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10-12-2013, 11:03 PM
I am building a new house, and in the master I would really like to add a curbless shower with a linear drain. I have done many renovations and I just built the house I am performing this work in, but have never done a curbless shower.

From the research I have done (not a ton of info on the net about TGI/curbless showers) it seems much easier to do this over dimensional lumber.

I was thinking I could sandwich 2x12's on each side of the TGI then 2x4's outside of that 3/4" below the top of the to add a new sub floor level with the top of the joists. That would give me a 3/4" drop, and if I add 1/4" hardi board to the rest of the bathroom that gives me 1". I really wanted the drain located at the door. The room is 16 long and 10 wide. You enter on a 10' side and the shower is opposite corner, shower door would be opening into the middle of the room, and its 4'x5'.

My other concern is not having a transition that is too high going from tile to the carpet that will be in the master bedroom.

Any help is greatly appreciated!

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chuck stevenson
10-13-2013, 06:42 AM
Welcome Chris:)

I agree sawn lumber will be better/easier. You may want the TGI supplier to weigh in.

I would head off the TGIs and either go with sawn lumber in the bath area or shorter TGIs to get the offset needed. Use top loaded joist hangers. The beauty of new construction is you can build it anyway you want to get what you need.

Have you considered a Euro style wet room? This may help with the room transition.

10-13-2013, 09:07 AM
Welcome, Chris. :)

I'm trying to figger out what a TGI might be? We're talking an engineered joist system similar to TJI, perhaps?

If so, the real way to deal with your proposed shower plan is to specify it in the original house design and have that area of the floor dropped sufficiently to accommodate what you have in mind, as Chuck is suggesting.

Should not be a significant problem for whomever is designing your engineered floor structure.

But first please tell us what a TGI is, won'tcha?

My opinion; worth price charged.

10-13-2013, 09:29 AM
Following up on what CX and Chuck said about dropping floor.....

I'd double the joists on boths side of the area to be lower and place a double between the double joists to create a separate structurally independent square that could then be framed with the joist hanger lowered by the desired offset (3"). If you used 2x12 as a band board around the lowered section you would be able to offset the hangers and still have plenty of wood to anchor into.

Agree with CX about talking to the builder/designer to get this in the plans.

Good luck.

10-13-2013, 11:20 AM
... Might need clarification from the OP on this, but it sounds like the house might be already framed...

10-13-2013, 12:28 PM
Thank you gentlemen for weighing in with your opinions. HomeTeam is correct, the house is already framed and finished (just the framing and weather tight).

CX: You are correct, I am referring to TJI, but around here everyone refers to them as TGI rolls off the tongue better I guess.

Another interesting note is 12' of the 16' length is over the garage, the TGI's are oriented parallel with the garage walls, so they are 35' in length and spaced at 12".

Chuck, I have seen an issue of Fine Home Building with a wet room install, and its an intriguing idea. I would still need to pitch the shower area though correct? Also, I would still have the hardi back, mud and tile height correct?

Thanks for the help guys! Ill try to post a photo of the room so there is a better idea of orientation.

John Bridge
10-13-2013, 01:43 PM
Hi Chris, :)

I think it might be possible to modify the I-Joists and lower the floor framing in the shower area. It would depend on what supports the bath area from below. Notice I said "might." I've never done anything like that. I think you should check with the manufacturer. :)

10-13-2013, 03:16 PM
I was thinking of that as I purchased the upgraded TGI's so they are 90 series @ 14", but inspectors really frown upon any kind of cutting on them as 90% of their strength come from the top and bottom. None really comes from the web. Im not sure of a way to modify them while conforming to code other than sandwiching 2x12s on each side to drop the sub, but again thats giving me 3/4". Ill check the manufacturers website to see if they have any information.

10-13-2013, 04:04 PM
Au contraire mon frère. I believe you have that backwards, the top and bottom flange are contributing less in bending resistance than the web. But modifying in significant way is usually a no-no or requires an engineered solution.

I really do think you could drop a section given the right details and support.

And FYI, TJI was the name the originator gave their engineered I-Joist, right here in Boise. Truss Joist International = TJI. There are many I-joist manufacturers now. I think TGI is a restaurant, isn't it :postitbg:

10-13-2013, 04:13 PM
I really really really REALLY think you do not want to cut into those I-beam joists.:shake:

10-13-2013, 04:17 PM
Marty it is possible to do. Think of a headed off stairwell opening in a second story floor. The key is engineering a solution.

chuck stevenson
10-13-2013, 04:41 PM

Our local engineered wood products supplier has a designer with a stamp. Whoever specified your floor system should be able to modify your floor structure for a dropped bathroom. Easier to do now than later.

FHB did have a wet room but that would require all wall hung fixtures. IIRC JLC had one a while back as well.

I like the idea of a curbless shower using a linear drain and locate the drain opposite the shower entrance, close to the wall. This will minimize the slope in the rest of the room, actually eliminate it. I would use a sheet membrane for the shower mud bed and a product like Ditra for the rest of the bathroom. Tape the seams with Keba, turn it up on the walls and you have a water tight floor. (less the toilet area if not wall hung) I would not use CBU on the floor.

Sounds like a nice project Chris.

10-13-2013, 04:44 PM
Chris, The only way I'd do this with those engineered joists is box off the section using double joists (like Chuck and Peter mentioned in previous posts). Similar to the picture below but using hangers and methods approved for your joists. This will allow the framing inside the boxed off area to to be lower meet the drain height requirements without degrading your framing.


Sounds like a cool project, I personally like working the framing on stuff like this. Have you verified the floor meets the L/360 max deflection requirements for ceramic tile?

10-13-2013, 06:41 PM
Dont worry, I wont be cutting into the joists =), this is the first time I used engineered joists. So sounds like I will cut some out and head them off with doubled up 14" beams. That way I can just cut to the depth I need.

What kind of pitch do I need to do this type of shower is I used a linear drain along the wall?

Thanks again guys, you have been a lot of help!

Houston Remodeler
10-13-2013, 06:51 PM
The same 1/4" per foot (2% slope) as any other shower.

10-13-2013, 08:46 PM
Au contraire mon frère. I believe you have that backwards, the top and bottom flange are contributing less in bending resistance than the web.Might wanna re-think that one, Peter. The "webbing" in those engineered I-beam style joists is there primarily to keep the top and bottom chords separated and stabilized. A surprising amount of that portion is permitted by the manufacturer to be removed when desired.

But they permit something close to zero alteration of the chords except where the ends are actually supported and then only in specific design applications.

My opinion; worth price charged.

10-13-2013, 09:46 PM
Here's the way I'm looking at it, Kelly.

Under load the top chord is in compression and the bottom in tension, so yes, they need to be continuous or they would have weaknesses at the point of compromise. They contribute to the lateral strength and give a nailing surface more than they contribute ability to carry vertical loads.

But the bending resistance of the two cords without the web is far less than with it. As the depth of the web increases and the top and bottom chord stays the same so goes the resistance to bending, even with holes that makers allow. Similar to steel in that regard. It's actually the marriage of the two that make them work.

I guess I don't see it much differently than dimensional lumber in that regard. You can't hack up dimensional lumber willy-nilly and specifications exist for what can be done in the way of penetrations, both placement and size.

All that being said, there's likely a way to do what original poster has suggested, but it takes more knowledge than I possess and would require the blessing of an engineer if being inspected.

10-13-2013, 11:36 PM
if you can go without the trench you could use an Arc form tile ready pan.

10-13-2013, 11:54 PM
I-joists can and do get headed off every day, similar to dimensional lumber. With I-joists, the manufacturers installation instructions have detailed information and drawings that illustrate what needs to be done. You must follow their instructions OR get an engineer involved. For common situations, which it sounds like you have, their instructions are all that's needed and no engineer is required. :)

Post a link to the I-joist install instructions if you're unsure about any of this. :)

10-19-2013, 04:31 PM
Thanks guys, may just end up heading them off. May just be the simplest way to do it. Ill keep everyone posted.