Is this enough PSF?

Hi folks! I planning to build an iso booth that's about 16'x11' in my current room. Nothing too crazy, but how can we figure out if it's safe according to the current PSF. I got these number from the architect/structural engineer who built the building... Live Load 50 psf Partition 15 psf Dead Load 35 psf How do I translate this into how much material (ie, 2x4 vx 2x6, # and width of drywall panels etc)? thanks! rich

Hi Rich - Sounds like you're in decent shape. When the architect/engineer allows for a 15 psf partition load in their design, they are assuming that you will be building partition walls on your floor. For an 8-foot high wall I usually estimate about 60 pounds per lineal foot. That would be for a wall that was 2x4 studs at 16"o.c. and one layer of gyp on each side. If your wall is just 2x studs at 16" o.c. + insulation + single layer of drywall each side, then don't worry... just build it. There are offfices built like this all over the country. I'm guessing that your wall might have two layers each side? Say your wall weighs 100 pound per lineal foot (abbrev. "plf"), and it runs perpendicular to your floor joists. If you built that wall every 8 feet, your load would be 100/8 = 13 psf and would be within the allowable 15 psf partition load that the architect intended. If your wall weighs 100 plf and runs parallel to the floor joists, it still might be okay but deserves a closer look by the engineer. I personally think it's reasonable to say that the load would be shared by three effective joists, but that works out to be (100/3/1.333) = 25psf* (too much?) *the 1.333 ft = 16" o.c. Ask you engineer how much "capacity" in psf the floor can hold in bending. Often times there is some extra cushion. Also, if the live load deflection criteria used is L/480, you can cheat on that a little when building a wall. (Code minimum is L/360) Creatch

How cow! That's awesome.... thanks so much! Yeah, I'm not planning to build a nuclear-bomb proof concrete shelter, just perhaps 2x4 floor joists to lift the room off the current floor (semi-float) and 2x4 studs 16"OC with 1 (maybe 2) drywall layers ON ONE SIDE. I don't care too much about some leakage, as the building is already really quiet. Plus one layer drywall (3/4") on the ceiling, on one side. So if you look at the new room from the outside, you'll just see the studs, and one drywall layer on the inside. Almost half a wall...to keep costs and weight down. Does that sound like a plan? Do I hear an Amen? :lol:

I don't quite get the lpf and psf though... I'm 200 lbs, and if I stand on one foot, isn't that 200 psf? or 200 plf? thanks for clearing that up!!!

If the bottom of your foot were a perfect 12" x 12" square, and you weigh 200 pounds, and you were standing on one foot, that would indeed be 200 pounds per square foot. If you were standing on two feet, you'd be 200 pounds on two square feet, and therefore 100 pounds per square foot, assuming you weren't lopsided. ;-) If the bottom of your foot were a perfect 4" x 12", and you were standing on one foot, the point load of your single foot, standing on one foot, would be 600 pounds per square foot. That's because you'd be standing on a spot that took exactly 1/3 of a square foot. Absurd examples, yes -- but do they drive the point home? --Keith :mrgreen:

Hi Keith. Great examples about distributing the weight, but I'm wondering why I should be worried about pounds per LINEAR foot when basically I'm building an enclosed box (11'x13' iso room). Shouldn't the calculations be made according the dead weight PSF?

Well, you need to concern yourself with both. In theory, it is possible for one to have all of the building materials spread around the floor and have there not be a problem with the weight, yet a problem could materialize when the materials are assembled and the weight is distributed around the perimeter of the floor. Illusionists do it all the time, lying on a bed of nails. They can manage to do that and not get killed because they carefully apply the weight of their body on the bed so that the nails don't penetrate their skin due to the relatively light average point loads. If the bed were to somehow have the middle section drop out of it, such that the illusionist were left lying on far fewer nails only around the perimeter, the point loads on the nails would increase dramatically and would probably penetrate the skin! :shock: This is the main reason why designing floated rooms is so challenging. (Not that you're doing that... But the same issue comes up in that context.) Starting to make sense? --Keith :mrgreen:

Ah-HA!!! I see! Thanks so much for your help! :D

but I'm wondering why I should be worried about pounds per LINEAR foot when basically I'm building an enclosed box

Hi Rich - Floor design loads are typically spec'd out in psf because it's impossible to predict exactly where the loads will be. If the designer knows about a heavy concentrated load he'll include that, too. When designing a beam or joist the design assumption is that all the pounds-per-square-foot act like a uniform layer. Your floor was designed to hold 100 psf. If you had a joist every 2 feet apart, then each joist would have to carry 2-feet worth of load... that's (2 feet)(100 psf) = 200 plf. (Your plywood deck makes sure that the load gets to the joist.) That's why you have plf. It's just a way of looking at a load that's collapsed down to a line. So... joists are designed to support some plf load as a load capacity in plf. Walls loads are collapsed to a line for design purposes as an applied load in plf. The applied load should not be greater than the load capacity. Creatch

Thanks everyone! I talked to the structural engineer who was involved in the design and construction of my building, gave him the dimensions of my build and materials etc...(including a standup piano, how many people etc). and he gave my the go-ahead (with about 30 psf to spare). So now I feel more comfortable!!