Bay window install

[Ben100]

Hi, I'm replacing my old bay windows and have questions about how the new ones should sit. The window sills on the new windows are shorter than the old ones, so the windows need to sit more forward on the brickwork.

 

This is the bay window space and new window.

 

 

 

 

 

Is the sill ok to sit like this below? And is it ok for the middle of the window (not recessed) to return to the brickwork?

 

 

 

 

 

 

Or does it need to sit more like this?

 

 

Thanks!

Ben

[JohnMo]

What's going inside the house or within cavity with respect insulation?

 

Ideally the window should straddle the insulation

[Gone West]

The sill should overhang by at least 30mm. It doesn't look as though the sills are deep enough.

[Ben100]

35 minutes ago, JohnMo said:

What's going inside the house or within cavity with respect insulation?

 

Ideally the window should straddle the insulation

I'm planning to fill the void with foam. S it looks like the window needs to sit back a bit more. 

[Ben100]

26 minutes ago, Gone West said:

The sill should overhang by at least 30mm. It doesn't look as though the sills are deep enough.

Yeah, I was thinking that. Maybe I need to replace the sill and sit the entire window back a little.

[JohnMo]

17 minutes ago, Ben100 said:

planning to fill the void with foam.

I would consider EPS beads, they will self drain any water away and gravity will fill any voids fully.

[JohnMo]

The window really needs to straddle the insulation

 

Some notes on here

https://nhbc-standards.co.uk/6-superstructure-excluding-roofs/6-7-doors-windows-and-glazing/6-7-3-in-service-performance/#:~:text=In cavity masonry walls%2C doors,layer of the external wall.

[ETC]

Get rid of that shit cement strap pointing for a start otherwise you’ll end up with spalled brickwork.

[Gus Potter]

4 hours ago, ETC said:

Get rid of that shit cement strap pointing for a start otherwise you’ll end up with spalled brickwork.

No mincing from ETC here on the pointing and I agree.

 

6 hours ago, Ben100 said:

The sill should overhang by at least 30mm. It doesn't look as though the sills are deep enough.

NHBC recommend 40mm of a drip which is what I spec as sometimes the render etc are a bit out of line.

 

Your starting point is to work out how you are going to insulate the reveals, cills and head of the window. Then make sure you can fix the window securely and last make sure it is all weather tight with DPC etc.

 

It's OK to mount a window on the outer leaf. Velfac windows adopt this principle. Have a look at their detail.

 

 

[Ben100]

15 hours ago, ETC said:

Get rid of that shit cement strap pointing for a start otherwise you’ll end up with spalled brickwork.

Yep. It’s on the list of jobs.

[Ben100]

So I guess my two options are to get a longer sill and sit it over the insulation or install it on the outer leaf of brickwork.

[Gone West]

3 hours ago, Ben100 said:

So I guess my two options are to get a longer sill and sit it over the insulation or install it on the outer leaf of brickwork.

Yup, if you get a deeper sill there will be a little less thermal bridging but it depends on whether it's worth it for you.

[Iceverge]

Have you cavity insulation only on and agenda?

 

If so long sill and straddle. 

 

If there is internal insulation you can do whatever you like provided you deal with and drips at the window head correctly.