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Support For Bathtub

4

4thorns

Bronze Member
Joined
Jul 7, 2011
Messages
65
Does anyone know of any code in the IRC that requires extra floor joists underneath a standard size bathtub? It seems that I was told by someone a while ago that a double joist was required but can't find it anywhere. Any thoughts?

Thanks,

Doug
 
Do not believe that such a requirement exists.

While the depth of water could exceed the 40 psf live load for residential construction I suggests that it is not a problem for seeral reasons which include:

-- The high loads are local and when averaged out they figure.

-- The water is only there for a short period of time. Wood has a higher strength when the load duration is short.

-- The rigid nature of the bath tub distributes the loads in ways that reduces the effect on individual members.

-- There are often partitions on the floor below that reduce the spans on the joists under the bathtub. When the spans are really long the member is controled by deflection consideations.

Bottom line for a standard size bathtub I would not worry.
 
Standard 30x 60 bathtub with 42 gallons water to overflow weighs about 350-400 pounds full and covers 12.5 sq ft.

400/12.5= 32psf

Leaves 100 pounds for parts of the occupant above the water line.

Does not include adjacent floor space with just bathmat.
 
Average tub can hold 40 to 60 gallons of water.

Water weighs 8.33pds per gallon.

Average weight of user??? yeah lets ask that on the application

If you calculated each tub using a known weight you will find a few examples of the need to close up the joist spacing or even throw in a double.
 
Buildings an structures and all parts thereof shall be constructed to safely support alllloads including dead loads, live loads, roof loads, snow loads, seismic loads, .... Section R301.1. That is the code citation. Having said all that, I would tend to agree that a normal type tub is unlikely to be much of an issue with regard to floor loading. I would say the bigger issue that is often overlooked is the need for a support ledger under the back flange of the tub.
 
What I see often is jet tubs suspended from their rims on framing with nada under the bottom. Also tubs and tub/shower units with little feet on their bottoms, that often do not touch floor. Where missing there is usually a little bag taped to the surface of the unit with shims and instructions on their use and placement...
 
JAT said:
The good plumbers use A bed of morter under tub and shower units
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Yeah but then you have to hire a laborer to mix it and a finisher to trowel it.
 
From the 2001 Edition of the Wood Frame Construction Manual (for one and two-family dwellings) :

3.3.1.5.3 Single or continuous floor joists supporting concentrated loads Where concentrated loads exceeding 300 pounds must be supported by floor joists, the joists supporting the load shall be doubled (see Figure 3.5d)

That figure, 3.5d, specifically shows joist doubled under the front and back of the tub.
 
JAT said:
The good plumbers use A bed of morter under tub and shower units
Click to expand...
A couple bags of sackcrete under the tub was popular in a lot of places I've worked. They left it in the bag and the ambient moisture would be enough to get it to set up.
 
keyhowey

Where is it stated that compliance with the Woof Frame Construction Manual is mandatory? Does this mean that a 310 pound man cannot walk across the floor unless the joists are doubled?

We have a practice in search of a code requirement.

The reality is that there is no code requirement. Tubs are typically installed without doubling a joist. In more than 30 years I have not heard of a problem resulting from the lack of a doubled joist under a bath tub.
 
What a bunch of nonsense. No one should be allowed to inspect a thing until they have worked in the specific trade for at least 5 yrs. In the 35+ yrs that I have been in the construction business, both doing the work and now inspecting, I have not seen one negative occurance of not doubling floor joist under the tub. It may be ok under the legs of the older cast iron clawfooted tubs where the load is more concentrated but even then it is not actually needed. The bigger concern would be the ability of the floor decking to support if legs did not rest directly over a joist. Modern cast iron tubs provide more bearing area so that the doubled up joists is not even a remote issue.
 
R301.1.1 references the WFCM as an alternative (subject to limitations of the IRC). I don't required double joists under bathtubs, but the OP asked a question that I could supply an answer that cites specific language other than "I've been doing this for 35 years and have never had a problem."
 
Yeah, the American WOOD Council probably doesn't know much about WOOD frame construction. Probably best to trust the guys who have all that field experience when it comes to design values for high wind, spans, beams, columns, fire design and code conformance.
 
Let us assume that myself and other engineers do not know what we are talking about. We have been designing buildings for many years without requiring doubling of the joists under tubs then it would be expected that there would be a lot of problems with these floor supporting bath tubs. Please answer why not only have I not heard of such a problem but I have not heard other engineers menntion that there is a problem.

Irregardless there is no mandatory requirement in the code. Thus the building official should not be requiring the additional joist
 
Righhhhtttt. It must be that steady stream of reports of people being killed by bathtubs falling through floors that has some thinking this is a legit concern.
 
If Frank is correct with the 42 gallons to overflow and water weighs 8.34 lbs/gallon. That gives us a max of 350lbs. for the water alone. If the standard tub covers 12.5 sq. ft., that gives us a live load of 28 psf. Floor has to be designed for 40psf minimum. Add a 150 pound person would equal 40psf.

Then throw some actual logic into the conversation....my kids are the only ones to in my house that take a bath. We don't even have a tub in our master. It's doubtful a person will ever fill the tub to the overflow line and then climb in. The other this is this only matters if the floor joist is at max span. We're talking basic, minimum code.

I'm really only watching this if there is a large, two-person jet tub in the master bathroom.
 
How about fat Yolanda and her king size water bed? We're talking some pounds now.

I had a case where there was a shower pan built that lasted about six months and leaked. This was a redevelopment project. There was a meeting at city hall where I met the owner for the first time, all 600 pounds of him. When a new contractor came to the counter to get a permit I told him that his best bet would be to put a foundation under the shower pan or it will fail again. I was summoned to the city managers office and asked: "Are you calling the citizens fat?" I said, "Well yes, yes I am."
 
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ICE said:
How about fat Yolanda and her king size water bed? We're talking some pounds now. I had a case where there was a shower pan built that lasted about six months and leaked. This was a redevelopment project. There was a meeting at city hall where I met the owner for the first time, all 600 pounds of him. When a new contractor came to the counter to get a permit I told him that his best bet would be to put a foundation under the shower pan or it will fail again. I was summoned to the city managers office and asked: "Are you calling the citizens fat?" I said, "Well yes, yes I am."
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I say you should hire him.

gbhammer said:
I thought we all agreed that the tied off over weight inspector was going to lean on the rail, and if it didn’t collapse it passed.
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Papio Bldg Dept said:
Yep, we draw straws for the week, shortest straw gets Monday, next Tuesday, and so on through-out the week. Any guard rail inspections that come up on your day, you have to lean on the rail. Wednesday's are my day in the barrell.
Click to expand...
 
don't forget displacement...right there you start losing Frank's 42 gallons.

kyhowey said:
If Frank is correct with the 42 gallons to overflow and water weighs 8.34 lbs/gallon. That gives us a max of 350lbs. for the water alone. If the standard tub covers 12.5 sq. ft., that gives us a live load of 28 psf. Floor has to be designed for 40psf minimum. Add a 150 pound person would equal 40psf. Then throw some actual logic into the conversation....my kids are the only ones to in my house that take a bath. We don't even have a tub in our master. It's doubtful a person will ever fill the tub to the overflow line and then climb in. The other this is this only matters if the floor joist is at max span. We're talking basic, minimum code.

I'm really only watching this if there is a large, two-person jet tub in the master bathroom.
Click to expand...
 
Papio Bldg Dept said:
gb...are you suggesting that inspectors are fat with code?
Click to expand...
Sitting at this desk for most of seven years, and playing darts in bars instead of working in the field has made me less than fit. Field work as an inspector at least here in our department must have a similar affect to sitting a desk because our guys are all pushing the limits on their belts loops. As a contractor I always had some muscle mass 6'2" 210 lbs. For the last 5 years I have been leveled off at 280. So yes I think I can safely say inspectors are fat with or with out code.
 
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