[gslenk]

TLDR:
1) Can I put a cast iron tub here? If so, do I need to add blocking and/or support? For either the joists (sister), the tub feet (perpendicular blocking), or both?
2) Is it worthwhile to drop the finished floor 1/2" by removing the 1/2" subfloor before laying advantech? Could the walls be supported by blocking (spaced how far?) and would it disturb/weaken the structure/subfloor for tile/tub/walls?
3) Sistering joists looks like it requires removing the 1/2" subfloor due to plumbing/electrical/hvac ductwork below, if it factors into the decision.

More details below.

Tub details:
Kohler Villager, 60"x30.25" (12.5sf), 316 lb (~25psf). Capacity 33 gal (+~280lb), a human might add 100lb if they take baths (not showers) standing up. So dead load, ~25psf, live load ~56psf.

Existing floor:
2x8" unknown species. I would say 16" OC (it is in general), but check the diagram, this is a funky area. Span is 10ft 11" from exterior bearing wall studs, to interior bearing wall below.
Subfloor is 1/2" plywood, not T&G. Would like to remove down to joists, but could keep/ignore when installing advantech 23/32 OSB.

Diagram: Left side is the exterior wall, brown/orange are joists, green/yellow is the walls (all 2x4). Rooms on "top" and "bottom" sides, hallway to the right.

Remodel plan:
23/32 Advantech OSB regardless of keeping or removing the 1/2" subfloor. Would I need to add blocking under the tub feet? I intend on using ~6" square steel plates as shims to level the tub. The feet do not land on studs, they are the little rectangles in the diagram. Also can the floor support this tub or should I abandon the cast iron idea?

I'd like to remove the 1/2" existing plywood subfloor down to studs, so I can match the tile height to the existing finished hallway floor. In the master bath I did, tile was somewhere between 1/4" and 1/2" higher. So, not a deal breaker if I keep the 1/2" plywood, but it should make for a cleaner finish. Maybe that's just me getting carried away...

Also, the (non-load bearing) walls do not lie on top of floor joists so I imagine blocking would be necessary to support the walls, and bathroom subfloor. Adjacent rooms are supported within 1.5-2.5" of the walls so they seem to be OK.

 

[Nealtw]

Can you draw in the plumbing below that can not be moved as well as HVAC
Do drain pipes go thru joists?

Is the space below finished?

 

[gslenk]

May have been a slight exaggeration, here's what's going on down there:

Mostly unfinished in this area, but it doesn't matter too much. Will be practically gutting and remodeling the basement after the main floor all done.

Red/blue: Copper water supply. Will likely be cut out and replaced around the orange circle, or further down if necessary. New copper will generally follow the same paths. Attached to bottoms of joists where perpendicular, up/in joist bays where parallel.

Maroon/brown: Drain/waste pipes, again, will be removed as far as the orange circle. Reinstall will likely take a similar layout (replacing cast iron with pvc) since the main vent stack is in the green circle area (3").
These are all below joists.

Purple (real problem): Big rectangle: HVAC return trunk attached below joists, goes the length of the house. Horizontal box:supply duct in joist cavity. Vertical box: sheet material sealing the joist cavity for return air to wall stud and joist cavities to rooms on the right of the diagram (both floors).

Electrical: Some wires are drilled through joists, some stapled to the bottom. Worst case, they all home run straight back to the breaker panel, so I can pull them if I need more slack.

Where it gets bad is the lower two joist cavities. I am not sure how much sister board I can shove up above the duct, then lift above water supply/drain pipe, and then rotate into place, also access for screws on the HVAC side.

Getting at it from the top seems easier to avoid obstacles, at the trouble of removing the subfloor and adding perpendicular blocking to support the walls/floor (if that is the proper way to do it).

 

[gslenk]

It appears according to this:
https://www.us.kohler.com/webassets/kpna/catalog/pdf/en/105009_1.pdf

"Floor support under the bath must provide for a minimum of
49 lbs/square foot (239 kg/square meter) loading."

So it seems that the joist structure is sufficient, especially since the tub is adjacent to an exterior wall.

How far should the perpendicular blocking be spaced to support the subfloor advantech OSB when/if I remove the existing 1/2" plywood?

 

[Nealtw]

It appears according to this:
https://www.us.kohler.com/webassets/kpna/catalog/pdf/en/105009_1.pdf

"Floor support under the bath must provide for a minimum of
49 lbs/square foot (239 kg/square meter) loading."

So it seems that the joist structure is sufficient, especially since the tub is adjacent to an exterior wall.

How far should the perpendicular blocking be spaced to support the subfloor advantech OSB when/if I remove the existing 1/2" plywood?

I think I would go in from above with t circular saw leaving 1 1/2" all around

You would like to work in upright 2x6 blocks brown no more than 20 inches apart on the side walls Then fill in the spaces between them with 2x4s on the flat orange 1/2 under old floor and half under new floor, put them on the ends too. Depending on how much trouble it is I would consider sistering the other joists too even with just a 2x6.

 

[Nealtw]

When we help putting tubs in we we build a wall on the flat under the flange at the back. If you are using cast iron tub there would be no bending so that back wall would look after the back leg support.

 

[gslenk]

In order to get the sisters in, I may need to cut the floor out, unless the sisters don't need to be the full span. I like the idea of sistering the two single joists, before the perpendicular blocks are made.

And it seems the perpendiculars should go in before the floor is cut out, or does that not matter too much? The adjacent room floors are supported by joists really close to the walls, and these are not bearing walls.

Kind of puts me in a pickle of either "figure out how to make it work with the floor intact" or "doesn't matter, cut the floor out."

And are your little grey "L's" suggesting I add structural hangers to that area in the top middle?

 

[Nealtw]

In order to get the sisters in, I may need to cut the floor out, unless the sisters don't need to be the full span. I like the idea of sistering the two single joists, before the perpendicular blocks are made.

And it seems the perpendiculars should go in before the floor is cut out, or does that not matter too much? The adjacent room floors are supported by joists really close to the walls, and these are not bearing walls.

Kind of puts me in a pickle of either "figure out how to make it work with the floor intact" or "doesn't matter, cut the floor out."

And are your little grey "L's" suggesting I add structural hangers to that area in the top middle?

Yes those are hangers, or something else if you don't have access.

How much longer would the joists be than the room inside.

You don't have access from below?

 

[gslenk]

Yes those are hangers, or something else if you don't have access.

How much longer would the joists be than the room inside.

You don't have access from below?

Room is 9 ft long, total span between bearing walls is ~10'6", add 7" to rest on top of both plates.

I have a decent amount of access, just not in the two corners from below (red rectangles)

I would likely have access from above once the floor is removed.

long skinny rectangle is a round supply duct in the joist bay, I would guess flat 2/4 or better could fit there.

Large rectangle is blocked off for a joist bay return. Could possibly remove the covers, don't know what else is lurking in there. Would still have to deal with the duct running below that area.

I think I can get one sister slid in from the other side of the wall, since that room is more open, and less stuff blocking the area. Must go on the sides indicated since the central bearing wall has joists resting on it in such a way that they overlap, and won't allow a full span on the other sides.

The upper wall in the picture is probably more supported, by the perpendicular joist splice thing there.

The lower wall I suppose would only be supported by the remaining floor not cut away.

 

[Nealtw]

Room is 9 ft long, total span between bearing walls is ~10'6", add 7" to rest on top of both plates.

I have a decent amount of access, just not in the two corners from below (red rectangles)

I would likely have access from above once the floor is removed.

long skinny rectangle is a round supply duct in the joist bay, I would guess flat 2/4 or better could fit there.

Large rectangle is blocked off for a joist bay return. Could possibly remove the covers, don't know what else is lurking in there. Would still have to deal with the duct running below that area.

I think I can get one sister slid in from the other side of the wall, since that room is more open, and less stuff blocking the area. Must go on the sides indicated since the central bearing wall has joists resting on it in such a way that they overlap, and won't allow a full span on the other sides.

The upper wall in the picture is probably more supported, by the perpendicular joist splice thing there.

The lower wall I suppose would only be supported by the remaining floor not cut away.

You only need 1 3/4" bearing on each end.
So the floor would be open to 105"

and the joist would be 129 1/2"
Can you slide them both in from the other room at your orange arrow.

The round duct can be dealt with by removing it put up the flat 2x4 and and a long 2x4 under each end of the blocks and replace the duct.



You would be surprised where you can put joists

 

[gslenk]

I just got the green arrow one in, no problem. But rotating it up has me a bit nervous. I'm thinking chamfer the edge where it will roll up on the center support, offset by about a foot. Then roll it up, and bang it longwise into place, a foot over. I wonder how much play time I have with PL premium to pull this off.

 

[gslenk]

The orange arrow one will be trickier, more robust ducting in that bay in the adjacent room. However, It seems like it does not matter whether the floor is out or not in that joist bay correct? So getting it in from the top might be the way to go as you pictured.

 

[Nealtw]

The orange arrow one will be trickier, more robust ducting in that bay in the adjacent room. However, It seems like it does not matter whether the floor is out or not in that joist bay correct? So getting it in from the top might be the way to go as you pictured.

I have drawn that out on the floor and cut a 2x4 to length to prove it will fit.

I would say it has a good chance but we always work with 2x10s so my estimate may be off.

If you are short you could put solid blocking over the bearing walls and hanger it in place that would save 3 1/2"

 

[gslenk]

Say the 2x8 ends up a foot short (due to lack of access/etc), would it be better to go 2x6 full span? At what point would the 2x6 full span be better than a glued and screwed 2x8 (not full span)?

 

[gslenk]

Also, is there a reason for the 1-1/2" of existing floor to stay besides that's what a typical saw would allow? Would it be better or worse to cut flush with the wall bottom plate assuming I get blocks up under there?

 

[Nealtw]

Also, is there a reason for the 1-1/2" of existing floor to stay besides that's what a typical saw would allow? Would it be better or worse to cut flush with the wall bottom plate assuming I get blocks up under there?

That is what the saw does with ease and straight with the wall for a guide and easy to screw the flat blocks in so you get a positive connection from old to new. But there are times that getting over to flush is worth the extra effort.

 

[Nealtw]

Say the 2x8 ends up a foot short (due to lack of access/etc), would it be better to go 2x6 full span? At what point would the 2x6 full span be better than a glued and screwed 2x8 (not full span)?

I would sooner have full span. A short sister can just move the weak spot to the end of the sister.

 

[gslenk]

That is what the saw does with ease and straight with the wall for a guide and easy to screw the flat blocks in so you get a positive connection from old to new. But there are times that getting over to flush is worth the extra effort.

If there are no bad side effects other than difficulty, I think I'll go with flush cut. Then the screws used to attach the old to new would also catch the bottom plates.

I would sooner have full span. A short sister can just move the weak spot to the end of the sister.

It is starting to look like I might be able to get a full 2x8, if I cut a corner off to get it in from above. Either that, or I might be able to remove some of the joist bay ducting to get the full length in.

So far I've got these done (attached):
Blue = double 2x6 in hangers
Green = single 2x6 in hangers
Brown = new sister
orange = flat 2x6 see pic, tons of screws in one, screws + simpson heavy angle brace +1/4" screws. Hope these are good.
Black = seem really tricky to get a good angle on with what I got going on. I'd like to wait till I pull the floor to see if that opens up some options.

In the bottom right, I think there's enough stuff so the wall won't budge while I get the last block in the corner.

In the top right, is the existing perpendicular, and the wall corner enough to hold things up while I rip out the floor?

I assume the perimeter blocking/scabs go in once the floor is up, so does this look ready to pull the floor, or should I keep fighting to get those last few blocks in?

 

[Nealtw]

It is starting to look like I might be able to get a full 2x8, if I cut a corner off to get it in from above. Either that, or I might be able to remove some of the joist bay ducting to get the full length in.

Put it in laying down then stand it up

 

[gslenk]

It is starting to look like I might be able to get a full 2x8, if I cut a corner off to get it in from above. Either that, or I might be able to remove some of the joist bay ducting to get the full length in.

Put it in laying down then stand it up

Thought it over again... cutting the top at an angle does absolutely nothing. At all. Seems like removing the duct-work so I can rotate is inevitable.