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Re: Concrete floor on wood trusses

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for those considering using concrete over timber

Concrete is a brittle finish & over a wood flooring system of insufficient stiffness will crack extensively.

It might be considered "just along for the ride" but once it is completely cracked up (depending on the level of foot traffic) it will be like walking on a gravel path.


On 12/6/05, Rhkratzse(--nospam--at) <Rhkratzse(--nospam--at)> wrote:
You know, a lot of this ping-ponging messages back and forth could be avoided if the original questioner gave just a bit more information about their situation.  The question mentioned "a concrete floor slab poured on wood trusses," so I pictured sort of composite concrete-wood T-beam construction, which is obviously absurd and illegal.  (Or maybe it reminded me of Bucky Fuller's suggestion to reinforce concrete with bamboo for low cost housing in tropical areas.)  If the question had mentioned concrete topping on a wood floor maybe we all would have understood the situation better. 

I've raised this issue previously:  Asking very general questions like "I have a building to design; can anyone help me?" really isn't very productive for anyone involved.

Ralph Hueston Kratz, S.E.
Richmond CA USA

In a message dated 12/6/05 5:50:38 PM, mailbox(--nospam--at) writes:
Exactly, Exclusion 1 of both the UBC and IBC provisions - up to 4 inches of concrete topping.

----- Original Message -----
From: Paul Feather
To: seaint(--nospam--at)
Sent: Tuesday, December 06, 2005 5:28 PM
Subject: Re: Concrete floor on wood trusses

If the concrete is non-structural it is perfectly permissible and is done every day.  Every multi-story wood building typically receives an 1.5 inch concrete topping slab or 1 inch of gypcrete or similar product.  The IBC does not permit support of structural concrete on wood, non-structural can be up to 4" thick.
Paul Feather PE, SE

----- Original Message -----
From: Eli Grassley
To: seaint(--nospam--at)
Sent: Tuesday, December 06, 2005 4:45 PM
Subject: RE: Concrete floor on wood trusses

The IBC does not allow support of concrete on wood.  See section 2304.12.  That's a pretty solid argument I would say J
~~ Eli Grassley

-----Original Message-----
From: David Smith [mailto: smith1129(--nospam--at)]
Sent: Tuesday, December 06, 2005 11:50 AM
To: seaint(--nospam--at)
Subject: Concrete floor on wood trusses
I have a prospective client wanting a concrete floor slab poured on wood trusses.  The building will be steel-framed on the perimeter.

I am trying to get him to use steel bar joists rather than wood trusses.  Anyone have some good arguments against this?


Dave Smith

Smith Associates