Concrete pier foundations

[Kent Belasco]

I am building a gazebo. My backyard has a fairly steep elevation and therefore my foundation will be 12 inch diameter concrete piers, using quick form tubes. My question is, when I dig my hole (42" deep per my village) do I dig a straight hole and fill the bottom with gravel and then pour the cement, or must I pour a foundation of concrete that is wider than the 12" quick form tube? Is this necessary to support the gazebo?

The gazebo is a 12 foot octagon and I live in the midwest. Another question, since my yard is not level I must level the concrete piers to support the floor of the gazebo evenly. What is the best way to precisely level the height of the concrete piers, since they will be at least 12 feet apart (front to back)?

[Harley Lewis]

Kent there are probably concrete people on the board that are more experienced than I am, but I have done a good number of piers. I suggest you dig your holes a bit deeper than needed, then put in your 12 inch tubes and pour the tube about half full. Then pull up on the tube to final ht. so the bottom of the hole will fill with concrete, then fill the rest of the tube to final depth. If you want the concrete piers level I would use a water level to get the concrete the final ht in the tubes. When I have done piers, I have not worried about the final ht of the concrete and I leveled the deck/floor with 4x4 treated wood risers and metal deck forms inbedded in the concrete.

[Jerry Olexa]

I'm a bit of a purist but...when I built my cabin on a slope on piers, I first poured wide pads -6" thick w rebar sticking up vertically. Then I poured a few days later the vertical forms for my piers w the rebar anchoring the pier to the horiz pad. I agree height is not a big issue. You can adjust later w brackets, cleats, etc

[Harley Lewis]

I agree with Jerry for house piers, you need a base pad. For your gazebo, you have no weight to speak of so a pier as I described should be fine.

[Brian Triplett]

Kent,

If I read your question right, you are asking if you need a bigger foundation at the bottom than a 12" diameter pier (113 sq in area). I would have to say no, let's say you have poor soil (2000 psf allowable soil pressure) that would mean that each pier can hold approximately 1500 lbs. I not sure where you live so I don't know how much wind you have to check the increase in load from wind but I would not think it would be that much. The reason behind the 42" deep is to probably get below the frost line in your area so your structure will not rise and fall due to the ground freezing. But just my two cents you can do whatever you want. I would also use the post to level the floor on the gazebo like Harley was talking about.

Brian

[Ryan Myers]

With that small amount of weight you shouldn't need any type of footing beneath the pier. To be below the frost line were I am located (Midwest) need to be at least 42" deep to prevent heaving. 8" dia piers are probably acceptable but make sure you check with the local building inspector.

The easiest way to get your piers all lined up to height is with the use of a transit level (requires two people) or a rotary laser level w/detector. You can usually rent these at just about any rental store.

[Fred Voorhees]

I would agree with Ryan. Using a transit level will get you to exactly level. Shoot the various locations with the transit and position the top of each tube at the exact height that you want the piers to be and fill to the top with the concrete. Of course, it's easy for me to say use a transit, 'cause I have one. A water level with a hose would work just as fine.

[Kent Belasco]

Thank you all for your great suggestions. This has been a big help.
Kent