# Concrete foundation for gabled pergola.



## iyacyas (May 11, 2015)

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In the planning stage of a gabled roof pergola (Pavilion). Pavilion will have a 22' x 23' covered roof. Held up with 6-8x8 Cedar post attached to patio (concrete slab) with stirrups using red heads, the post will not be place into concrete. 

There is an existing concrete patio that we will need to be extend. The size of the new concrete patio (extension) will be roughly 16' x 25'.

I had a contractor quote me for a patio that is 3.5" with no footing, no rebar but using mesh. Not sure that's the best advise from a pro, I do not know. I need to be better educated on the needs of the concrete base for this structure. I live in Oklahoma so we have lots of wind and moderate snow and ice. I do not believe the frost line is an issue. I will try to attach a PDF of the drawing.

Here are two options I am thinking about.

*Option 1:*

Dig individual footings under the locations of each cedar post (2' deep and 12" wide tapered down to 8"), then pour those footings and the patio at the same time. If I do it this way could I get away with 3.5" thick patio or do I need 6". Rebar or Fiber-reinforced or Both?

*Option 2:*

Pour individual footings then come back and pour a 3.5" slab around those. Just not sure I like the look of that.


Not sure what to do with the existing patio as it is only 3.5" thick, may have to cut 2 holes in it and dig footings in it.

Any ideas?


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## joecaption (Nov 30, 2011)

Yes you need footings.
The way there drawn in that picture is wrong, there up side down.
You need the biggest foot print at the bottom and the sides tapered so the frost or shrink soils will not have a wedge to lift up on.
Could also just use Sono Tubes.
There is no need for a slab to any thicker then 4" unless it's going to be driven on.
I've never seen anyone use mesh or rebar in a slab.


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## iyacyas (May 11, 2015)

Thanks for the reply, I am in Oklahoma. Sorry for that I thought I'd put that in the post. I am glad that you pointed out the footings being upside down. Can't believe I had them that way in the drawing.

So would you pour the footings and the slab at the same time as a continuous pour, for lack of better words?

Should I be concerned about cutting the existing slab to put footings under the 2 post closest to the home? Or will the other 4 footings be supportive enough. In other words only 4 of the 6 post would be on footings. May sound like a dumb question but I do not want to have to cut the existing slab if not necessary.


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## joecaption (Nov 30, 2011)

Unless you can afford to hire a real engineer to spec the size of those beams stick with the 6 post.
Not sure what the issue is cutting the old slab, that's the easy part.


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## Msradell (Sep 1, 2011)

I certainly agree with Joe that you need footings under all your posts and each one of them should be larger on the bottom than on the top. It really confused me when you said that the "Frost Line" isn't a concern for you. By looking at charts it looks like the average frost depth in Oklahoma is about 20 inches but it varies from the southern to the northern parts of the state. You need to check with your local building officials to see what the requirements are for your area.


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## iyacyas (May 11, 2015)

Thanks Joe and Msradell for the information provided. I love information. All three local OKC contractors that I have bids with so far have expressed lack of concern for the frost line and/or footings. I ask them about footings and they say, uh ya I'll just beef it up a little where the upright post beams are going. Maybe that really is there slang for a good quality footing. But all of them said the frost line was not a problem here.

The city of OKC shows a minimum frost depth of 18".

So with this in mind I am now thinking of 4 footings in the new 3.5" -4" pad that will be minimum 24" below grade, 18" +/- base tapered to 10" with rebar. In the pad, rebar 24" apart in a grid pattern. with the footings tied to those.

I'll cut the concrete in the old slab and pour those 2 footings when I'm ready to start putting up the pavilion, but there I'll most likely use Sono Tubes and then dress the pavilion post with a couple of nice cedar planter boxes to cover it.

Is it normal for a contractor to tell you the slab will be between 3.5 - 4" due to a 2x4 being 3.5"? I would think one would try to assure that it is at least 4".


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## iyacyas (May 11, 2015)

*Plans have changed...*

My plans have changes slightly, we are now willing to rip out the old patio so that the new slab under the pavilion will be one contiguous slab with 6 piers (footings) one for each cedar post. 

Contractor 1 tells me that he will do 6 - 2ft x 2ft x 2ft deep piers with a 25 ft x 25 ft slab no steel but with fiber reinforcement. Under the slab will be sand for leveling and no rock.

Contractor 2 tells me that he will do 6 - 8" x 2ft deep piers with a 25 ft x 25 ft slab w/ 3/8" steel on 36" centers plus fiber reinforcement cement. Under the slab will be crushed rock instead of sand. This estimate is $400.00 cheaper than Contractor 1.

I personally think that Contractor 2 is the better way... Not just because it's cheaper but seems that it will provide better support for the pavilion. 

Any feedback is appreciated.


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## Canarywood1 (May 5, 2012)

If it were mine, i would forget the rebar and the fibre unless you want "hairs" sticking up all over the place, and the stone will be a better base if it's compacted properly.


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## Daniel Holzman (Mar 10, 2009)

Parts of Oklahoma have expansive clay soils, which make a real mess out of slabs. You may want to check with your local building inspector if your area has such soils. Or maybe your contractors understand the issues and can help you design a slab and footings that will work. Or maybe you don't have expansive clay soil, in which case carry on.


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