Small Construction Office Floor System

[woodman1967]

Have another small project. This one is a small construction office at a manufacturing plant, it will be permanent. The office will be basically a mini home (16"x34"). The floor system is typically 2"x10" supported by (2) 3 ply 2"x8" that run lengthwise with the floor joists cantilevering 24" on each end. According to NBCC 2015 9.23.9.9 we are allowed to cantilever floor joists 24" as long as the floor joists are supporting roof loads only. Problem is, this is an office and they've gone with engineered joists (floor live loading is 100psf, instead of the residential loading of 40psf). I've seen the calc sheet for the joists and I have a question. Does Part 4 of the code have a provision for cantilevered joists? The calc sheet for the joists shows only floor loading applied to the joists. Shouldn't the roof loading be applied to the joists as well?

Thanks in advance

 

[jayrod12]

You haven't given enough information. Is there a roof? How is it framed? What supports the roof?

A cross section through the proposed structure would really help clarify things.

 

[woodman1967]

Yes, that would help for sure. I've attached a typical cross section for a unit like this. Please note that some of the material will be different but the overall layout will be the same. For instance it shows a standard 2"x10" floor system, in this case it will be engineered joists

 

[ChorasDen]

5/8" subfloor with 100psf office loading? I guess it technically works with joists at 16" o.c., but sheesh, I would be suggesting a thicker structural panel here.

 

[woodman1967]

This is a typical section for a minihome. As I mentioned above there will be some changes to make this work for 100psf floor loading, including the floor sheathing.

 

[phamENG]

Not familiar with Canadian codes, but here in the states that 100psf would kick you out of anything prescriptive and into engineered design. You can make those joists cantilever 24 feet if you can prove they work (and, you know, can get long enough stock).

 

[jayrod12]

Agreed with Pham, you can't use the prescriptive part 9 code for non-residential loading. The tables do not account for that.

Regarding your engineered joist calc sheet, if no one told them what was sitting on the end of the joist, they wouldn't of included for the roof loading. You'd need to tell them what loads to design for.

 

[lexpatrie]

100 psf live load is assembly occupancy on my planet. 40 psf sounds more reasonable unless they are intending to store heavy materials or something. Office is 50 psf under ASCE, won't speak for NBCC.

This fixation with cantilevers doesn't seem necessary, support them at the ends.