Young couple building patio and pergola

My wife and I are in the process of building a 450 sq ft paver patio adjacent to our existing concrete slab. I'm sure we'll have many questions regarding that but my question now is regarding the pergola we are planning.
We just finished the excavation for the patio to approximately 9inches. We are planning on building a 12x12 pergola and my question is about the posts. I'm planning on cementing the posts in the ground(I know that isn't the best for posterity but were only going to be in this house a couple of years and it appears to be the most cost effective). My question is how far below ground do I need to cement the 6x6's since they will also be in at least 6 inches of compacted crusher run and in between the pavers?
We live in Columbia SC and frost heave isn't an issue. Thanks in advance

 

Your local building department (the people who will issue the building permit you'll need) will have minimum requirements for embedment of the pergola columns. Or they may even require minimal concrete footings under each column.

 

The general rule of thumb for a free standing post or a fence post is to bury 1/3 of it in the ground. So a 12' post would have 4' underground and 8' sticking above ground. While that's proper I very rarely see anything done much deeper than about 30" since that's what most manual post hole diggers can do and is about the time your arms are tired and you say "that's good enough".

 

Thanks for all of the replies. I'm waiting on the building dept to get back to me and I'll keep y'all "posted"(I know, terrible pun).
Also, does anyone have experience getting pavers flush with an existing slab? I'm planning on compacting the base extra well next to the slab and I'm hoping that will get it.

 

Add up the thicknesses of everything going into your patio; pavers, sand & base. That will tell you how far to dig down. Then make sure each layer ends up being the thickness you need. It helps to make your measurements from the slab you have to match and go down from there. So if your pavers are 3" thick and you have an inch of sand and 6" of base your overdig needs to be about 10" below your existing concrete. Then when you put the base in and have it all compacted measure again and you should be 4" below the slab... If you are off correct it before going on to your next layer.

 

We uncovered this wire running from the house to my building while digging. We only uncovered it in one spot and it wasn't in any conduit. My question is do I need to pull all of the wire up and run it through conduit or can I just add the base over the wire as is?

 

By the way, it's the electrical that feeds the back building and I have killed the breaker it's on.

 

Look closely at the cable and see if you can see writing printed or imprinted on it. You are looking for the letters "UF" which would indicate that the wire is approved for direct burial in the ground. Often the cable is gray in color but some brands are white.

 

Thanks. It was labeled UF so we're good to go.
Back to the posts. The building dept said I only need 2 ft underground. I have 2 questions.
1. My holes are currently 30 in deep and 12 in diameter. For a 6x6 post, will 2 bags of concrete fit/be sufficient?
2. Will the 6 in compacted crushed stone and pavers above the footings give additional support?

Also Pilot Dane, you were spot on about 30 in being the limit for manual post hole diggers. I can barely move my arms.

 

Also, it looks like we're going to have rain on Sunday and we had planned on laying the pavers then. Is it ok for it to rain on the compacted crusher run? I know you don't want it to rain on the screeded bedding sand but should we wait to put down the crusher run until after it rains?

 

The arithmetic shows you'll be a bit short with just 2 bags of concrete mix per column. Assuming you're using the large bags (0.6 C.F. each, for an 80-lb. bag), each hole will take 1.43 C.F. of mixed concrete, and somewhat more if you don't run the columns all the way to the bottom.

Don't know the answer to your second question, as I don't know what you're trying to support with the pavers and crushed stone.

 

Thanks for the reply. We realized when we were doing it we needed more and adjusted accordingly. Sorry I wasn't clear but I meant would the crusher run give extra support to the pergola posts. Also, still curious about rain on the compacted crusher run. Any thoughts?

 

A relatively thin layer of crushed stone will provide very little in terms of lateral support for your columns. Dig deeper holes and use more concrete if you think they are lacking support. I don't think normal rainfall would be detrimental to the compacted crusher run, unless the rain becomes heavy enough to cause significant movement of mix particles. Throw a tarp over it if you have concerns.