Welcome to the DoItYourself Forums!

To post questions, help other DIYers and reduce advertising (like the one on your left), join our DIY community. It's free!

Need to strengthen floor/joists for new bathroom addition?

yottaflops's Avatar

Join Date: Sep 2008
Posts: 101

04-07-13, 06:43 PM   #1  
Need to strengthen floor/joists for new bathroom addition?

I am having a contractor build a new bathroom (in what used to be a walk-in closet). It's ~8' x 6' with a walk-in shower, toilet, vanity. The new bathroom will be on the 2nd floor, over an open garage area.

He said he would put mortar/cement over the existing floor to create a slope, then tile around the walls and floors.

I was buying and hauling the tiles this weekend, thinking, wow--this stuff is heavy. So I did a quick calculation. Assuming 4lbs/sq ft of tile, I'd have about 800 lbs of tile. That, + the mortar/concrete underneath, + toilet, + vanity and everything else, are we not talking ~2000 lbs of stuff?

That got me a little worried. I was looking at the joists beneath another (existing) bathroom, also over the garage, I noticed that one joist (2x10) is doubled up over that bathroom. (That bathroom does have a bathtub, however, which the new one won't have.)

A bit about the floor structure:
-2x10 joists 16" oc
-The house is old but the joists look to be in good condition
-The span is ~12ft.
-I have no idea what grade of lumber they used, as I can't find a stamp anywhere.

Should I be concerned at all, or am I just making things up to worry about?

P.S. I did try to use these online max span calculators, but since I don't know the lumber grade/material, I'm not sure what to do. I tried Douglas-Fir No. 1, with 50lbs live + 15lbs dead load, and the span came out to ~14.5 ft.

Sponsored Links
Nashkat1's Avatar

Join Date: Mar 2012
Posts: 8,470

04-07-13, 09:51 PM   #2  
It may be fine the way it is as far as supporting the load goes, but I would want to stiffen it a little bit. Cross-blocking with 2x10s - or even 2x8s - 16" o.c. would do that.

I did that after cutting existing joists down by more than 3" and before installing nearly 3' of plywood, concrete and tile in a second floor bath. It never budged.

Gary in WA's Avatar

Join Date: Mar 2013
Posts: 457

04-09-13, 03:35 PM   #3  
Figure #2 grade, west coast is usually Doug-fir (if older), if really old, could be #1 or Redwood...

A handy help; The Amazing John Bridge Forums Deflect-O-Lator :-)


PJmax's Avatar
Group Moderator

Join Date: Oct 2012
Posts: 42,500

04-09-13, 06:52 PM   #4  
As Nash mentioned.....add cross bridging to help.

If you were inclined to double up the beams (and I think I might be).....you'd need to remove a good bit of sheetrock in order to get them in.

If you go by that deflect o lator.....the span is too long for masonry.

yottaflops's Avatar

Join Date: Sep 2008
Posts: 101

04-09-13, 10:03 PM   #5  
Thank you guys! Much appreciated =) I'll talk to the contractor and see what he can do.

Search this Thread