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Unread 04-15-2020, 01:47 PM   #31
zink88
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Quote:
Originally Posted by PC
Also, the blocking is tricky to install right and can cause squeaky floors due to joist movement against the blocks.

I recommend either 2x4 laid flat to bridge the gap or the plywood as CX described. Both are simple, effective and fast.

OK. I will use one of the recommended methods. I will have to install blocking where I am removing the subfloor back to the doorway which falls in the middle of two joists. I have seen mention on multiple occasions that blocking, if not done correctly, can create squeaks. What is the "correct" method to avoid squeaks when installing blocking?
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Unread 04-15-2020, 02:08 PM   #32
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Jim, using the rips of plywood I suggested is far, far better structurally than would be T&G edges on your subfloor panels.

The 2x4s you would install between joists for the purpose is also quite suitable and more than you need. Yes, I would glue and screw them to the joists. I glue everything in any wood framed subfloor package.

The 2x4s would give you very little, if any, improvement in your joist structure. The only purpose of proper mid-span blocking is to keep the joists from twisting under load and to allow them to exhibit their full capacity. The blocking, even when properly done, does not improve the design deflection of the joists.

If you still plan to sister your joists (I don't think it necessary), you will have even less need for any mid-span blocking. If you do want to install blocking with or without the sisters, cross bracing with 1x or 2x material is more effective than solid blocking.

My opinion; worth price charged.
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Unread 04-16-2020, 06:04 PM   #33
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I was planning to use the rips of plywood between joists on adjacent sheets of non-tongue & groove plywood subfloor as suggested.

The interior wall separating the bedroom from the bathroom runs parallel to the joists and is in between two joists...so I will have to use blocking to support the interior wall when I cut the subfloor back to the wall inside the bathroom...correct?

This interior wall is 7' in length.

Should the blocking under this wall be 16" on center?

Does it have to be the same 2x10 as the joists to which it is fastened...or can I use 2x8, 2x6, or 2x4?
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Unread 05-24-2020, 02:17 PM   #34
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OK...so I have to win the slowest moving project award. Surprisingly, my wife has not yet filed for divorce given that our master bath has been out of commission for at least two months.

Subfloor has been removed and I have sistered all of the joists except for one using 12' 2x10s (joist span to wall support is 13'-6"). Sistered joists were attached with (3) 3" deck screws & washers every 12" and Great Stuff construction adhesive.

The joist that remains to be sistered has a 6" x 1.5" notch in the top where the bathtub drain was located. The notch is 6' from the support edge...so almost dead center in the joist. It also has a 2.5" diameter hole where drain pipe went through 5 feet from the other support end. The center of the hole is 1/4" above the center of the joist. These are circled red in the pictures below.

This joist also has some significant knots as shown in the pictures below (also circled red) and a 0.75" knothole 8" from one end (also circled). It runs perpendicular under an interior closet wall and the centerline of the joist is 9.5" from the beam that supports the exterior wall.

I had planned to keep the plumbing lines that come up through the closet wall which would mean the sistered joist would need to be ripped to only about 8" in height in order to rotate up into position.

Should I sister another 12' 2X10 joist on the other side??

Am I running into potential floor load issues in the 3.5' x 8' shower if I add sister joists on each side that are not supported by the walls...particularly if mud is used for the shower floor?

Instead of sistering a 2nd 2x10 on the other (exterior wall) side, I could maneuver a 2x6 full length sister joist into place on the exterior wall side of the existing joist which would be fully supported by the wall plates on both ends. Would that provide more support and, if so, should the 2x6 be positioned flush on the bottom with the existing 2x10 joist or flush on the top with 4" of wood shim between the wall plate and 2x6 joist?
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Unread 05-24-2020, 05:39 PM   #35
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Jim, the drilled hole is acceptable. The notch in the center of a joist is never acceptable. The grade of the joist is clearly poor. Can you find a grade stamp on any of the joists?

Quote:
Originally Posted by Jim
I had planned to keep the plumbing lines that come up through the closet wall which would mean the sistered joist would need to be ripped to only about 8" in height in order to rotate up into position.
'Fraid I don't understand what's going on there, but you do not wanna rip your sisters to a smaller size to be able to roll them into place if you plan to make them full length. It is acceptable to notch the ends for that purpose, but it's much easier to simply stop them short of the end supports. Makes no difference at all in their functionality if they are properly attached to the joists.

And I'm still a bit confused in general on your plans, but if you don't really need the sisters for improved deflection, adding a 2x6 flush with the bottom of the existing joist would be more helpful than any other location.

My opinion; worth price charged.
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Unread 05-25-2020, 06:04 AM   #36
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The joist in question is stamped SPF No 2...same as the other joists. Disregard the plumbing line issue. I will remove the plumbing lines from the closet wall to get them out of the way.

(1) I know sistering the joists short of the support walls on both ends improves deflection which is my initial goal, but how does it impact the load capability of the joists? By sistering with no supports at either end, does the weight of the sister joist now reduce the load that can be carried by the weight of the added joist or does the increased stiffness improve the load capacity above the original design?

(2) This joist is 1/4+ inch lower than it needs to be, but the closet wall prevents me from raising the sister joist without “notching” out a similar amount at this location which is 5’ from an end support. Would adding this notch on the sister joist be ok, or should I add 2 other pieces of 2x on the opposite side running from the wall back towards each end of the joist?
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Unread 05-25-2020, 10:09 AM   #37
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1. So long as the original joist has a sufficient footprint on the load bearing supports, you can add the sister joist with no contact on the supports at all. If you are somehow able to exceed the shear capabilities of the original joist at that location you have far more serious structural problems than we're discussing here.

2. Technically, no, but there are occasions when a judgement call is in order. I can't see the situation from over here, but I'd be likely to approve some "relief" of the small amount you describe at the location you describe. I'd make the notch clean and tapered at the ends to eliminate the potential for any splitting. I would not want to see even that much notching at the bottom of the joist or sister.

In my day I don't think that joist could not possibly have passed as #2 grade, but with the last major revision in the grading standards with which I'm familiar (2006?) the allowance for knots became such that I could no longer guess at the grade by sight. And we didn't use White Wood (your SPF) for floor framing at all. Times change. We try to keep up.

My opinion; worth price charged.
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Unread 06-06-2020, 04:46 PM   #38
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So I have sistered all of the joists and am will be putting down subfloor of 3/4" plywood and another layer of either 1/2" or 5/8" plywood.

The shower area will be 8' x 3.5' = 28 sq feet.

Are my calculations for floor load correct...?

The wall on the left is 8' x 3.5' so cement board (2.5 lbs/ sq foot) & tile (6 lbs/sq foot) is estimated to weigh 8.5 x 28 = 238 lbs.

An online calculator indicates I need 9.9 50 lb bags for Mud floor at avg thickness of 1.5" over 28 sq feet. Say 10 bags...so another 500 pounds.

Tile on floor at 6 lbs/sq foot over 28 sq feet = 168 lbs.

3/4" plywood (2.2 lbs/sq foot) & 5/8" plywood (1.8 lbs/sq foot) = 4 lbs/sq foot * 28 sq feet = 112 lbs.

Frameless glass & door area of 40 sq ft (8' long x 5' high). 3/8" thick at 4.91 lbs/sq foot * 40 sq ft = 196 lbs.

The long exterior wall with window at the back is over a beam...so not including any of the cement board and tile weight on this wall.

We will be adding an interior wall on the right built just inside the exterior wall to handle the shower head and niche without disturbing the insulation in the exterior wall. Similar area as the wall on the left, cement board and tile add another 238 pounds.

Total weight = 238 (left wall cement board & tile) + 500 (floor mud) +168 (floor tile) + 112 (2 layers of plywood) + 196 (frameless glass & door) + 238 (right wall cement board & tile) = 1452 pounds over 28 square feet of floor which equates to 51.9 pounds per square foot...and this doesn't include the weight of the lumber in the left & right walls, the weight of the 2x10's sistered to the existing joists, weight of thinset, and say a 200 pound person taking a shower.

Because of the size of the shower, is a mud base out of the question? Am I mis-understanding floor load calculations? How do similar sized showers get built on 2nd floors without issue?
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Unread 06-17-2020, 03:48 PM   #39
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Bumping this up in an attempt to obtain feedback.

Because of the size of the shower, is a mud base with membrane out of the question? Am I mis-understanding floor load calculations?

Since most floors are built to handle 50 lbs/square foot between dead load and live load, how do similar sized showers get built on 2nd floors without issue?
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Unread 07-06-2020, 06:06 AM   #40
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Given the lack of any reassurance that my floor will be able to handle a mud base, I will most likely use a foam shower tray for the floor.

On a separate note, the joists change direction in the closet as shown in the picture below. The first layer of 3/4" plywood will be screwed and glued perpendicular to each set of joists with the joint between the plywood sheets laid in opposite directions occurring in the middle of the double joist just to the left of where the plumbing comes up from below.

How should I lay the second layer of 1/2" plywood? The joints of the second layer of plywood are supposed to be offset from the first layer. If the second layer spans over the joint of the plywood sheets that are running at 90 degree angles to each other, a portion of the second layer will be running parallel to the joists rather than perpendicular to the joists on either the left or right of the double joist.
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Unread 07-06-2020, 09:18 AM   #41
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Jim, I think you weren't getting response to your load questions because of the mass of data provided (unintentional pun). In general I can just say, without benefit of being on site to evaluate your framing, that if you've constructed your floor structure such that it meets building code you can either build a shower using a mud bed or you cannot build a shower at all.

Orientation of the subflooring layers in conditions such as yours is not a simple matter. Technically you would need to orient both layers perpendicular to the joists and honor that joint where the direction changes up through the tile installation. I would not do that. I'd orient the second layer such that it was in the correct direction in the section of the floor that would see the most traffic and let the other portion be in the incorrect orientation. I'd want the second layer to span that joint in the first layer, extending as far as possible on either side. Then I'd not honor that joint in the first layer at all. See my warranty information below.

My opinion; worth price charged.
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Last edited by cx; 12-31-2020 at 10:46 AM. Reason: typo
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Unread 07-07-2020, 02:36 PM   #42
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CX,

If I understand correctly, the first layer of 3/4" plywood should be laid perpendicular to each set of joists as shown in the picture below with the red lines and blue lines showing the grain orientation, correct?

I would guesstimate that it will be close to 50/50 foot traffic in the red/blue area...maybe 60/40 heavier towards the blue area.

If I lay the second layer in the same direction as the blue lines over the blue section and 7.5" into the red section, that will take me to the bathroom side of the left door opening. I could then lay the second layer for all other areas in the same orientation as the red lines.

Is the 7.5" overlap from the red/blue joint where the first layer of plywood changes direction too close?
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Unread 07-07-2020, 10:25 PM   #43
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Given that it's a closet and unlikely to have a lot of heavy traffic, I think you could get by with that plan, Jim, without much concern with that change of framing area. See my warranty information below.

My opinion; worth price charged.
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Unread 11-25-2020, 12:50 PM   #44
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Flat Floor that Slopes

My bathroom floor is flat (any dips are less than 1/8" over a 10' span), but it slopes continuously from the exterior wall to the interior wall. The shower area is 3.5' x 8' and the floor slopes 7/16" from the exterior wall to a closet wall over the 8' shower length (from right to left when looking at the picture with the level shimmed to show level). The level is placed where the curb will be with the shower between the level and the window on the exterior wall behind it.

The drain will be in the center of this 8-foot span. If installing a Schluter shower tray, what is the best method to level the floor to achieve the required1/4" drop per foot from left to right when placing the tray? Contractor has indicated he could do so with thinset.

How should the curb be leveled to accommodate the frameless glass panel above the curb so it aligns correctly with the vertical walls?

The floor outside the shower which will also be tiled continues to slope at the same rate from right to left as looking at the picture for another 5 feet until reaching an interior wall. I am OK with no leveling outside the curb and letting the tile follow the slope of the floor.
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Unread 11-25-2020, 01:03 PM   #45
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Thinset is never designed as a leveling material. What may be the cheapest way would be to forego the foam pan and make it out of deck mud. Kerdi works just fine installed over deck mud. You could extend your mudbed to be underneath the curb to level it (you might then want to cut it off so it isn't so tall). You'd need a temporary surface to pack the mud against.

As to the curb, yes, you want the top level L-R, but it should have a slope in towards the interior of the shower. The foam curbs are easy to cut with a sharp knife or saw. I haven't tried a belt sander, but that might work, too, for a small change.

If you want to use the foam tray, then something like Ardex LiquidBackerboard could be used to level the area inside of the shower and for the surface where the curb would go.
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