To Bury the Post or Set on Pier
Good morning everyone, I’m attempting to build my first deck this spring. I’ve dug holes for footings and just passed my footing inspection. The Deck code here in Maryland dictates that holes are to be a minimum of 30″ deep with an 18″ wide by 10″ deep concrete footing.
Once you have that you can either use concrete piers to get your posts out of the ground or you can place the post right on the original footing. I would like to know what the benefit is of using the concrete piers. Furthermore, although it may be acceptable to place the post in the ground on the 18″x10″ footing, is this option a promoted practice?
Most of my research states that the posts are less likely to rot if they are out of the ground (which makes sense), however i still read and hear of people placing them in the ground all the time.
My building inspection office has stated that both options are code acceptable. Since I’m pouring the concrete myself, cost and labor time are of concern. I’ve estimated that it’s roughly a $600.00 difference between doing the piers w/ post base connectors and just setting them on the original footing. I’d like to know what the pros and cons are to either option.
Any guidance or discussion on this topic would be greatly appreciated.
Side note: ( If I do decide to set the post in the ground, and back-filling with a mix of gravel and dirt, would wrapping the section of the post below grade with a flashing like GRACE to help to prevent rot)?
Replies
Did a deck about 30 years ago with buried posts, and while there is some evidence of rot on the redwood posts, it doesn't apper to be severe. You can pretty much eliminate the rot issue, though, by using "ground contact" pressure-treated lumber.
But still, consider drainage. You should not embed a post IN concrete, but rather have the post sit ON TOP of the concrete, so any tendency of water to sit around the post base is minimized. What we did was pour concrete in the hole to precisely the proper depth, and, while it was still "wet", set in place the post, with a length of rebar in a hole drilled in the bottom. The post was anchored with temporary braces so that it was at the proper height to sit ON TOP of the concrete, and be vertical. Once the concrete set we backfilled and removed the braces.
(We actually cut the posts to length before setting, and the tops of them came out even when we installed the railings on the top ends -- a bit of planning and care involved.)
We bury posts in the ground all the time but we use pressure treated posts that wil last 30 to 40 years in our climate. I have used above ground piers ocasionally but am not comfortable with the lack of side load strength. When the hurricane blows a buried post has to either break off or hinge from the bottom of the post. One set ona pier witha bracket hinges from the top of the pier and is more open to lateral forces.
Grace makes a product to wrap posts to prevent rot. It's only necessary to wrap the post where it exits the ground since that's where they rot.