patio cover

[phoenix68]

Hello to all ,newbie here this is my first post and need help with a project i want to start.I want to build a patio cover thats 30x29 I have basic know hows and here is my question. Concrete slab is already down its 6 inches thick and i and wondering if i should just build on top of this or dig and pour new concrete for the post.any help would be greatly appreciated , and if anyone has a patio cover plan would you shared with me. Sorry for the long statement.

[drumpriest]

Interesting how timing works, but we are just finishing a porch roof for my Dad's house. We just built on top of the slab, the corner posts bear the load, and it's mostly straight down, so you don't have shear stress issues.

Note: I'm not a structural engineer, so take this for what it is worth.

[Ken Weaver]

Welcome aboard Rick, glad to have you! With a 6" slab I woud think you'd be ok, but I'll defer to some of our members with more engineering expertise than I have.

[monte]

Welcome to the group Rick!

Is the slab reinforced with wire mesh or rebar? If so I would think you'll be ok.

[LarryG]

I'm not a structural engineer, either (architecture), but the purpose of a footing is to bear and distribute the load down to solid bearing. If the bearing area (footing's footprint) is too small, the footing will slowly be driven into the ground and the structure will sag. If the footing isn't deep enough to get below the frost line, the whole thing can heave up and down as the seasons change (not something you're likely to have to worry about in Arizona, unless you're in the mountains). In the case of exterior columns, the footing also resists wind uplift so your patio cover won't end up in someone's swimming pool three blocks away the next time you get any high winds.

Here in the south, we could probably sit the columns on concrete footings about 12" square by 18" deep and then pour a 4" slab around them, isolated by fiber expansion joints. Note that this is a minimum size; depending on the loads, it might be bigger. We'd tie the columns to the footing either with a base plate and anchor bolts (steel column) or a Simpson-type column base connector (wood column).

In your case, assuming a simple and lightweight roof structure, bearing the columns on a 6" slab might not "figure" but they'd probably be okay. I would locate the columns in from the edges and corners of the slab at least 6", to distribute the load over a wider area. I'd also devise some way to positively tie the bottom of the columns to the slab, to prevent uplift (you'll need this up top, too, of course).

[phoenix68]

WOW thanks for the replies guys, all great information that i will keep in books . After talking to some contractors this morning I think that I will just dig and pour some cement mix and set my post on them .I guess better safe than having to pull my patio cover off my neighbors BMW. Here in AZ the winds and monsoons are very hard and unpredictable .I will try post some pics of my work if possible .

[crokett]

When you pour your footings get some J-bolts to sink in the wet cement. These let you bolt down metal post anchors. The anchors tie the post down to the footing while also keeping it up off the concrete to prevent rot. You will need to measure fairly accurateky where you will put the J-bolts. The anchors are adjustable, but IIRC, only about 1" to either side.