Joist meets Drain - now what?

[lhartl]

Without ripping up the entire floor, I could not tell you how long the joists are. I will also post on John Bridge site and see if there are more ideas out there for reinforcing the joist.

Linda

 

[AdrianMariano]

Tile must be supported by joists which don't deflect too much. If the joists deflect too much then the tiles, which are very rigid, will crack, or the grout between them will crack. If you plan to install tile you MUST have an adequately rigid floor. Most floors are adequate for tile. (Natural stone requires an even more rigid base and presents more of a problem. My bathroom has joists that are (barely) adequate for tile but definitely not good enough for natural stone.) The allowed deflection for tile is L/360 where L is the length of the joist. (Unfortunately I'm a little hazy on what the load is that you're supposed to assume when doing these deflection calculations. I think it's the live load---people walking around---that matters since that's what will make the floor go up and down and stress the tile installation.)

If you cut a joist then the floor for the entire length of that joist (possibly the entire width of your house) is weakened along that line and it will deflect more along that line. If "more" equals "too much" then you could get cracked tiles or grout. You could get cracked tiles at the other end of the house if this joist happened to hold up a tiled kitchen floor, say. If you do all the work and then something starts to crack later it's going to be VERY hard to fix at that point.

So the issue about cutting this joist raises questions about EVERYTHING which is above the joist, not just about stuff in the bathroom near where you make the cut. A careful analysis of the minimum you need to do if you cut out 7" of the joist depends on knowing how long the joist is, what the joist spacing is, and what it's holding up over it's entire length, not just about the bathroom you're working on. You need a fix which guarantees the L/360 deflection maximum.

Depending on what's underneath the joist you might be able to get an idea of how long the joist is. It has to rest either on the foundation or on a big beam of some sort. In my house the basement is partially unfinished so I can see what's going on. There is a big I-beam which actually rests on steel pillars that goes down the middle of the house. The joists span from the edge of the house to this I-beam. The joists can't just end abruptly.

 

[Sponsor]

 

[Geniescience]

clear one thing up first please.

linda

yes or no: you need to cut the joist a whole lot because the drain is located right above it. Something like that?

Apart from the reason why you need to cut the joist, it is clear to me that you and others believe you need to cut it.

Thus the big question is whether or not cutting the joist is going to be serious damage to the structural strength of the floor. If you floor becomes springy or springier because of this weakened joist, you may get hairline cracks in the tiles or grout joints. It may rip the orange membrane and you end up with moisture rot in your wood structure.

Joists are better left uncut. Second best is to strengthen to compensate whenever you do cut them. Least best is to do nothing to strengthen and just cross your fingers.

So you need to cut the joist a whole lot because the drain is located right above it. Something like that? Yes or no.

info: Coquitlam BC is a 15 minute drive from the US border, in Canada.

david

 

[lhartl]

YES, I need to cut the joist a whole lot because the drain is located right above it.

Earlier posts suggested that I should cut the joist but more recent posts have me worried about the porcelain tile that I plan to put in the shower. I have no way of judging what is sensible risk management and what is overkill.

Two inch steel seems lke a big hit for a shower drain problem, so my only other alternative (that I see) is to abandon the Schluter shower kit for a mud deck and drain placed between the joists.

Linda

 

[Leejosepho]

The Schluter shower drain is 2" and the old (existing) tub pipes are 1.5", so I must make the conversion somewhere in there ...
Do you think that I need to start at the SanTee with the 2"?

A transition from larger to smaller would have to be done vertically. To make the same transition horizontally would be like expecting a funnel to work sideways.

 

[Leejosepho]

YES, I need to cut the joist a whole lot because the drain is located right above it.

No, the bottom of your drain fitting is a 2" hub, and a 2" x 1-1/2" bushing placed right there would accept a 1-1/2" street 90 to go sideways immediately and on into a trap connected to the nipple already available at your tee ... if that first 90 is at least just a little higher than the nipple at the tee.

What exactly do people mean when they say to build a box around the drain?

Here is a crude graphic: ----I I----

The dashes are the cut joist, and the top and bottom bars of the "I" used in that graphic are the neighboring joists on either side of the cut joist, with the vertical line of the "I" being a short piece of joist added at each cut end to pass the load along to the neighboring joists.

I can't figure out how this would work without compromising the strength of the joist.

The cut joist is no longer capable of bearing any load across the original span. And, therefore, the neighboring joists are now loaded more heavily than before the "box" was added.

I think the idea of bolting a sister joist in next to the existing one and then drilling out the hole in the center for the new drain is good for the structural integrity. The result will be stronger than what was there before.

Yes, it would, but a hole (up to a certain size) in the center of a joist would not actually weaken it in the first place.

 

[Geniescience]

Measure your room downstairs

(too much advanced detail and information, leejoseph.) Linda needs less data and more overview right now.

Linda, it is the styrofoam tray. It's the tray that is the problem. You can keep the rest of the Kerdi kit. Linda, I don't want to go over to the JBF forums and see what they have been advising you.

B.T.W., you also have other options besides mud and Kerdi. Later, if needed.

Yes, you can off-center the drain in the shower pan. You can also keep it in the center, cut the joist and work around that in many possible ways that Adrian and Lee and others are discussing with you. The best person to advise you on-site is someone intelligent and experienced in home renovating. Not a repair plumber, and also not most plumbers who build new construction either. This joist thing is a structural thing.

Adrian already mentioned that it is important to know how long the joist is. Go downstairs and measure the distance between walls. All your parallel joists will be resting on the structure inside the two walls. Hope that is simple. Can you do it?

David

 

[Leejosepho]

(too much advanced detail and information, leejoseph.)

Really?!

Adrian already mentioned that it is important to know how long the joist is. Go downstairs and measure ...

Hope that is simple. Can you do it?

Oh, come on!

The length of the joist is irrelevant -- a cut joist is a cut joist, and a joist should not be cut!

 

[Geniescience]

woops

i'm referring to the joist length in order to calculate the deflection. Nobody is going to deny that this is a good thing to do.

i realize that a lot of one joist has been cut already. Let's wait for the facts before advising on what to do. Joist length, of all the joists, or all except the cut one.

david

 

[Leejosepho]

i'm referring to the joist length in order to calculate the deflection. Nobody is going to deny that this is a good thing to do.

I apologize for not thinking of that thought of yours prior to posting.

Overall, this shower (replacing a tub full of water) appears to be going into a corner of a room, and there are likely walls (or foundation) below those walls, thereby making the matter of a weakened joist or even that entire corner of the floor system less critical since a little tile is going to weigh far less than a tub of water. Nevertheless, yes, let us be sure the floor is quite solid!

 

[lhartl]

Joist length

There is a major wall running through the main floor of the house at 15 feet. I am sure that this is the joist that we are looking at upstairs. This bathroom is directly over the laundry room on the main floor. The very next joist is above the wall with a door to the garage.



Linda

 

[Geniescience]

.... at 15 feet.... the joist that we are looking at upstairs..... The very next joist is above the wall with a door to the garage.

Not yet as clear as it could be. Sorry about that. Linda, all these things called joists are parallel to each other, and the whole set of them run from wall X to wall Y, and that is the "ensemble" we all look at to ensure that the floor is ready for tile.

If I understand what Lee said, and what you said, then your answer implies that the one joist is .. (sorry, I don't know what you have to say about it) but then it mentions another joist, close to a wall, and that is good news.

Your shower is in a corner and the joists are 15' long. Is this right? Please answer this, even though I am going to continue by writing out the next question.

Next question: have you told us somewhere how many inches the drain is from the edge of the shower pan? Your first and third photos show the drain close to the wall. I guess you are thinking of using the new model of Schluter shower pan. Until last year, Schluter pans had the drain the center (centre) of the pan. Now they have another option. But doesn't if give you some wiggle room? That is my third and final question.

david

 

[lhartl]

Three answers

Hi David,

Yes the shower is in a corner.
Yes the joists are 15 feet long.
From the wall to the centre of the drain is 10" (exactly the same as a tub).

.... at 15 feet.... the joist that we are looking at upstairs..... The very next joist is above the wall with a door to the garage

I guess this wasn't very clear. Let me try again. The very next joist aligns with the wall downstairs that envelops a door to the garage. I hope that is clearer. I guess I see this as positive because it means we are extremely close to another major structure.

Linda

 

[Jadnashua]

This is what we are talking about...cut the joist in the way, add a header on either side to hold up the ends. Joist hangers can be used. Depending, you might want to double up on the headers. Cut out enoughto do what you need to, but keep it as small as practical.

 

[lhartl]

Wiggle Room?

No, there is no wiggle room because the drain lip goes almost to the edge of the foam tray and built into the slope. (I thought of cutting off some of the foam but there would be a steep slope to the perimeter of the wall.)

 

[Geniescience]

if you had wiggle room

Linda

If you had a couple inches play, would you use it?

If you cut the tray and a little bit of the large flat plate of the drain, the slope of the tray remains the same and you don't need to increase it just to align the tiles at the corners. The height differential would be about 1/16th". The "crease" line separating the flat sloped plates in the tray would not go totally into the corner, it would run up to, and stop at, the wall near the corner. In case you have a perfectionist's eye.

My asking you this question is not an indication that this may be the right way to go. I am asking if you would use the wiggle room.

david

 

[Geniescience]

but this is a joist, not a stud.

hi jim

Adrianmarino raised a big concern, and I think it is interesting to you too. Did you see his post from today? Joists are necessary and can only be tampered with after a serious amount of study. I'm sure you know more about this than I do. What did I miss here?

david

 

[Jadnashua]

Boxing things out and putting in headers is done all the time. You need to do it for say a skylight, an opening into the attic, stairwells, etc.

You need to be careful when you do it - you might want to install some temporary bracing until you get the things back together.

Check with your building inspector. But, be careful, it will NEVER be accepted to downsize the drain from 2" to 1.5". To do this right, you really should replace that 1.5" line with 2" until it connects into something either the same size or larger.

Now, if you don't get it inspected, will it give you grief? Maybe. Drains should not be necked down - it is a likely location for a clog, and if you ever wanted to snake it, it might not work. If the inspector ever DOES find out you did work and it wasn't permitted and then inspected, they CAN make you show them it was done per code. This MIGHT mean you have to tear it all out. Then, you will likely still have to pay a fine, and still get a permit.

Sometimes, when you want to sell the house, if a problem is caught during the inspection, you won't be able to complete the sale until it is fixed if it is determined that it was done after the code changed (i.e., not grandfathered). Normally, any time you change something, what replaces it needs to be brought up to current code to the extent you made modifications. If it is simply a remove and replace and the part you changed was not impacted by code changes, you don't need to tear up more to make it right (although it might not be a bad idea).

Another thought, ask this over at www.johnbridge.com. They have a structural engineer that can give you some professional opinions.

 

[lhartl]

Wiggle Room

David,

Yes I would consider using the wiggle room if I thought I could do a good tile job and not compromise the slope. I am not sure that Schluter would support cutting the plate. The drain is a pretty integral part of the system. This may be better than starting from scratch and building the mud bed myself.

I have posted on the John Bridge site, maybe their engineer will have a solution for me.

I can see a larger pipe connnected to the SanTee so it is possible to do the entire drain in the 2" pipe. BUT, it appears to me that the 2 to 1 1/2" bushing and elbow may take up less vertical space (i.e. the joist) than a complete 2" elbow, although I haven't measured that out. I definitely want to do this right.

Linda

Linda

 

[Jadnashua]

If you box it out with the headers, you have the entire height of the joist to work with in that boxed area...i.e., there is NO joist right there.