Ground mount solar footings and frost depth

Frost heave can lift a ground mount an inch a winter. Here is how deep the posts go, who sets that number, and which footing to pick.

Short answer: in the Hudson Valley, a solar ground mount needs footings that reach below your town’s frost depth, and that number comes from your local building department, not a national map. Upstate tables commonly land around four feet (the Town of Ithaca’s 2025 code table lists 48 inches). Go shallower and freezing soil can grab the posts and jack them upward a little every winter, which racks the frame and stresses the glass.

If you’re planning a ground mount for next spring, now is a good time to sort this out. Here is how frost heave works, what your footing options are, and the order to do things in.

Why frost depth matters for a ground mount

Frost heave needs three things at once: soil fine enough to wick water upward, freezing temperatures that reach into the ground, and a supply of groundwater. When they line up, ice lenses grow in the soil and push up. Silt is the worst offender. Sand and gravel drain too fast to feed ice. The fine-grained glacial till common across the Northeast is especially prone to heave.

The movement can be fast. Solar Builder reports heave rates from about 1/64 inch to 3/4 inch per day, depending on conditions. Frozen soil also bonds to steel (called adfreeze), so a post set in the frozen layer gets lifted with it. When the ground thaws, the post can settle into the gap it left. Repeat that each winter and you get warped rails, loose connections and cracked modules.

A roof doesn’t have this problem. A ground mount lives in the soil, so the footing is the part that decides whether the array still sits square in year ten.

Who sets the frost depth in New York

New York adopts the 2025 Residential Code of New York State through 19 NYCRR Part 1220. The code’s climatic and geographic design table (Table R301.2) has a frost-depth line, and each jurisdiction fills it in. So the number for your address is whatever your town, city or village building department says it is. Some towns adopt a deeper number than their neighbors.

For example, the Town of Ithaca’s published 2025 table lists a frost line depth of 48 inches. The Town of Marbletown’s plan review checklist in Ulster County has the same frost-depth line for the local figure. Call your own building department before you buy pipe. Ask for the frost depth, whether a ground mount needs a permit, and whether they want stamped drawings.

Footing options compared

Footing	How it resists heave	Good fit	Watch for
Concrete pier with steel post	Weight and depth; base sits below frost	DIY with an auger; most racking manuals assume it	Rock and cobbles; bracing posts while concrete cures
Helical pile	Helix plate anchored in unfrozen soil	Wet or silty ground; no concrete; installs in a day with a rig	Needs an installer and machine; size it with an engineer
Ground screw	Threaded section below the active frost zone	Fast installs on soil without much rock	Ledge and large stones stop it

Solar Power World notes that bearing-type footings like helical piles and concrete spread footings perform well in frost-susceptible soil when local recommendations are followed. For helical piles, Hubbell’s Chance engineers say the key is to place the helix below the maximum frost depth plus at least one helix diameter. In one Massachusetts field test over a single winter, a drilled concrete pier heaved about 1.4 inches while a larger helical pile moved about 0.2 inch.

What racking manuals actually ask for

The IronRidge ground mount manual is typical. It calls for 2 inch or 3 inch Schedule 40 galvanized steel pipe, set in concrete, braced until the concrete cures. It does not give you a depth. It sends you to its design tool and PE-stamped certification letters, and notes that a local geotechnical report may be required. Treat any depth you see in a forum post as a guess about someone else’s dirt.

Two more details from the frost-heave literature: galvanizing helps, because corroded steel holds frozen soil more tightly, and the electrical side needs room to move. Leave slack in cables and use expansion fittings where conduit comes out of the ground.

Step by step, in the right order

Size the array first. The number of panels sets the number of posts and the wind and snow loads they carry. The free design app gives you a system size and panel count.
Call the building department. Get the frost depth, permit rules and setback requirements for your lot.
Get the racking’s engineering. Run the manufacturer’s design tool for your site and keep the stamped letter. That letter sets post spacing and embedment.
Call 811. In New York, place a locate request at least two days before you dig. It’s free.
Probe the site. Dig or auger one test hole to full depth. Hudson Valley lots often hit ledge or cobbles; that can change your footing type.
Set posts and cure. Brace, check plumb and line, and let concrete cure before loading rails.
Plan the wire run. Ground mounts usually sit far from the house. Size the trench conductor for distance with our voltage-drop method.

Timing in late fallOnce the ground freezes, augering and pouring get harder and concrete needs cold-weather care. If you can’t get posts in before the freeze, use the winter for permits, engineering and ordering, and dig in spring.

Weighing a turbine instead of panels on an open lot? Our wind vs solar comparison covers that call. Want the posts done for you? We install in Ulster, Orange and Dutchess counties, and our install guides cover the equipment that bolts on top.

Quick answers

How deep do solar ground mount footings need to be in New York?

Below the frost depth your local building department sets, plus whatever the racking engineering calls for. Upstate tables are often around 48 inches.

Who decides the frost line depth in New York?

The local building department. The state code leaves the frost-depth line in Table R301.2 to each jurisdiction.

Are helical piles better than concrete for a solar ground mount?

Both work when designed for your soil. Helical piles suit wet, silty ground and avoid concrete; concrete piers are the common DIY route with an auger.

What soil is worst for frost heave?

Silt and fine-grained glacial till. Sand and gravel drain water away, so they heave far less.

Do I need to call before digging post holes?

Yes. In New York, call 811 or use UDigNY.org at least two days before digging. The locate service is free.

Solar ground mount footings and the frost line: a Hudson Valley guide