Floating concrete slab on wood trusses 1

[Costin Ruja]

Is it feasible to pour a 2 - 2 1/2 inch concrete slab over wood trusses? The trusses are overbuilt by a quite large margin and covered with a 7/8'' OSB. The slab will have some rebar and also fibers. The calculated sag in the middle span of the truss will be 6mm. Is that safe considering concrete on top? Will it crack? Is there a best practice for this kind of construction?


Regards,
Costin

 

[jhnblgr]

You need to hire a competent engineer in this area. This would likely crack everywhere. What is the intent of this. In the plastic state the concrete will likely develop cracks in it and the stone size with reinforcement might cause cracks.

 

[Costin Ruja]

The main reason for the concrete slab is using hydronic heating.

 

[jhnblgr]

Is concrete a finished product or flooring?
The only time I have done this was when a sand cement slurry with high area and sleepers for wood flooring. 2” with radiant and steel is very difficult in nature it isn’t wise, you could use composite metal decking. Really need to check the rest of the structure to confirm the added load doesn’t have impacts below.

 

[XR250]

Might want to go with thicker concrete - maybe 3 1/2" and put some wire in it. If the floor is stiff, it should work. We do 3 1/2" slabs on wood framing for radiant frequently around here and they hold up fine. I put #4 @ 24" O.C. each way in them though.
I did it at my old house and never had a single crack. I was pretty careful about using a lot of construction joints which required it to use two separate pours.

 

[phamENG]

Important caveat: XR250's trusses/joists were either designed for that load or he, as a competent structural engineer, performed a sufficiently rigorous analysis to determine that it was safe.

Why do you consider the existing trusses to be "overbuilt"? Unless they are in a church or other large gathering place that was converted into a house, I'd seriously doubt that they are truly overbuilt. The goal of floor trusses is to get as much performance out of as little material as they can. That concrete is going to add a lot of weight. Just that concrete is going to weigh almost as much as the entire system was designed for - dead AND live load.

Something like this should absolutely be checked by a competent structural engineer.