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#154059 - 02/20/04 08:02 PM Trenching Concrete Floors
Joey D Offline

Registered: 10/10/03
Posts: 263
Loc: Arlington MA U.S.
I am on a job in a apartment building where the floors are all concrete. The contractor is framming a few areas in he middle of the ceiling to install recesed lights in. He has cut a 2inch deep trench in the ceiling from one lowered ceiling to the new one. The floors are only 8" deep. Would this be a smart thing to do?

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#154060 - 02/20/04 09:09 PM Re: Trenching Concrete Floors
crash Offline

Registered: 10/21/03
Posts: 130
Loc: Calgary Canada
The only person who could answer that question is the Engineer who designed the building. If the engineer gave the contractor the go-ahead for this trench and the corresponding repair, then it should be okay.

#154061 - 02/21/04 02:36 AM Re: Trenching Concrete Floors
iwire Offline

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
I agree with Crash.

Any chance these are precast cement decks?

If yes as long as the pre-stressed cables inside are not cut it seems you can do a lot to them, with an engineers OK.

Without an engineers OK this sounds dangerous.
Bob Badger
Construction & Maintenance Electrician

#154062 - 02/21/04 07:05 AM Re: Trenching Concrete Floors
Roger Offline

Registered: 05/18/02
Posts: 1779
Loc: N.C.
I agree with Crash and Iwire. A structural engineer would need to be involved, and it would seem to me that there would be some specific instructions to the cutting.


#154063 - 02/21/04 07:54 AM Re: Trenching Concrete Floors
DougW Offline

Registered: 06/08/03
Posts: 1083
Loc: North Chicago, IL
I was going to ask if they were Spancrete, or another type of cellular concrete. Taking 2" out of that could be, uh, problematic.

Get a Structural Engineer's opinion.

#154064 - 02/21/04 09:20 AM Re: Trenching Concrete Floors
u2slow Offline

Registered: 09/18/03
Posts: 198
Loc: Salt Spring, BC, Canada
I work in mainly new highrise construction. Typical floors are 190mm (approx 7-1/2") and having to chip a shallow trench in the ceiling or floor (to bury BX cable or 1/2" ENT) has not been an issue with the engineers or inspectors so long as the steel isn't cut. Usually we don't have to go deeper than 1" or so, unless there's a spot where the rebar is too shallow and we have to go behind it.

Check with YOUR engineer first though

[This message has been edited by u2slow (edited 02-21-2004).]

#154065 - 02/21/04 04:31 PM Re: Trenching Concrete Floors
Joey D Offline

Registered: 10/10/03
Posts: 263
Loc: Arlington MA U.S.
Thanks. I was thinking the same.


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