Suggestions for insulation around steel

[Furnace]

A pal of mine is having a small extension built to his cottage. I'm not sure thermal efficiency is the builder's or architect's strength, but before it gets covered up I thought I'd ask the assembled experts what they would suggest to mitigate cold bridging around the steel.

[Furnace]

These steel members apparently form part of the inner leaf of the cavity wall, sitting on the warm side of the rockwool. Since steel has a high thermal conductivity (and higher than the surrounding thermalite blocks) will that not form a localised cold area on the inside wall? Apparently the architect has not detailed any insulation around the steel which seemed odd to me.

 

[mike2016]

Wrapping the outside of that steel is key. Aerogel or this product possibly:

https://www.ecologicalbuildingsystems.com/product/phonotherm-200

Covered here:

 

Yours is not an i-beam though so may be overkill? But may give you ideas...

 

[Furnace]

13 hours ago, mike2016 said:

Wrapping the outside of that steel is key

That's what I thought. I'll pass on the suggestions. Definitely easier to deal with at this stage of his build than when it's all covered up and dripping with condensation.

[Iceverge]

If there is a continuous layer of mineral  wool as per the cavity at the outside of the steel it'll be fine. 

 

 

[Furnace]

1 hour ago, Iceverge said:

If there is a continuous layer of mineral  wool as per the cavity at the outside of the steel it'll be fine. 

Thanks @IcevergeApparently it's like this. I thought that the steel would be an easy route for room temperature heat to enter the rockwool insulation - certainly easier than through the thermalite blocks. The cavity is only about 100mm. Would it not make sense to put an additional insulation barrier in the highlighted areas? The steels are fully exposed to the internal air since there is glazing above the brick/blockworkshown. The glazing sits outside the steels.
I'd appreciate your thoughts/explanation since I'm not up to speed on this stuff and trying to help out a friend.
Cheers
 

[Iceverge]

No that'll be fine. 

 

Almost all the heat loss is stopped by the rockwool anyway. 

 

 

 

 

 

 

 

[Furnace]

@IcevergeThanks. Do the thermalite blocks assist much in insulation terms? The only difference I can identify is that the current wall buildup replaces a bit of thermalite with the steel.

Is rockwool a good option for a brick and block cavity wall? Any better alternatives he could use? Clearly better to do this to a high level now rather than later when the wall is closed up.

Thanks a lot 

[Iceverge]

13 hours ago, Furnace said:

Do the thermalite blocks assist much in insulation terms?

 

The difference in swapping to dense blocks is about 15mm of rockwool. The wider the cavity the less % difference the blocks it make. 

 

 

[Furnace]

Do you mean the difference between swapping from steel to thermalite blocks could be offset by only 15mm of additional rockwool?

Given they have a 100mm cavity, could they improve the performance significantly using an alternative material to rockwool?

Cheers

[Iceverge]

No sorry, thermalite Vs standard 7N blocks. 

 

Rockwool (other brands available) or EPS beads is practically the best solution here I would say. If they had wanted better performance then I would have widened the cavity. 

 

Given they're extending to a solid walled house going much better with insulation on a small extension won't make much difference due to all the thermal bridging interfacing with the old walls. They could put some insulated plasterboard on the internal walls including the "internal" wall that used to be the external one. 

 

All this pales into nothingness without a solid airtighess strategy mind you. 

 

Another option to materially improve things at this stage is decent triple glazing Vs double. 

 

 

[Furnace]

That's really kind.  I'll pass it on

 

Mark

[Osman]

Hi Furnace, I am in a similar situation as yourself, where I have Square Hollow Steel (stainless steel) installed to support a mono pitch roof above a bay window, I wonder if you could give an update on how you got around insulating the steel in your situation. My stainless steel is sitting in a 100mm cavity (brick outside and dense blocks inside). The brick will go up half way, then a window will be installed so part of the steel will be covered by the window frame. The build is in progress and I am seeking advice.  

[Nickfromwales]

If it’s already installed, not a great deal you can do now, other than drop the cavity insulation down into it.

 

The biggest issue here will be where the internal tongue of steel protrudes into the internal block leaf, so best practice here would be to use an insulated plasterboard to finish the block wall, making 1000% sure that nothing like dot & dab (board adhesive) etc is in contact with the steel. 
 

Covering it externally will be of benefit, with perhaps Compacfoam or PIR, but without seeing a section drawing of where the head of the window ends up it’s a bit difficult to say much more.

 

Can you pencil up a sketch? Architect drawing for this detail? 
 

 

PS, I have hidden your duplicate thread to keep the replies in one place   

[Osman]

Thank you Nick for your response, much appreciated. Here is a picture, build has progressed, 1 of the steel columns has been wrapped with bricks on the 2 sides, the other 1 in the corner will have a window (bay window) turning around and UPVC frame/corner to hide the corner steel. 

Would there be a need for fire rated board rather than PIR/insulated plasterboard? the builder suggest to use PIR, but researching it says to use fireboard, I am more concerned about condensation and cold bridging. 

 

 

Edited 20 hours ago by Osman

[Nickfromwales]

11 hours ago, Osman said:

Thank you Nick for your response, much appreciated. Here is a picture, build has progressed, 1 of the steel columns has been wrapped with bricks on the 2 sides, the other 1 in the corner will have a window (bay window) turning around and UPVC frame/corner to hide the corner steel. 

Would there be a need for fire rated board rather than PIR/insulated plasterboard? the builder suggest to use PIR, but researching it says to use fireboard, I am more concerned about condensation and cold bridging. 

 

 

This isn't holding up any of the second floor is it? If not, I can't see any reason to introduce FR here unless the BCO has mandated it? #canofworms

 

A 'better' architect would have instructed you to thermally break the steels at their feet, but maybe not so much of an issue if they're in the cavity / cold spaces vs faced into the room.

 

I would reduce the size of the window to accommodate some tile backer type XPS insulation board, wrapping 4 sides around it to thermally break it; 6mm would be 'better than nothing', but 10 or 15mm better, 20mm if that doesn't wreck the look etc. Stick the XPS boards to the steel with a non-silicone mastic, leaving no pathways for cold air to convect (horizontal lines, joining at the 4 corners, two or three of, plus some extra blobs in between).

[Nickfromwales]

I assume the steels are all galvanised?