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Unread 06-19-2010, 07:36 PM   #1
tomj8104
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Deflection / Subfloor Q for Tile Floor

Hi all,

If anyone has expertise on the effects of deflection on a tile floor, I'd love to get your thoughts on the following:

I am remodeling a small 2nd floor bath due to sig water damage to the floor.

After reading about deflection, I'm wondering wether excessive deflection caused the tile and water damage (more than poor maintenance). See the deflection calculations below:

Deflection: I keyed the following into the Deflection Calculator: 1 X 8 floor joists, 16" on center, joist span appears to be 13.5 ft. Even assuming the joist were Doug fir or YP, the calculator's answer came back with a deflection of .734 inches or, at best, L221 vs. the needed L360 for tile. So the calulator's recomendation was that this was not suitable for tile and suggested vinyl or wood flooring. Should I go with the calculator and skip replacing with tile?

Current Original Floor Construction: subfloor of OSB 23/32 glued and stapled to 2x8joists; then 1/2" plywood nailed to subfloor; then 1-1/2" tiles in sheets apparently glued to the 1/2" plywood; then grouted.

My Original Tile Floor Replacement Plan: cut out bad OSB 23/32 TG & replace with 3/4 Plywood T&G on the 2x8 joists (with subfloor adhesive and screws); then layer of thinset; then 1/4" hardiebacker screwed to subfloor; then set 6" tiles on thinset on hardiebacker.

With the calcualator saying the joist deflection is below that needed for tile, I don't know if installing a sheet of 1/2" ply between the current 3/4" ply/OSB subfloor and a 1/4" hardiebacker would reduce the deflection enough to go with a tile install or whether I should discontinue the tile option due to the calculator's deflection issues.

Any thoughts are greatly appreciated.

tom
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Unread 06-19-2010, 07:53 PM   #2
Deckert
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First thing I would do is confirm that your joists actually span that 13.5' unsupported.

Adding more ply and backer won't compensate for insufficient framing, so lets make sure you got the right numbers for your unsupported span.
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Unread 06-19-2010, 09:27 PM   #3
tomj8104
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Floor Deflection

Thanks for the quick reply Brannigan.

In order to find evidence of the 13.5 ft. unsupported span, I went to my basement.

The visible joists in my basement supporting the 1st floor are 1x8 joists with a 13.5 ft. unsupported span on the same side of the basement as the location of the bathrooms on the 2nd floor. So the 1st floor of my house has unsupported spans of 13.5 on one side of the I-beam and 14'-4" on the other side. I can often feel the deflection on the 1st floor when someone (or our large dog) walks close by!

The only possible support for the 13.5 span is the framing for an extended hollow or void in the ceiling below these 2nd floor bathrooms used to fit the plumbing. But a brother of mine who used to frame and is a plumber said that framing is usually not structural and just used to create the void for the plumbing and utilities.

Any conclusions or advise?

thanks
tom
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Unread 06-19-2010, 10:13 PM   #4
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Welcome, Tom.

I think we need maybe you should change measurin' devices and have another peek at them joists for us. I'm a bit loathe to believe you've got "1x8 joists" under there and I'm hopin' maybe you got the other dimension wrong, too.

While I know in some older structures we usta think L/240 was an acceptable deflection standard, folks wouldn't generally consider less than that.

With the right span tables, I might could get you to the more common current code requirement of L/360 with the right wood in a very, very good grade on nominal 2x8 lumber at 16oc spacing for that 13.5-foot span. Ain't gonna make it on the 14+, though.

But first you gotta know what's really under the floor in question, eh?

If, in fact, you have nominal 2x8 lumber and can't verify that it's Douglas Fir or SYP or equivalent, and of a grade of #1 or better, you'll need to do some sistering unless you can make a way to add a structural support under the joists to reduce the span.

You gonna be able to do one of the above?

Presuming you don't discover you actually have bigger joists. If you measured only 1" where there's gotta be at least 1 1/2", maybe you really have 9 1/4" where you thought you had only 8"? This would be a good thing.

My opinion; worth price charged.
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Unread 06-20-2010, 06:50 AM   #5
tomj8104
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Unhappy to CX

Thanks for your thoughts CX,

The 1x8 in my original comments was a typo. Meant to say 2X8's. I've rechecked all other measurements.

To recap, I have 1-1/2" by 7-1/4" joists, 16"oc, 13.5'span and can't verify Douglas fir, SYP or quality of wood. Joists are definately NOT 9-1/4" (I wish). The John Bridge calculator calulates a deflection of L221 assuming quality wood.

I knew my house was built on the cheap but I think I'll take a poll to see how many friends & relatives have 2x8 vs 2x10 joists under their floors.

Sistering the 2nd floor joists may be problematic without tearing out my 1st floor kitchen cieling below. I like the idea of new cross supports to shorten the span but a cross support would need up-posts cut through to the basement floor to carry the load and probably not worth it.

Is going to a flexible flooring possibly the best / easiest solution?

thanks

tom
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Unread 06-20-2010, 07:20 AM   #6
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Nothing at all wrong with using 2x8s for floor joists, Tom, you just need to keep your spans within acceptable limits. Don't think anyone was paying much attention to that when they framed your house. Again, how old is the structure?

You could do the sistering from above if you removed alla subflooring. You indicate that you intended to remove some of it, anyway.

But otherwise, yes, changing to a floor covering other than ceramic tile might be your best option. Your floor structure isn't likely to meet your local building code at this point. May never be a consideration, of course.

My opinion; worth price charged.
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Unread 06-20-2010, 08:22 AM   #7
tomj8104
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to CX - Sistering Questions

Hey CX,

The house is a 25 year old, 2 story frame. Interesting that the house may not be to code. I think I'll take that poll now and see what size joists/spans others have.

Interesting thought on possibly sistering from the subfloor. I've cut out some of the subfloor exposing 2 joists for 60" across the bathroom. Was sistering in 2x4 framed boxes to add support for the non-T&G edges of the
replacement subfloor only. Wasn't even thinking about the deflection issue being the main problem/cause until now.

Now I've got a problem.

On a 13.5 ft span, any thoughts on the minimum lengths sister boards need to be to reasonably reduce deflection....assuming I can open the floor up enough to do this.... I'm thinking I can only sister the 1st 5 feet of a couple of the joists unless I really start cutting!

Otherwise, I'm starting to lean towards the flex flooring option recognizing its a poorly designed/built house.

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Unread 06-20-2010, 08:38 AM   #8
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Could have been code when built, Tom. Can't say. Actually, your compliance jurisdiction may still be using that same code today. Onliest way to know is to axe'em, eh?

For joist sistering to be effective you must sister at least the center two-thirds of the joist span. In your case you'd really need to get some ten-footers in there, properly attached.

Axe Mrs. Tom wouldn't she like to have a nice new closet at one end of the span of those joists. And still another inna basement? Mrs. Toms alla time like more closets, eh?

And we'll permit you to build the whirl-famous TYW support closet at each level of your house without any of the usual commission. Just this once.

My opinion; worth price charged.
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Unread 06-20-2010, 01:31 PM   #9
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thanks CX

CX, you have been a "plethora" of information (my new word for today). Yesterday, I my word was "deflection"! Mrs. Tom got a big laugh at your new closet ideas. She loves closets! Probably can't sister 10ft or even close to it easily. I'm leaning towards looking at flooring options that'll flex with the apparent joist deflection. Assuming I go with flex flooring options, my tile failure issue is taken care of / solved.

One flooring issue to go: How to reduce the liklihood that a new toilet will rock over time from the deflection causing a failure in its wax seal. I'm guessing deflection may have contributed to the last wax seal failure and subsequent water damage.
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Unread 06-21-2010, 08:07 AM   #10
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Quote:
How to reduce the liklihood that a new toilet will rock over time...
You start with a good subfloor. Everything is attached to the subfloor, so if it flexes, so will everything else. It also needs to be flat in the immediate area of the toilet. Next, secure the toilet flange to the top of the finished floor surface. Use a single wax ring to seal the toilet horn to the flange. there are waxless seals that you could try, but if you follow everything else I said, you won't need anything but a cheap wax ring. Set the toilet in place, and secure the bolts snug tight. Use nylon wedges (or pocket change) to shim the toilet if necessary. Finally, either caulk or grout the toilet base to the floor, leaving a gap at the back as a tell-tale.
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Unread 06-21-2010, 01:00 PM   #11
tomj8104
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thanks bob - flange q

seems like a stable subfloor should sit on non-deflecting joists. back to where i was in my tile predicament! My earlier notes show floor joists size and spans that are not suitalble for a tile floor due to excess deflection .......unless I was to support a shorter span or sister on.

I can frame a box within the floor joists before replacing the sub-floor to add stability to the toilet flange area. Do you think that might help with stability of the toilet area given deflection of my joists noted above?

Also, being a novice. You say to place the toilet flange on top of the finished floor? Does you mean the floor is completely finished (tile, wood, or vinyl) around the rough in plumbing and then the flange is the last thing put back and sits on top of the tile or wood or vinyl? I thought the flange was screwed to the subfloor before the flooring was put in.....but then I'll be letting a plumber do that.
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Unread 06-21-2010, 02:55 PM   #12
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Quote:
Originally Posted by Tom
Do you think that might help with stability of the toilet area given deflection of my joists noted above?
Yes, a little extra framing under the toilet is a good idea. It doesn't take much to make a big difference - a few blocks between joists, for instance. Still need adequate floor framing though...


Quote:
Originally Posted by Tom
You say to place the toilet flange on top of the finished floor?
The height of the bottom of the toilet flange is set to be even with the top of the finished floor height. If installing the flange before the finished floor is installed, then rough it in to the finished floor height & support it adequately, then screw it down. It doesn't actually have to be attached to the finished flooring material, just needs to be at the correct height.
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Unread 06-21-2010, 05:53 PM   #13
tomj8104
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thanks dana

thanks for the info on the toilet flange. sounds like, in the end, its all about deflection..... you either have it or you don't......and my 2x8's over 13.5 feet have a lot of deflection.

I told CX that I probably can't sister the 2x8's over 13.5 ft properly because the joists run under 2 back-to-back baths (one I'm remodeling and one to be remodeled later) and a hallway on the 2nd floor.

ALTHOUGH I could possibly start the sistering process by sliding the timber to be sistered into the open floor I have in the current remodel. Then attach 4 to 5 feet of the 10 foot sister during the current remodel. Then finish the 1st bath's remodel. Then start on the 2nd bath remodel, open that bath's floor and finish the sistering process. yea, that's the ticket.

Or I could use a flex flooring option (not tile) given the the deflection, block, frame, and stabalize the toilet area as best I can and call it a day.

decisions, decisions, decisions, I'll have to grab the flashlight one more time and become one with my floor joists.
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Unread 06-21-2010, 06:03 PM   #14
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How about sistering from below. Drywall repair is relatively easy/cheap compared to ripping up flooring.
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Unread 06-21-2010, 06:58 PM   #15
tomj8104
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sister sister

Hey dana,

below is a 1st floor kitchen ceiling that runs most of the 13.5 joist length.

I think your thoughts are accurate and true: pulling down the 1st floor kitchen drywall ceiling would expose 2 or 3 of the 13.5 ft joists under the 2 - 2nd floor baths which have the water damage / deflection problems. Doing a proper sister act on the joists under these 2 baths would probably take care of the underlying deflection problem in both baths.

Not where I wanted to be right now. I have a bath gutted down to partially exposed floor joists. cleaned the joists of adhesive, had new plumbing roughed in. was ready to close up the floor and retile...THEN realized my real problem is excessive joist deflection. Wasn't expecting to get into this issue Perfect time to leave town. We're taking a road trip to Lake Erie! Closest beach to Cincinnati! I'll think clearer after a day or two away from this!

see ya'll soon. thanks everyone!
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