Steel Beam into Cavity Wall without pillar?

[GeorgeWBush]

Hi,
I'm having a double storey extension done, straight on the back of our house.

Double storey part is 4 metres in length, downstairs by 8 metres, all at a width of 6 metres.

To support the upstaits extension, architect has put a steel beam in the ceiling of the downstairs extension at 4 metres out.

This steel will be supporting the back end of the upstairs house inc the new roof.

This beam will be hidden into the new upstairs floor so downstairs there will be no ridge in the ceiling.

My question is around how the steel will sit in the cavity wall. Wall is 100mm block, 100mm cavity, 100mm block.

Questions:

• 1. What are the options for this steel to sit in the cavity wall such that there are no pillars in the ground floor wall.
  i.e. so that the wall is completely smooth internally.

• 2. Can the steel rest on just the internal wall (100mm) if we use an extra wide padstone?

Appreciate this is the realm of structural engineering but would like to arm myself with some knowldege before consulting.

This link to the plans will hopefully help https://picasaweb.google.com/lh/photo/nNvHfRHKhPPDMg9gfkkL2A
.... i've drawn a big arrow on the left of the plan where the beam is to go.

Thanks for looking.

 

[^woody^]

Yes it's possible

 

[ChapiTheBricky]

i would imagine not i'm afraid, i'm not a structural engineer but a 6m beam carrying the whole upstairs should carry a minimum bearing of 150mm (usually more) in my experience. If i were designing this i would probably insist on engineering brick piers built into the existing structure. Consult an engineer though.
You could ask him to design a set of steel "goalposts" but this will be very expensive and in my opinion, not worth the expense.

 

[GeorgeWBush]

Thanks for the responses.

How about the beam resting on both the inner and outer wall? Or not have a cavity at all underneath the beam, so the beam is resting on a 3 brick deep column?

 

[ajrobb]

A solid column would cause a thermal bridge that could lead to condensation. Typical recommendation for solid wall window reveals is 20mm PIR. If that would spoil the lines of the design, it might be worth going to 10mm Aerogel.

 

[freddiemercurystwin]

You'll not be able to bear onto the outer skin as that will bridge the cavity which is a big No-No!

For a non masonry solution this is typically what your engineer will come up with, I'd be amazed if you can do it without a nib.

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• freddiemercurystwin
• 15 Feb 2011
• 2

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• freddiemercurystwin
• 15 Feb 2011
• 2

 

[jeds]

You need to consult an engineer because it depends on the loads involved and where the lateral restraint will come from for the whole of the rear elevation. It's not imposssible but it needs to be carefully designed.

Usual solution is that the supporting beam is part of a frame which includes columns and possibly a foundation beam. But there are other options.

 

[GeorgeWBush]

This is very helpful to me, thank you for the responses.

A solid column would cause a thermal bridge that could lead to condensation. Typical recommendation for solid wall window reveals is 20mm PIR. If that would spoil the lines of the design, it might be worth going to 10mm Aerogel.

If we go with a solid column, could insulating externally rather than internally be an option? We are going to be having the external wall rendered. So perhaps external insulation and then render?

The old part of the house is solid wall anyway (built in the 30s) and we have condensation issues. So external insulation may help with this as well.

 

[^woody^]

Don't get hung up on thinking that a large bearing is necessary. It is the vertical stress on the beam where the beam projects from the wall which is the crucial factor, not how much wall it is sitting on.

The beam will normally happily sit on the inner leaf with no pier and just a suitable padstone or plate to spread the load and take the stress at the front edge of the wall

 

[GeorgeWBush]

Thanks - I think I understand

 

[geraint]

You'll not be able to bear onto the outer skin as that will bridge the cavity which is a big No-No!

For a non masonry solution this is typically what your engineer will come up with, I'd be amazed if you can do it without a nib.

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• freddiemercurystwin
• 15 Feb 2011
• 2

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• freddiemercurystwin
• 15 Feb 2011
• 2

unfortunately your bolting method is unsound.....

 

[Deluks]

unfortunately your bolting method is unsound.....

 

[freddiemercurystwin]

unfortunately your bolting method is unsound.....

Thanks, I'll let my structural engineer know to inform their PI insurer!

 

[GeorgeWBush]

Found an engineer now - keen to see what she comes up with.

Thanks for all the input

 

[Ossy]

unfortunately your bolting method is unsound.....

Go on then I'll bite, I'm struggling to see any major problems with this, so what's the problem with it?