Posi joist or beam and block

[bissoejosh]

We're laying our external beam and block elements at the moment, all going fine. Whilst loading the bays I've realized that potentially I could use beam and block above our basement/lower ground floor. It would sit between the inner skins of our cavity wall and project/overhang 100mm in to a 200mm full filled cavity. This would provide the necessary support (beam and block guys are OK with it projecting a max 155mm) for our 300mm frame going above without bridging the cavity at all. Compared to our existing posi detail this is an improvement as there would always be a minimum 100mm of insulation whereas the posi top chord is currently detailed to run across to the outer skin so a small cross section but a bridge none the less.

 

The main advantage I can see is that we would be able to run our preferred choice of flooring and UFH across all of our upper ground floor whereas previously we had to consider the join between beam and block and posi deck.

 

My questions are what downsides does a 1st floor beam and block have with say a 70mm screed? How soundproof is it compared to our current proposal of 225mm posi joists? Services are certainly an issue but our lower basement level is pretty small and I think I can provide the necessary runs through internal walls rather than ceiling lengths. Access to install is easy as the HIAB could drive right upto the building.

 

Detail attached for reference.

 

Thanks

[Dudda]

I'd get conformation from you're structural engineer. Usually structural engineers specify a block on flat to support concrete floors. A block and beam with screed will weight a lot more than a timber floor particularly with a large floor and span (which we don't know the area or size of). The dead load would be a lot greater and the existing foundations, walls, etc might not be capable of supporting the additional load.

[nod]

Regarding sound proofing the benefits are massive

You could hang an independent mf cieling for not a lot of money 

Far superior job to any kind of joist

Financrs permitting