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Unread 08-26-2019, 07:05 PM   #1
Wthockey
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Will this meet deflection?

My house was built in 58, and has an older pier and beam foundation. We’re midway in a bathroom remodel, and I’m just wondering if I need to add any additional support while the floor is opened to support a tiled floor. Previously there was linoleum floor with an incredibly bulky tiled shower that wasn’t showing any issues outside of being very outdated.

The beams are doubled up 2x6 Doug fir, with an unsupported span of 44” oc between piers. The beams are nearly 4’ apart.

Plan is to use 1 1/8” subfloor, and wanted to use sites underlayment, but looking at the required specs, not sure that will work for this install?

So before I even get too far going down that road, will this meet deflection for a tiled floor? Or do I need to add to the structure? Is this enough info?

I’ve included an image of where I’m at currently if that’s of any help.

Thanks in advance for your help!
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Unread 08-26-2019, 07:28 PM   #2
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Welcome to the forum, Thomas!

You need more support. A pier and beam genius will be along soon enough, like Dr. CX or somebody. But I wanted to give you a quick shout, just in case you were about to choose a fork in the road before someone got back to you. Hang tight...


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Unread 08-26-2019, 08:11 PM   #3
jadnashua
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IF I remember, the pier and beam setup common on the west coast was checked by an engineer, and it would work, but that assumed the subflooring was something like 2" planks with a layer of ply on top. Not sure if what you have would work, as it's different.
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Unread 08-26-2019, 09:25 PM   #4
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Welcome, Thomas.

What Jim is describing is a typical Left Coast floor construction that we see here frequently (helpful if you'll add a geographic location to your User Profile) and for sure it works with the T&G 2x6 "car decking" most commonly used. I know one or more of our engineer types has also done the calculations with 1 1/8th" plywood instead of the car decking, but I just don't remember if it proved workable without additional subflooring.

In any case, you'll need to provide some blocking around the entire perimeter to support whatever material you decide to use as your subfloor. And I'd recommend you add joists to reduce your between joist span to 24 inches or less. At 24 inches on center your 1 1/8th-inch plywood would be satisfactory for a ceramic tile installation, but a double layer, starting with nominal 3/4-inch and adding nominal 1/2-inch plywood would give you a better subfloor and be so very much easier to handle than the 1 1/8th-inch panels.

My opinion; worth price charged.
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Unread 08-26-2019, 10:03 PM   #5
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Thanks for the warm welcome all. I’ll get my profile updated, but dang you guys are good, could be part of a CSI episode or something I’m in southern Oregon, so the west coast bit checks out. There was 2x6 car decking that was removed, so you’re spot on there.

For adding additional joists, that would require poring additional footings correct? Or can I hang them off the perimeter blocking? (That seems too easy)

I’ve always wondered if two sheets of plywood was better than one, assuming the same finished thickness. Is that the case? The handling bit dies sound much easier for sure.

Thanks again!!
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Unread 08-27-2019, 05:21 AM   #6
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Thomas,

The beams are a bit undersized for my liking, I’d add a third 2x6 to each beam section. Are there other concrete piers with the framing removed to either side single beam we see in the center?

You’ll need to frame up new beams with optimal beam spacing of no more than 6’ and then frame 2x6 16” OC between the beams using joist hangers.

You could use single layer of 3/4” subfloor with that framing configuration.

Last edited by PC7060; 08-27-2019 at 05:27 AM.
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Unread 08-27-2019, 07:47 AM   #7
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Quote:
Originally Posted by Thomas
The beams are doubled up 2x6 Doug fir, with an unsupported span of 44” oc between piers. The beams are nearly 4’ apart.
Quote:
Originally Posted by PC
The beams are a bit undersized for my liking,
At a span of only 44 inches, PC, I found those 4x6 "beams" to be more than satisfactory in design deflection and was concerned only with the intended subflooring. What am I missing here?
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Unread 08-27-2019, 09:05 AM   #8
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This is a bit crude, but hopefully it helps. There is another beam just under the wall to the right, I've tried to show the beams in this picture using the blue lines. The right side is the exterior wall, and foundation wall.

Just to be sure I'm correct, the suggestion would be I run blocking around the perimeter (red) attached to the current beams with joist hangers, and then run additional joists (orange) parallel to the beams, 16" oc, again with joist hangers? Am I following that correct, or am I missing something? Is that just distributing the load better, I was under the impression blocking alone wouldn't help with deflection, but maybe this is a different scenario. Or am I just glossing over the fact that I need to add footings to the joists?

I should add, this picture is taken from the entry door, so there is another wall just out of frame. In general, the room itself is ~7' x ~7'.

Thanks again!
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Last edited by Wthockey; 08-27-2019 at 09:16 AM.
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Unread 08-27-2019, 10:56 AM   #9
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You have the right idea, and you shouldn't need to add footings, as long as your existing footings are adequately sized and in good condition.

Blocking between joists doesn't help with joist deflection. However, it does help with subfloor deflection, as the subfloor is supported more often. The 2x6 car decking, with a layer of 1/2" plywood on top, would have been stiff enough to span the 4' between beams. Anything less than that would likely not be stiff enough, which is why you need to add intermediate joists to reduce the subfloor span to 24" or 16".

BTW, once you've supported all the walls of rooms, as far as I can see it doesn't matter which way you run the infill joists, they could be perpendicular to the old car decking, or parallel to it. The new plywood needs to be installed with the long dimension perpendicular to the infill joists.

Cheers, Wayne
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Unread 08-27-2019, 12:21 PM   #10
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Thanks Wayne! Okay that makes sense, and glad to hear I can avoid additional footers.

Taking that all into account, it seems like my best bet is to attach a ledger board to the foundation wall (on the right of the image, pressure treated, any suggestions on best approach for this case?), and then add perimeter blocking and then run infill joists 16" oc (with blocking) and run those either direction, as long as the plywood runs perpendicular.

This seems like it will give the ability to both support the floor (most important), and use Ditra as well, so this is definitely better than what I was hoping for

If I've missed anything, please let me know, really appreciate the help all!
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Unread 08-27-2019, 12:40 PM   #11
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If you run the joist as shown in the orange orientation, you will need to use 2x8 joists. 2x6 will work if you use install perpendicular to the center beam (which you should reinforce per my earlier post).

Whichever orientation you choose, use a long straight edge to verify the beams are all in plane before you install the joists. For example, if the center one is low or high relative to the others your floor will not be flat.

The board with the notch cut into the top for the pipe should be replaced.

Good luck!

Last edited by PC7060; 08-27-2019 at 12:48 PM.
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Unread 08-27-2019, 01:21 PM   #12
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Just so you don't end up having to undo anything later on, are you by chance planning to install natural stone?
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Unread 08-27-2019, 01:48 PM   #13
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FWIW, 2015 IRC allowable span for 40 psf live, 20 psf dead, and #2 DF-L 2x6 is 9'-3". That means infill 2x6s could run either way in a 7' x 7' room. But if you run them parallel to the existing beams, you'd need at least a double 2x6 header at the ends to carry the infill joists. So as PC7060 points out, it is probably better to run the infill joists perpendicular to your existing beams.

When planning your joist layout, bear in mind that the full perimeter of your plywood infill needs to be supported; walls perpendicular to the existing beams on intact car decking are already adequately supported; walls parallel to the beams not over the beams should be supported on blocking; and the cut ends of the car decking need to be supported on blocking. If some of the necessary blocking would be tight up against the existing beams, you can avoid some cuts by instead sistering a 2x6 against the existing beams and making your infill joists 1.5" shorter.

Cheers, Wayne
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Unread 08-27-2019, 02:02 PM   #14
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Awesome, thanks all! Really appreciate all the help and insights on this, very informational for me.

I'll stick with running perpendicular then as that seems to be the best avenue here. The wall on the right is still supported fully by the foundation and layer of car decking that needs to be trimmed.

The left side wall is just past the beam, so it sounds like I can just sister a 2x6 to that, and that will also reinforce as per PC's suggestion. Add another 2x6 to the middle beam, and it sounds like I would be in good shape to lay the infills.

What about the ledger, will a single 2x6 connected to the foundation on the right wall be sufficient?

Kman, we're not using natural stone for this one, thanks for checking.

If I end up doing a curbless shower on the backwall, my understanding is I'd have to notch the joists to support the lowered floor for the shower. Would I still have enough support with the above? Should I sister with a 2x4 in the middle beam instead of a 2x6?
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Unread 08-28-2019, 05:06 AM   #15
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If you are planning on a recessed base for a curb less shower, you’ll want to avoid notching those 2x6 joists. Much better to frame a recessed section in now while you can.

The only area you can’t easily recess is the center beam.
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