Canadian question (NBC 2015), what Dead load should be used for residential projects.

[woodman1967]

This is a Canadian question (NBC2015). I have seen floor dead loads of 10psf used for years. Now I've been told that we are to use 15psf for floor dead loads. I can't find anything in the code, except for in the user guide for wood foundations where 11psf floor dead load is used, of course I may be missing it.

Thanks for any help.

 

[dik]

I'm not aware that there is a prescribed value. Generally add the weights of components and finishes, and generally get about 10 or 12...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[woodman1967]

That's what I thought. Thanks.

One more question, how are walls included in that load? I've seen calculations where the Roof and Floor Live and Dead loads are listed but nothing for walls (exterior or interior). Is it part of the floor dead load?

Reason I am asking is we build manufactured housing. Usually the foot print of the home is rectangular, I guess they are called double wides in the US. There is a beam in the basement that supports the main floor and roof. We've had work reviewed by different engineers over time and was told to make different changes. For the longest time we used floor and roof loads (dead and live) only. The latest reviewer requested the floor dead load be increased to 15psf. He also requested that the supporting wall (supports roof load and bears on the floor beam) be added as a dead load. The earlier engineers did not request that be added.

Does this make sense?

 

[jayrod12]

I've done a whole bunch of residential in the central prairies. I've never used less than 15 psf for a floor. Unless extremely desperate to get an existing condition to calculate out.

Usually for a residential floor I use 20 psf.

I also use 20 psf for exterior wall loads unless there's stone.

 

[skeletron]

Article 4.1.4 covers dead loads and gives very loose requirements. The clause does indicate that an allowance be made for partitions.

The CWC has a manual for Engineering Guide for Wood-Frame Construction. In the front section there is a discussion of light-, normal-, and heavy-construction dead loads for floors, walls, roof, etc. 10psf is probably the absolute lower-bound.

I would add up the weights of the assembly and use that with a bit of contingency.
There are also two standards for manufactured/mobile homes:
CSA A-277
CSA Z-240
I'm not familiar with either.

 

[Pmtottawa]

I agree with jrod and use 20 psf as a basis for dead load.
When I was working for a floor joist manuf. We would use 15 psf dl as standard and bump it to 20 psf when tiles were used.

 

[Canuck65]

It is common to use 15 psf for floor and roof dead loads as long as they don't have tile or stone or similar heavy floor finishes.

For stud walls, it is common to use 10 psf for dead loads, and yes, if the mate line beam supports a stud wall, that loading should be included. For residential there is no allowance for partition loads.

If you add up the weight of all the components of a floor, it will normally come in at less than 15 psf and if you want to take the extra time to optimize your design then that would be code compliant. However, pretty much everyone just uses 15 psf, higher if you are doing custom houses.

 

[woodman1967]

Thanks everyone, this has been very helpful.

One more follow up question: for the wall deadload how is that applied? Jayrod12, you had mentioned 20psf for typical exterior wall...is that applied over the entire tributary area or just a portion?
Same for Canuck65, you mentioned 10psf for stud walls...is that applied over the entire trib area?

Thanks again everyone.

 

[jayrod12]

No, if you multiply that wall dead load (whether it be 10, 15, 20 etc. PSF) by the height of the wall, you'll get a UDL in lbs/ft.

I use 20 PSF for exterior walls to account for almost any type of finish but full thickness stone. Even stucco weighs a fair bit so going to 10 or 15 could be unconservative. For interior partitions with drywall on each side, I'm more in the 10 PSF range, even though if you run the numbers its actually only 5.5 PSF.

I should probably elaborate on my use of 20 PSF for floors, that is for floor over basements, or floors above occupied spaces. Everyone wants that click laminate flooring nowadays, so that weighs about 2 PSF on it's own. When you add up just the 3/4" plywood, floor joists and ceiling drywall you're in the range of 10 PSF right there. Plus a mechanical/electrical allowance and you're at 15 PSF with no wiggle room for someone to come in last minute and want to put tile floor. I find being a bit conservative on my dead loads leads me to not have to re-check stuff as often when design changes are made during construction.

Too often when we design homes the finish schedule is preliminary, i.e. specifies floor finish by owner(Is that painted plywood, vinyl sheet, vinyl plank, tile, hardwood?), siding (is that vinyl, wood, cement? It never says and they each have drastically different weights) etc.

I had a home I designed recently where it is fully finished, and I get a question from the homeowner, "We want to use this table, but the supplier has recommended that we confirm the floor has the capacity to support the table. So does our floor have the capacity?" The table weighed 1600 lbs, sat on 4 legs that were 6" square, and then complained when I indicated that it did not have the capacity to support that without some re-work being done inside the floor framing. The ceiling drywall was already installed and taped in the basement so they didn't want to have to do anything. I'm not saying I'm going to start designing for a 1600 lb table in all of my homes, but I do like leaving a bit of slop in there so that I can cover myself in many of the situations that arise.

 

[Canuck65]

As jayrod pointed out, it is the wall dead load x the height of the wall. So for modular, if you have an interior stud wall along the mate line, you would add a dead load of 10psf x height to the beam, in addition to the floor loading. Exterior walls tend to line up with the foundations, so don't really come into play except perhaps for lintels over windows below. Or I have worked on some modular on steel frames where they cantilever the floor joists beyond the steel frame. When analyzing the floor joists you need to put the wall dead load and supported roof snow/dead load on the cantilevered ends of the floor joists.

 

[Ron247]

I have always used 10 psf as my bare-bones. 2x12s at 16" oc, one layer of 3/4" plywood subfloor, 1 layer of 5/8" drywall and one layer of 1/2" on the floor. It comes to about 10 psf on the nose. Then you add your final floor such as ceramic tile, 1.5" of gypcrete or whatever else you have for you scenario. I may then kick 3 more psf after that for electric, hvac and plumbing. After that, round up to the nearest 5.
You will wind up with 15 to 20 psf unless you have gypcrete and for those, it is greater than 20.