Plotting strategy for my very first tile job(s). I’m not ready to begin yet, but I’m doing some interior framing and want to plan ahead as much as possible.
I’m planning to tile both bathrooms as part of my remodeling project. I currently have 2×8’s, 16″oc. The subfloor is currently 1/2 ply, but I plan to replace it with 3/4 ply. I’m concerned about deflection and would like to sister each joist where the tiling will be laid. Unfortunately, there is wiring passing through the existing joists and it would be a real PITA to remove it so it could be fed through an additional set of holes. I could simply notch the sistered joists to accomodate the cables, but I’d have to notch more of the joist than is normally allowed.
1. In regards to notching, would a supplemental joist be subject to the same codes as the existing joist?
2. Since the sistered joist will be securely fastened to the adjacent joist, can it withstand a greater degree of notching and still retain its rigidity?
Thanks in advance for any feedback on this.
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Used knowledge is even more valuable.
Replies
Unless you can get the new joist to extend to the bearing points on each end, and unless they are only notched or drilled as allowed for a 'regular" joint, then all you have is blocking. There would not be a code issue for the new joists since the existing joists are ok, and you're just trying to stiffen the floor. But if you notch the bottom of the new joist so it can be dropped over the top of the wiring, you have taken out most of the strength. Same for if the new joist is only as long as the bathroom floor: it doesn't do any good unless each end is supported on something.
"Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
The joists extend from the exterior sill to the center sill (ranch house - basic rectangle). I can acces each sill and rest the ends of the joists on them with no problem other than interference from the wiring. My plan was to notch the topside of the joists.
Would blocking serve just as well?New knowledge is priceless.
Used knowledge is even more valuable.
Yes, if you can nothch the top and leave the bottom continuous, that would be much better."Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
You posted whilst I wuz typing.If you're notching the tops, fill the notches with tight fitting parallel grain blocks. It's all compression there.SamT
Good point, Sam
I'll just add to glue and screw the sisters.
Also, 3/4" ply by itself is not a sufficient substrate for tile. You need either mesh and scratch coat or another layer of ply.
If you have 1/2" (odd?) sub floor in place and the floor is flat, you could cover with 3/4" and tile from there.If you didn't have time to do it right the first time, how come you've got time to do it over again?
"it doesn't do any good unless each end is supported on something."Yes, it will stiffen the existing joist. It may not increase its' ultimate shear failure strength at the bearing points, but it will definately stiffen the floor.Also, if the original is notched on the bottom and the sister is notched on top, that is better than both notched the same.It would be best to get some tensile strength added to the bottom notches on the sister. Add a strap under the wire across the notch and thru nail or bolt to the original joist.SamT
>>Unless you can get the new joist to extend to the bearing points ... then all you have is blocking.It is my understanding that one need not have bearing at the ends of a sister joist to increase stiffness.
May your whole life become a response to the truth that you've always been loved, you are loved and you always will be loved"
Rob Bell, Nooma, "Bullhorn"
You might be right, since you're not using the new joists for load support, but I think you have to come close to the bearing points. "Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
pull th ewire and sisten, then rebore an repull it. If yoiu don't do it right, not much sense in adding the sisters
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"If yoiu don't do it right, not much sense in adding the sisters"
I agree, Piffin. I just need to be sure that "right" will require drilling the holes and re-routing the cables. This is in a tight area of my crawlspace. With my arthritis like it is, it takes me just about a day of recovery for every hour I spend down there. Getting to be kind of wimpy in my old age.New knowledge is priceless.
Used knowledge is even more valuable.
Would it be possible to cut the wire and add a short section
of new wire with two junction boxes (one at each end) permanently
accessable from below?
"Would it be possible to cut the wire and add a short section of new wire with two junction boxes (one at each end) permanently accessable from below?"
I may have enough slack in the cables to pull that off with just one junction box. I'd just rather not have to.New knowledge is priceless.
Used knowledge is even more valuable.
" I'd just rather not have to."That mental block is your problem. It is easier to pull the wire, drill, and re-run it than to finaegal around them.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
I'm with Piffin on this one. You'll be way ahead of the game if you just re-do the wire. If you're in a crawl space, it'll only take about 15 minutes since you only have to patch in a splice between a couple of boxes. That's nothing compared to the extra grief of trying to accurately notch and align the sisters you'll be installing. If you REALLY don't want to mess with the wire, just hire somebody to do it. If I was putting in a tile floor over 11-1/2' 2X8s, I'd be pretty worried about having to redo the tile (and framing) later if I wasn't real sure about the framing.
Mike HennessyPittsburgh, PA
You haven't said what the current joist span is. In general terms, 2x8s at 16" oc should be good for up to about 11 feet. So if your existing span is at or below that (and your existing joists haven't been butchered), once you add your floor sheathing and concrete board, I think you'll be good to go.
If stiffening the floor is required, I don't think the sistering will be worth the effort if you cut deep notches to accommodate the existing wiring. If you decide to stiffen the floor, I'd either pull the wiring and do it right or look for an alternate solution, such as strapping the bottom of the joists.
Y"ou haven't said what the current joist span is."
11' 8", if I remember right.
"In general terms, 2x8s at 16" oc should be good for up to about 11 feet."
John Bridges' "deflectolator" (I think that's right) says it's not quite good enough.
"So if your existing span is at or below that (and your existing joists haven't been butchered), once you add your floor sheathing and concrete board, I think you'll be good to go."
I doubt if I'm good to go with what I have, but I feel like a sistered joist (even notched), with the proper substrate, should be adequate.
"If stiffening the floor is required, I don't think the sistering will be worth the effort if you cut deep notches to accommodate the existing wiring. If you decide to stiffen the floor, I'd either pull the wiring and do it right or look for an alternate solution, such as strapping the bottom of the joists."
You guys are smarter than I am about these things. I was just hoping to get by on this one.
Thanks for all the feedback.New knowledge is priceless.
Used knowledge is even more valuable.
I'd agree that 11'-8" is a little too much span to give you a solid floor in this case.
I had a similar situation in my own house --- 2x8's at 16" oc, and about 12''-3" span. To make it worse, careless remodelers had cut up many of the joists. The floor was springy enough that I finally got sick of it, and bit the bullet. I had to pull out ALL the wiring from the panel, and I sistered on 2x10s all the way down. Then I had to redrill all the holes, and reconnect all the wiring. Major PITA, to be sure.
You mentioned your tiling project will be over a crawl space. Any chance you could put in a few of piers and a beam?
Otherwise, I'd seriously consider strapping the joists.
Hope your project doesn't turn out to be as painful as mine was! ;)
From the previous post:
You mentioned your tiling project will be over a crawl space. Any chance you could put in a few of piers and a beam?
But actually I'm thinking you are overthinking the matter and letting yourself in for a whole lot of unnecessary work in sistering.
Edited 7/27/2007 11:50 am ET by rez
I remember seeing in a fairly recent FHB article a method for stiffening joists that would seem to do well in this situation.
They used steel strapping (16ga?). The strapping was fastened to the top the joist at one end, angled down so that it was at the bottom of the joist at mid span, wrapped underneath and then anbled back up to the top at the other end.
I assume they nailed in every hole along the length of the strapping.
It seemed to be a handy way to stiffen the joist - especially if there is wiring or plumbing running through the joists.
Not to go against the grain here, but there should be no need to sister joists in a bathroom. Before the availability of products like Advantech, typical house construction used 1/2" CDX as subflooring covered with 5/8" underlayment. Plywood underlay was used in kitchens and baths and particleboard was used under carpet. 3/4" hardwood flooring was typically placed over the 1/2" CDX, when that option was used. 2x8 16" OC were often used up to a 12' (nominal) span. There must be a million homes built this way, I've built hundreds myself.
Once you get into the floor, I think you may find you have a double layer as I described. This isn't a ballroom you are talking about. Is the floor bouncing now? If you are in a terribly, poorly, built house, 1/2" subfloor only and cannot add another layer of 5/8" because of height restrictions, you can beef up the joists. You don't have to sister them with a 2x8. A couple of 2x4s on each side screwed and glued will stiffen things up and likely miss the wiring. How big are these bathrooms? You probably don't even have 8' of open width. A floor has to be noticably weak to effect tile. I think you are worrying about nothing in a small bath.
Beat it to fit / Paint it to match
"Before the availability of products like Advantech, typical house construction used 1/2" CDX as subflooring covered with 5/8" underlayment...There must be a million homes built this way, I've built hundreds myself."
Both bathrooms actually had tile floors to begin with, and there weren't any cracks in them as I recall. The floor consisted of 1/2" ply, backerboard, and tile. That's all. The ply had a noticable dip in it where the tub was located, but other than that, the subfloor is fairly stable, but obviously not very rigid with only 1/2" ply. My plan was to simply beef up the joists a little and re-sheet with 3/4" ply. I'll be installing the tile with a schluter underlayment.
"How big are these bathrooms? You probably don't even have 8' of open width. A floor has to be noticably weak to effect tile. I think you are worrying about nothing in a small bath."
I have two rooms back to back that will be getting tiled. They're sharing the same joists in one area. One will have a tub, toilet and vanity. The tiled portion won't span more than about 5 feet. The other will have a 60x34 shower, toilet, and vanity. The tiled portion in that one will be close to 8' in the longest span, and that will be perpendicular to the joists. This tiling will also be installed over an uncoupling material.New knowledge is priceless.
Used knowledge is even more valuable.
I'll go against the grain here... pun intended.
I think that solid blocking/bridging would do just as much, if not more, to stop deflection than would sistered joists. That is assuming that your joists are adequately sized in the first place.
Deflection can be caused by warping or twisting joists. If this area is over a crawlspace, then it is possible that it is subject to periods of twisting relative to differing amounts of dampness with seasons.
Furthermore, if sistering is what you wish to do, you don't necessarily have to use a full-height joist as a sister. You can scab on 3/4" plywood for instance... which has more resistance to bowing than standard lumber. Do that AND add blocking and the floor will be bomb-proof. The plywood doesn;t even have to go the full length of the joist. Assuming you are under 12', you can center an 8' strip of plywood and be more than good.
http://www.petedraganic.com/
"You can scab on 3/4" plywood for instance... which has more resistance to bowing than standard lumber. Do that AND add blocking and the floor will be bomb-proof."
I think I'll combine this strategy with a thicker underlayment. That should be more than sufficient for the size of these floors. I just need to be sure that I can accomodate the plumbing without negating the improvements.
Thanks again to all of you.New knowledge is priceless.
Used knowledge is even more valuable.
If your gonna open it up from the top I would look at as mentioned byRagnar17
"You mentioned your tiling project will be over a crawl space. Any chance you could put in a few of piers and a beam?"
Then all else can just remain and not near as much low crawling.
How about thick metal strapping firmly attached along the bottoms of the joists to resist the 'stretching' which necessarily accompanied deflection?
May your whole life become a response to the truth that you've always been loved, you are loved and you always will be loved"
Rob Bell, Nooma, "Bullhorn"