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Deck footers

user-6253285 | Posted in Building Code Questions on

Good evening 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’d like to know what the pros and cons are to either option. Any guidance or discussion on this topic would be greatly appreciated.

Thanks!
Andy

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Replies

  1. DIYJester | | #1

    Andy,
    I am building two decks this year (hopefully) and both will be on piers for the reason you have stated:rot. If you do decide to use posts underground make sure you use ground contact rated treated lumber as normal treated lumber will still likely rot fast. Someone may be able to comment on expected life of ground contact rated lumber.

    For me, the risk of rot and having to replace the posts are too great in my area as I have mostly clay.. So when you dig a hole like this, unless you fill it back in with clay, it usually becomes an area that holds water and moisture. I also only have to pour 10" or 12" diameter footers which makes for considerably less concrete. I am planning on using a decent amount of rebar in my footers as they will be about 36" tall by 10" around when all is said and done.

  2. GBA Editor
    Martin Holladay | | #2

    Andy,
    Q. "I would like to know what the benefit is of using the concrete piers."

    A. Concrete lasts longer than pressure-treated wood. I've done it both ways. I haven't seen any of my pressure-treated posts rot, however, even after 30 years in the ground.

    Sonotubes are easy to fill. Brace them well before filling. Put in a few lengths of rebar. Mix up a few bags of Sakrete in a wheelbarrow. Vibrate well. Remember an anchor bolt for your post anchor.

    --Martin Holladay

  3. charlie_sullivan | | #3

    My bias is against toxic chemicals. Even though the chemicals used are not nearly as bad as they once were, and ground contact rated wood will last many decades, the chemicals will presumably eventually be released into the ground. Also, if you use concrete under ground, you can use untreated cedar for the above ground posts, and thus avoid PT completely.

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