Deck Footer Question
NCJeff
| Posted in Building Code Questions on
I live in NC. My local building code for decks says “Minimum footing depth shall be 12 inches below finished grade”. That being the case, I should be able to use these forms without tubes and mount my posts to the top, correct? The dimensions say they are 22″x 22″ by 16″ high.
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Replies
Tubes are just a way to corral concrete and control the pour, particularly if you have to go a long ways to reach frost depth and/or undisturbed soil.
Other forming methods work fine as long as you meet the correct size for the load and soil type. Can't say if the footing you've described is sufficient for your deck, but the American Wood Council Prescriptive Residential Wood Deck Construction Guide (https://www.awc.org/pdf/codes-standards/publications/dca/AWC-DCA62015-DeckGuide-1804.pdf) is a decent start.
That code section tells you how deep but not how wide. That footing is deep enough. Whether the width is sufficient depends upon the soil type and how much deck the footing is being asked to carry.
Jeff,
There are three reasons most deck footings include a smaller square or round pier in top.
- You don't need anything like a 16" deep footing, so you waste a lot of concrete between the required depth and the required 6" to 8" above ground you need by code before you can attach your wood post.
- Large footings exposed above grade don't look very nice. Large footings just below grade don't allow anything to grow on top of them.
- The posts above are better protected when water can't pool ar0und their base or splash up onto them.