Steel lintel cold bridge - any solution?

[DannyG]

Hi Folks

 

We have a few large spans (5m) and my SE has specified steel lintels resting on the inner block leaf with a 10mm bottom plate spanning the 200mm cavity to the outer brick leaf.

 

I raised this with my architect as I'm concerned about it being a cold bridge and his reply was that it was standard detail and unavoidable.

 

Is this the case? I appreciate this is a large span and we might well be stuck without another option but I also think they're fed up with me querying everything so might just be fobbing me off 😳

 

On the smaller spans such as windows, the SE has detailed catnic thermally broken lintels. Before we sign off, is this the best option here? I've seen some threads talking about using prestressed concrete instead as it's much cheaper but I'm not entirely sure how that would work... would there also be a steel on the inner leaf and they're just not connected? If so, what's the general method of closing the cavity?

 

Thanks!

[JohnMo]

I challenged our SE on several issues, well worth it.  Sometimes a different slightly more expensive grade of steel, gets you a smaller size and fixes the issue. 

 

Could you add an internal or external mid span vertical support.  This reduces the work the lintel has to do, so size drops considerably.

 

Or batten the internal wall and add internal insulation to cover the cold bridge and the rest of that wall.

 

Many ways to get things to work.

 

We have a wall of glass and the steel holding the roof up was massive and somewhat killed our views.  A few challenges ended up with a more expensive steel frame in 90mm square section.  We now have very small sight lines around our windows.

 

[PeterW]

34 minutes ago, DannyG said:

We have a few large spans (5m) and my SE has specified steel lintels resting on the inner block leaf with a 10mm bottom plate spanning the 200mm cavity to the outer brick leaf.

Bifolds ..? What deflection has been specified ..? That’s your first issue with these big steels with welded plates, as is torsion rotation of the centre. They need to be a accurately propped with a slight upward camber then built in correctly. When all masonry has gone off you can remove the props. 
 

Also have you got a 200mm cavity or a 100m cavity and 100mm outer leaf as Catnic limit is 165mm cavity. You could also use catnics on the large spans but you would need to reduce the spans by 500mm. Tbh that’s a brick either end and not many people would notice. 

 

[Nickfromwales]

Battens and insulation on the internal faces will create the thermal break with relatively little impact and be quite effective. You could line the internal faces of the reveals with Compacfoam or Marmox to go belt n braces. 

[DannyG]

11 hours ago, PeterW said:

Bifolds ..? What deflection has been specified ..? That’s your first issue with these big steels with welded plates, as is torsion rotation of the centre. They need to be a accurately propped with a slight upward camber then built in correctly. When all masonry has gone off you can remove the props. 
 

Also have you got a 200mm cavity or a 100m cavity and 100mm outer leaf as Catnic limit is 165mm cavity. You could also use catnics on the large spans but you would need to reduce the spans by 500mm. Tbh that’s a brick either end and not many people would notice. 

 

 

It's a 200mm cavity (400mm total wall width), so I guess I best query that.

 

Sliding doors rather than bifolds, I've attached the relevant bits of the calculations.

 

11 hours ago, Nickfromwales said:

Battens and insulation on the internal faces will create the thermal break with relatively little impact and be quite effective. You could line the internal faces of the reveals with Compacfoam or Marmox to go belt n braces. 

 

Thanks - I best raise this with the architect then to ensure we have the space to add this detail.

 

[Mr Punter]

For the smaller openings a separate lintel for each leaf should work OK.  They may need propping during construction.  For the big openings you could use a course of Marmox on the inner leaf on top of the steel which will help a bit.

 

@tonyshouse did a wide cavity (400mm) masonry build and there is some info at http://tonyshouse.readinguk.org/mitigation-of-thermal-bridging/#more-247

[AdamSee]

We had the same problem with a 10mm bottom plate on the RSJ. I didn't pick up on this issue until after it was fitted so had to make do with what the builders left me. The gap I had left with just too thin for insulated plasterboard, so I instead used plasterboard held in place with a lot (full coverage) of low expansion foam. Theres a lip on the frame which helps hold it in place while its setting the the inside edge of the wall was a MF structure which allowed an additional screw fixing. Seems pretty solid. 

Problem here is that there's no vapour barrier, it's a working progress.