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Discussion Starter · #1 ·
I am thinking to remodel a bathroom which is about 7 by 10 with floor joists along the longer axis with 12 inch between them. The joist are 2 by 8 and lying on two supports (a metal beam and a concrete wall). Everything will be covered with plywood and .5inch Hardieboard (I have it lying around from one of the previous projects, that's why it might be too thick but I'd say i'm okay with that). I am planning to install 2 by 2 tiles and put a vanity on top of that. The vanity is rather heavy (about 340 lbs with a quartz counter) so my question if it is possible to put that load without going over.
In particular,
- can I consider that vanity as a life load (in that case it becomes close to 35psf)?
- The load on beams will be rather flat (I know that all moments have to be considered but approximately it can be considered to be a flat load) and considering that the floors will be reinforced with Hardie I think it should be ok to put that load on three beams (the vanity is abut 20 by 65) - would anyone who knows better be able to provide an opinion on that, please.

Thank you in advance for your help!

P.S. I do not know the grade of my beams so I assume that they are the worst possible for the above calculations (to be on a safe side)
 

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Naildriver
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And use 1/4 hardiebacker on floors. 1/2" is for walls. Likewise with a heavy load, I would install the vanity first and tile around it. Excess weight on small tile could cause problems.
 
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FYI, Hardi backer contributes zero to carrying capacity of the floor. That said, you should be fine with the 12” joist spacing as even the crappiest grade of lumber gets you 10’ 3” at 12” centers, 40 psi live, 10 dead.
 

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Discussion Starter · #5 ·
Thank you to everyone for the responses! They are extremely very helpful!! I have some follow up questions/clarifications if I may: @ront02769: I have read that the floors with .5" hardi are sturdier do they distribute loads better than ply, dont they?
@chandler48: .5 vs .25 hardie = to around 1.2 psf in the deadweight but, as far as I remember, the floor with tiles (24X24 in my case) has up to 15 psf instead of up to 10 (so the only thing that I have to think about is the total thickness) - am I wrong? Please correct me if I do not remember/understand something

THANK YOU ONCE AGAIN to everybody for your help!
 

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Naildriver
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Hardiebacker nor Durock adds any strength to the floor as @ront02769 indicated. If you need it beefier, add plywood, then cbu. The CBU gives a flat surface that does not contract or expand like wood, and it is ideal for adhering with thinset.
 
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