What steel sheet to use

[tony1851]

What do you doubt Tony? I may have made a mistake somewhere but I think the basic nunbers are right.

I was going to add a bit about the geometry but decided to keep it simple.

I don't doubt your figures on the relative heat loss between steel and timber. But if I've read the OP right, he's putting a thin (3mm) sheet across the top of the cavity, presumably to spread the load over both skins. If so, only the edge of the steel will
show internally and externally (ie a surface 3mm x 100mm). Even though there will be a high heat loss through that little bit,
it's only over a very small area relative to the beam and wall as a whole.
Just my two-cents worth
PS just noticed JDs post re condensation; you may both be right as it will tend to chill the blockwork around it.
Maybe I've been talking out of my ar$e, which isn't unknown (except when it comes to Brexit).

 

[trevorbayliss]

Well the plate will sit inside the block by 10mm. so you have mortar. then you have plasterboard over that. Plus i may be also using extra internal kingspan of 25mm, so i really don't think the heat loss / condensation will be an issue.

 

[endecotp]

It is spanning the cavity. It's called a thermal bridge.

 

[John D v2.0]

i really don't think the heat loss / condensation will be an issue.

What you say sounds plausible but if you want to be sure at the design stage rather than later, you can do a condensation risk analysis on your thermal bridge. Plenty of tools online to help there.
However if you do go for kingspan internally, make sure there's a good vapour barrier on the warm side and that warm damp air can't get through to the cold side.

 

[^woody^]

Its a thermal bridge, it is a condensation risk, and it is a crap design. But it may be ok and you may not end up seeing and shading or staining.

 

[trevorbayliss]

Ok, so this will probably be what i need. The inner skin has a concrete lintel cut, so a standard padstone. The outer brick may have a 3mm bearer plate on this brick only, so no bridging.

I just thought using a bigger plate would be a better idea to spread the load more evenly.

I am making my bearing area bigger though as i want more timber on display. So 250mm bearing each side.

If you are worried about the thermal bridging on the 3mm plate, what about the bridging through the oak purlin ?