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zadeluca
01-10-2014, 01:26 AM
Hello! First, thank you for such a helpful forum. Second, I apologize that my posts will probably always be very long. I try to be concise but instead I end up painting a picture with words. I won't be mad if you stop reading right now...

I have a modest 1400 sq. ft. house 2-story house. I am going to be installing about 400 sq. ft. of ceramic tile on the first floor (see picture, yellow areas will be tiled).

I have done a ton of research and planning and I'm sure I will have many questions, but for now I'd like to focus on one thing: floor joist deflection.

The layout is pretty simple, the floor joists run front-to-back, attaching to a center beam with joist hangers. The span on either side of the beam is 14'6". Here's where it gets interesting (see pictures). The house was built in 1882 and the original floor joists are 3"x8" (actual size) spaced 24" O.C. While this would be close at L/316, that point is moot because the original joists were all destroyed years ago by powder post beetles.

The remedy for this (previous owner) was to replace the main beam in the center with a 4x 2x10, cutting away about 6" from the joists on either side of the beam. New 2x8s (nominal size) were then hung with joist hangers next to what remained of the rotted joists. I would not consider the old joists at all in the deflection calculation, so what I currently have is essentially L/121. Needless to say, it's hysterically bouncy.

My current plan is to remove/replace all of the floor joists for the entire first floor. I will use 3x 2x8s in triple joist hangers spaced 24" O.C. I plan to reuse the newer 2x8s that are already installed and buy the rest that are needed.

Question: When using the Deflectolator, can I use 4.5" for the joist width since that is the total width of the 3 joists in the hanger? And if so, how do I need to connect the joists together? Since they will be all fully supported by hangers at both ends, I don't think they need to be attached together the same way as when joists are sistered (i.e. glue and a million nails/screws from both sides). If my assumptions are correct, this will get me to L/364, and I will add some solid blocking as well just to be on the safe side (I'm thinking 3 sets; the center of the span and 3-4' away on either side).

Some Q&A about why I plan to do it this way:

Q: Why stick with the 24" O.C. spacing?
A: I'd like to do all this work from the basement and retain the original sub floor. Except for where the center beam was replaced, it consists of 1-1/8"x8" (actual size) T&G planks that are in good shape despite the damage to the original joists. So I need to put the joists back in the same places in order to support any joints where the planks meet. The plank thickness plus the additional layer of 3/8" plywood/OSB underlayment that I will be adding below the cement board should be more than adequate for the unsupported span between the joists (19.5").

Q: 14.5' is a decent span, why not use wider lumber or I-joists so you don't need to triple them up?
A: Since I am not planning on removing the sub floor, I only have 8" of space on top of the front and back foundation walls for the joists to fit. I know I could build additional load bearing walls adjacent to the foundation walls so that a wider joist would not have to extend all the way to the rim joist, or I could add additional beams/columns to reduce the overall span, but I'd like to avoid those options... just because I guess. I'm not worried about finding the fastest/easiest solution, but rather the one that will leave me the most satisfied with the finished product, and that includes the usability of my basement when I'm done.

Q: This is gonna be a pain, you're crazy. Are you sure you're ready for this?
A: Yes. I'm going to need to deal with a lot of plumbing and electrical that will be in my way. It will be time consuming as all hell but I'm not worried. It's not like I really have anything better to do.

If you've made it this far, thank you very much for reading. Does my plan for replacing the floor joists sound good? Any better ideas?

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Kman
01-10-2014, 02:47 AM
I'll start by saying that someone with more experience will need to come by and verify that what I'm telling you is correct. I had to sit here and scratch my chin a few minutes thinking about whether there is a reason to laminate your joists in threes.

Here's my conclusion: I think you're going to have to bite the bullet and laminate them. Although they will be attached at each end, the spacing is going to be effectively the same, so it's not like you're going from single joists on 24" centers to 12" centers (which, by the way, would still have too much deflection).

In order to gain the full strength of all three 2x8's, they will effectively have to function as one joist that is 4 1/2" wide, thus allowing you to use that calculation in the deflectometer. Otherwise, you have three individual joists.

Forget the blocking, you won't need it, and it won't do much for you. You have enough work ahead of you without adding on more.

Here's the good news: According to my calculations, and these are just rough calculations based on what you've posted, you won't need to use a million screws to laminate the joists.

It'll only take a half-million. :stick:

cx
01-10-2014, 09:53 AM
Welcome, Zach. :)

Please post your photos using the paper-clip icon above the Reply dialog box to attach them to your post rather than linking to third party storage. Those third party sites tend to change urls over time and make your photos disappear from your thread. You can attach any .jpg 2Mb in electronic size or smaller.

Your original joists, even if of good species and grade, were substantially undersized for a code compliant floor today. L/316 is not at all close to L/360 when it comes to deflection measurement.

For replacement you would be far better off using two 2x10s than your planned three 2x8 joists. The three 2x8s, even if of good species and grade, will barely get you to L/360 on a good day. Two 2x10 of same grade and species, on the other hand, will get you a good structure.

If you have 8 inches of vertical space above your supports, there is no problem notching the bottom of the 2x10s to fit in there. You can notch a maximum of 1/4 the depth of the joist at the support without losing strength or rigidity.

Sistering joist by fastening them with glue and mechanical fasteners is a good idea if you're gonna sister them, but installing the same number and size joists independently gives you the same structure at a narrower joist spacing. I would always recommend gluing and screwing if you're gonna sister, but it's not a requirement for full length joists that rest on end supports.

For your subflooring, you must use a minimum of nominal half-inch exterior glue plywood over your current board subfloor for a ceramic tile installation.

My opinion; worth price charged.

zadeluca
01-10-2014, 01:40 PM
Thank you for the replies Kman and cx. I have attached the images properly now.

Forget the blocking, you won't need it, and it won't do much for you. You have enough work ahead of you without adding on more.

Less work? Sounds good to me!

... installing the same number and size joists independently gives you the same structure at a narrower joist spacing. I would always recommend gluing and screwing if you're gonna sister, but it's not a requirement for full length joists that rest on end supports.

Exactly what I was thinking. I understood Kman's reasoning, but using the Deflectolator I realized that a 4.5" wide joist is exactly 3 times stronger (with respect to deflection) than a 1.5" joist. Now if it were more than 3 times stronger, laminating them to achieve that strength makes more sense.

For your subflooring, you must use a minimum of nominal half-inch exterior glue plywood over your current board subfloor for a ceramic tile installation.

Got it. Any objections to 5/8" (19/32") OSB? I'll be using Durock and they seem to allow it. Although 1/2" BC plywood is only about $125 more for 400 sq. ft. worth so...

If you have 8 inches of vertical space above your supports, there is no problem notching the bottom of the 2x10s to fit in there. You can notch a maximum of 1/4 the depth of the joist at the support without losing strength or rigidity.

I was thinking about this but started to shy away from it for 2 reasons:

1) This video talks about the consequences of notching the bearing portion of joists (youtu.be/26eRXS0ThnU). While I understand what he is saying with respect to the structural load of the joists, I didn't know if it impacted deflection as well (i.e. would the deflection ability of the joist be reduced to that of the un-notched depth?).

2) While the depth of the notch can be D/4 as you mentioned, the length of the notch as far as I know is allowed to be D/3 max, or a little over 3" in the case of a 2x10. I say "as far as I know" because while the code differentiates between notch depths at the interior (D/6) and the ends (D/4), it only lists D/3 for notch length, so my understanding was that applied to end notches as well?

In my case, the foundation walls are stone and about 18" thick. The distance between the rim joist and the interior edge of the foundation wall is 12", so that is how long the notch would need to be? I was thinking I could put a ledger board (right term?) on the interior edge of the foundation wall and build sort of a "mini-floor" over the 12" thickness of foundation wall (i.e. small floor joist segments between the rim joist and the ledger board to support the floor in that area). But then I thought that since the interior edge of the foundation wall is very uneven (stones are round, some are missing, etc.), it would be difficult to properly support this ledger board on the edge of the foundation wall.

The three 2x8s, even if of good species and grade, will barely get you to L/360 on a good day.

I know, this is pretty much as borderline as it gets. What is the current opinion on solid blocking? I know Kman says to forget it, but in a borderline case like this is there any merit at all? I suppose if I am hell bent on the 2x8s I could always bump it up to 2x 2x8s at 12" O.C. For an extra $300 give or take, that would yield L/486, along with loads more plumbing relocation.

cx
01-10-2014, 11:49 PM
1. Can't see your video. Perhaps if you provided a link?

2. If your joist is being supported by the rim joist, your end notch would be excessive. But if your joist is supported by what's under the notched portion, it would be fine. I'd need a photo of what you've got to comment further.

Between-joist blocking or cross-bracing (the better method) does not change your design deflection at all. And I agree with Kevin that with three 2x joists sistered together the addition of any such bracing would be a waste. There will be no appreciable twisting of that joist package.

My opinion; worth price charged.

zadeluca
01-11-2014, 01:30 AM
I wasn't allowed to post URLs before so I just included the YouTube short link in parentheses, it was easy to miss. Here is the link: http://youtu.be/26eRXS0ThnU

2. If your joist is being supported by the rim joist, your end notch would be excessive. But if your joist is supported by what's under the notched portion, it would be fine. I'd need a photo of what you've got to comment further.

Well with 2x8s (nominal) I was planning to use joist hangers on both the girder and rim joist ends since the rim joist is 8" and the joist is only 7.25". There are no sill plates; just rim joists sitting on the foundation.

With notched 2x10s the notch depth would be 1.25" to fit the 8" opening, that's fine. But the distance between where the foundation wall starts and the rim joist is about 12", so in order to extend all the way to the rim joist it would have to be notched the whole 12" (and therefore violate the D/3 notch length constraint?). I will get a picture tomorrow.

I think I get what you're saying about it being supported under the notched portion (i.e. if it had full bearing on the foundation wall), but I can't find an actual exception that allows that either in the code or anywhere online. I know it is common practice, though. In fact, my 4x 2x10 girder is notched like that in order to sit on top of the side foundation walls (but I'm not concerned about that since it is supported by steel columns on pad footings every 5').

I understand about the blocking/bracing now. I was thinking that they would help "distribute the load" between multiple joists, but that should already be accomplished by the 1-5/8" thick subfloor/underlayment combo. Plus, I will need to firmly screw all the planks to all of the floor joists since the old joists they are currently attached to will be gone, so they shouldn't be able twist.

Thanks for your continued help.

cx
01-11-2014, 09:31 AM
Now with a proper link to your youtube, I declare your youtuber to be incorrect. See my warranty information below.

My opinion; worth price charged.

zadeluca
01-14-2014, 12:53 AM
Hah! I like you :lol2:

Despite your declaration, I've done some more research and decided I'm not comfortable with the notching of the 2x10s, and it would also cause some other problems which are not really worth getting into. So rather than take a risk on the bare minimum of my original plan (L/364, 3x 2x8s 24" O.C.) I think I'm gonna go with 2x 2x8s 12" O.C. for L/486. The cost is pretty much the same as going with 2x10s anyway because, although I will need twice as many 2x8s total, I already have 30% of what I'll need.

Considering the amount of work involved in replacing an entire floor worth of joists (disconnecting all the electrical from the panel to pull it through the joists and then putting it back after I'm done, same with water, drain, and gas lines that go through the joists), the complications added by going from 24" O.C. to 12" O.C. are very minor. Luckily, it appears I will be able to work around all the boiler pipes, which is good because it's cold in NY. :)

And obviously since I will be cutting the old joists away, I will need to secure the plank sub floor to the new joists. I plan to use 3" deck screws for that; 2 screws whenever a plank crosses over a joist, and 3 screws at the end of each plank. Sound good? Overkill? My rough math for that comes out to ~1800 screws, crap...

Thanks again for your help. This is going to take a while, I'll be back to discuss the next step hopefully in a month-ish. :smash:

cx
01-14-2014, 10:16 AM
Fine with me if you really wanna do that, Zach.

With boards that wide I'd want three fasteners per joist in those wide boards, but two might do if your boards are very flat and you use construction adhesive at the contact points. You'll want to pre-drill all those screw holes, too, unless you get screws designed for the application. Even then, though, you might experience a good bit of splitting of the old boards at the ends and have a good bit of trouble pulling the boards tight to the joist tops.

The 3" screws would be fine, but you could get by quite well with 2 1/2" or even 2" screws. The requirement is to have a minimum of 3/4" penetration into the joist top. I'd likely wanna go with the 2" if it were mine.

But then, I'd also most certainly go with the 10" joists, too. :)

My opinion; worth price charged.

zadeluca
03-21-2014, 02:47 PM
Hi guys, a little over 2 months later and I'm finally making progress on the joists. I had to finish pulling up the 2 layers of 1/4" plywood and linoleum so it took a while to get started. I should be wrapping up all the joists in the next week or two (hopefully).

I've started shopping around for plywood underlayment and have a question. I called a local company asking for 1/2" BC plywood and they want to sell me "1/2-in UL Sturd-I-Floor" because "it's made to be an underlayment and is sanded as good or better than a BC plywood." He stated that the "UL" in the name means it's specifically intended to be used as an underlayment. It is not a T&G panel.

I found the manufacturer's website (Georgia-Pacific I think) but the problem I have is that I can't find any product with "UL" in the name. I found their Sturd-I-Floor but it says it's for subfloors and the smallest size is 19/32". The only grading it says is "Exposure 1." I tried calling the manufacturer but could not get anyone on the phone.

So my question is does anyone know anything about a "1/2-in UL Sturd-I-Floor" and would it be appropriate here? Otherwise I can just get 1/2" BC from Home Depot, it's only a few $ more per panel but they charge much more for delivery...

Thanks!

cx
03-21-2014, 02:51 PM
This is still a second layer of subflooring, Zach?

zadeluca
03-21-2014, 03:12 PM
Correct, my current subfloor of 1-1/8" T&G planks will remain intact. This would go on top of that, and then the Durock. Earlier you said:

For your subflooring, you must use a minimum of nominal half-inch exterior glue plywood over your current board subfloor for a ceramic tile installation.

I'm trying to determine if this mystery "UL Sturd-I-Floor" qualifies under that recommendation.

cx
03-21-2014, 10:01 PM
I would prefer plywood, and that may be the Plytanium stuff, but in any case it should satisfy the requirement, Zach.