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Unread 04-07-2021, 11:19 PM   #1
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Join Date: Jan 2019
Location: Toronto, CANADA
Posts: 87
Upstairs New Bathroom Project

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!
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Last edited by otrex; 04-09-2021 at 02:13 PM.
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