Cold Bridging of Steel for Structural Opening

[grahamA]

I'm concerned with regards to a steel that my SE / Architect have specified and its liklihood of causing a cold bridge. The steel sit on the inner leaf on one side and an outer leaf coloumn on the other side via a an 8mm bottom plate (and fabricated plated coloumn) to support the wall above (two storey extension). This is part of a corner glazing detail and bi-fold doors. 

 

I've kind of fallen out with my architect given the lack of details he has provided when it has come to the build therefore i don't hold out much hope getting an answer from him anytime soon, however i am trying! I have no sectional detail for this part of the build and therefore i am guessing somewhat as to what to tell my steel fabricator in terms of sizes. 

 

What options do i have to reduce or elimate this thermal bridge of the steel plate span over the cavity? I assume the bridge it will be similar to that of most catnic type lintels therefore am i making a big deal out of nothing? The large span worries me though. Should I be allowing more height in the steel coloumn section so i can install insulation / insulated plasterboard to the underside of the steel plate? Will that affect how the bi-folds / glaxzing is fixed? What about the top side of the plate / steel?

 

[Radian]

1 hour ago, grahamA said:

Should I be allowing more height in the steel coloumn section so i can install insulation / insulated plasterboard to the underside of the steel plate?

Yes. The door frames don't need a continuous contact with the steel. That would be a recipe for disaster as the flex in the steel would transfer load to the doors. So long as there's a lateral restraint provided by the fixings through insulation that would be fine. At a guess 50mm PUR between steel and frame and then insulated PB on the inside head of the opening. The aim should be to bring the steel inside the insulated envelope so you need to work out how to make space for insulation on the outside.

 

I'll show you a horror-show photo of the  6m span 'I' beam over this elevation containing sliding doors:

 

The 'I' beam has a 300mm welded 'foot' on the underside to carry the timber frame above. Nobody thought about how this would end up in the cold on the outside. I think this might qualify for the worst cold bridge of all time 😂

 

1 hour ago, grahamA said:

I've kind of fallen out with my architect given the lack of details he has provided when it has come to the build therefore i don't hold out much hope getting an answer from him anytime soon, however i am trying! I have no sectional detail for this part of the build and therefore i am guessing somewhat as to what to tell my steel fabricator in terms of sizes. 

 

Now when I complained of a similar case of 'to be designed by others' I was met by a frosty response from a certain member of the community. But this is what happens. The SE does the calcs to make sure it won't fall down, but rarely will they be thinking about the thermal performance. The lack of sectional detail ends up being resolved by the builder who's too busy thinking about how to get the quarter tons of steel into place. Now I've got the leisure time to study what happened, I can easily see how it could be improved and have described exactly that to you.

[grahamA]

Apprcieate the lengthy response, thank you! When you say bring the steel inside the insulated envelope, i totally agree but won't adding insulation between the steel / frame and on the inside head put the steel outside the envelope? I would have thought to bring it inside the envelope I would have to insulate outside of the frame over the edge of the lip and then around the top of the steel? Not sure how to acheive this though. Is using something like Maramox thermal block an option above the steel? 

[grahamA]

19 minutes ago, Radian said:

Now when I complained of a similar case of 'to be designed by others' I was met by a frosty response from a certain member of the community. But this is what happens. The SE does the calcs to make sure it won't fall down, but rarely will they be thinking about the thermal performance. The lack of sectional detail ends up being resolved by the builder who's too busy thinking about how to get the quarter tons of steel into place. Now I've got the leisure time to study what happened, I can easily see how it could be improved and have described exactly that to you.

Yes this is what i am experencing in. A lot of things seem to fall through the gap in the detail. The consequences of one detail affecting something else (thermal, asthestics, structural) is often overlooked by each profession. My builder just wants someone to tell him what to do so can't relay on design decisions from them.  

[Dan F]

https://www.armatherm.com/thermal-break-materials/

 

You need to design steels to use this though.