RSJ with top plate support for 400mm cavity walls - cold bridging?

[NandM]

My SE has specified using steels plates to give the RSJs the width they need to support the 400mm external facing cavity walls.  Would the external-facing leaf of bricks cause a cold bridge via the top plate? As the RSJ's are within the thermal envelope - except for the support above, I'm wondering what can be done to minimise it....if it is an issue. (Beams 1, 3 & potentially 5)

 

[Dave Jones]

We have a 6M opening, I had the SE spec vertical fillets at 600 centres that were welded to stich the outler L shaped and internal box section steel. That was can fill the gaps with PIR.  Overboarded with 25mm PIR backed plasterboard. Best compromise I could come up with and still guarantee zero flex in the middle to pinch the doors.

[Mr Punter]

I have used Marmox blocks for the first course on top of the steel plate.  Probably better than nothing.

[Conor]

Ask the SE if the beam can be moved in so it sits over the inner leaf, and the plate extension out to take the outer leaf. This will greatly reduce the crossectional area that's bridging. The plate will likely need to be thicker.

[ETC]

4 hours ago, Conor said:

Ask the SE if the beam can be moved in so it sits over the inner leaf, and the plate extension out to take the outer leaf. This will greatly reduce the crossectional area that's bridging. The plate will likely need to be thicker.

Or change it to two beams - one for each leaf.

[George]

25mm thick top plate! Bloomin' heck.

 

Switch to two beams, one for each leaf. Put in a row of thermoblocks if you want but it's not a major cold bridge so long as you can get 50mm PIR around it.

[Canski]

44 minutes ago, George said:

25mm thick top plate! Bloomin' heck.

 

Switch to two beams, one for each leaf. Put in a row of thermoblocks if you want but it's not a major cold bridge so long as you can get 50mm PIR around it.

I had a design like this for mine. I switched to 2 beams bolted together because they were easier to handle on my own and less cold bridging.

[saveasteading]

7 minutes ago, Canski said:

2 beams bolted together

That's the most elegant solution, and easy to handle. then stuff all spaces with mineral wool. the heat transfer through he bolts is tiny but you could cap the ends if you wanted, to avoid a cold spot.

 

The bolts make the whole thing into one mechanism so it is stiffer horizontally.

[joe90]

Yes although I used concrete beams I used one per leaf so NO cold bridge

[mjc55]

On 01/03/2024 at 16:03, joe90 said:

Yes although I used concrete beams I used one per leaf so NO cold bridge

What was the opening size?

[joe90]

9 hours ago, mjc55 said:

What was the opening size?

Can’t remember exactly but about 3m