Finished cedar 4x4s are to bear on a concrete slab, with the posts supporting roof structure above.
Simpson makes post anchors, but they all show the steel cup edges lapping up the post. We want a hidden method.
The architect has dreamed up something far sillier than what I’m showing on the attached. But, I’m wondering if I am being silly, too.
Her version had the square plates, same as mine, but with embed anchors going down, and a 2-1/2″ wide 1/4″ steel plate tongue going up, and a thru hole near the tongue top. The method requires placing the plates at slab pour time, something I am not comfortable doing, because it takes work to get them placed exactly right.
Her version would require deep square mortises in post bottoms for the tongues, and then a crossbore for a fixing bolt through the post, going through the hole in the tongue.
My version has us doing the layout for the posts atop the cured slab, then hammer-drilling sockets for the pins. Post bottoms will be bored for the pins. We’ll use Hilti anchoring epoxy for anchoring the pins in the sockets in both slab and post, and shim under the plates to level the posts. Grout afterward.
The porch finish, thick slate tile in a mortar bed, is cut and finished around post bottoms.
If you’ve got a better way to do this, tell me about it.
Replies
I don't see any reason you couldn't drill the holes just before installing the posts. I don't even see why you'd need epoxy or welding. All the force will be downward. All you need is some pins to keep the posts from getting kicked sideways.
Is this a wet location? I think it might be good to get a little air under there. I'd worry about water getting wicked between the plate and post. Seal the post bottoms well. Maybe a piece of ice and water membrane stuck to the bottom would help.
Will you be pouring footings under the slab? The slab alone may not be an adequate foundation.
Al Mollitor, Sharon MA
I agree with Al... you need to have something to lift that post from direct contact and get some air between the post and the porch surface.
Use the standard anchors, and cover with a skirt.
6 16 17 97 99
I have yet to see a 4x4 post that doesn't look wimpy. Use PT with the standard anchors that get it off the floor and then wrap it with the cedar.
Simpson makes an anchor very similar to your drawing for round posts. Same idea.
I would not grout under the plate, I would weld small flanges to the bottom of the plate to provide support, and also create air space.
You do need anchor against uplift.
Another thing:
I would think about the bottom of the post being above the slate tile.
Luck.
Heck If I know....
Gene, I've used a system, similar to what your archy is suggesting, when building widow's walks. It's a pain to properly flash the post bottoms; we found the best way was to weld two aluminum plates, so one sits flat on the roof and the other (the "tang" sticks up into a slot in the post. The slots are easy to make with a top-bearing straight router bit. Pin with SS carriage bolts. The difference is that while your archy wants to embed the anchor in the concrete, we lagged the plate down to the roof after the fact.
That's probably overkill for a ground-level post. I don't see why your system wouldn't work.
Mike
As HECK says, you need some (fairly significant) anchoring against uplift, especially if the porch isn't enclosed. Epoxy should be sufficient to anchor to the concrete, but isn't quite reliable enough (after a little rot and weathering does its thing) to assure that the anchor doesn't pull out of the post.
The scheme your archy proposed is pretty much SOP for this sort of thing. Since the anchorage is a critical part of the engineered roof uplift protection, be sure that you don't change it without clearance.