Best way to add footings after the fact?
 

I'd like to build a nice patio cover/pergola the length of the rear of my house. I have an existing patio and the vertical posts would be placed along the outer edge. Am I better off extending out a bit further and putting in new footings (currently grass), or can I cut a "U" notch at the edge of the current patio dig it out, and re-fill with concrete? I think extending out would look funny, but would be easier. I think it's a typical 4-5" slab.

Hope that makes sense...

Thanks for your thoughts!

-Brad

I assume it's just for more support? Foundation folks will dig under the edge of a house and stick columns under the existing edge. I don't see why you couldn't do something similar.

Yeah, just for more support, and I assume required by the bldg department. Need to check, though.

Interesting approach. I guess i could dig under the edge of the patio and fill with concrete. Seems I'd want to tie the slab to the footing somehow...perhaps rebar drilled thru the slab?

Thanks!

If its a pergola, and won't be subject to load bearing forces from rain/snow, couldn't you just build it on top of the existing slab?

I am not sure if I understand you? More depth is needed, the distance from the edge of the house to the outer edge of the patio but you already have the outer post there from an existing structure?

Is the existing structure free standing, but you want more space between the post and the house?

Sorry my post is confusing. I have an existing patio, but no structure. If I build a structure, the vertical posts will be placed along the outer edge of the existing patio. I assume I need additional strength at those locations to support the posts and carry the load.

Thanks
-Brad

I guess I should do my research first :--) I have a tendency to over build everything....

Assume they are 4x4 already, that should plenty strong. Increase in length, a thicker beam is needed to carry the weight (its own weight to keep from sagging). How long is this thing? Wind load would be more of a concern, so bracing maybe necessary.

Ovwer building is great, I am that way too, but sometimes, the end product end up looking too bulky or like crap but it will stand up for a long time.

Couldn't you just use these on your existing patio?

http://www.homehardware.ca/products/300/26108011.jpg

Maybe this, Diamond Pier for Residential Construction Pin Foundations

Are you intending to have a full roof or is it an open framed structure? If it is open framed, and the slab is 4-5" thick there is no compelling structural reason to add footings. I would likely pour little concrete posts for the wooden posts to sit on to keep the end grain from sitting in pools of water. I would drill and grout in some rebar pins into the existing slab and cast in a saddle to accept the wooden post. Anyway, good luck with the project.

IF I underdstand this correctly.

Pre cast Pier blocks
Concrete Pier Block with Metal Bracket-8053112 - The Home Depot

Lots of of options at your local lumber store.

i see you are from CA. Note the potential need for seismic considerations

Im a concrete contractor but not an engineer (he said mournfully...)

Anyway, I don't know a building code/method in CA that would permit you adding the posts to the top of an existing slab.

The approved method would be to sawcut the slab, excavate down approx 12-15", and then fill with concrete creating what we call a pier. There are a large number of approved hardware pieces designed to be set it the wet mud at the top of the pier- they are galvanized and built to handle CA seismic loads and other forces (look up Simpson hardware).

That said, you do have options:

As we do new construction this doesn't come up much, but I've often wondered how big a diameter you could drill/core the concrete for a reasonable sum. For example, could you rent the tool/bit/saw necessary to do a 12" diameter cut? And if you only need a half dozen or so, it might be a pretty neat project.

Another option, like you suggested, is to simply have the roof extend a bit further and place your columns beyond your existing patio slab. There are probably dozens of ways you could make this look quite cool. The first that comes to mind to me is a red brick ribbon. You will be mixing mud anyways, why not create this final brick ribbon with mortar when your done pouring the piers for your posts?

Creative folks will probably give you better advice than I, but what you need can be done quite easily and without a lot of $$.

I did the exact thing last summer. Large pergola over existing slab. Concrete guy dug 4 foot cassons at the corners of the existing slab, inserted cardboard tubes and rebar, then filled with concrete to form the post supports. I would say if you don't know how thick or what's under the existing slab (rebar, etc) then this is probably the best solution.

After reading some of the solutions, it appears that I must not understand the magnitude of what you're doing. I envisioned a low (or no pitched) structure, perhaps 8 to 10 feet wide running the full length of the house. I build custom residential homes for a living and there is a world of difference between the foundation needed for an open framed structure and a structure that may have to carry not only the additional load of a roof, but a potential load of a snowfall. What is also important is to know the span of the rafters and the plan of how the house end of them are being supported. Obviously codes vary from area to area but in our area at least, the inspection office is assuming less and less responsibility and expecting an engineering stamp to be on many simple reno's that 15 years ago would never have warranted one. There are a number of ways to do what you proposing, some are very expensive and some rather cheap. In the foundation area it's easy to throw more concrete at a project, but is it really doing anything if the actual load, frost level and ground conditions don't warrant it? Cheers

This ^

Here is a 10 ft. x 12 ft. pergola at HmDep. It weighs under 800lbs. That makes for 200lbs per corner.

Ask, will the slab crack if a 200lb man stands on a corner? --read: shouldn't be a problem.

The slab isn't built on a swamp, is it? (I would expect that it's on solid ground)

I have to agree with Island here. There's almost no weight on this structure, so I would just drill and anchor a "clip" to hold the post and build the thing. That slab should be about 3.5" typically. Any less then that, saw cut and pier may be necessary. https://www.menards.com/main/tools-hardware/fasteners/connectors-reinforcements/caps-bases/post-anchors/post-anchor-2-sided-6-x-6-with-display-box/p-1342920-c-8828.htm Home Depot has them too.

don't put that post right on the edge of the slab if you are trying squeeze most out of the space there. Come in 8-10". If you go beyond the slab, then dig out a hole and pour a pier and install a metal connector to the post. I like a 6x6 base on looks. it just look so much more robust compare to a 4x4.

Thanks for the replies! Good information and food for thought.

While the spans, for the most part, are not that long, I plan on using 6x6 posts, 2x12 ledger boards, with 4x12 and 2x8 making up the rest. One section will be a 12'x12' square and I hope to use 4 4x8 'beams' to create a 12/4 pitch roof, which I will cover with either Sunbrella canvas or perhaps tongue & groove wood.

At this point, I like the idea of just digging footings at the edge of the patio, rather than trying to cut the existing concrete.

I built a similar structure on a house 15 years ago and it's really holding up well. In that case I got to do the footings before the patio was poured...