Not sure what Lintel to use for pillarless cavity wall

[carlmeek]

I'm creating an extension to my kitchen, this is all planning and building regs approved, but now we are coming to actually build it!

The difficult part is the opening in the former external wall. We want to make this pillar-less and also not have a visible beam across the ceiling. Note that the external wall will become internal, as there is a small sloping roof on top of the extension which will flash into the brickwork about a metre above the ceiling level.

Anyway, The only way to do this is for the floor joists to actually rest "in" the beam, therefore the beam only extends a few MM below the joists and i can make the ceiling seemless. I always imagined an RSJ with the beams resting on the lower plate, or something similar.

I called Catnic technical support who told me that ALL their cavity lintels must have 1 course of brickwork before any joists.

I'm now wondering if 2 lintels is the better solution, 1 for each course of bricks, the inner one supporting the floor loads. However, I can't even find any lintels to do this! Is this allowable by building regs?

Any ideas? Any suggestions will be much appreciated.... any specific model numbers or suppliers would be very helpful.

Regards,
-Carl.

 

[^woody^]

You'll have to use steel beams

 

[carlmeek]

I assume you mean UBs?

The bit I don't understand is how to connect the joists into this... perhaps Joist hangars, but they would need to hang directly on the UB.

Still puzzled!

 

[JohnD]

I'm surprised you didn't have to include it in the BCO drawing.

Or are you going to build it differently to what was approved?

 

[^woody^]

The awkward way is to get the joists into the web of the beam - they will normally need to be cut from the presumed existing 100mm bearing by about 50mm to fit in the web

The less awkward but still awkward way is to cut all the joists flush with the wall, put the beam in, and then fix the joists with hangers

 

[carlmeek]

Well this is the funny thing....

I thought it wasn't on the drawing at all, but it actually is.... i just found it in very small writing listed as "2 No. 203x102x23 UB"

So this is fair enough, 2 Universal Beams... but it doesn't really explain how to hang the joists.

Ah ha! Looking further, i suddenly understand why.... it has "assumed direction of joists" written on the plan THE WRONG WAY!

So basically, we now need to come up with a plan that the inspector will approve.

If you're interested.... The drawing is here:
http://wam.brighton-hove.gov.uk/Pla...LUME3&contentType=application/pdf&pageCount=1

 

[^woody^]

I'm surprised you didn't have to include it in the BCO drawing.

I'd be surprised if the designer even bothered to go into this detail

Normally, you will find that on the drawings it just says "new opening with lintel/beam above", and bizarrely, that is enough to get the plans approved

 

[freddiemercurystwin]

So what do the engineers details show, to which your drawing refers? It is their design and they ought to dictate what bearing/connection the joists need.

 

[carlmeek]

Unfortunately the achitect was being a complete arse and got very aggressive on the phone when asked such questions, so we've severed ties.

I'm not even sure he actually did any engineering calculations - they certainly were not submitted as part of the planning process.

 

[^woody^]

You probably need to do something like the image in this thread

//www.diynot.com/forums/building/fitting-joists-to-rsj-is-there-a-hanger.300035/

 

[carlmeek]

Thanks, that looks great!

 

[Static]

You may need the engineers calcs anyways for building regs..

 

[simonjay]

You may need the engineers calcs anyways for building regs..

Yes, if the original UBs were spec'd for zero floor load (due to assumed joists the other way), and are now to have the floor load on them, the beams may need to be increased in size.

My struct eng thought I'd need new beams after the original RSJs gained some extra load from an extension roof. He had assumed they were bearing floor load. When I showed him the direction of the floorboards upstairs, he was happy to stick with the original beams.
Lucky !

Simon.