Deck Railings and the 4-Inch Rule
Deck guards must be 36 inches tall with gaps under 4 inches. Learn the rules, the warning signs, and how The Great House fixes unsafe railings.
OUTDOOR LIVING & DECKS
12/26/20263 min read
ASK MASON · DECK
Deck Railings and the 4-Inch Rule: Is Your Railing Safe for Kids?
Mason shows the railing height and 4-inch rule, the warning signs, and how we fix unsafe railings.
A deck railing has one job: to keep people from falling.
Watch Mason’s video, then read the rules, the warning signs, and how we fix unsafe railings.
IN THIS GUIDE
01
What Mason Checks
The Railing Rules
OVER 30 INCHES
Decks that high need a guard.
36 INCHES TALL
The minimum guard height.
UNDER 4 INCHES
Gaps a 4-inch ball can’t pass.
If your deck is more than 30 inches off the ground, it needs a guard.
That guard must be at least 36 inches tall, and the gaps between balusters must be small enough that a 4-inch ball can’t pass through, so a child’s head can’t slip through.
Many railings were built too low, with gaps that are too wide, and posts that are just nailed on.
Mason’s diagram: a safe railing vs. an unsafe one
The 4-inch rule is measured with a child in mind.
02
Warning Signs
Signs Your Railing Isn’t Safe
WOBBLY
A railing that moves when you lean on it.
WIDE GAPS
Gaps a ball can pass through.
ROTTED POSTS
Rot at the bottom of the posts.
Nailed posts wobble when someone leans on them, and the nails work loose over time.
The wood rots at the bottom of the posts, and one day the railing can give way.
Check this today
Push firmly on the top rail at each post. Measure the height and try a 4-inch object between balusters. Any wobble or wide gap needs fixing.
03
How We Fix It
A Small Job That Prevents a Fall
We check the height, the gaps and every post. We bolt the posts with proper hardware, replace rotted wood, and install new balusters with the right spacing.
Caught early vs. caught late
It’s a small job that can prevent a serious fall.
In Northern Virginia
Fairfax County’s deck guide, based on the 2021 Virginia Residential Code, requires a guard when a deck is more than 30 inches above grade, at least 36 inches tall, with no opening a 4-inch sphere can pass through. We fixed this on our Bracken Ct deck in Springfield.
Planning a bigger project?
Building a new deck? Our railings are bolted, measured and inspected. See prices and real projects on our deck and outdoor living page.
The rules: gaps under 4 inches and a guard at least 36 inches tall
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.