How to fix a measuring mistake

[Aunt Angus]

I just saw that you plan on using 3/4 in plywood. That should be good to support just a few inches.

 

[SourRoses]

It's not a terribly heavy structure so I'm hoping that I can get away with not having to re-build the base.

Thoughts?View attachment 3308586

I'm not a carpenter by any stretch of the imagination. In fact I clicked on this thread because we're making our own craftsmanship mistakes with our current build...
But one thing I have learned is that your horizontal lumber is supposed to sit on top of your posts. Otherwise, you are hanging a lot of the weight on the fasteners, and a few stress points in the lumber where the screws are sitting.

The other day we were raising a wall we had assembled on the ground, beam over post design and the whole thing full of long #10 screws. It still twisted slightly during the raising process and the whole thing fell apart over my head (ouch).
The screws had simply ripped out of the wood. We broke it down and rebuilt with more metal brackets.

 

[perkolator]

4" overhang on opposite sides could ok, as the other two sides are fully supported underneath -- but the strength is relying on the framework of the playhouse, and I'm guessing a commercially built structure like that does not have much of a structure at all. You're going to want some redundancy in the support structure.

In my experience, 3/4" plywood can and will definitely deflect in a short 4" overhang if there's any weight on it, especially if it gets damp like in an exterior application. Will it be detrimental? Probably not, but personally I would just go buy two 2x4s and make the frame the correct dimensions as intended, so the whole perimeter is fully supported. While I'm at the hardware store, I'd be picking up lag screws or through bolts to replace those screws on the posts, if my design is relying on my fastener's shear strength. I'd probably add triangulation to the legs too so they can't deflect - my inlaws have a small coop about the same footprint as this, and it had non-triangulated legs about the same length as those. Gophers got to the area under the coop and sunk a corner enough to shift the weight and the leg snapped off where it was connected with 4 screws, all 4 screws sheared off.

If the plywood floor ends up the same footprint as the perimeter, you're going to want to cover the plywood edge with furring strips to protect the wood.

 

[SourRoses]

While I'm at the hardware store, I'd be picking up lag screws or through bolts to replace those screws on the posts, if my design is relying on my fastener's shear strength. I'd probably add triangulation to the legs too so they can't deflect - my inlaws have a small coop about the same footprint as this, and it had non-triangulated legs about the same length as those. Gophers got to the area under the coop and sunk a corner enough to shift the weight and the leg snapped off where it was connected with 4 screws, all 4 screws sheared off.

Not to derail the thread (sorry OP), but do you think triangulation is important for all builds?
Our design is 8x8, with an 8ft /7ft tall, sloped roof. We are using 2x4's, the 4 corners each have two in a ... a pointy corner configuration (darn I just can't remember what it's called) like an arrow, but square.
The middle of each beam has a vertical 2x4 post (4ft apart).
And our roof is lightweight polycarbonate (no snow here ).
Does that sound like adequate support or should we add triangulation?

 

[aart]

I live in Minnesota, so frost heave is definitely a concern. What would you recommend to make sure the building won't have structural issues due to the ground?

Bury the legs below frost level.