Pennsylvania Frost Line Depth for Footings and Decks

There is no single frost line depth for Pennsylvania. Each municipality or its code agency sets it locally, and the official values we found run from 30 inches in Philadelphia to 48 inches in Lawrence Park Township near Erie. The number your local code office publishes is the one the inspector will hold you to.

Is there a statewide frost line in Pennsylvania?

No. Pennsylvania’s Uniform Construction Code adopts the 2021 International Residential Code, and the IRC doesn’t print a frost depth. Its climate table, Table R301.2, is left for each jurisdiction to fill in. In Pennsylvania that’s done by the municipality or its code agency, usually in the ordinance that adopts the UCC or on a design criteria sheet. Two townships next to each other can publish different numbers.

Call the code office before you dig. Our Pennsylvania building permit lookup lists who enforces the code in each municipality and how to reach them.

How deep is the frost line in Pennsylvania towns?

Municipality	County	Depth	What the source says
City of Philadelphia	Philadelphia	30 in.	Deck footings 30 in. below grade (the frost line) on undisturbed soil
Lower Providence Township	Montgomery	36 in.	Frost line depth in the township’s design criteria
Lower Pottsgrove Township	Montgomery	36 in.	Frost line depth in its IRC Table R301.2(1)
Palmer Township	Northampton	36 in.	Deck footings at least 36 in. below grade (2026 deck details)
Loyalsock Township	Lycoming	42 in.	Footings at least 42 in. below grade
Lawrence Park Township	Erie	48 in.	Design frost depth of 48 in. to the bottom of the footing

Read the fine print on each one. Palmer and Loyalsock state a minimum footing depth rather than calling it the frost line, and Lawrence Park measures to the bottom of the footing. Ask your code office whether its number is to the bottom of the footing and whether it’s measured from existing or finished grade.

Many towns don’t post a number at all. Altoona’s deck checklist, for example, says only that post footings go below the frost line, measured from finished grade, and that the footing inspection has to pass before any concrete goes in.

What does the code require for footings?

Under the 2021 IRC, every exterior footing has to sit at least 12 in. below undisturbed ground (R403.1.4). Section R403.1.4.1 then requires footings, piers and other permanent supports to be protected from frost in one of four ways:

• Extend below the local frost line
• Build a frost-protected shallow foundation under Section R403.3
• Design to the ASCE 32 standard
• Bear on solid rock

Footings can’t bear on frozen soil unless the frozen condition is permanent. That matters for winter work in central Pennsylvania: if the bottom of a hole froze overnight, thaw it or dig past it before the pour.

The same section exempts small freestanding accessory buildings from frost protection: up to 600 sq ft of light-frame construction, or up to 400 sq ft of other construction, as long as the eave height is 10 ft or less. That’s why a typical wood shed on a gravel pad doesn’t need frost footings.

How deep do deck footings need to be in Pennsylvania?

Deck footings follow IRC Section R507.3, and the answer depends on whether the deck is tied to the house:

• Attached to the house: footings must be protected from frost, so they go to your town’s depth. Palmer Township requires at least 36 in. below grade.
• Freestanding: Palmer Township, applying the code’s frost exception, allows footings 12 in. below undisturbed soil for freestanding decks up to 600 sq ft and 10 ft or less in height.
• Small decks on pier blocks: a freestanding deck of 200 sq ft or less, with joists bearing directly on precast pier blocks and a walking surface no more than 20 in. above grade within 36 in. of the deck, needs no footings at all, as summarized by Lower Merion Township.

Two details trip up attached decks. Palmer requires any footing within 5 ft of an existing house wall to bear at the same elevation as the house footing, so a post can’t sit on the loose backfill against your foundation. It also won’t allow a ledger on a cantilever, open-web trusses, or stone or masonry veneer; in those cases the deck has to be freestanding.

Footing size depends on the load the post carries. Philadelphia’s prescriptive deck standard, for decks up to 160 sq ft (216 sq ft with intermediate posts), calls for footings at least 6 in. thick, 16 in. across at end posts and 19 in. at intermediate posts. Palmer’s 2026 details size footings by tributary area, from 8 in. round at 5 sq ft to 31 in. round at 160 sq ft on 1,500 psf soil.

Can you use a frost-protected shallow foundation in Pennsylvania?

Yes. A frost-protected shallow foundation (FPSF) uses rigid foam insulation and the heat lost from the building to keep the soil under the footing from freezing, so the footing can sit well above the frost line. Penn State’s Pennsylvania Housing Research Center (PHRC) says it suits slab-on-grade homes, sites where digging is limited, and walk-out basements. Its FPSF guide (updated June 2026) assigns each county an air freezing index:

Air freezing index	Example counties	Minimum footing depth	Vertical insulation
2,000	Centre, Clinton, Lycoming, McKean, Potter, Tioga	14 in.	R-5.6
1,500 or less	Union, Erie, Allegheny, Dauphin, Lancaster, Philadelphia	12 in.	R-4.5

The guide’s simplified method is for heated buildings that average above 64°F indoors every month, and it doesn’t cover unheated buildings. PHRC also notes the energy code often calls for more insulation than the frost minimum, so check both before you order foam.

What to have ready for a footing inspection

• Holes or trenches dug to your town’s depth, on undisturbed soil, with loose material cleaned out of the bottom
• Depth measured from finished grade. If a patio or walk will lower the grade next to a footing, measure from the final grade, not today’s.
• Footing size matched to the plan or the town’s table
• No concrete placed until the inspector signs off

Sources

• 2021 International Residential Code (ICC), Sections R301.2, R403.1.4, R403.1.4.1 and R507.3
• City of Philadelphia, EZ deck permit standard (2021 code)
• Lower Providence Township, design criteria
• Lower Pottsgrove Township code, Table R301.2(1)
• Palmer Township, 2026 deck details
• Loyalsock Township, building and construction
• Lawrence Park Township, building code ordinance (design frost depth)
• City of Altoona, deck checklist
• Lower Merion Township, 2021 IRC key changes
• Penn State PHRC, Frost-Protected Shallow Foundations
• Last checked November 14, 2026.

Common questions

How deep is the frost line in Pennsylvania?

It’s set locally. Official values we found range from 30 inches in Philadelphia to 48 inches in Lawrence Park Township in Erie County, with 36 inches in several southeastern townships and 42 inches in Loyalsock Township, Lycoming County.

How deep do deck footings need to be in Pennsylvania?

Footings for a deck attached to the house go below your town’s frost depth. Freestanding decks can often use footings 12 inches deep, and small freestanding decks on precast pier blocks may need no footings at all.

How deep should footings be in central Pennsylvania?

Ask your code office for its number. Loyalsock Township in Lycoming County requires footings at least 42 inches below grade, and Penn State puts Centre, Clinton and Lycoming counties in the colder group for shallow foundation design.

Does a shed need frost footings in Pennsylvania?

Usually not. The IRC exempts freestanding accessory buildings up to 600 square feet of light-frame construction with an eave height of 10 feet or less, and sheds under 1,000 square feet at a single-family home are outside the UCC unless your town says otherwise.

See every Pennsylvania building, digging and contractor rule on our Pennsylvania guide. Related: Pennsylvania building code, Pennsylvania shed permits and 2021 IRC rules in plain English.