I’m in a remodel and the spans seem right, but the tub is on one side of teh beam/support wall. This house has sagged abit around this area for a variety of reasons (rotted joists in basement, missplaced structural wall). as I put it back together, I’m thinking that the bathtub represent an anusual load. It’s just a built in 60″ unit so nothing exceptional. My question is…
When I look up joist spans/loads/spacings they never mention extra loading caused by a bathtub, is this because they’re way over the laod posed by a bathtub?
Thanks as always to any and all, Patrick.
Replies
The tables do not take into account loads due to bathtubs.
Joist spans in tables are based on uniform loads. 40#/sqft is a typical design load. A bathtub might have a design load of 120#/sqft.
It might have but not likely.
If you figure 16#/gal for thirty gallons, that's 480# total of water.
Double that for human flesh and divide by fifteen sq ft and you have a live load of 64#/sq ft.
That is a little over the 40 or 50 normal design loads but far short of 120 for typical bath room.
Excellence is its own reward!
Piffin, you think somebody weighing 480 pounds is gonna fit in a 60" bath and still have room for 30 gallons of water?
Got any pictures?
Joe H
I always allow for saftey factor. I don't know what george was allowing for. .
Excellence is its own reward!
My estimate is based on Kohler tubs. 6' long x 4' wide x 18" to the drain.
(I mis-estimated the drain as 2'. 24" of water weighs about 120#/sqft.)
18" of water weighs about 90#/sqft. The weight of the tub - not much. (People displace their weight in water.) These tubs have 4 pads that they sit on.
You have not lived until you have used a large tub.
I haven't lived for sure. After walking to school two miles through blizzards, uphill both ways mind you, I had to take my saturday night bath in a galvanized tubd about 28" across.
;).
Excellence is its own reward!
The rule I learned was, "A pint's a pound the world around."
Did I miss something, or did you mean to figure 16 pounds per gallon of water?Any jackass can kick down a barn, but it takes a carpenter to build one.
You be right! 8#/gal. I was thinking four pints to a quart for some strange reasson.
So in the end answer, i'm righter than I thought. Must've been another subconscious safety factor.
Thirty times eight is only 240 plus the human flesh at maybe 320 gives us 560# divided by 15 ( hey George you got This? Your tub has more water but spreads it over a greater area) is only about 38#/sq ft, welll under any normal design load for floors.
Now that we've done that, what's next? Waterbeds or refridgerators?.
Excellence is its own reward!
Yes, piffin.
Surely someone makes a combination waterbed, hot tub, and refrigerator! ;-)Any jackass can kick down a barn, but it takes a carpenter to build one.
Piffin ---
You were wrong.
A standard tub holds 12" of water to the overflow drain. About 60#/sqft.
18" of water in my tub is 90#/sqft load. 22" of water in other standard tubs is 110#/sqft.
Good design might be to overflow not to the overflow drain.
Certainly, you can design for less. I suppose it really does not matter. Most baths sit on short joists. Most tubs are near a joist support. Most joists machine grade well above visual grade. Most joists are designed for less deflection than 1/360. Most joists are limited by deflection not fiber stress. Most tub usage is short term. Most ...
Allright Piff, you wiley bast...
How do you handle this.
The floors are already framed in with 12inch TJI's, hanging from joist hangers on 8x10 beams. The subfloor is in. The joists span 15 feet.
How do you beef that up to carry a hot tub, or some such heavy device?Stef
About all you can do at this point is add more joists or LVLs. Adding stuff along the sides of the existing joists will do little or nothing.
They'll be tough to get in, though.Don't be too choosy or stingy about whom or how often you love.
hope that your plan isn't to tile the floors...
Bet that tgis are 24 oc...
brian
120 PSF sounds like plenty. You might see if the tub maker has actual numbers you can use. I designed my master bath using the numbers from Jacuzzi's web site.
-- J.S.
What about a fridge?
A full fridge is about 70lbs/sqft.
never doubled up under a fridge.
The code allows floors to be designed to support a uniform load of 40#/sqft.
It does not require that the actual load be limited to 40#/sqft (or equiv.).
It does not require that actual loads be considered.
Good engineering practice might consider actual loads.
I usually consider all appliances, cupboards, and shelves to loaded at 30#/cfft.
around here, it is 50lbs per sq. ft, 40 lbs live, 10 lbs dead, for interior floors. That may be what a uniform load of 40 lbs equal. Then when an individual walks out on their deck, the design load goes to 65 lbs per sq. ft, this one, I believe is 55 lbs live and 10 lbs dead. Location is Prescott Arizona. Be safe out there Jim J
Your code also specifies a "uniform load".
The code specifies only the live load, 40#/sqft for most rooms, 30#/sqft for sleeping rooms, something for decks ....
The dead load depends on the construction. 10#/sqft is reaasonable for most construction. Add a tile floor over a mud bed and you have may have more. Add built-in islands or built-in appliances and you have even more.
Deflection is computed using only the live load. Fiber stress is computed using both the live and dead loads.
GeorgeR, I thank you for your reply, things such as this , is one of the things I really enjoy about Breaktime, I learn. Jim J.
Standard floor loads are AVERAGES - So a typical bathtub is no big deal, sine some of the adjacent floor will typically not have load on it most of the time.
The only reason I would worry about it is if the tub is parallel to over-spanned joists. Then you might get into trouble.
If you're remodelling, add an extra joist or 2 under it. Won't hurt anything, and it might save you trouble when the plumber comes in and hacks away at the joists around the drain...............(-:
It is easier to get older than it is to get wiser.
In the olden days, (yes, long long before I did any of this, I swear), they used to double the joists under the tub face and under walls. We, I mean they, would also go off layout for tubs.
Wham, like a smack from the past!
In the dimm recesses of my memory, I think I did that once or twice. Doubled a joist under a wall that is.
Got tired of hearing sparky complain though.
Excellence is its own reward!
It was a fairly common thing, when I was a kid. You know, like walking to school uphill, both ways.
Piffin..... I still double joist's under tubs , drives my competition nut's telling me I don't have to do that, but my home owners think I'm the greatest thing since Skippy Peanut Butter when they hear others talking about it.
I also go off lay off for plumbing ,the extra laying out is well worth it knowing the plumbers can't find anything to cut with a sawzall drives them crazy,hehe
I had a homeowner taking some friends through their new house and I overheard one of the friends say , " at least this builder knows where to put the wood ,you oughta see how they cut up the wood in our basement"
Small investment for entertaining an old builder, kind of like useing that extra SR screw just to make sure those cabinets stay up there......heheheee
"Small investment for entertaining an old builder, kind of like useing that extra SR screw just to make sure those cabinets stay up there......heheheee"
You are an evil, very evil man. But I like your style.
But if you where the Quality builder that you claim to be you would be using DW screws instead of the cheap SR screws <G>.
Edited 5/6/2003 3:09:50 PM ET by Bill Hartmann
B. H. .....Ahh....the expert at Lowe's has been trying to get me to use the "new Multi-Purpose Dichromate screws" suggests I don't mess around with the 25lb box's , just get a couple of 50lb boxes but reminds me they are for interior use only and the phillips heads aren't really that bad. Do you need some ? I think Piffin has the web address listed under "my favorites. hehehee
i guess in short spans it can't hurt to double up. But, at what point does it become the straw that broke the camels back. Every second joist may add strength , but your actually increasing the dead load, as well as the live load. I'm not an engineer. It's just haven't done the math, and It makes me wonder. I am sure how ever it depends on the span.Where there's A wheel there's a way, got any wheels?
I don't think you'll ever get to the point where a joist fails to support itself, no matter how many of them run parrallell..
Excellence is its own reward!
Another "old way" of dealing with it? (My best guess, feel free to correct me)
My house, a 1950s Philly row, has the bath joists perpendicular to the others. 17' wide house, most joists run in the 17' direction, but the bath joists run front to back (about 7' f to b, 10' out of the 17' width). The joists are all (roughly) true 2x10, bath joists notched out on one end to rest on nominal 2x4 ledger. Other end rests on bearing wall. I assume this was done for the weight, but not just the tub. Bath has good ol' tile on mud floor, w/ recessed sub floor. (Pepto pink, floor and wall; boy was that a bright bath when empty!) I would NOT reccommend this method, as the joist with ledger is sagged compared to others, about 1/2" lower than its neighbor about 1' away - nice dip in ceiling, but apparently stabilized. Not certain about it, but again, apparently stabilized.
Incidental question: doesn't notching the joists, as for the ledger above, turn those former 2x10's into (effectively) 2x6's?If everything seems to be going well, you've obviously overlooked something.