Residential Floor System
Residential Floor System
(OP)
Hi All,
Given a simple residential floor system situation, joist ends sitting on a wood girder, dead load only...
2x8 SPF floor joists @ 16" o.c. weigh 2.2# +/- per square foot
5/8" OSB weighs 2.2# +/- per square foot
That's a total of 4.3# per square foot. I design at a minimum of 10#. I received some calcs for a girder today that used 15#. I ran the numbers on a smaller girder
to carry these joists @ 10# and it passed.
This seems like a situation where the engineer wasn't given privy to the finished floor materials and made sure that whatever went over the sub floor
wasn't going to make it fail. Seems to me that a little communication could have avoided extra cost for the consumer, a little less sweat for the builder
and no guesswork for the engineer.
In a situation such as this do you "Overkill" to make sure you're covered?
Doug
Given a simple residential floor system situation, joist ends sitting on a wood girder, dead load only...
2x8 SPF floor joists @ 16" o.c. weigh 2.2# +/- per square foot
5/8" OSB weighs 2.2# +/- per square foot
That's a total of 4.3# per square foot. I design at a minimum of 10#. I received some calcs for a girder today that used 15#. I ran the numbers on a smaller girder
to carry these joists @ 10# and it passed.
This seems like a situation where the engineer wasn't given privy to the finished floor materials and made sure that whatever went over the sub floor
wasn't going to make it fail. Seems to me that a little communication could have avoided extra cost for the consumer, a little less sweat for the builder
and no guesswork for the engineer.
In a situation such as this do you "Overkill" to make sure you're covered?
Doug






RE: Residential Floor System
RE: Residential Floor System
RE: Residential Floor System
In this case it took under 3# per square foot to make the difference. I have almost 6# to work with. Research has shown me that it takes quite a bit
of finished floor to make that up. Usually if the homeowner is going to have tile or the like for a finished floor that is insanely heavy, they make
it known during design.
RE: Residential Floor System
1.8 psf for OSB Sheathing
2.2 psf for GWB ceiling
3.5 psf for hardwood flooring
This adds up to close to 10 psf. I have seen cases where, the owner wanted to use 3/4" gypcrete with carpet finish instead of hardwood floor. In that case the total load reaches 13 psf easily.
RE: Residential Floor System
Now, making sure your decimals are in the right place can make all the difference in the world. Last week I was lost to figure out why a beam was failing when I KNEW it should work, only to relook at my loads and realize that 100psf DL and 400 psf LL were a bit off. *sigh*
RE: Residential Floor System
RE: Residential Floor System
RE: Residential Floor System
RE: Residential Floor System
The more I think about it this should have been my OP.
Thanks,
Doug
RE: Residential Floor System
What is the deflection criteria?
When I have a "cheap" client (and I mean very simple house) I use 10psf as an average and hope for the best. In most of the homes that actually get an engineer involved, the finishes are all over the place. Any coffer beams in the ceiling below, High end marble flooring, Kitchen counters made out of 2"-3" thick stone. 15psf is not very conservative and the averages will even out a bit. Don't forget about compound deflections (a beam holding a beam holding a joist, which is supported by beam on the next level down...). I often don't get the luxury of a finish schedule at the outset of structural design.
If you know the dead loads then you know them - enough said and you go with it. If you are confident with 10 the that is fine. But if you don't then you must improvise with what you do know and I have seen some very heavy finishes put into a house.
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MAP