# Support For Bathtub



## 4thorns

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


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## Mark K

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.


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## Frank

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.


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## Keystone

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.


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## Big Mac

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.


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## jim baird

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...


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## JAT

The good plumbers use A bed of morter under tub and shower units


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## gbhammer

JAT said:
			
		

> The good plumbers use A bed of morter under tub and shower units


Yeah but then you have to hire a laborer to mix it and a finisher to trowel it.


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## kyhowey

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.


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## Keystone

picking up on JAT's comment, not only good plumbers, a few MMI's require a mortar bed.


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## ICE

JAT said:
			
		

> The good plumbers use A bed of morter under tub and shower units


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.


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## Mark K

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.


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## incognito

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.


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## Keystone

The only question thats nonsense is the one that was never asked!


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## kyhowey

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."


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## Sandman

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.


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## Mark K

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


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## incognito

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.


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## kyhowey

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.


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## ICE

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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## gbhammer

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."


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.





			
				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.


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## Papio Bldg Dept

gb...are you suggesting that inspectors are fat with code?


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## Papio Bldg Dept

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.


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## gbhammer

Papio Bldg Dept said:
			
		

> gb...are you suggesting that inspectors are fat with code?


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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## Rio

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."


_One of the engineers I work with used to be a plan checker and told me about a phone call he got one time from a concerned tenant regarding a water bed on a second floor.  My friend explained that waterbeds are obviously quite heavy and that a certain amount of deflection could be expected, depending on a number of factors.  Before he could start explaining what these factors were he was interrupted by the tenant saying, 'Okay, I see it', referring to the sagging floor!  He managed to get the garden hose connected and the bed drained before the floor collapsed._


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## gbhammer

Rio said:
			
		

> _One of the engineers I work with used to be a plan checker and told me about a phone call he got one time from a concerned tenant regarding a water bed on a second floor.  My friend explained that waterbeds are obviously quite heavy and that a certain amount of deflection could be expected, depending on a number of factors.  Before he could start explaining what these factors were he was interrupted by the tenant saying, 'Okay, I see it', referring to the sagging floor!  He managed to get the garden hose connected and the bed drained before the floor collapsed._


See when that place was framed a six hundred pound inspector would have found out the floor joist were inadequate during the rough in.


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## GBrackins

either that or every building department should hire a 600 pound gorilla! besides, they'll work for bananas. And they would be great in a best ball golf tournament! after some of the exchanges lately on the forum it's nice to see some humor.


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## Sandman

My point is not to argue for or against the additional joist under a bathtub. I have been directly involved in the design, construction and inspection of over 3,000 residential units in the last few years and none of them had an additional joist under any of the upstairs bathtubs and, so far, we have not had any warranty issues. However, I would never make the argument that because "I have been doing this for X amount of years or have built X amount of units without incident" we do not need to consider what is recommended by the American Wood Council in the Wood Frame Construction Manual which is in fact referenced in the International Building Code. In the event a floor system failed due to loads in and around a bathtub the statement, "I have been doing this for X amount of years or have built X amount of units" doesn't mean anything. Instead, the designer and builder need to be prepared to argue that the building was designed and built at or above the minimum. And, finally, how many people in this forum weigh just 150 lbs? My guess is that the average weight will be closer to 200 lbs and all the literature suggests we are getting bigger, not smaller.


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## Big Mac

Yeah, a couple of times.  OK, that might be a bit of an exageration but...............


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## Min&Max

I think someone alluded to this before but I would be more concerned---and I am not at all concerned---about the actual floor sheathing/decking supporting the weight of the tub and its contents, especially if the tub is cast iron. The last cast iron tub I looked at had several supports located on the bottom of the tub floor which would appear to have the potential to dent or puncture the 5/8" - 3/4" osb or plywood floor. I wonder if it is possible that companies such as Koehler, Eljer and American Standard have any smart engineers who account for the weight of their product and its future contents on standard code compliant products and floor assemblies?


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## Mark K

You are not compelled to design based on your perception of the weights of the occupants.  The code only requires the building be designed to support the loads listed in the code.  If this were not the case one might suggest that all residential projects be designed for 100 psf since you could have a party where everybody is sholder to sholder.


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## Papio Bldg Dept

GBrackins said:
			
		

> either that or every building department should hire a 600 pound gorilla! besides, they'll work for bananas. And they would be great in a best ball golf tournament! after some of the exchanges lately on the forum it's nice to see some humor.


Can you teach Gorillas how to play darts?  I would prefer orangutans...then they can write "any which way but loose" for their guard rail comments.

Have you visited the Palaearctic–African Bird Migration Forum, a Discussion of the Palaearctic-African Songbird Migration traffic across the Sahara...and other things?  It could probably use a few more posts every week in my opinion.


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## gbhammer

We need a "Cut Loose" area of the forum.


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## TJacobs

[video=youtube;SkZsSydzQjM]


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## Daddy-0-

Of course a hot tub on a deck is an entirely different story.


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## ICE

Daddy-0- said:
			
		

> Of course a hot tub on a deck is an *entirely different story*.


None that I could tell here.


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## Architect1281

Oh ICE Magnificent one you are correct...

May your lips never freeze to your margharettia.

The correct answer from the sealed mayonaise jar on Funk and Wagnells front porch is.

Multiple design loading conditions based on time;

7 day loading, 30 day loading, and long term 100% loading................

7day and 30 day would calculate ot at  somewhat reduced load factors...

those would be for live loads like fill / empty tubs and snow in moderated climates -

the calculation adjusts the Fb bending stress in parallel grain wood fiber b increasin that number to 115% 115%

and in some wind cals to 133% and   as this is in the denominator of the fractional calc it is an increas in capacity.

The water bed would be a load that could and should not be reduced - same for filled spa pool type tubs - not drained

the water mattress 6 to 9 inc weighs 32 to 45 pounds per foot all the time well above the code 30 lbs LL/SF (15 sheets of 1/2 in gyp??)

so the typ res loads do not account for them. Sales people of such devices say the place the same load as a refrigerator. to which I reply Good try filling your bedroom with refrigerators.

Other items that designers (RDP or not) should consider are Kitchen Islands on large size tile floor with stone countertops.

The code lets them build and us approve the "Worst Possible"

Carnac divines the answer:

Siss Boom Baah!!!

Question??

What souds does an exploding sheep make????


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## Architect1281

There are also table sections that provide 20 PSF DL and those are more conservative and applicable to the island and some larger tubs.

as the reviewer IF proper plans address built in or increase load areas then we have something to review and advise..

otherwise we with experience can stand back and say here is where the stress (permanent deformations) vracks will appear.


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## jim baird

ICE said:
			
		

> 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.


A plumber I knew would put down a sheet of plastic and dump a bucket of drywall joint compound on it to bed a tub.


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## ICE

jim baird said:
			
		

> A plumber I knew would put down a sheet of plastic and dump a bucket of drywall joint compound on it to bed a tub.


Mortar and joint compound crumble too easily.  Sackcrete has rocks that will poke a hole.  Tapioca pudding costs too much (well the good stuff with the large pearls).


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## Architect1281

ICE on the tub support idea I recently watched a "This old house" segment where after install the plumber half filled the tub and the applied expansing closed cell foam beneath, let set and drained.

Actually not a bad idea as the water weight prohibited the foam from lifting the tub base and created a solid foam base.


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## Papio Bldg Dept

Architect1281 said:
			
		

> Question??
> 
> What souds does an exploding sheep make????


My son plays my old warcraft dos games...exploding sheep make a baaaahhh-ploop sound.  I could send you a wav file if you like.


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## GBrackins

send it .... send it .... everyone needs an exploding sheep sound on their computer. I use Dorothy from the Wizard of Oz for my error sound, "What would you do if you had a brain?" Might make for an interesting sound for emptying the trash.


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## HForester

Victoria,
Reading something on the internet may not be accurate with what is required by the _building codes. Note the name of this forum: _The Building Code Forum. We can appreciate your desire to play in this "sandbox" but you have "hijacked" a posting that is nearly* 5 years* since the last posting. I suggest that you try to keep your comments focused on relevant topics (recent postings) where it seems that your input will provide useful information from either personal experience or further reflection on what the Codes (the UBC, IBC, IRC and state codes) require.  
Please don't go away. Stick around and you will learn many things just by standing around!


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## Seth_Thomas

Good question, currently dealing with this.  Using a "free standing" tub.  So there is no decking/framing to support the tub which sits inside.  2 story home.  Was told that code required that an elevated 2x4 structure with decking needs to be created to support the tub.  Decking then will be tile flooring.

Is this really necessary?  Free standing tubs often don't look that great sitting up on a pedestal/raised 4" decking and not sitting level on the same tile flooring.

Thoughts?


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## mark handler




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## north star

*@ ! @*

Seth,

Please provide the applicable Code & Edition that your
are referencing.......Also, does your "free-standing tub"
have support legs ?.......Some do and some do not !

*








*


*@ ! @*


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## my250r11

Thanks Mark for showing us people are not always that bright.


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## Seth_Thomas

north star said:


> *@ ! @*
> 
> Seth,
> 
> Please provide the applicable Code & Edition that your
> are referencing.......Also, does your "free-standing tub"
> have support legs ?.......Some do and some do not !
> 
> *@ ! @*



I'm not the builder/contractor.  This was what I was told by a friend who is having a home built with a big home builder.  The projector/construction manager told him that. Of course, they didn't reference any code.

The tub has no legs.  It sits on the floor so the load is distributed across the entire base of the tub.

Enjoy that photo of the beam being cut for the plumbing..haha...nice.

Thanks


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## tmurray

Not required here and can't imagine why it would be.


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## my250r11

Seen some manu. installation instr. that may have this in it to provide room for the plbg. on a ground floor slab.


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## Seth_Thomas

It's on the second floor in this case of a 2 story home being built.  The project/construction manager told my buddy this.  I said this sound riduculous, basic code should account for enough pounds per sq.ft. on a residential structure on the 2nd floor to handle 600lbs, to include water/tub/person in tub for 20-30 minutes without some beefed up platform for it to sit on.

Since the builder never put on in this house before like this, I think they are just guessing.  Told my buddy to ask for a reference to the building code.  The construction manager is probably getting offended at this point by him taking precautions and asking these questions (questioning their knowledge I guess and EGO being hurt).  Too bad I told him to tell the guy. 

"No offense guys, but show me the code!"


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## north star

*@ ! @*

Seth,

From the `15 IRC,  



While no specific requirement for supporting a freestanding tub
is in the Codes, the framing underneath must be able to support
fully the loads imposed on them.

FWIW, ...a lot of construction managers & contractors are known
to talk the talk, but NOT be able to support it with actual Code
references.   

*@ ! @*


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## Pcinspector1

Mr. Seth, do you have a picture or a name brand of this tub with stock number that we can research? I'm curious what this tub looks like?


northstar posted some pictures but I take it that they're not the same.

Mark, that FJ cut is just every day cobbling that we see in the field
Also northstar and I like to see the purple primer being used, its code! Depending on which one your on!


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## Seth_Thomas

I would have to work on getting the brand name of the tub for you.

@north star, hard to read that image.  When I click on it says I can't access the image.  Too small to read!!

Thanks!  Would love to read and reference that.


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## north star

*@ ! @*

PC,

Sorry to disappoint you on the Purple Primer thingy, but
that went away with the `15 IRC.......They no longer require
it on drain lines, rather, it is [ acceptable to some ]  to use
that Blue Glue crap as the only visual identifier......Refer to
*Section **P3003.9.2 in the `15 IRC*......Of course your AHJ
could legislate to keep on using our well loved "Purple Primer !"

Seth,

Here is a Link to the ICC Codes, the `15 IRC, Section R502.3.2:
*http://legacycodes.iccsafe.org/app/book/content/2015-I-Codes/2015%20IRC%20HTML/Chapter%205.html*

*@ ! @*


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## Seth_Thomas

Found a photo of it.


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## Seth_Thomas

north star said:


> *@ ! @*
> 
> PC,
> 
> Sorry to disappoint you on the Purple Primer thingy, but
> that went away with the `15 IRC.......They no longer require
> it,rather, it is [ acceptable to some ]  to use that Blue Glue
> crap as the only visual identifier.
> 
> 
> Seth,
> 
> Here is a Link to the ICC Codes, the `15 IRC, Section R502.3.2:
> *http://legacycodes.iccsafe.org/app/book/content/2015-I-Codes/2015%20IRC%20HTML/Chapter%205.html*
> 
> *@ ! @*



Yes, found it...thanks for the shortcut.


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## north star

*@ ! @*

Seth,

That sure does look like a "Watering Trough !"
 Ha !  

*@ ! @*


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## Seth_Thomas

Apparently women love this...and a trend on many of the designer/home shows.  Heard it is a nearly $5K option...rolls eyes...


Here is a picture of the approximate location it would be and to the left where the photo cuts off.  Kind of imagine not far off that concrete wall above it, likely just on the other side of that main support running left/right.


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## ncbreef

north star said:


> *@ ! @*
> 
> Seth,
> 
> From the `15 IRC,
> View attachment 2538
> 
> 
> While no specific requirement for supporting a freestanding tub
> is in the Codes, the framing underneath must be able to support
> fully the loads imposed on them.
> 
> FWIW, ...a lot of construction managers & contractors are known
> to talk the talk, but NOT be able to support it with actual Code
> references.
> 
> *@ ! @*


Thanks Seth.  So here is how I ended up at this forum.  I have rebuilt a 1300 sq ft house in Raleigh - all new framing in every direction.  2nd bathroom will get a tub, (like the cat iron pictured a few posts up)   Tub with 60 gallons weighs about 750#s, then the big faucet and plumbing have to add at least 10#s and I weight 200.  It is a two person tub, so that adds a tiny bit more.  either way we are about 950 with just me.  at 121/2 sq ft or so of overall load space that is about 75lbs per sq ft.  This house started out as a 600 sq ft bungalow and was added on and on over the years  - hence having to totally rebuild.  it is on a crawl space and there are numerous foundations, not just a simple rectangle.   we put new, treated sills, band and the entire floor system.  this particular span is about 10'.  we used some 2/10s where the tub was going to be (not knowing the actual weight when we built) and the rest of this part of the floor system is 2/8s.  we did do a box in (have to get pics to explain) as per the framer for extra strength.  now that I know the actual weight not sure if it is strong enough.  Options I have considered ; pouring a pier or two and using a 6x6 treated to sit under the floor joists resting on the pier - that would distribute the weight to the ground and take a lot of strain off the joists, no?    I got the idea from the way the engineer designed the cathedral LVL system,  5 piers, one post at 15'    thoughts?


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## ADAguy

Moving in the right direction, shorter span, closer spacing, add pier, better support. no inspection in your area?
My 1905 has a C.I. claw and ball on original framing and it supports both of us.


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