Residential Wood-Framed: Dead Loads

[BrianMCE]

I've been designing using the dead loads from Design of Wood Structures ASD/LRFD - these dead loads would yield roof, floor and wall assemblies of approximately 20 psf. A lot of other engineers use assemblies closer to 15 psf, which is significantly less than the 20 psf for interior wall with plaster on both sides. For other wood framed residential engineers out there, what is the typical dead load you use for interior wall with plaster? Also, where do you obtain your dead load values from?

 

[phamENG]

I take the architect's sections and add up the components. Then I usually add in an allowance for miscellaneous stuff - lights, ventilation, etc. ASCE 7 has a pretty comprehensive table in the commentary for the dead load chapter. AISC also has a section in the back of the steel manual with several building material weights. If available, I prefer to use manufacturer's published data. That's hard to get your hands on in the early stages of design, though.

Looks like you're in California, so I can see why you would need to be pretty accurate. Too light, and you underestimate seismic loads. Too heavy, and you punish your lateral design pretty severely. If you can find a way to automate as many of your calculations based on distributed loading as you can, then it will be easier to go back and re-run your calcs with a more accurate dead load as the design progresses.

 

[BridgeSmith]

A lot of other engineers use assemblies closer to 15 psf, which is significantly less than the 20 psf for interior wall with plaster on both sides.

This is not my area of expertise by any stretch, but according to my AISC steel manual, a 2x4 stud wall with studs at 12"-16" o.c. weighs 2psf and 1" of gypsum "plaster" weighs 5psf. So a typical wall with 1/2" drywall on both sides has a nominal weight around 7psf. Am I missing something?

Rod Smith, P.E., The artist formerly known as HotRod10

 

[FoxSE14]

I look at the arch dwgs and, based on the room with gov'ng dead loads, try to prove 15 psf or 20psf blanket DL will work. Typically 20 psf does the trick. However, when I need to sharpen the pencil, I take into account the weight of framing + finishes. When it comes to the DL component which represents weight of interior walls, I usually check via:

{Wall Wt in PSF} * {Total LF of Interior Wall * Wall Ht} / {Floor Area}

 

[FoxSE14]

phamENG has got it - those references are also my "go-to" documents for DL estimation.

 

[Boof19]

By looking at the architects wall and floor assemblies. It can depend quite a bit on the intended usage of the space. I’ll always double check and confirm floor assemblies with architects. Last thing you want is to assume and find out later the architect has an 1-1/2” of gypcrete topping and you only assumed 3/4”, or the space has a pager system, etc etc

 

[BrianMCE]

Thank you all for your responses - they are very helpful. I just want to clarify that I always check with the architect for the correct assembly before estimating the dead load. My question is mainly aimed towards published references/resources that will justify a lighter dead load... 20 PSF for interior wall with plaster definitely punishes the lateral design significantly, not to mention the footings.

 

[TheDW]

ASCE 7 table C3-1 shows a wood stud wall with gypsum on both sides as weighing 8psf...I usually use 15psf for everything you listed except floors where I start with 20psf.

My house, built in the 50's, was built with plaster...its much heavier than sheetrock.

 

[phamENG]

TheDaywalker - it may be heavier, but that stuff has load carrying capacity of its own. Inspected a church once - the belfry framing had rotted out and failed at the pockets into the brick (what wood was there turned to powder when I touched it). That's when I noticed the plaster had a slight bow in it that the wall didn't share. I got out of there real quick.

Disclaimer: don't rely on load carrying capacity of plaster...

 

[KootK]

I've been known to dip into the HUD design guide when I feel like sharpening my pencil/mouse.

 

[gte447f]

To the OP, I assume you really do mean plaster as you say and not gypsum board (drywall). Plaster (and wood lath) is much heavier than gyp board according to most references I have seen. For a 2x4 wall plastered on both sides I would use 20 psf. For a 2x4 wall w/ gyp board on both sides I would use 10 psf (maybe 8 psf if I needed to sharpen my pencil). For the record, I have never designed a building that had real plaster walls in 18 years.

 

[BrianMCE]

Sorry for any confusion, I definitely do mean plaster with wood lath when I mentioned plaster. It appears that the general consensus is to use 20 psf for 2X4 wall with plaster on both sides.

 

[phamENG]

If you've got wood lathe then you're dealing with a historic structure, and the only way to know if for you or the architect to demo the walls. I seriously doubt anyone would consider building a modern structure with wood lathe.

If you're doing incredibly high end residential and they're using plaster (it's popularity is growing again if you have more money than sense), it'll be on expanded metal lathe. Important distinction if you've finished sharpening your pencil and are starting to polish the tip...

 

[NorthCivil]

I've added up the components by weight and I came out to approx 12-15PSF for floors. Which is where a lot of engineers get the 15 figure from.

Am I the only cheeky one out there who ignores the dead weight of walls? I just use 20PSF for floors and figure that more or less will cover it... I bloody wish architects would give me enough walls that calculating the dead weight of walls was a meaningful exercise.

 

[phamENG]

NorthCivil - I don't usually bother, but then checking seismic forces is just a formality. Unless the house is 3 stories and only 12 feet wide (only happened once), wind is usually stronger around here by a factor of 4 or 5. If it's a partition, I usually just make sure there's an extra joist or two under it and call it a day. Maybe bump up the dead load if most of the walls are perpendicular to the joists.

 

[skeletron]

I've automated the task because I got so tired of tallying up loads and can't stand the old "just use XX psf" strategy without understanding it. The listed value in my table is 18psf. That is from a "typical wood stud, lath, 20mm plaster" listing in either S16, A23, or O86.

I typically will only pay attention to interior wall loads if they don't stack. Otherwise I use a contingency load in my floor loading that gets me off the ground during the initial stages of design.