Plywood subfloor for a shed/playhouse

[ak_bat]

I am building a 8x12 playhouse and am planning to install 3/4" plywood subfloor. I am following a book for plans & directions. Now, I would have installed the 3 8x4 plywood sheets one next to the other (8ft dimension of plywood aligning to the 8ft side of shed) to cover the

8x12 area.

However the book suggests to cut one of the sheets into half (4x4) and then use one 4x4 and then an 8x4 (8 ft dimension of plywood aligning with the 12 ft side of shed) on one side, and reverse on the other (ie. first the 8x4 and then 4x4).

I am sure there is a good reason for it, but it does not say why. Could someone explain?

Also, what kind of tolerances are "acceptable" when building something like this? That is, if the size of floor or walls is within 1/8" inch it is OK or 1/4" inch etc. Is there any particular dimension that needs to be more exact (e.g. height of walls has to be more exact than size of floor)?

Thanks

AK

[Duane Bozarth]

...snip...

Simply to stagger joints to avoid one joint all the way across...it'll tie the whole floor structure together more solidly than w/ a continuous break.

1/8" is a good target....it's significant to make sure your spacing isn't off enough to have to trim "just a smidge" off the finish materials on any surface to make it simple...it's a real pita if the ceiling height turns out to be 7' 11-1/2", for example and every wall panel has to be trimmed to make it fit.

[Mark and Kim Smith]

Read his description again. 8' x 12' floor, 3 sheets with the 8' side along the 8' joist. As long as the joist run along the 8' side, there will be no joint to stagger. No continuous break. Lay three sheets, square it up, and nail it down! Otherwise, you are correct, you want to stagger your joints.

[tim124c41]

This approach doesn't make much sense to me. I assume the joists are running in the 8 foot direction. Laying three sheets side by side will give you joints between the panels directly over joists, so the sheets will be fully supported around all their edges.

Putting the sheets the way you described will give you one unsupported joint between the sheet edges along the middle of the floor for the whole 12 foot length.

It could be this practice comes from floors with larger areas where single sheets won't span the whole floor, and you have these butt joints between the ends of sheets anyway.

[Odinn]

On 7/26/2005 1:46 PM ak [e-mail] mumbled something about the following:

I'm assuming they're wanting you to lay the plywood like such (make sure you use a fixed font to view this)

+----+----+ instead of +---------+ | | | | | | | | | | +----+ | +---------+ | | | | | | | | | | | +----+ +---------+ | | | | | | | | | | +----+----+ +---------+

on 16" on center floor joists.

[C & S]

I'm with Tim on this one.

In "regular" contruction, it is good preactice to stagger the joints, but that need goes out the window when you can span the room with a single sheet. For this appplication (Sheet-sized room, in a playhouse) it just doesn't matter.

Cheers,

Steve

[ak_bat]

Thanks all for your replies. They are most helpful

Regards

[Duane Bozarth]

I'll note in addition to Odinn's nice drawing, that doing it the way on the left eliminates the 8-ft alignment along the length of a joist (assuming the joists run shortwise, of course) in lieu of two 4-ft sections. This makes layout alignment slightly less critical.

[fredfighter]

Plywood subflooring is typically laid with the face grain accross the joists rather than parrallel to it. This is because plywood is

15% stiffer accross the face grain, than parrallel to it.

On most 4 x 8 plywood the face grain runs parrallel to the long edge so the plywood is laid with the 8 foot edge accross, that is to say perpendicular, to the joists.