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Unread 01-19-2022, 06:39 PM   #1
Triple T
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deflection

Doing some remodeling on a house built in the mid 70's. trying to figure out the deflection for tile for the floor. the floor consists of 6x10 beams that span 14 feet, and are 8 feet apart. there is 1/2" plywood, then 2 1/2" of foam, another layer of 1/2 " plywood, then 1/2" particle board. There are no floor joists. just this plywood, foam combination over the beams. anyone run into this before? and have any idea how to figure if it will hold ceramic tile?
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Unread 01-19-2022, 06:45 PM   #2
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Welcome, Tim.

Just when we think we've seen it all..........

Was this house constructed within a code compliance jurisdiction at the time of construction?

Do you know if this was an ad-hoc sort of construction, or are there maybe some sort of identification stamps somewhere on one of these foam sandwiches that would indicate it was an engineered product?

I'm first wondering if it will hold Mr. and Mrs. Tim, let alone a ceramic tile installation.

These beams are full dimension, or nominal?

My opinion; worth price charged.
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Last edited by cx; 01-19-2022 at 10:05 PM. Reason: Add Question
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Unread 01-20-2022, 12:13 AM   #3
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All those sheets of 1/2" have got to feel a little "trampoleney" when walking across it.

I think the simple answer is, without some support between those beams, and a stable subfloor of at least 5/8" (assuming you get the joist spacing to 16" or less), tile won't survive on your floor.

Here's a bigger question though. How are those sheets attached to the beams? And there must be something in there to support the edges running perpendicular to the beams.
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Unread 01-20-2022, 09:25 AM   #4
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This sounds like it may be an early iteration of SIPS (structural insulated panels) construction. At one time, floors were considered a good candidate for SIPS, in addition to walls and roofs. As far as I'm aware the method has been largely abandoned for floors. I can't imagine what you describe as being very stiff, but who knows.

I don't know if it will provide the deflection info you're looking for but might be interesting if you want to learn more about structure.

1. Are the plywood layers bonded to the foam?
2. What does the foam look like? EPS looks kinda like a styrofoam cup. Polyiso foam boards are usually kinda creamy in color and denser than EPS. XPS foam boards are typically blue or pink, but not all that common with SIPS, as far as I know.
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Unread 01-20-2022, 09:30 AM   #5
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Talked to an old timer supplier, said they did use them at least in this area, for a short time in late 70's early 80's. Have no idea how they are fastened to the beam. The beam is 5" wide and 10" tall laminated. I don't know how the plywood and foam layers are secured to each other. there are no labels that I can see indicating they are a manufactured produce, or just put together. There is a 2x4 framing system under the plywood to run electrical and plumbing, and hang rock. 24" centers. I'm leaning towards calling an engineer to see if there is any way a deflection could be determined. Thanks for the input.
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Unread 01-20-2022, 09:38 AM   #6
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Plywood appears to be bonded to the foam, and it is a creamy in color. I'll do a little more looking and see if there is any info on sips. thanks for the info.
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Unread 01-20-2022, 09:52 AM   #7
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Even at only 5" wide, I think those 10" beams would actually qualify as having a design deflection of L/360 if they are of good grade and species.

I don't recall ever having heard of the SIPS panels being used for floors even back when they were popular for a while in manufactured housing in this area. But I wasn't interested in them and didn't pay particular attention to them. I know they can be pretty rigid, but, again, I just don't know if we're actually talking about meeting building code for a residential floor structure with an eight-foot unsupported span.

I'll be interested in whatever you find out about your floor, Tim.
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Unread 01-20-2022, 10:22 AM   #8
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did a little research. They do have SIP for flooring now, BUT, they incorporate an I joist in the foam section, which would make sense. That's what makes remodeling interesting
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Unread 01-20-2022, 10:45 AM   #9
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Does your floor feel solid, Tim?
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