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Unread 07-18-2011, 11:00 PM   #1
mvbellamy
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Newbie doing bathroom from scratch - need advice!

Although I consider myself handy, I have taken on a very large project - redoing my bathroom. From scratch. The room is pretty much ripped down to the studs at this point, and I will have a lot of questions.

I will have to replace the old (absurdly tiny) tub with a shower, because I can't seem to find a tub to fit. (Plus I haven't taken an actual bath in well over 9 years, so it doesn't seem necessary.) I'm not worried about a lack of tub lowering the house's resale value, because in this part of Alaska, just having running water raises the value.

And now, to start the list of questions:

1) I want to put in a mosaic tile floor (with radiant heat underneath). When I took out the old linoleum, I found that the house's original hardwoods extend into the bathroom. I am planning on cutting them out. I understand that I can't install the tile directly onto the subfloor, so what should I put down? 3/4 plywood? Cement board? Backer board?

2) The age-old question of cement board and vapor barrier. Since the shower will be along an outside wall, I'm curious. I need to replace the insulation on that wall, and was planning on hanging a vapor barrier. I understand that I shouldn't use both a vapor barrier and a waterproof membrane with cement board. But don't I need a vapor barrier against the insulation in general? Do I run a vapor barrier under the short walls too?

For reference, I am including a floorplan of my bathroom with some dimensions.
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Unread 07-18-2011, 11:10 PM   #2
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Welcome, Mary.

1. First use the Deflectometer in the dark blue bar above to determine the suitability of your joist structure for a tile installation.

Then tell us what you currently have for a subfloor under your hardwood flooring.

2. It'll help if you'll put that geographic location in your User Profile so folks will be able to see it later in response to questions such as this.

In your geographic location, a "vapor barrier" is probably required by code or at least recommended by local custom over the inside of all exterior walls.

If you install a backerboard shower with a direct bonded waterproofing membrane on the inside, you'll have complied with the spirit of the vapor barrier requirement even though your waterproofing may not actually qualify as a vapor barrier (the vapor barrier on all your other walls is not likely installed such that it qualifies, either, but that's OK ).

You can use a moisture barrier behind your backerboard walls and make it compatible with the barrier behind the rest of the wall, too, if you'd rather. Tell us the method you prefer and we can help you achieve it.

My opinion; worth price charged.
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Unread 07-18-2011, 11:42 PM   #3
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OK, I added my location to my profile. I live outside the city boundaries, and thus am not really governed by building codes. There actually is no vapor barrier in place in my house, so I've been adding it as I take down walls to replace insulation. (It sounds like an extreme project, but I will see big rewards this winter.)

I've calculated the deflection as L221, though I can't get an accurate measurement of the joist length right now. Which seems to put me out of ceramic tile usage. What does all this mean? It's a very small room. Does this mean I can't do a tile floor in the shower either? The subfloor under the hardwood is also wood planks. Not sure what kind of wood, and it's set on a diagonal.

If I go the moisture-barrier behind method, how should I cut out and seal openings for plumbing? And if I go for the barrier over, can I use it on something other than cement board? Like green board?
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Unread 07-19-2011, 07:17 AM   #4
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Hi, Mary!

At L/221, your floors should feel very springy. If they don't, you've probably missed something. The span is the most critical dimension, so verify that you are measuring between the inside edge of one support (like the foundation wall) to the inside edge of the next support (which may be a beam down the center of your house). We're not interested in the size of the room, but the maximum unsupported span of the joists under that room.

Even if you can't do a tile floor, you can do a tile shower. You can build a shower that is self-supporting and isolated from the movements of the floor.

If you end up able to to a tile floor, you will have to either remove the planks down to the joists, or install 1/2" plywood over the bottom-most layer of planks, then install a tile underlayment (backerboard, etc.)

For moisture barriers behind the backerboard, you typically make the tiniest cut necessary for the plumbing to poke through and call it a day. After the tile is installed and grouted, you will install the rest of the plumbing fixture trim, which you can caulk around to complete the waterproofing. If this was a steam shower, you'd have to be more aggressive in sealing these openings, but normally, what I've described is adequate for a regular shower.

If you use a surface applied membrane for your waterproofer, you'll still need to use backerboard unless you decide to use Kerdi. None of the other membranes are approved for use over drywall (greenboard) in a shower.
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Unread 07-19-2011, 03:30 PM   #5
mvbellamy
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I was measuring from the center, as that's what the Deflecto seemed to indicate. If it's just from the inside edges, that will change things. I hope to get into the crawl space tonight to get more accurate joist measurements and hang out with all my new-found spider buddies.
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Unread 07-19-2011, 03:45 PM   #6
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Tell 'em Bob says "hello!"
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Unread 07-19-2011, 03:51 PM   #7
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Quote:
Originally Posted by Bob
Tell 'em Bob says "hello!"
Oh, that's just silly. They ain't gonna have no eye-dee who Bob is.

Tell'em Injineer Bob says "hello!"
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Unread 07-19-2011, 04:11 PM   #8
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Spiders aren't so formal...
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Unread 07-21-2011, 10:39 PM   #9
mvbellamy
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The spiders say hi.

I spent some quality time under the house after work today. My joists are 10.5" on the inside, 12" from center, 7.25" high, 1.5" wide and they run 15' between supports. According to the great Deflecto, this gives me L / 221. (What is the L?) Does this mean I absolutely cannot do tile? Does it make a difference if I am using mosaic tiles? I understand that solid 12" square tiles would be affected, but I'm kind of hoping small mosaic would be able to go with the flow, so to speak. Every time I think of linoleum, a little piece of my soul dies.

Also, I am mulling moving a wall and the plumbing so that I can put in a full-size tub instead of doing the shower. There's a 12"x6" opening from the previous tub installation that I will have to patch, but it looks like all the plumbing can be moved back about 7" under the house.

If I'm doing tile walls, I will still put up cement board, right? If I want to only tile partway up the wall, can I hang greenboard above the cement board? I'm imagining that stuff doesn't take paint very well.
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Unread 07-22-2011, 12:01 AM   #10
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Not good news.

The L is for Length in inches. What we're looking for is the ratio between the unsupported length of the joist and the vertical distance it will be displaced when fully loaded with a given weight as specified by code or by some other requirement. In your case the residential building code and the tile industry both want you should meet a minimum of L over 360. You don't.

I can find you a span table that might indicate that if you had the world's best framing lumber of the highest structural grade in new, perfect condition, it might just squeeze by so long as your measurement is accurate within a 16th of an inch. You ain't got none of the above.
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Does this mean I absolutely cannot do tile?
No, it means you absolutely should do something to reduce your joist deflection before you consider doing tile.
Quote:
Originally Posted by Mary
Does it make a difference if I am using mosaic tiles?
Technically? No. Realistically? Yes, it makes the situation worse. Consider that you'll essentially be installing a thin layer of grout on your floor with little tiles mixed in.

You really should consider adding a support beam somewhere down there to reduce the unsupported span. Sistering is not a realistic option with that narrow joist spacing if it were mine.

My opinion; worth price charged.




So, now the truth! Did the spiders have any eye-dee at all who Injineer Bob was?
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Unread 07-22-2011, 11:47 AM   #11
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The spiders all knew you and said to send you their regards. Except for one, who yelled he didn't know you, and then stomped away. I think you've made an enemy.

OK, I'm reading up on how to add support beams in the crawl space. Doesn't seem to difficult, just annoying. One 4x4 and a couple of concrete bases ought to do it. Plus I've got to figure out how to jack up the joists a smidge to get a tight fit.

Another question: How can I figure out the floor load for a bathtub? I previously had a very heavy (but small) iron tub that I am now thinking of replacing with a lighter full-size tub. The floor could obviously support the old heavy tub, but I have no idea if anyone ever filled it with water and took a bath. I found a formula for FBd^2/9L, which seems to give me a floor load of about 31. I assume this will be higher when I install supports.
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Unread 07-22-2011, 12:15 PM   #12
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Tub got a footprint of 12 and half or 13 square feet? You and the new tub and maybe thirty gallons of water gonna gross out at maybe 450, 500 pounds? Barely gettin' to customary residential floor loading allowance, eh?

Not to worry.

My opinion; worth price charged.
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Unread 07-22-2011, 01:46 PM   #13
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Hi, Mary.

I also had to add a beam to my crawlspace prior to starting my bathroom/office reno. The whole area above the crawlspace is about 12' X 13' with a 36" high crawlspace. I had an architect and a foundation specialist (they were way cheaper than I thought) take a peek and they agreed with my assessment that I should shorten the span by installing a beam if I was going to go ahead and add tile, and the very deep tub, and all of the new walls, etc. needed for this reno. The crawlspace had 2" X 8" joists, 16" OC, and a 12' span. The beam was placed mid-span, and was made of three 2" x 10" boards which were glued and bolted together and then set onto two key posts, which were in turn set into two, reinforced concrete footings which were 24" wide X 24" long X 24" deep. If you went this route, I'm not sure how far down you'd need to dig for these types of conrete footings in Alaska per code/ground conditions/earthquake issues. I covered the ground floor of the crawlspace with 18 ml., flame retardant poly...but then, dealing with a crawlspace is a whole other thread...twitchin' just thinking about it...

After all of that, there is NO bounce at all in the rooms above the crawlspace as one would hopefully expect after all of that fuss and bother.

Good luck!
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Unread 07-22-2011, 09:51 PM   #14
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So, having done a bit of reading on the Internet, it seems that this is my best method of creating more support for the floor.

Buy or build a cross beam (either a 4x4 or 6x6 or glue/nail together several 2x6s for the desired effect).

Create a cement footer for the dirt crawlspace. I don't suppose I can just use the spare cinder blocks I have outside? Or deck supports? If not, I'll have to dig and pour cement. Sounds like fun.

Use adjustable metal floor jacks to create the support between the beam and the cement footers. I'm assuming I need to screw these into both beam and footer, yes?

How does this plan sound?
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Unread 07-22-2011, 10:29 PM   #15
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Mary, consider that what you're constructing here is a permanent part of your building's foundation. As such, it must be "grounded" the same as the rest of your foundation.

In your part of the world I'm sure you have a specific "frost line" designated for your foundation and similar work. Actually, I think they call it perma-frost up there and presume that it has no bottom, but that's another discussion. I think.

Your best bet is to talk to your local code compliance authority or county engineer's office or some local building contractors of good repute. See what's required of foundation structures in your area.

Might be that y'all make special provisions for crawl space conditioning and that the frost line under there is presumed to be less deep than at the perimeter. Or not. Or there may be other considerations. Check that out first would be my recommendation.

Then you gotta do what you gotta do to have suitable hard points for your beam supports.

Then you gotta have a beam. Without knowing where you'll pewt the beam in relation to the existing joist system, nor how many joists you need to support, nor how far apart your support posts will be, nor much of anything else, it's not possible to say just what sort of beam you require.

But for sure you wanna change your thinking from making the beam wider to making it deeper. You can, for example, get more support from a single 2x10 than from the 4x6 you've suggested. And a 4x4 beam is generally pretty much worthless unless you just wanna support a couple joists.

Tell us where you can pewt two posts (to minimize digging) and Injineer Bob will right quick tell you what to use for your beam.

My opinion; worth price charged.
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