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