Hello all,
I’ve been a lurker here for quite some time and have a great appreciation for the knowledge shared on this forum (almost as much as I appreciate the different personalities of those who share that knowledge). I’m a DIY’r but my wife thinks I’m more of a tool collector. Regardless, I have a project that I will start in a couple weeks that will allow me to get back at her for all the snide comments – a bathroom renovation.
My question to the experts has to do with floor joist deflection. I will be laying some travertine tile in a small bathroom (4 x 8) and have found from the tile guys that the 2 x 8’s that are 16″ OC spanning 11′ 6″ from mud sill to the support beam allow for too much deflection for laying stone tiles (or anything else except maybe some very thin VCT).
My thought is to sister the offending joists but I also want to use the “sisters” as support for a new subfloor that will be 3/4″ ext grade plywood ripped and fastened between the joists (at joist height)- bringing the subfloor down to the level of the tops of the floor joists. Question – will it do any good in terms of stiffness to use 2 x 6 “sisters” (witty comments regarding “stiffness” and “sisters” may be “inserted” here). If so, do I need to shim them to rest on the mud sill on one end and the beam on the other or can I simply use construction adhesive and nails (screws?) to attach them to the floor joists leaving an inch or so floating above the beam and sill?
Sorry to be so wordy and thanks to anyone who responds.
Replies
Yes to all. Use shims at the bearing points and glue and nail the "sister" to the joist. I have also used 1/2 to 3/4 ply between them to stiffen even further. Like making a header. May be overkill but your floor is going to be expensive.
"It is what it is."
You can just glue and fasten to the existing, but it will do you better to also shim under at ends too.
My concern here is with the drop to rip ply for fitting BETWEEN the existing.
A floor is a SYSTEM not a bunch of discrete parts that can be re-arranged. Like a jigsaw puzzle, you have to fit them together properly for it to work out right.
So the subfloor needs to run across the tops of the joists for the load sharing function to work. By interupting at each joist, you cause more flex individually and those tiles will not be happy, giving your wife yet more ammunition for snide comments. Let's do this right and make her apologize for once.
So if you need depth, plan to rip the existing down. It is not easy to do that accurately so you might want to rip deeper than needed and then use the top of the sister to create the new plane.
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I see your point about the floor being a system. My goal was to create enough depth to accomodate roofing felt, floor heating element, and metal lath, all covered by a traditional mud floor that didn't rise above the toilet flange or make a sloppy transition to the bedroom that adjoins the bathroom.
Ripping the existing joists down to size is more than I want to tackle in order to accomplish that. I think I'll go measure the depth again and perhaps use cbu's or Ditra directly over the new subfloor (which will be glued and nailed or screwed to the sistered joists). If that makes it still too high, then I suppose I could adjust the flange (gotta get another book) and consider ripping out the old thin parquet in the bedroom and replace it with 3/4" hardwood. (And she wonders why my projects never get finished!)
Why is it that every step of a project that I finish creates two more!
That's the bummer on doing baths. You could still rip the existing joists, but consider using micro-lams to sister to the existing. Much, much stiffer than 2x dimensional lumber, and these can be ripped too if headroom below is an issue. I would rip down to the level necessary to keep your subfloor on top of the joists.
You can use the plastic spacers to raise the toilet flange.
Just silicone it on top of the existing flange, no need to move anything. Use two if needed.
A plumbing supply house will have them.
Thanks - I'll check that out. Since we're both in the NW Chicago suburbs, can you recommend a plumbing supply house?
Also - Cubs or Sox?
I go to Ultimate in Palatine, it's a little towny supply house. Ferguson is in Addison (and elsewhere) and large nation wide business.
Go White Sox
Thanks! Since I'm in north Hoffman, I'll check out Ultimate. Since you're a Sox fan, I know that you are a discerning person with high standards.
My 9 year old is a Sox fan also. He was disappointed when I told him I got free tickets to Wrigley and I thought we should check it out. No sooner did we sit down then he got sick to his stomach. We didn't make it to the restroom in time and he hurled in the entryway to our seating section. I think he got carsick, but he swears it was the Cubs who made him sick. "Never Again!"
I think it wouldn't be that hard to cut the height on the existing joists, if you sistered on the new joists at the dropped level, used a recip saw to get within an eighth, and finished up with a router and bearing guided trim bit.
It isn't hard for me and it doesn't sound hard to you, but this is a guy who thinks it is hard and his wife nips at him for being less than proficient, so I think that for him it is hard.One where I did this was a large kitchen where in about 26' the old place was 2-3/4" off level.
I screwed two bys to the existing, one and a half inches lower than I wanted the joists trimmed to after marking them all to the level reference.Then used that two by for a guide to rail my circ saw along. Finished them out at ends with the sawzall.Had another where I was on my knees in a crawlspace reaching around one to get to the next and sawdust filling my shirt and ears
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OK Mr. Piffin, I am answering the challenge (maybe you didn't post it as a challenge but here goes). I actually did consider doing the rough cut with the recipricating saw and finishing it off with a router and flush trim bit. This way I can put in a mud floor underlayment that is at least 1 1/2" thick and everything will be done right.
By the way, my wife is actually a sweetheart. I'm a much bigger smart a_s than she is. Celebrated our 23rd anniv. 2 days ago. Well if either one of us had remembered, we would have celebrated it.
You and I have a lot in common then. I was always the cut-up in the back of the classroom making wise replies that broke up the boredom in school.And we have been married about the same amt of time.Here is your big chance to have more in common with me and rip joists while balancing on them feeling upside down
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Is head height below a factor? I assume the ceiling below is open. Will that space ever be finished?
It used to be until the wax ring in the toilet failed and started this whole thing. Our garage/basement is below the bathroom. It's one of those typical ugly raised ranches (but it's home to us). Unfortunately, the bathroom "straddles" the wall dividing the garage from the rest of the basement, which makes access to the joists below the shower part more challenging.
Another option if you have an extra 1.5" below the joists is to add a 2x4 on flat to the underside (ie a tee beam). The moment of intertia (stiffness) of a single 2x8 is 47cubic in, so by doubling you double the stiffness (94cu in); however, a 2x8 with a single 2x4 centered on the bottom has a moment of inertia equal to 117 cubic in or 24% better. It never seems to be mentioned, but this is a little more efficient and sometimes easier to achieve depending upon the location of your elec/mech. You must use many nails and a structural adhesive such as PL400 for this to work. An elasitic subfloor adhesive will not work properly. The nails must be close enough together to ensure the bond pressure is sufficient to develop a proper bond. Try to find dry 2x4's because shrinkage of the 2x4 could cause a bow in the floor joist.
Just an idea.
Never heard of that one. interesting idea though.
"It is what it is."
That could be do-able because I don't have any height issues in the garage. I'm not sure that it would be sufficient for the stone tile that I intend to use. I'll have to review the deflection calculation process, but I think I need to just about double the stiffness. Also, on the other side of the bathroom wall is another bathroom that will have to have the same treatment next year - further adding to the need for maximizing the strength of the joists. At least I think that it will.
Thanks for the suggestion.
I may get corrected here. but I think you might want to consider "Sturdifloor" for the subfloor instead of ext, ply. It will be stiffer.
That is over double the stiffness (263%increase) with a single 2x4 you simply air nail to the bottom. Height is always more efficient in increasing stiffness due to a cube factor when calculating the moment of inertia (there is a limit). I have some 2x10@16 floor joists that span around 17' and bounce in my house that will be getting this when it comes to finishing the basement. Matching the wood species is preferred so the old section has a similar elasticity, but in common dimensional lumber the variation from D-Fir to say SPF is not huge and should not be a problem. We did this in a school retrofit years ago, but then we used an epoxy. I discussed the pros/cons of the PL400 with Piffin some time ago, and have since spec'd that on a few projects.
Brad
I asked about the ceiling below because I was going to suggest sistering 2"x10"s, which would dramatically increase the stiffness. Shear is not your concern here so there is no need to run them the whole length of the joists, as long as they span to within 6" or so of the ends of the existing ones. Brad805's solution might be easier for you to do and brings the deflection well below what you need to lay tiles. Some 2"x4"s, PL Premium, decking SCREWS and you're all set.
Thanks for the input (to everyone). It sounds like either way I go (2x4 t's or sistering on 2x10's or 2x8's) I'll have enough strength for the tile. The earlier comments I made about replacing the old parquet with hardwood strips were only half in jest. That is going to happen somewhere down the line so the extra floor thickness won't be a huge issue (for too long). I don't want to take on ripping the existing joists even though that may give the best results for what I want. That would add extra time to the project and when it comes to bathrooms and kitchens - time is almost as important as quality.
Thanks again!
Why isn't it referred to as "brothering?" Or "siblinging?"
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