Timber-Concrete Moisture Barrier

[asixth]

Hi guys,

I have a situation where a client would like a 300mm (12") raised floor on top of an existing 150mm (6") slab. I provided a detail that consists of a packing plate and 270mm (11") floor joists that sits on a vapour barrier.

However, the guys on-site keep coming back and asking me whether they can glue the timber joists to the concrete slab before the plywood floor is attached over.

My questions are:

1. Is there anything wrong with the detail I have provided?
2. Is there any reference material for this situation?
3. Is gluing the timber joist to the concrete slab a credible solution?

Any advice will be greatly appreciated.

 

[apsix]

My thoughts;
Your detail will work but is a little fiddly.
I would lay down 90x45 battens at say 1500 crs and nail joists to those, with blocking between the joists so they remain vertical. If the slab is uneven packing could be provided between battens and joists.
Glueing the battens down should be OK, perhaps with a few concrete nails for added security.

 

[apsix]

I see the title mentions moisture barrier.
If it's a normal dry interior slab I don't see the need. It's no different to fixing the bottom plate of a stud wall down.

 

[ronster]

Assuming it is a slab on grade and has the potential to get damp then I would not allow the joists to be glued to the slab and all lumber should be pressure treated. While not the easiest way to skin a cat there is nothing wrong with your detail. The detail can be simplified by using continuous 2x4 P.T. sleepers lagged into the slab and then nail the joists from sleeper to sleeper.