What’s Under Your Deck Posts? Deck Footings
Shallow deck footings heave with frost and make posts lean. Learn the 24-inch rule, warning signs, and how The Great House fixes footings.
OUTDOOR LIVING & DECKS
12/19/20263 min read
ASK MASON · DECK
What’s Under Your Deck Posts? Footings and the Frost Line
Mason shows why footings must go below the frost line, the warning signs, and how we fix them.
Your deck is only as strong as what’s under its posts.
Watch Mason’s video, then read how footings work, why shallow ones fail, and how we fix them.
IN THIS GUIDE
01
What Mason Checks
Footings Below the Frost Line
CONCRETE FOOTING
Every post sits on one.
24 INCHES DEEP
At least 24 inches below grade here.
BELOW THE FROST
Where the ground doesn’t freeze.
Every deck post sits on a concrete footing.
In our area, footings must go at least 24 inches deep, below the frost line, where the ground doesn’t freeze.
When footings are too shallow, the ground around them freezes every winter. Frozen soil expands and pushes the footing up.
Mason’s diagram: a 24-inch-deep footing vs. a shallow one pushed up by frost
What you can’t see under the post decides how long the deck lasts.
02
Warning Signs
Signs Your Footings Are Moving
LEANING POSTS
Posts that tilt or lean.
BOUNCY DECK
A deck that feels bouncy or sloped.
CRACKED CONCRETE
Cracks at the base of a post.
In spring the ground thaws and the footing settles back, a little differently each year.
Year after year, posts sink, shift and lean. The deck starts to slope and bounce, and the connections get weaker.
Check this today
Sight down each post against a door frame or level. Look for gaps under post bases and cracks in the concrete around them.
03
How We Fix It
A Few Footings Now, or a New Deck Later
We support the deck with temporary posts. Then we dig below the frost line, pour new concrete footings, and set the posts on proper metal post bases.
Caught early vs. caught late
Caught early, it’s a few footings. Caught late, it’s a new deck.
In Northern Virginia
Fairfax County’s deck guide requires footings at least 24 inches below grade. Every deck in Fairfax County needs a building permit, and inspectors check the footing holes before concrete goes in. We fixed this on our Bracken Ct deck in Springfield.
Planning a bigger project?
Building a new deck? Our footings go below the frost line and get inspected before we pour. See prices and real projects on our deck and outdoor living page.
The fix: a new footing below the frost line
ASK MASON · DECK
Want to know another problem?
SPOTTED ONE OF THESE SIGNS?
We’ll check it before it turns into a big repair
Free in-home visit from a Class A licensed team. We check the problem and the rest of your deck, then give you a clear written plan.
ABOUT THE AUTHOR
The Great House team
Written by the team at The Great House LLC, a Class A licensed builder and remodeler in McLean, VA (License #2705197237). We have renovated 30+ Northern Virginia homes since 2022.
PLANNING A PROJECT?
Our deck and outdoor living service
See prices, real photos and how we work: our deck and outdoor living page. Real projects: our project gallery.
Serving McLean, Vienna, Great Falls, Fairfax, all of Northern Virginia.