of the structure. In this case that might not be possible but it only needs some thin insulation material to create a thermal break for the frame resting entirely on the cill. A rebate might also be cut in the concrete cill to better accomodate this.

[IGP]

So when the window is removed, cut a rebate out on the internal side of the cill and place something like compacfoam to fill the rebate before installing the new window? 

[SteamyTea]

1 hour ago, IGP said:

So when the window is removed, cut a rebate out on the internal side of the cill and place something like compacfoam to fill the rebate before installing the new window? 

Or just totally replace it with something thermally better.

I am sure @craig will know of a suitable product.