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Old 06-16-2012, 09:27 AM   #1
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Dead Loads / Struct. Eng


Trying my damnedest to figure this all out.

Basically, its an old 1920's home that I decided (naively) to put a walk in shower on the second floor.

I'm paranoid neurotic; and want to be sure that this walk in shower will hold. I don't want to spend all this time and $$$$$ building a house to have it collapse under me in 10 years or whatever.

I worked it out, and my deadload appears to be about 37 psf, and my live load is about 61 psf so... mynah.....

I can understand and work the formulas here:
http://www.ehow.com/how_7485788_calc...-capacity.html

but I have no idea how to calculate the max deadload of a joist system with irregular spacing.

P L E A S E H E L P ! ! ! ! !

tldr; Please help me understand what my maximum live and dead loads will be for this detailed walk in shower area.

pics attached related; they are diagrams of what I'm working with.
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Old 06-16-2012, 09:32 AM   #2
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Originally Posted by Ghengisconrad View Post
Trying my damnedest to figure this all out.

Basically, its an old 1920's home that I decided (naively) to put a walk in shower on the second floor.

I'm paranoid neurotic; and want to be sure that this walk in shower will hold. I don't want to spend all this time and $$$$$ building a house to have it collapse under me in 10 years or whatever.

I worked it out, and my deadload appears to be about 37 psf, and my live load is about 61 psf so... mynah.....

I can understand and work the formulas here:
http://www.ehow.com/how_7485788_calc...-capacity.html

but I have no idea how to calculate the max deadload of a joist system with irregular spacing.

P L E A S E H E L P ! ! ! ! !

tldr; Please help me understand what my maximum live and dead loads will be for this detailed walk in shower area.

pics attached related; they are diagrams of what I'm working with.
Do you have plans, permits and getting inspections for this?

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Old 06-16-2012, 09:36 AM   #3
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I have permits. Inspector says it will be alright. I don't trust/believe him. I believe I can understand the basic concepts behind load capacity, I just have a few questions.
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Old 06-16-2012, 09:51 AM   #4
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It's not quite as simple as following those figures in e-how. There are other considerations when designing structural timber, such as maximum allowable deflection, and bearings.
IMO, your live load seems a little on the high side, though there will be stipulations on this in your local Code.
This is a DIY site and it's fine doing the physical work yourself - which I've no doubt you could do - but sizing the members and justifying a design is a different matter, usually best left to a SE.
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Old 06-16-2012, 09:52 AM   #5
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if you have any questions about the floors' weight holding capacity then add sister joists next to existing joists and nail really well and do not give it another thought after that. for open span floor joists you have to sister to get more joist strength.
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Old 06-16-2012, 09:55 AM   #6
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Was there a bathroom in the space before? I can't read your plans as they come up all blurred. Are you thinking you will be cutting in to any floor joists to run plumbing (drains) or is everything running parallel to the joists? Are you doing a tile floor? Is the shower floor also tile or acrylic? Depending on the spacing of the floor joists (typically further apart on older homes) you will need a thicker substrate if doing a tile floor. Vinyl doesn't matter so much other than to eliminate creaks. As for the shower stall itself, you want to ensure the subfloor is good and secure. Unless you already have structural issues or intend to add an especially heavy tub or vanity too, it would be unusual to have weight load issues as the structure "should" be just fine.

Look at schluter.com to get some ideas on fairly bullet proof shower installations as well as guidelines on subfloor thickness for various types of construction ... We are certified installers so I can help if you have further questions on their products. There is also another German company called Wedi who do similar products depending on what is available locally for you. Mapei also have some great products widely available here in Canada.

Disclaimer: I absolutely am not recommending cutting in to floor joists ... Merely wondering if that is what the OP was considering as so often happens.
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Last edited by Bonzai; 06-16-2012 at 09:57 AM.
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Old 06-16-2012, 09:58 AM   #7
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I guess I'm trying to understand the big picture in order to put my mind at ease.

If 2x8 16 o.c. spanning this distance can handle a deadload of say 10 psf, then would doubling up the joists make me able to handle 20 psf? would making it 8 o.c. make it double?

With me, its always as much a theoretical curiosity of the limits and possibilities of the task at hand as much as it is the actual accomplishment of it.

Like I said, my inspector looked at it and said 'pfaw, its fine'. But he has no liability if this overpriced build collapses.
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Old 06-16-2012, 10:01 AM   #8
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Quote:
Originally Posted by Bonzai View Post
Was there a bathroom in the space before? I can't read your plans as they come up all blurred. Are you thinking you will be cutting in to any floor joists to run plumbing (drains) or is everything running parallel to the joists? Are you doing a tile floor? Is the shower floor also tile or acrylic? Depending on the spacing of the floor joists (typically further apart on older homes) you will need a thicker substrate if doing a tile floor. Vinyl doesn't matter so much other than to eliminate creaks. As for the shower stall itself, you want to ensure the subfloor is good and secure. Unless you already have structural issues or intend to add an especially heavy tub or vanity too, it would be unusual to have weight load issues as the structure "should" be just fine.

Look at schluter.com to get some ideas on fairly bullet proof shower installations as well as guidelines on subfloor thickness for various types of construction ... We are certified installers so I can help if you have further questions on their products. There is also another German company called Wedi who do similar products depending on what is available locally for you. Mapei also have some great products widely available here in Canada.

Disclaimer: I absolutely am not recommending cutting in to floor joists ... Merely wondering if that is what the OP was considering as so often happens.
The forum resized my very good photos....

Temp link here:

https://images.4chan.org/diy/src/1339813187345.jpg

and here:

https://images.4chan.org/diy/src/1339772670872.gif

There is no cutting happening. I have all the plumbing done. I asked about exactly what I need to know;

to recap, what I want to know is:

How can I know/understand that my joist system will support the dead-load psf of 37?
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Old 06-16-2012, 10:01 AM   #9
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If in doubt spend the $$ to have a structural engineer look ... They may just say you don't need me and charge you for one site visit.
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Old 06-16-2012, 10:04 AM   #10
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I "D O" plan to add an especially heavy tub. I have factored all of the tub, sheetrock, tile, etc. Its a total of about 3000 lbs in that small space, plus another 1400 when the bathtub is full.
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Old 06-16-2012, 10:05 AM   #11
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I HATE paying people for things I don't understand myself, because they usually do what I come around to realize is a poor job after my understanding/ability catches up with what they have done, and money is already EXTREMLY tight.
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Old 06-16-2012, 10:12 AM   #12
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Originally Posted by Ghengisconrad View Post

If 2x8 16 o.c. spanning this distance can handle a deadload of say 10 psf, then would doubling up the joists make me able to handle 20 psf? would making it 8 o.c. make it double?
Yes; and Yes.
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Old 06-16-2012, 10:14 AM   #13
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cool, so if it doesn't matter the spacing (assuming they are reasonably regular), a joist in a system is a joist in the system, and dead load capacities stack? So I have 10 joists inside 80 inches, thats like having it 8 inches on centre?

Last edited by Ghengisconrad; 06-16-2012 at 10:20 AM. Reason: wording was clumsy
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Old 06-16-2012, 10:20 AM   #14
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I'm guessing that what you took out (demo) from the original bathroom is about as heavy as what you will be going back with. for floors usually 1 1/2" of concrete and tile comes out of older baths and that stuff is heavy.

Also want to mention, get yellow pine to sister with as it is a stronger wood than standard whitewood, if you can find old floor joists like what are in the floor now and add them in there they would be stronger than yellow pine most likely. joists used to be 2" thick or bigger and made from heavy duty heart wood from big trees. if you want to be really seriosly satisfied then put in an lvl floor system, you could build an entire house off of your bathroom floor!

Last edited by hand drive; 06-16-2012 at 10:26 AM.
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Old 06-16-2012, 10:20 AM   #15
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Quote:
Originally Posted by Ghengisconrad View Post
I HATE paying people for things I don't understand myself, because they usually do what I come around to realize is a poor job after my understanding/ability catches up with what they have done, and money is already EXTREMLY tight.
An engineer does this for a living. What makes you think you know more than they do and come on a Diy'er forum and get the answers? What makes you think that you will understand what they do overnight?

Why are you doing the job if money is extremely tight and not want to do it the right way and ask for professional help? Coming to a DIY'er forum and asking free structural advice is comforting and smart to you and makes you feel safe? Couple hundred dollars isn't going to break you since you can afford to do this type of job.

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