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Old 05-22-2019, 02:44 PM   #1
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Sister floor joists for bathroom floor - need advice to proceed


Hello!

I find myself on this new forum because of a similar post I found where someone repaired their uneven floor by sistering joists, but my problem has some unique concerns that I am requesting some advice on.

My scenario is for a very small bathroom ~5'x8' and I've just pulled the 1x6 slats to sister my floor joists to relevel my floor and add strength to accept my tiles. My existing joists measure 1.75x7.5 and run about 12' to the center support of my house, 16" on center.

When I pulled my floor I saw a few things that made me question my next step.
1) There was more water damage than I thought with the outer most joists (from the tub). Do I need to remove this part of the joist or will sistering the joist be enough?

2) I have some strange obstructions (HVAC ducts) between my joists. When I sister these joists, does it matter what side I add the new joist to? Also, looking at the joists on the left, I have close spacing for some reason. Is there a typical way to handle this?

I have enough questions that I could probably write a book, so I'll stop here and provide some pictures in hopes of receiving some feedback to my immediate concerns. Thank you for your time!
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Old 05-22-2019, 04:01 PM   #2
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Re: Sister floor joists for bathroom floor - need advice to proceed


How far out of level are they? Can't be accomplished with shimming?

The close o.c. spacing by the left wall probably has to do with the chase for the vent, or something else next door, or they thought the bathroom was flipped and was framing for a wide wet wall. Nothing to worry about.

The water damage on the left looks more surface. The right damage looks like someone already sistered part of it there (BTW nice notch for the tub pipe). A return in a bathroom is not allowed. Looks like you have a 16" flex pulling in from a vanity toekick?

Last edited by 3onthetree; 05-22-2019 at 04:03 PM.
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Old 05-22-2019, 04:13 PM   #3
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Re: Sister floor joists for bathroom floor - need advice to proceed


The double on the left was intended for the wall to sit on, so on the other side of that I would put a 2x4 to close the gap and then a new joist beside that to support the wall.
I know that adds more questions about the furnace or?

On the right side I would remove that 3 ft scab and replace that with a full length. And I would not be concerned about the return air.


Any time we deal with rot, we remove all that we can and anything left, even with just water stains we paint with a copper treatment just like they use for treated lumber.
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Old 05-22-2019, 08:54 PM   #4
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Re: Sister floor joists for bathroom floor - need advice to proceed


So the unevenness looks like it was from the fact that the 2 middle joists are low. The shims would be less than 0.5 inches I think, not terrible. The other reason to sister these joists is to remove floor deflection for the tile I'm about to lay. (online deflection calculators say I'm on the edge with strength which could explain why the previous tile was damaged)

The furnace exhaust is only 2" from the nearest joist so not sure I can run a new joist the full span. I had thought about just adding cross members between joists to support the wall sine its essentially just floating on the remaining 1x6's.

3onthetree,
To clarify the intake, its actually pulling air from the hallway, not the bathroom. The installer used the sub floor and floor joists as a transition to the intake vent...its ridiculous, I've never seen anything like it. BUT NOW that intake vent is in the way of me running a sister joist...making getting my HVAC replaced and intake installed in a new location (correctly) that much more important.

Nealtw,
When you cut the rotten parts, would you cut the section of the beam (complete cross cut) or just remove partial cut outs of the beam? I assume complete sections as I've seen other do online.
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Old 05-22-2019, 09:05 PM   #5
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Re: Sister floor joists for bathroom floor - need advice to proceed


Quote:
Originally Posted by willkyl View Post
So the unevenness looks like it was from the fact that the 2 middle joists are low. The shims would be less than 0.5 inches I think, not terrible. The other reason to sister these joists is to remove floor deflection for the tile I'm about to lay. (online deflection calculators say I'm on the edge with strength which could explain why the previous tile was damaged)

The furnace exhaust is only 2" from the nearest joist so not sure I can run a new joist the full span. I had thought about just adding cross members between joists to support the wall sine its essentially just floating on the remaining 1x6's.

3onthetree,
To clarify the intake, its actually pulling air from the hallway, not the bathroom. The installer used the sub floor and floor joists as a transition to the intake vent...its ridiculous, I've never seen anything like it. BUT NOW that intake vent is in the way of me running a sister joist...making getting my HVAC replaced and intake installed in a new location (correctly) that much more important.

Nealtw,
When you cut the rotten parts, would you cut the section of the beam (complete cross cut) or just remove partial cut outs of the beam? I assume complete sections as I've seen other do online.
That return air is normal stuff done all the time and if the bay was 1 1/2" smaller at the time, he still would have used it.
We usually just carve away the rot, the good part left will still add stiffness to the new joist.
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Last edited by Nealtw; 05-22-2019 at 09:27 PM.
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Old 05-22-2019, 09:19 PM   #6
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Re: Sister floor joists for bathroom floor - need advice to proceed


Quote:
Originally Posted by willkyl View Post
So the unevenness looks like it was from the fact that the 2 middle joists are low. The shims would be less than 0.5 inches I think, not terrible. The other reason to sister these joists is to remove floor deflection for the tile I'm about to lay. (online deflection calculators say I'm on the edge with strength which could explain why the previous tile was damaged)

The furnace exhaust is only 2" from the nearest joist so not sure I can run a new joist the full span. I had thought about just adding cross members between joists to support the wall sine its essentially just floating on the remaining 1x6's.

3onthetree,
To clarify the intake, its actually pulling air from the hallway, not the bathroom. The installer used the sub floor and floor joists as a transition to the intake vent...its ridiculous, I've never seen anything like it. BUT NOW that intake vent is in the way of me running a sister joist...making getting my HVAC replaced and intake installed in a new location (correctly) that much more important.

Nealtw,
When you cut the rotten parts, would you cut the section of the beam (complete cross cut) or just remove partial cut outs of the beam? I assume complete sections as I've seen other do online.
Your idea of blocks under the wall will work.
I am guessing that you have a chase next to this wall for the furnace pipe.

The bottom of the chase should be fire stopped and this area between the wall and the floor needs to be fire stopped. You can do that with sheet metal nailed to the joist and the bottom of the wall or just a flashing between the floor and behind the drywall.
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Old 05-23-2019, 07:26 AM   #7
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Re: Sister floor joists for bathroom floor - need advice to proceed


Quote:
Originally Posted by Nealtw View Post
Your idea of blocks under the wall will work.
I am guessing that you have a chase next to this wall for the furnace pipe.

The bottom of the chase should be fire stopped and this area between the wall and the floor needs to be fire stopped. You can do that with sheet metal nailed to the joist and the bottom of the wall or just a flashing between the floor and behind the drywall.
That explains what that sheet metal is doing, I had figured the pipe was double walled but did not think about the sheet metal also being part of that.

I think I will be blocking both walls since they both have similar issues, lacking a joist directly under.

I've made plans for what I am thinking I could do. Is there anything that would be incorrect in my drawing?
- one 12" span on the right side of the joist.
- two 10" spans (to cover 2/3 of the total span) secured to the left side of those joists.
- blocks spaced 2-3ft apart under the wall for support.
-reroute tub spout due to interference with beams. I would like to use something like the Watco Flex tub drain system.

I was looking to secure with 16D nails (2 or 3 rows) spaced no more than 16" apart. Construction adhesive would be applied to the mating faces.

One question I had was, with my existing beams being 7.5" and the new beams being 7.25" is it best practice to have the beam level at the top (leveling a floor) or at the bottom (supporting a load if running the full span)? OR should I get 2x10's and cut to exact size?
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Old 05-23-2019, 12:21 PM   #8
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Re: Sister floor joists for bathroom floor - need advice to proceed


Quote:
Originally Posted by willkyl View Post
That explains what that sheet metal is doing, I had figured the pipe was double walled but did not think about the sheet metal also being part of that.

I think I will be blocking both walls since they both have similar issues, lacking a joist directly under.

I've made plans for what I am thinking I could do. Is there anything that would be incorrect in my drawing?
- one 12" span on the right side of the joist.
- two 10" spans (to cover 2/3 of the total span) secured to the left side of those joists.
- blocks spaced 2-3ft apart under the wall for support.
-reroute tub spout due to interference with beams. I would like to use something like the Watco Flex tub drain system.

I was looking to secure with 16D nails (2 or 3 rows) spaced no more than 16" apart. Construction adhesive would be applied to the mating faces.

One question I had was, with my existing beams being 7.5" and the new beams being 7.25" is it best practice to have the beam level at the top (leveling a floor) or at the bottom (supporting a load if running the full span)? OR should I get 2x10's and cut to exact size?
It would be better if you could do 12 feet on the two in the middle,

The one on the right can stop short of the tub drain and put in a double block across under the wall with hangers for the double block and the single hanger on the cut one.

I would put the new joists crown up with shims under the ends for the 1/4". If the crown brings them above the old, that will likely fix the out of level
3 nails 3" 16" OC
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