Corner Window Post Insulation

windyboy

Hi,
Builiding an ICF house and engineer is designing some steel corner posts 90mm x 90mm. We hope to install timber alu-clad windows. One supplier suggested stuffing insulation like rock wool down the corner post to help reduce cold bridging. I would have thought by compressing the rockwool you would loose the effectiveness of the insulation. Just wondering has anyone done this. I was thinking if I cut a square section of rigid polyeurethane to push down and fill the post.

Thanks,
windyboy

CJhaughey

Cold bridging will occur where the heat is transferred through the material in this case the steel and inside.
Stuffing the centre of the square bar will do very little to combat cold bridging, it might stop the movement of air within the post but the problem of CB will remain.
It sounds like a bad detail to me.

Mellor

I agree with CJ.
The bridge is through the steel, filling the inside will do nothing (or very little).

Paulyh

i agreed with the others........the two window frames should meet at the corner with the steel post in the internal face of the frame. therefore the steel would not be exposed at all.......and no problem.
but if this is not the case then somebodt f**ked up with the detailing :eek:
the only thing i can think of, without actually seeing it, is fixing an insulated cladding piece to the outside of the steel post where it is exposed on the outside. but this would have to be done very well to look anyway acceptable, and will also add to the bulkiness of the corner which takes away from the whole idea of having a nice corner window.

Graaaaa

The likes of Keystone and IG do cornerposts with their lintels practically off the shelf, including top and bottom plates. It's all a matter of where exactly you position the post in relation to the cavity. Give them a call for technical advice - they may be more cost competitive than a separate lintel and post.

Naturally some sort of insulation and/or cladding will be required too. Maybe a high quality window manufacturer has a custom solution? I've seen these slender glazed corners in architectural publications and always wondered how they did it - possibly cantilevered beams are used instead of lintels, negating the requirement for a load-bearing corner post at all? Talk to your engineer about alternative structural designs.

Jimbo

Graaaaa wrote: »

The likes of Keystone and IG do cornerposts with their lintels practically off the shelf, including top and bottom plates. It's all a matter of where exactly you position the post in relation to the cavity. Give them a call for technical advice - they may be more cost competitive than a separate lintel and post.

Naturally some sort of insulation and/or cladding will be required too. Maybe a high quality window manufacturer has a custom solution? I've seen these slender glazed corners in architectural publications and always wondered how they did it - possibly cantilevered beams are used instead of lintels, negating the requirement for a load-bearing corner post at all? Talk to your engineer about alternative structural designs.

Yea, some steel lintel manufacturers do cantilever lintels especially for corner windows but of course there's extra cost when you dont have a supporting column.

windyboy

The engineer is going to specify extra rebar to be placed above the window openings to form lintels within the 150mm concrete ICF cavity and there is a special header and buck stop with an edge the window sits up against. See attached pics.

The advice I got was the following in blue

When using a wider say 90 mm metal post I would advise

- moving the window position to create a say 30 mm gap between post and alu which would be filled with insulation.

Rockwool is good because you can cut and fit to post and use the alu corner to compress/hold in position.

- filling the post with an insulation material

A pumped foam insulation would do a good job as it would be easy to ensure that the full cavity was filled. You could also use a rockwool or beads.

- moving the window out will mean that the post will ahve to clad on the inside. I would leave a sufficient gap of say 20mm-30mm for insulation ( rockwool) between the cladding and the post.

It is of course very important to ensure that a completely air tight bond is achieved between the window frame and the metal post/wall. We use taping and sealing products form both Ecological Building Systems and Siga.

I'm not sure about setting the window off the post though, as this would increase the width of the post, and obscure the view more. Can you guys advise what alternative insulation products are out there which are thin and can be dressed as a DPC would be?

Thanks.

Graaaaa

Matbe if you are using thermally broken window frames then the post can be fitted tight, and only the two external faces of the post need insulation and cladding (thin aluminium flashing folded to shape for instance, and powder coated to match/contrast as you require)? I agree with previous posts, I don't see a huge benefit in filling the centre of the post with insulated foam... will think about it more, I did it once but it was a 193mm circular section protruding through a flat roof - different kettle of fish.

Rigid insulation has slightly higher thermal properties than rockwool, so slightly thinner piece required - can't see that it will make a huge difference in this case though.

Nick Elsulphide

If you want the corner to be thermally robust treat the steel support as an independent of the windows and insulate it accordingly. If you try and keep it concealed within the line of the windows it is virtually impossible to install adequate insulation. I have yet to see an Irish architect provide what I would regard as a robust detail when the structural support is hidden within the plane of a 115mm window frame. Cornerwindows of this type are very rare in Passiv houses for this very reason.

Ideally you should cantilever the wall which will allow the window manufacturer to install a non-load bearing insulated post.

I recently viewed an installation of composite windows (indigenous manufacturer) where structural steel posts were clad in nothing more thena plastic sleeve. It satisfied the aesthetic requirement for nice clean lines but you canimagine how it would show up on an FLIR.

Mellor

Nick Elsulphide wrote: »

If you want the corner to be thermally robust treat the steel support as an independent of the windows and insulate it accordingly. If you try and keep it concealed within the line of the windows it is virtually impossible to install adequate insulation. I have yet to see an Irish architect provide what I would regard as a robust detail when the structural support is hidden within the plane of a 115mm window frame. Cornerwindows of this type are very rare in Passiv houses for this very reason.

I agree with Nick here.
If you want to have the post well insulated, its going to be bulky. If you want it to be streamline, then is going to perform less well thermally.

Ideally you should cantilever the wall which will allow the window manufacturer to install a non-load bearing insulated post.

The best solution for corner windows is a cantilever. In my opinion, its the only way to do corner windows. They preform better, and look better.
But if you are cantilevering the wall above, then an insulated post is not required. (obviously, depending on window type)

I recently viewed an installation of composite windows (indigenous manufacturer) where structural steel posts were clad in nothing more thena plastic sleeve. It satisfied the aesthetic requirement for nice clean lines but you canimagine how it would show up on an FLIR.

Sadly, i've seen it done this way more than any other way.

soldsold

Any details on how to cantilever the wall on a standard cavity wall? I know it will depend on the house design but is there a general guideline “i.e. RSJ/ rebar, etc of x size and length is used normally”?
I have 4 corner windows planned in my extension.

Carlow52

soldsold wrote: »

Any details on how to cantilever the wall on a standard cavity wall? I know it will depend on the house design but is there a general guideline “i.e. RSJ/ rebar, etc of x size and length is used normally”?
I have 4 corner windows planned in my extension.

This is not a quetion that will garner an exact answer here.

I dont know if you understand how a cantilever works but the longer the 'overhang' and the greater the loading the deeper the section that is required.
it wont be done easily in a standard cavity wall.

Any solution will make maintaining good insulation very difficult, not just over the windows but for a substantial length of the wall also.

My advice is dont even go there.

However if you do decide to go there consider a solid 225 mm block up to window height and then a reinforced concrete ring beam all the way around, or a custom made steel frame. The insulation can then be either external or internal.

A continuous concrete beam or steel frame will work much better than 8 individual cantilevers

You will need structural advice.
Hope this gives u food for thought

soldsold

Thanks for the advice!

A continuous reinforced concrete beam seems like a good way to do this job if I can’t get a window that hides a vertical bar without a significant cold bridge.


Steve

Carlow52

soldsold wrote: »

Thanks for the advice!

A continuous reinforced concrete beam seems like a good way to do this job if I can’t get a window that hides a vertical bar without a significant cold bridge.


Steve

I was just putting ideas together and not giving advice:) Cant on b.ie:)

However glad to give u food for thought, think it through insulation wise and revert once u get to the next stage of questions.
Depending on the span of the over hang, the beam will be deep:) ie if a single story extension may be an issue