Frostline.info

Frost line depth in Fairfield County, Connecticut

Frost reaches about 27 inches in typical soil across Fairfield County, from 25″ in the mildest ZIP code to 32″ in the coldest. Codes in this climate commonly set footing depth at 24 to 36 inches.

Moderate frost
Estimated frost depth
27″
typical silt/loam soil
Typical code footing depth
24–36″
rule of thumb for this climate
Design freezing index
781
°F-days, 100-year winter
ZIP codes covered
48
#8 of 8 counties in CT (1 = deepest)
27″ 0″12″24″36″48″ ground frozen
Est. frost (typical soil) Typical code footing depth Clay–sand range

Frost depth by soil type

Soil typeEst. frost depth
Sand / gravel (drains well)35″
Silt / loam (typical yard soil)27″
Clay (holds water)24″

County average. Methodology.

Verify before you dig. These are climate-based estimates. The legally required frost depth is the figure your building department publishes in its IRC Table R301.2 (climatic and geographic design criteria). Call the Fairfield County building or permitting office in Connecticut and call 811 before digging.

Frost depth by ZIP code in Fairfield County

ZIPCityEst. frostCode range
06468Monroe29″24–36″
06470Newtown30″24–36″
06482Sandy Hook30″24–36″
06484Shelton28″24–36″
06604Bridgeport26″24–36″
06605Bridgeport26″24–36″
06606Bridgeport27″24–36″
06607Bridgeport25″24–36″
06608Bridgeport26″24–36″
06610Bridgeport26″24–36″
06611Trumbull28″24–36″
06612Easton28″24–36″
06614Stratford26″24–36″
06615Stratford25″24–36″
06784Sherman32″30–42″
06801Bethel30″24–36″
06804Brookfield30″24–42″
06807Cos Cob26″24–36″
06810Danbury30″24–36″
06811Danbury30″24–36″
06812New Fairfield31″24–42″
06820Darien27″24–36″
06824Fairfield27″24–36″
06825Fairfield27″24–36″
06828Fairfield26″24–36″
06830Greenwich25″24–36″
06831Greenwich25″24–30″
06840New Canaan28″24–36″
06850Norwalk28″24–36″
06851Norwalk28″24–36″
06853Norwalk27″24–36″
06854Norwalk28″24–36″
06855Norwalk28″24–36″
06870Old Greenwich26″24–36″
06877Ridgefield30″24–36″
06878Riverside26″24–36″
06880Westport27″24–36″
06883Weston28″24–36″
06890Southport27″24–36″
06896Redding29″24–36″
06897Wilton28″24–36″
06901Stamford26″24–36″
06902Stamford26″24–36″
06903Stamford27″24–36″
06905Stamford27″24–36″
06906Stamford27″24–36″
06907Stamford27″24–36″
06910Stamford26″24–36″

What this means for your project in Fairfield County

Deck footings & piers

Footings must bear below the frost line and at least 12″ below undisturbed ground. For planning in this area, budget for holes around 36″ deep until your permit office confirms the exact figure.

Fence posts

Set posts at least one-third of their above-ground height. Where frost heave is a problem, carry concrete footings below the frost line (about 27″ here in typical soil) and bell or taper the bottom.

Water & irrigation lines

Bury supply lines below the frost depth. Your water utility or plumbing code sets the minimum cover; add a margin below the estimate above for unusually cold winters.

Slabs & frost-protected foundations

Frost-protected shallow foundations (IRC R403.3) use the 100-year air freezing index — 781 °F-days here — to size perimeter insulation, letting footings sit shallower than the frost line.

Weather stations used

NOAA weather stationDistance100-yr AFI
Norwalk Gas Plant, CT6 mi786
Danbury, CT13 mi903
Setauket, NY22 mi452
Carmel 1 Sw, NY22 mi1,093

Nearby counties

Common questions

What is the frost line depth in Fairfield County?

About 27 inches in typical soil, based on NOAA's 100-year air freezing index. Across the county's ZIP codes the estimate runs from 25 to 32 inches.

How deep should footings be in Fairfield County, Connecticut?

Codes in climates like this commonly require 24 to 36 inches. The Fairfield County building department publishes the required frost depth in its adopted code (IRC Table R301.2).

Does frost depth vary within Fairfield County?

Yes. Estimates differ by 7 inches between the coldest and mildest ZIP codes, mostly from latitude and elevation. Check your own ZIP below.