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Code Slinger 07-05-2005 11:52 AM

Kitchen joists and subfloor
Hello to all. I have been lurking around for a little while, but this is my first post. I have gutted my kitchen in preparation for a remodel, and that includes the ripping up of the old subfloor - I am now down to the joists. I would like to put down ceramic tile on the floor, however the floor may not quite meet the standards necessary (according to the Deflecto).

Relevant information (or irrelevant, depending on your perspective):
The house is a 1956 cape cod located in Cincinnati, OH.
The unsupported joist span is 11'7". At that point, a steel beam in the basement offers support.
The dimensions on the joists are 1 1/2 x 7 1/4 (2 x 8)
I am unsure of what wood makes up the joists, but they are in good shape. I will try to find out for sure once I get home this evening.

Will I need to "beef up" the floor before laying tile? The deflecto gave the thumbs up for an 11' span, but not for a 12' span. Since I am halfway between those two numbers, I may be on the edge of what is acceptable.

Second part of this question: What about the subfloor and underlayment? I had bought 3/4" BC plywood for the subfloor, and I was going to put backboard of some type on top of that as the tile underlayment. For my bathroom, I used 1/4" Hardibacker on top of new 3/4" plywood, and it has seemed to work just fine. I have seen references to Ditra - is that preferable to Hardibacker? Perhaps because you can use 1/8" Ditra? I would like the floor to be as level with the neighboring 1" hardwood floor as possible. What is your recommendation?


cx 07-05-2005 01:33 PM

Welcome, Jon. :)

I'm gonna assume your joist spacing to be 16" on center judging by your results from the world-famous deflectometer. That being the case, you're not gonna meet the required L/360 deflection criterion for a tile installation. Close, but no cigar.

While you have the whole thing open, I'd suggest you sister those joists with additional pieces. Your sisters would not need to be the full depth or length of your existing joists, which would make the job rather easy in the grand scheme of things. Best to sister the full length if possible, though.

If you sistered with 2x6s, you could avoid having the sister touch the subfloor if you want, thus eliminating a possible source of squeaks. But you would also not gain any reduction in span of your subflooring (you'll be at the minimums for that also with only a single layer of 3/4 ply).

A further consideration would be the plane of the top of the existing joists. You could correct any un-flat/un-level condition while adding the sisters and kill a couple birds with that same rock. That would be my first choice in your situation, I think.

Ditra's advantage over CBU is ease of installation and thickness, or lack thereof. Its disadvantage is cost. Either will work in your project.

My opinion; worth price charged.

Code Slinger 07-05-2005 10:38 PM

Thanks for your response, cx. Yes, most of the joists are 16" OC. A couple are less than that, but not enough of them to make a difference. I also found that there are some perpendicular 2 x 8's attached to the joists, not sure how much support that actually adds. Since I have a digital camera that I love, I am adding a picture to show the current situation (it would be best to ignore the utility room below:))


There is an issue with electrical cables on the far left running through the joists, so I may not be able to easily sister the joists all the way across the full length. So you are saying that I wouldn't have to put the new 2 x 6" boards even with the current joists? Just out of curiosity, how does that help add more support? I would think that the subfloor would need to be attached to the sister, also. But, I'm also a computer geek and not a flooring expert :). And how would you suggest I sister the joists? Do you use construction glue? Or nail the sister to the joist? Sorry for all the questions, I just want to get this right.

NVC 07-05-2005 11:02 PM

Hi Code Slinger, Whew! We thought you might have been an inspecter slingin' building code. :) Is it C, C++,C#, ASM, Java, perl (interpreted, but close)? Just kiddin' I digress, an old compsci dropout here, and I don't use boolean algebra too much on the jobsites.

What CX said.

Regarding the electrical . . . you can cut the wires (make sure power is off, this ain't Cat-5) then you can put each end of the cut in a new box, and run a new piece of romex (same gauge) between the boxes. This is fine as long as the utility room ceiling isn't going to be closed up, otherwise the boxes will have to have covers and be accessable from the utility room. Just an option, if it's holding you back on the twisted sisterin' :)


cx 07-05-2005 11:59 PM

Two kinds of deflection to consider here, Jon: Joist deflection, and subfloor deflection. The sistering of the joists stiffens that part. It can also aid in reducing the spacing between joists if the sisters also support the subflooring, but that's not a necessity. The subflooring can be augmented separately if necessary.

When you install a sister that is not as deep as the existing (2x6 sister on 2x8 joist, for example), the optimum location of the sister for maximum stiffening is at the bottom of the existing joist and well attached to it. That means it doesn't touch the subfloor, but that ain't what we're fixin' with the sisterin'.

Attaching the sister the full length of the existing joist is the most effective method, but you can do a great deal of stiffening if you can sister at least two thirds of the center of the joist. I prefer all sistering be done with wood glue and screws if at all possible, and it looks possible with what you've got. You can do it with construction adhesive, but not as well in most cases.

Like Mark, I'd remove the wires where necessary and re-do'em after. Some of'em you might find enough slack to make only one splice, looks like.

Oh, and just by the color, if my monitor don't lie too much, I'd say that's Doug Fir, but not a real good grade. Unless it's Cedar. :rolleyes:

My opinion; worth price charged.

jdkimes 07-06-2005 01:08 PM

The photo is a great help.
Couple of thoughts from a DIY'er.
-Those cable (wires) running through the joists are against code anyway. Holes/notches cannot be made through the middle 1/3 of the joists.
- If you do sister cut those cross braces (2x8's between joists)out with a sawzall (tiger saw whatever brand you want :) where needed. You can save some work by removing a brace and sistering two adjoining joist on the same sides(between them).
- When I sistered mine floor I liberally applied construction glue and 16d nails fired from a nail gun and it ended up noticeably stiffer, where possible I used 2x8s about 3/4 t0 7/8 of the joist length. which it looks like you could do.

- The big question is: Is there a reason for not considering a support beam at midspan?? That would be the easiest and most effective from what I can see. You'd cut the deflection in half (I think).

NVC 07-06-2005 09:51 PM

I think what Jeff is saying is,

You cannot notch in the middle 1/3rd of the joists, but holes are OK if they are are 2" from the top or bottom and the dia. is no more than 1/3 the joist depth.

If they're off, you can re-route them to better positioning in the sisters'z. There is one 14-2 ? in the pic that looks like they drilled the hole a little low, but it could just be the angle.


Code Slinger 07-06-2005 11:15 PM

Mark - no, I'm not an inspector. But even I knew that some of the crap the multitude of previous owners had done is wrong :) . I am a .NET guy, I prefer C#, but I have to do VB.net on the current project I'm on.

As far as the electrical work... I am not sure I get your code reference. In all my reading on DIY electrical boards, I was led to believe that a hole in a joist or stud is acceptable if it is in the center, since that does not weaken the structural integrity of the joist significantly. Unless you are refering to the horizontal middle as opposed to the vertical middle? The diameter on the holes is mostly 1/2" - 1", and that is certainly less than 1/3 of the 7.25" vertical height of the joists. Mark, you do seem to be correct about one of the old 14-2 cables, I measured the distance from the bottom of the joist and it is right at 2". I will remediate that once I do the re-wiring.

Jeff - a support beam does not seem likely. Not pictured is the other side of the utility room, where such things as the furnace is in the way (and the unfinished utility room is only half of the width - finished area on the other half). There are also plumbing lines and gas lines that do seem to be in the way of such a thing. I will have to give it a better look, although I don't know how comfortable I would be doing that work since the steel beam that is in place looks like it might be beyond my capabilities. However, I am comfortable putting up some sisters (I've put up with my own sister for years, after all :rolleyes: )

As far as the sistering goes, I may just buck down and temporarily remove the electrical cables so I could go the full length. The panel is in the corner of the utility room rather close to the cables in questions, and I installed half those circuits anyway... so I could just take Saturday and re-attach them. I have to do the electrical work for the new kitchen anyway, and some of the aforementioned 14-2 is going away due to not having the grounding conductor.

CX - if my joists are cedar, that is problematic, correct? I don't think they are cedar - they didn't have much smell to them whenever I drilled through them for my electrical work. I always thought cedar had a distinct, but pleasant, aroma.

Thanks again for all the advice. I do appreciate all expertise offered on this board, as I do like to learn to do things the proper way.


NVC 07-06-2005 11:29 PM

Hi Jon,

Kewl, on the C# I never got to play with it. C and C++ and ASM mainly, .NET . . . .Never, did a few TCP and UDP sockets though, in 'nix.

I was referring to 'verticle middle' and 2" is right on the border if that measurement is to the bottom of the hole.

<begin digress>
Is the Avitar 'Big Helmet' by chance? LOL Good flick if so, if not I'll need to explain Mel Brooks "Space Balls"
<end digress> :)

A lot of the old houses had romex w/o a ground or even knob and tube w/o a ground. While not ideal, it still works fine. If you're talking electronics/servers/etc. then you'll want to put in something with a ground. (We use isolated grounds and neutrals in computer rooms/buildings to cut back on 'noise' . . . but they have halon dump fire extingushers in 'em too, and that 'ain't ' good in a house) <shrug>


MarcusEngley 07-07-2005 10:24 AM

Hi Jon, Mark...

Just had to drop in -- the avatar is indeed Space Balls, but it's Dark Helmet. "I see your Schwartz is as big as mine!" Ahhh, great movie...

Jon, I *think* Cx was joking about the cedar -- that'd be a bad choice for a joist, I think. Not as dense as pine or fir, though it sure is pretty. Might be wrong though...

Back to work!

cx 07-07-2005 04:33 PM

Only half joking, Marcus. We hear about cedar and redwood having been used for framing in some parts of the country. Not likely in Ohio, I wouldn't thing.

And you're correct, cedar is definitely not high on the strength and rigidity scales.

MarcusEngley 07-07-2005 04:41 PM

Sure would make for a nice smelling (if bouncy) house!

NVC 07-07-2005 06:36 PM

Ahh, Dark Helmet, that's right. Good flick.

Cedar wouldn't surprise me either.
A lot of the old houses I've worked on have had redwood (actual 2"x 4" studs)

Sometimes barnwood underneath plaster, never know what you'll find, just when you do find it, you know you'll just have to deal with it.


Code Slinger 07-07-2005 10:53 PM

"I always have coffee when I watch radar." Yeah, Space Balls is one of my favorite comedies - classic Mel Brooks.

I am guessing that the joists are not cedar - the house does not seem very bouncy at all. And it doesn't smell that great, of course that could be thanks to my niece and nephew's dogs visiting for the last week :rolleyes:

I'm not too concerned about the electrical wiring - I already replaced most of the circuits in the house with grounded 12-2. The only few circuits that still have the ol' ungrounded NM cable are the ones in the laundry room and the now defunct kitchen. Additionally, that project gave me a good chance to run cat 5 everywhere, despite the fact that I am also on wireless lol. Despite the fact that I have a few computers, I have figured that an isolated ground is probably overkill for my use.

I'm going to work on the joists and subfloor this weekend, since the new cabinets do arrive then - meaning it will soon be time to put the kitchen back together. As much fun as grilling brats and drinking beer on the porch is, lacking a kitchen is a pain. I also have my copy of Tile Your World on the way, I hope to work on the actual tiling within a few weeks. Yes! No laminate flooring :)

Thanks for all for your help, and of course for the good sense of humor in appreciating Dark Helmet and all his imperious glory.

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