Deep cills

[Kernow]

New build ICF question
 

How has everyone got over the need for very deep cills when you have external wall insulation, or a large make up of horizontal cladding fitted.  I don’t really want to move my windows out to be flush with the wall. 
 

upvc cills only going up to max 180mm for a possible window choice, or 220mm for another.  What has everyone done?

ideally they’d need to be somewhere around 300mm 

 

I know we can get pressed aluminium cills, but how would these look with pvc windows?

 

Thoughts appreciated

[keith65]

I would fitted slate cills  and have a stub cill on the window mine are wood but it will work with UPVC

[ToughButterCup]

15 hours ago, Kernow said:

New build ICF question
How has everyone got over the need for very deep cills when you have external wall insulation, ...

 

Made our own cills.

Had to be careful about the detailing

 

This was the initial drawing.....

In the end I tucked the DPM underneath the window frame and secured it to the back of the window frame with a long batten. The outer frame is also sealed properly to the cill (sill).

Pulling the cill backwards (into the house) with a 120(ish) stainelss screw by pre-drilling into the back of the cill was quite tricky (for me anyway), but it compressed the seal extremely well.

The image misses the external membrane, and I'm sure I've missed a few details, but here's a start....

 

 

[Russell griffiths]

Why are you building an icf house and fitting plastic windows?

as far as I’m aware you will struggle to find upvc with a good enough u value, the frames are just not deep enough to get enough of a thermal break in them. 

Ive worked on 5 different new builds this year and everyone of them had aluminium clad timber windows. 

These also change your options on window location as the frames are so thick it takes up a big chunk of the reveal, which gives you a narrower cill. 

 

sorry but to me building a highly insulated house and putting in poor windows is a bad idea. 

[Adrian Walker]

20 minutes ago, Russell griffiths said:

Why are you building an icf house and fitting plastic windows?

as far as I’m aware you will struggle to find upvc with a good enough u value, the frames are just not deep enough to get enough of a thermal break in them. 

Ive worked on 5 different new builds this year and everyone of them had aluminium clad timber windows. 

These also change your options on window location as the frames are so thick it takes up a big chunk of the reveal, which gives you a narrower cill. 

 

sorry but to me building a highly insulated house and putting in poor windows is a bad idea. 

 

Agreed, however depending on the numbers, you can get an UPVC Passive House Certified window system - https://www.liniar.co.uk/upvc-windows/passivhaus/ 

[ToughButterCup]

Ermmmmm  Russ,  I think the OP mentions plastic cills only, not windows. ?. But the point you make about plastic windows and their low U value is spot on.

 

PS Woops: speed reading: Russel Griffiths is always right, should have learned that by now .....?

Edited December 4, 2021 by ToughButterCup

[Russell griffiths]

2 minutes ago, ToughButterCup said:

Ermmmmm  Russ,  I think the OP mentions plastic cills only, not windows. ?. But the point you make about plastic windows and their low U value is spot on.

 

PS Woops: speed reading: Russel Griffiths is always right, should have learned that by now .....?

You know it. 

[Gone West]

3 hours ago, Russell griffiths said:

as far as I’m aware you will struggle to find upvc with a good enough u value

You've not heard of Rehau Geneo profiles then.

[craig]

5 hours ago, Adrian Walker said:

you will struggle to find upvc with a good enough u value

 

Believe it or not but uPVC are actually better performing that timber alu clad windows, with approx. 5 chambers the frame value is better on a good profile (Internorm, Gaulhofer, Alu plast, Liniar) to name but a few systems.

 

 

[Kernow]

8 hours ago, Russell griffiths said:

Why are you building an icf house and fitting plastic windows?

as far as I’m aware you will struggle to find upvc with a good enough u value, the frames are just not deep enough to get enough of a thermal break in them. 

Ive worked on 5 different new builds this year and everyone of them had aluminium clad timber windows. 

These also change your options on window location as the frames are so thick it takes up a big chunk of the reveal, which gives you a narrower cill. 

 

sorry but to me building a highly insulated house and putting in poor windows is a bad idea. 

We haven’t fully decided what we are putting in in terms of window yet. But u values between a quality pvc and alu-clad wood aren’t that different from what we have been looking at. 
 

Definitely not planning on putting poor performing windows in

[Kernow]

9 hours ago, ToughButterCup said:

 

Made our own cills.

Had to be careful about the detailing

 

This was the initial drawing.....

In the end I tucked the DPM underneath the window frame and secured it to the back of the window frame with a long batten. The outer frame is also sealed properly to the cill (sill).

Pulling the cill backwards (into the house) with a 120(ish) stainelss screw by pre-drilling into the back of the cill was quite tricky (for me anyway), but it compressed the seal extremely well.

The image misses the external membrane, and I'm sure I've missed a few details, but here's a start....

 

 

Interseting, I’d not thought about making our own fills up. 
What material have you made them from? Timber?

 

 

 

23 hours ago, keith65 said:

I would fitted slate cills  and have a stub cill on the window mine are wood but it will work with UPVC

 

Yes slate is an option, did you increase the insulation height on the inside to reduce the potential cold bridging?

 

 

[keith65]

I cut back the front block to the depth of the cill left a gap of 25mm to the insulation and concrete and then put airtight foam in then window sits over the joint. Then on the inside fit window board or slate cills as normal.