Spray foam on cold bridge steels

[NCXo82ike]

We have most of the steelwork up in our wraparound extension and loft conversion. 1905 mid-terrace, solid wall construction. We have picture frame steels sucking heat into the ground and steels bearing on to (and/or supporting) cold brick walls. I'm looking to minimise the impact of cold bridging.

 

The wraparound is brick and block with mineral wool cavity, pitched vented roof. The loft conversion is timber, vented cold roof (unfortunately necessary).

 

Priority 1 is to avoid condensation, priory 2 to reduce heat loss. No cold steel near bathrooms, but plenty near the kitchen in the wraparound.

 

The builder suggested PIR or mineral wool around the beams, but I worry if we insulate without a vapour barrier against the steels it will worsen interstitial condensation? I wonder if spray foam is a sensible way to do this, cutting the cold bridge with a continuous vapour barrier I can tape against other membranes. 

 

I've sent the horror stories but get the impression the issue is where critical ventilation e.g. cold roof is compromised by the spray foam.

 

Other relevant measures are:

-internally insulating solid walls (planning on vapour-open with thermactive plus wood fibre).

-windows uprated

-We'll be getting as airtight as reasonably possible

-MVHR system fitted which I will control based on internal humidity

 

Grateful for any thoughts- couldn't see similar in the forum surprisingly

Edited 3 hours ago by NCXo82ike