TomS

I have finished rebuilding my deck and screen porch and now need to fix the stairs. I need to replace the stair treads and fix the settling that has occurred. Currently the base of the stairs sit on a green treat 6 x 6 that sits directly on the ground. I want to raise the stairs to the proper height. I am thinking about putting in two piers with a footings to support the 6 x 6 to prevent future settling.

I know I need to go down at least 42” in Minnesota but am wondering how large of a pier I need. I would like to keep the pier size as small as possible to reduce the amount of cement I need to haul and mix.

So my questions:

1) How large of a pier do I need to support six steps that are 4’ 6” wide? I thinking about a 4 – 6” pier and then flaring out the footing at the bottom?.
2) Would a piece of rebar down the center of the pier help for added strength?
3) I have seen pier forms that are 8 to 10” inch but not smaller. Would a PVC pipe of some kind work well as a form? What else would work in a 4 – 6” diameter?

nealtw

Sonotubes come as small as 6" but any kind of pipe will work. You don't need much of a footing, If you hold the tube 6" from the bottom of the hole, you will have lots. When you have started poring concrete drop three 12" rebar in the tube and that will stop the concrete from running up the outside of the tube.

mudmixer

The good thing about Sonotubes is that they have a surface that allows "slip" between the soil and the forms. - Far better than a rough surface on the hole since the soil cannot heave the post up.

Soil freezes from the top down daily and possibly as low as the theoretical frost line, so it is important every year instead of the cold years with no protective snow cover.

Dick

BridgeMan

You didn't mention it, but I'm curious as to what sized piers you used for pouring the main deck's column supports?

A few years ago, I designed a large deck for a buddy of mine in Colorado (elevation 8800 feet, 110 lb./s.f. snow load). My conservative design came up with 8" sonotubes for the main deck, and 6" for the stairs. We went 4 ft. down with all holes, and used elephant paws in the bottoms of each (they're adjustable, to fit the sonotube size) to minimize concrete waste. It was probably overkill, but we used 3 No. 5 rebars in the big tubes, 2 No. 5s in each small. Worked our butts off, getting the readimix from the truck (in wheelbarrows) in the front of the house to the tubes in the back yard. I think that was the day I began to realize what a wuss I was.

Suggest you beat on the tubes (for concrete consolidation), "gently" to prevent knocking them out of plumb, if you don't have a spud vibrator.

TomS

I am not sure I follow the 12” rebar at the bottom? I thought the concrete would be firm enough and was not expecting a lot of flow coming up around the out side of the tube. I could let the concrete at the bottom firm up a bit before filling the rest of the tube? Does the short rebar just lay across the bottom?

TomS

The 6” Sonotube sound like the way to go. Now I need to find where to buy a 6” tube. I guess I could also go 8” too

Also can you please confirm my calculation?

I have found on line:

• 6" Sonotube uses .20 cu. ft. of concrete per foot; 8" Sonotube uses .45 cu. ft.
• Quickrete volume just under half (0.45) of a cubic foot in a 60 pound bag of quikrete

So if I go with 6” at 48” depth ill need 4 60# bags of Quickrete, if I go with 8” at 48” depth ill need 7 60# bags of Quickrete.

TomS

I replace the decking and posts (plus screen) for the screen porch on an exciting structure so I did not need to pour piers for the rest of the deck.

nealtw

Most of the time the concrete will stay where you put it and stiffin up for the rest of the pore but sometimes. So now we just put them in.