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otrex 04-07-2021 11:19 PM

Upstairs New Bathroom Project
2 Attachment(s)
Hello again everyone. As requested, I am starting a new thread to cover the new upstairs bath I am putting in since it is unrelated to the kitchen below (covered in my previous thread).

This room is a loft rustic-style bedroom, probably built sometime in the 1920s. It uses lath and plaster on the walls and has a ~3/4" thick knotty pine floor with some pretty big gaps/irregularities between the boards -which makes sense since I suspect it was handcut by the owners of the house using trees from the back yard.

In any case, with my mother-in-law moving into this space and being elderly, I felt it would be wise to not have her traversing the stairs to use the washroom at night and so given the size of the loft (19' x 13.5") I felt there was plenty of room to add a special ensuite 3-piece bathroom.

The planned size is 8'2" x 7'5". That should include a 32 x 32" shower and a toilet with the recommended 15" of space from center on either side. Then a simple vanity.

Because of the slope of the roof on the East side of the proposed bath (you can just see a bit of it in the upper right of the photo), I also intend to build a large storage cupboard/shelf across the entire width of the area. My testing with someone of similar height shows that a depth of 23" from the kneewall would be suitable so as to fully utilize the space without affecting actual full-height walking room.

Looking at the floor, I was pleasantly surprised to see it is actual full 2" x 10" joist at 16" centers spanning across the 13.5'. There is a small 2-piece washroom below which supports at least a couple of these joists, though I am not counting them in my calculation for deflection. Using the Deflecto tool, I come up with an L/516 which seems pretty reasonable to me for attempting porcelain tile.

For the shower, my plan is to build a dummy wall in front of the existing North wall since I do not know how deep that wall is and it backs onto a double-thick brick wall which would have been the original outside wall of the house before the apartment was built on. That will also allow the plumber to bring water in without having to hack through lath and plaster.

For the shower bed, though I previously did a curbless shower (in another thread on this site) I feel this time around I'd like to not cut into these old timbers and instead will do a dry-pack mortar bed on top of the floor sloping down to a Schluter linear drain. Of course, given there will be a senior living here, I'll want to keep the step up into the shower at a minimum.

Here are my thoughts/questions:

i) I will be cutting out the original pine planks in this area (and saving them because they are really nice). I'd like to avoid too much of a step up onto the bathroom tile and as a result was considering 3/4" plywood screwed/glued directly onto the joist. While I was initially considering T&G plywood, after having read some of CX's advice from previous years, I think I would just use regular plywood and, if necessary, tie them together with plywood underneath the sheets screwed into each sheet on the joint. Fortunately at this size of bathroom we are only talking about 2 sheets total so it would only be 4 blocks total with that method.

On top of this 3/4" plywood I would use Ditra since I'd want to protect against joist movement affecting the tile.

Any concerns with this plan? It does appear to be acceptable according to Schluter standards.

ii) Tile would be the same as the kitchen below - which is a 13" x 13" porcelain tile. This would not apply to the shower itself where I'll use some simple/nice white tile to keep it bright inside and perhaps some wood-plank type porcelain in the base of the shower.

I plan to use 1/2" Kerdi board throughout the shower, and Kerdi on top of the dry-pack mortar bed. I am tempted to put a layer of Hydroban on top of the Kerdi on the floor and then up onto the walls to a height of a couple of inches to prevent moisture wicking through the thinset that goes between the Kerdi and the Kerdi that makes up the Schulter linear drain flange.

iii) The position of the bathroom is as shown in the picture. Because of a sloping gable window nearby I think it is foolish to build the South wall right to the edge of the stairwell. At the very least the current position (as shown by the green tape) does put that wall right onto the next available joist which I think is probably a good idea. Still not sure what I'll do with the ~20" space between the bathroom wall and the railing of the stairs, but it does have some very nice natural light pouring in there from the little gable window, so possibly just some nice decoration.

iv) Plumber has stated that the 2" cast iron stack in the photo will have to be replaced with 3" ABS (and a wet vent added). Further the cold water supply line from the bathroom below will also feed this bathroom and be stepped up to 3/4" to ensure good flow.

I have suggested to the plumber that I will start by placing only the first sheet of plywood down and fully constructing the shower with the drain in the correct position which should allow him easy access and exact positioning on the drain to connect everything before I complete the job by putting the final plywood sheet down and building the wall across the stairs for placement of the vanity. I think this is superior to asking him to plumb it with nearly no reference points for shower drain placement.

If I use this plan, I have two options. Position the water supply and drain on the North dummy wall, but to do this I will need to leave the upper half of the dummy wall open with no Kerdi Board (lower will need to be installed before the dry pack mortar). I think this would be necessary to allow him to get the water supply into that wall but also to allow him to plumb the mixing valve and shower head.

The other option here is to place everything in the East wall of the shower since I can then finish the entire shower interior and he can simply plumb it all from the back (open) side of the East shower wall. I am tempted by this option since it seems less complicated. I may need to utilize the Schluter offset drain in order to have it fall between the joist that carries it over to the stack directly (without having to cut through joist to get it there).

v) Anyone have any thoughts/worries/suggestions in relation to this build plan?

Thank you, as always, for your feedback!

EDIT: Oh wow, that little cat managed to sneak into yet another photo!

John Bridge 04-09-2021 09:07 AM

Hi Kevin, :)

I'll give your thread a boost to the top, but I'll let the other guys address your questions. Gotta run. :)

otrex 04-10-2021 11:45 PM

Thank you kindly for the bump-up. Hopefully no responses as of yet are a sign that my plan is sheer perfection (but I'm not holding my breath on that!).

cx 04-11-2021 07:51 AM


Originally Posted by Kevin
Of course, given there will be a senior living here, I'll want to keep the step up into the shower at a minimum.

Kevin, not sure there is much use in concern for a step into the shower in a bathroom that requires climbing a set of stairs for access, but that's up to you.

ii. If you use the Schluter products as instructed there is no need at all for an additional waterproofing membrane from another manufacturer and it could result in other problems.

iv. Can't speak to the vent stack, but the increase to 3/4" water plumbing is probably not warranted. I'll leave that to your plumber, though. And you're running only cold water to MIL's shower?

My opinion; worth price charged.

Davy 04-11-2021 10:01 AM

A 32 inch shower is pretty small. If there's any way to add a few inches, I'm sure your MIL would appreciate it.

otrex 04-11-2021 10:46 AM

Thank you for the feedback.

CX, in answer to your questions/comments:

Step into shower: Yes, that is a fair point. Fortunately my MIL is able to handle stairs rather well, and the stairwell into the loft has excellent railings and lower-than-standard rise. But, fair enough, I suppose one more step into the shower is not adding a whole lot more concern.

ii) The additional waterproofing was considered after seeing someone on Youtube test water wicking through thinset under Kerdi band. In fairness they left it submerged for a day or two, so perhaps a bit unrealistic for a properly-sloped shower.

iv) Yes, it was actually the plumber that wanted the increase to 3/4" cold supply line for the upstairs. Not sure I can describe his reasoning accurately but with a two piece bathroom and kitchen below which will share that line he did not want to risk any reduced pressure for a good-quality shower experience. His feeling on that hot line was that it did not need to be upgraded, but I cannot recall his reasoning on that (less demand on the hot line, I suppose).

CX, no concerns about my 3/4" plywood plan for the subfloor?

Davy, my MIL has indicated her biggest fear is a fall in the shower and so she seems to feel most comfortable with a wall nearby. That being said, I was thinking about trying to expand it to 34" x 34" or at least 32" x 34". Once I get the plywood down I'll fool with a couple of layouts. I should mention for clarity that the original 32" x 32" plan was a measurement of the total area inside the shower once finished as opposed to the footprint of the walls themselves.

Are there any minimum widths that I should adhere to for passage in front of the shower when heading towards the toilet? There will need to be a vanity on the South wall, so want to make sure I at least meet minimum standard for width to pass by safely.

cx 04-11-2021 12:39 PM

The nominal 3/4" plywood subfloor over 16" joist centers satisfies the minimum requirement of all known tile substrate manufacturers.

While the minimum required size of a shower is as little as 30"x30," I'd rough that shower in at no less than 36"x36." Keep in mind that while a MIL might shorten a bit with advancing age, they never get any narrower. Appropriately placed grab-bar(s) might make her more comfortable than closer walls and would certainly be safer.

While I believe the absolute minimum distance from the front of your toilet to an obstruction to be only 21," I'd opt for at least 24" were it mine.

My opinion; worth price charged.

otrex 04-11-2021 04:09 PM

2 Attachment(s)
Well, the plot has thickened, but sadly the floor has headed in the opposite direction!

As it turns out, when I was putting my measuring tape down into the tiny gap in the floor I was indeed measuring exactly 10" of depth, but sadly it's only because my tape was happening to fall into a small void created by some damage made when the original electrical work was passed through!

I discovered this after I carefully removed the well-attached baseboard (taking a good bit of plaster with it) and removed one of the floorboards completely.

What I ACTUALLY have then is true 2" x 8" joist on 16" centers spanning, at worst, 13.5' which gives a deflection rating of L/292. Close, but not quite enough for tile.

This assumes that I am using the full span of 13.5' but truth be told the north side of the room has a bathroom underneath with load-bearing walls and on the other side there is a load-bearing closet wall which holds up both the landing and the southern part of this floor.

Those supported areas have a maximum run of 8' on the north side and 9.5' on the southern side once those load-bearing walls are taken into consideration. So, they achieve an L/1040 and L/622 respectively.

This leaves a 53" wide span which is not supported by load-bearing walls underneath and no reasonable way to add a load-supporting wall either. By my count it is 3 but possibly 4 joists where are unsupported over that larger span.

Some other considerations:

i) Those pine floor boards turned out to be 7/8" T&G, which is a bit odd to me given that they are a lot of different widths. Given that in the Western half of the room these boards are going to remain (and I can put extra screws into them for support) I imagine they help reduce deflection considering how many supported joists they cross over?

ii) Joist condition, in my estimation, is excellent.

I am thinking that given the worst deflection here will be L/292 that it is possible to beef up the floor enough to get to a "suitable for tile" rating? Can I achieve this by using some bridging? I have no access from below, but could probably nail the tops and use some construction adhesive for the bottom of the bridging.

Any other thoughts/ideas?

Related note: This floor is nailed down with square nails, implying to me the addition may be significantly older than the 1920s. They look like blacksmith-made nails to me, in fact. Between that and the cut fieldstone foundation, I am wondering if we're looking at more like an 1890-1910 addition here. It doesn't particularly matter, of course, just wanted to mention it.

cx 04-11-2021 04:27 PM

If you can determine what species of wood you have for joists, Kevin, you may find that your structure is suitable for tile as it is. But L/292 is not really "close" to L/360. You can certainly tile over anything you're comfortable with.

Between-joist bridging does not improve the design deflection of the joist structure.

Site cut lumber was commonly at least 4/4 (four-quarter) as I recall as a kid in Pennsylvania where is was pretty common for folks to do some of that. I'm surprised at the T&G edges, though, if it was site cut.

To install tile over the board subfloor you still need to add a minimum of nominal 1/2" exterior glue plywood over the boards.

My opinion; worth price charged.

otrex 04-11-2021 06:10 PM

Thank you, CX.

Is there anything I can do/add to decrease the deflection in this situation? Essentially it would seem that about half the joist in the floor are extremely suitable to tile and the other half (in the middle) achieve only L/292.

I definitely want to remove the pine floor in the bathroom area, so at present the plan would still be 3/4" plywood screwed/glued onto the joist with Ditra on top if at all possible and reasonable.

In the meantime I will attempt to determine the wood type in the joist. Now that they are exposed I suspect my father may be able to identify them. I'll also take some time to review/recheck all the measurements to ensure that I have the correct deflection estimate.

cx 04-11-2021 08:05 PM

I can't tell what you'll have where the stair ends in that room, Kevin. You've got to pay serious attention to the rise of that last step when you're changing floor elevations at that landing.

otrex 04-12-2021 12:21 AM

Hi CX,

Apologies, I am not sure I understand your reply. Just in case it's a bad explanation on my part, my intention is not to change the elevation of the whole floor. Rather, my plan was to cut out the floorboards in the bathroom area and put down the 3/4" plywood and Ditra. I was hoping to avoid screwing the 3/4" down into the existing floorboards because they are not secured well and, in addition, did not want a big step up into the washroom. But also, the plumber has to swap out the stack, put in a wet vent, and then plumb inside that floor with no access from below, so it seems tearing up the floorboards is imperative.

On the areas outside the bathroom footprint, my intention was to leave the existing pine T&G (though I'm going to add some hidden screws to help improve the performance of the square nails that hold those planks down.

In the area around the top of the stairs, then, no elevation changes planned. If someone were to go to the top of the stairs and turn right into the bathroom there would probably be a mild elevation change equal to the mortar thickness and the tile itself (since the 3/4" plywood and Ditra would equal the thickness of the T&G outside the door). But even that is not terribly close to the top of the stairs - my schematic implies that it is, but I'd say it's 30" away from the top of the stairs.

All this being said, if you feel I really should screw the 3/4" plywood down first and then have something else on top before the Ditra, I could add a 3/8" plywood on top of the 3/4" if you think that would help.

otrex 04-13-2021 09:41 PM

I was up marking the pine floorboards for removal (plumber insists he needs them gone for plumbing access) and I noted that at least two of the joist (including one which is running the full span with no wall underneath are actually 3" x 8", which I find a bit unusual to be mixed with 2x8s with seemingly no rhyme or reason.

I also discovered that the joist running along the north wall is mostly under the wall itself, and that wall has some pretty big vertical timbers behind the lath that rest on top of the floor, so I'll have to use a cutting tool to cut them off flush at the north wall and then scab over from that joist to give my plywood something to sit on. Otherwise I'd be building a trampoline!

Will have some photos tomorrow once I am able to cut the floorboards and pull them up.

cx 04-14-2021 07:23 AM


Originally Posted by Kevin
Apologies, I am not sure I understand your reply. Just in case it's a bad explanation on my part, my intention is not to change the elevation of the whole floor. Rather,..

Once again, evidence of the single most common problem with human communication - the misperception that it has taken place. :)

otrex 05-03-2021 10:07 PM

3 Attachment(s)
Project Update:

I carefully lasered the floor for a nice straight cut and then removed the pine decking. Now I am of the opinion that this apartment is actually from the 1890s given that the nails holding the flooring down were blacksmith nails (square)! No matter, a relative just happened to be looking for some and so I was able to supply him with about 100 - which means after 100+ years those nails only got a 2 week vacation before being put back to work again!

I do note that, in the end, it was not a couple of 3x8s in the floor but rather someone put down the decking a bit out of square and so they were using quite a lot of scabs to finish the job near the wall (the only place I could peek in). Because of the passing of time enough dust had settled on top to camouflage the scab into looking the exact same as the joist - so mystery solved, and it is just a series of actual 2" x 8" joists. Really tough wood though - not sure what it is and a couple carpenters I showed it to were unable to guess as well. Some have suggested Douglas Fir, but it's hard to say. I do note, at least, that even a full glass of water sitting at the edge of the plywood and me jumping up and down less than 1' away results in no spillage at all. These joist seem really tough and/or the deflection minimal.

Working steadily on the project I now have one sheet of 3/4" plywood down and I've framed until I ran out of lumber. That allowed me to get all walls standing except the East wall of the shower which I'll finish as soon as my overpriced lumber order comes in (tomorrow hopefully).

Sadly the lumber coming through the system is of poorer quality. Despite using screws in this stick framing job a couple of them are twisting a bit.

In the end I was able to squeeze a bit more space into the shower. Now it will be a 32" x 36" shower when completed instead of the original 32"x32" planned. It is also planned to have a 22" wide glass door which opens both ways. It was important to me to preserve the 30" wide space for the toilet since it is half-ways under a sloped ceiling, and the 32" dimension is necessary to allow the door to the bathroom to swing inwards without hitting the shower. A tight space certainly, but if I can walk around at my height (6'5") feeling relatively comfortable I think most people will be okay in the space.

Because I am stick framing I ended up using toggle bolts in the top plate to secure them to the ceiling. It's a lath and plaster ceiling and it really does not like holding screws very well, hence the toggle bolts. Being 100+ year old plaster, it's pretty dry/crumbly if disturbed. This leads me to another concern - the ceiling of the shower.

This shower measures 7' from the plywood to the plaster ceiling. Obviously I cannot leave an exposed plaster ceiling inside the shower itself (though it will be left exposed elsewhere in the bathroom), but once I get my dry pack mortar down and tile we're going to start losing height quickly. I'd rather not use 2x4s to create a ceiling to mount the 0.5" Kerdi board because I think we'd end up with a shower height of only 6'7" or so, and that's before the shower head is installed.

What I am wondering is, can I simply use a high-grade adhesive such as "No More Nails" (LePage) to adhere the 0.5" Kerdi board directly to the plaster ceiling? That would preserve as much headroom as possible and the Kerdi board itself would have the full support of the ceiling behind it. This would also leave me with a nice 1" edge all around the top for securing the Kerdi board to the walls.

I suppose I *could* run a couple of the approved Kerdi mounting screws into the ceiling too, but based on the behaviour of the ceiling that I have observed with screws I don't think they'll hold very much. The wooden strips seem to flex quite a lot when screws bite into them.

Any thoughts on that plan? I have worked with this glue before and it is unbelievably strong. Probably stronger than nails, in fact. I am not sure there is any downside to this plan, but wanted to ask as it's a bit unconventional.

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