The flooring in the picture is tongue and groove design---and is installed correctly.

I have never heard of an expansion gap requirement for subfloor installation. Seems to me that if a sub floor needs to move, only a floating floor could be installed---precluding using anything else save carpet. How would a builder communicate that for an owner 40 years later?

Check your source of info. that told you you needed expansion. Sounds like it's for roofing. If you were using a "Do it yourself" book you might have looked at Plywood & thought it was for floor & you were reading about roof preparation!! If you left space between tongue & groove & someone had heels & walked across the gap they just might leave a good dent. Would be very unstable!

The sources of information are three different books on framing. One of them states the procedure may be avoided in dry climates. Maybe this has more to do with open framing that experiences exposure to rain before the roof and walls are built.

Thanks

Just another two cents to say it's not an issue with flooring.
BTW, adding depth to joisting, or any beam, increases deflection resistance...width, not so much.

"BTW, adding depth to joisting, or any beam, increases deflection resistance...width, not so much."

The deflection goes directly with width, twice as wide gives 2x stiffness.

It goes by the cube of the height, so even a small increase in beam height has a large affect on stiffness.

A 10% increase in height increases the stiffness by ~33%.

Brickeyee, I think we're saying the same thing- a 2x6 is much stiffer than a 2x4, whereas a 4x4 doesn't yield the same result.
I used "depth" to indicate vertical dimension of floor surface to bottom of beam.

The beam deflection equation is pretty easy to find.

I just used real numbers.

If we're going to parse, depth = height, not width.

4x6 joists. That's a new one on me! The only floor sheathing gaps required in the Ontario Building Code relate to a second layer of sheathing as an underlayment for ceramic. (OBC9.30.6.3)

It's true water often swells T&G joints. But not more than a quick run with a belt sander can level off before the finished floor is laid. And maybe if I were in the Seattle/Portland/Vancouver area gaps on non T&G might be a good idea.

"If we're going to parse, depth = height, not width."

You seem to be the only one parsing anything.

The beam equation usually uses w for the width of the beam, and h for the height of the beam since it is normally shown in a side view so that it can be annotated with a shear diagram if required.

If a 2x4 has a strength of 1, a 4x4 has a strength of 2, while a 2x6 has a strength of (5.5/3.5)^3 = ~3.9

You got it.

methinks you're a little late to a six year old thread.