Why Frost Depth Matters for Deck Footings in Central Pennsylvania

When homeowners hear that deck footings need to be dug “below frost,” it often sounds like an arbitrary rule — one more box to check on a permit application.

In reality, frost depth requirements exist for a very specific reason, and ignoring them can lead to serious long-term problems.

For homeowners in Selinsgrove, Shamokin Dam, Sunbury, Northumberland, Lewisburg, and Danville, here’s what frost depth means, why it matters, and what happens when it’s ignored.

What Is Frost Depth?

Frost depth is the maximum depth at which the ground is expected to freeze during winter.

When soil freezes:

• Moisture in the ground expands

• The soil pushes upward

• Anything resting above the freeze line can be lifted

This process is called frost heave, and it’s one of the most destructive forces acting on decks and foundations in cold climates.

Why Deck Footings Must Be Below the Frost Line

Deck footings are designed to:

• Transfer weight safely into the ground

• Remain stable year-round

• Resist movement from seasonal changes

If a footing sits above the frost line:

• It can be pushed upward during winter

• It may not settle back evenly

• The deck can shift, tilt, or pull away from the house

Once that movement begins, it usually gets worse with each freeze–thaw cycle.

Frost Depth Requirements in Central Pennsylvania

In most parts of Pennsylvania, current building codes require:

• Minimum frost depth: approximately 36 inches

• Footings must extend below the frost line, not just to it

• Depth may increase depending on:

  • Soil conditions

  • Elevation

  • Local amendments to the code

This applies to:

• Deck posts

• Footers

• Piers

• Any structural support bearing on soil

Local municipalities may vary slightly, which is why zoning and building departments are always consulted before construction begins. For example, in places like Selinsgrove, Sunbury, Lewisburg, and Danville, frost footings are required to be 42".

Why Frost Codes Exist in the First Place

Frost depth requirements weren’t created to complicate construction — they exist because of real-world failures.

Historically:

• Decks and porches were often built shallow

• Structures moved after winters

• Railings became unsafe

• Doors and stairs went out of alignment

• Entire decks had to be rebuilt prematurely

As building science improved and failures were studied, frost depth requirements were standardized to prevent these problems before they occur.

When Did Frost Depth Codes Change?

Earlier deck construction — especially pre-1990s — often:

• Used shallow footings

• Relied on surface pads

• Was built before consistent enforcement

Over time:

• Building codes became more uniform

• Frost depth requirements were clarified and enforced

• Decks began to be treated as structural systems, not temporary add-ons

Many older decks in Sunbury, Northumberland County, and surrounding areas were built before modern frost depth standards and may not meet today’s requirements — even if they’ve “held up” so far.

What Happens If You Don’t Dig to Frost Depth?

Skipping frost depth doesn’t usually cause immediate failure — which is why it’s tempting to ignore.

Instead, homeowners often see:

• Posts slowly rising out of the ground

• Decks tilting or becoming uneven

• Stairs pulling away or shifting

• Railings loosening

• Gaps forming at the ledger board

These problems are difficult — and expensive — to correct after the fact.

In many cases, the only real fix is:

• Removing sections of the deck

• Installing new, deeper footings

• Rebuilding affected areas

Why “It’s Been Fine for Years” Isn’t a Guarantee

One mild winter doesn’t test a deck.

Frost issues often appear after:

• An unusually cold season

• Repeated freeze–thaw cycles

• Saturated soil conditions

• Snow melt followed by deep freezes

A deck can seem stable for years — until one winter exposes its weakest point.

Why Proper Frost Depth Is Non-Negotiable

Digging to proper frost depth:

• Protects structural integrity

• Prevents seasonal movement

• Extends deck lifespan

• Ensures safety

• Avoids future repairs

• Meets inspection and resale requirements

It’s one of the least visible parts of a deck — and one of the most important.

Final Thoughts for Central PA Homeowners

Frost depth requirements aren’t arbitrary rules — they’re the result of decades of experience building in cold climates like ours.

For homeowners in Selinsgrove, Shamokin Dam, Sunbury, Northumberland, Lewisburg, and Danville, understanding why footings must be dug to code helps explain why quality deck construction starts long before the first board is installed.

When it comes to frost depth, doing it right the first time prevents problems that no amount of surface repair can fix later.