Digging in a Chicago Winter: Frozen Ground Problems

Chicago ground freezes. The National Weather Service normals for 1991 to 2020 put the average at 121.3 days a year with a low at or below 32 degrees F (NWS Chicago). So the question is not whether you will meet cold ground. It is what that changes about a dig, and what it does not. This page sits inside our excavation and foundation guide.

What stays the same in winter?

The rules do not take a season off. A non-emergency dig in Chicago still needs a call to 811 Chicago (DIGGER) with at least two business days of notice, excluding weekends and holidays, and the call applies to homeowners too (City of Chicago, City of Chicago). See how DIGGER 811 works.

Permit questions stay the same too. We did not find a City rule that treats winter excavation differently, so use the depth rules in Chicago excavation permit rules and check with the Department of Buildings if you are unsure.

One practical point: snow, ice and mud can cover the paint marks the utilities leave. If you cannot see the marks, do not guess. Call back before the first cut.

What does frozen ground change?

The honest answer is mostly schedule and risk, not a different law. Frozen soil is harder to cut, which usually means slower work and different equipment on the site. We do not make a promise about how much, because it depends on the soil, the depth and the weather that week.

What matters more is what happens after the hole is open. An open excavation along a foundation wall is a bigger exposure in winter. Plan the dig so the repair, the backfill and the follow-on trades are lined up, instead of leaving a hole open while you wait for a thaw. For repair jobs, when foundation repair means digging outside explains why the dig is rarely the whole job.

What happens to the concrete and masonry that go in after?

This is where winter digs go wrong. Three rules from the industry sources we use:

• No concrete on a frozen subgrade. The Ready Mixed Concrete Association says no concrete should go on frozen ground (NRMCA).
• Fresh concrete freezes. It can freeze below about 25 degrees F, and frozen fresh concrete can lose more than half its potential strength. It needs protection until it reaches about 500 psi, roughly two days after placement (NRMCA).
• Masonry has cold weather rules too. Below 40 degrees F is "cold" for masonry, and below 20 degrees F masonry units that are frozen or carry ice or snow should not be laid (BIA).

That means a winter footing or foundation repair needs thawed, prepared ground and a plan to protect the work. We cover pours in concrete in winter in Chicago. If a contractor says winter is no problem, ask exactly how the ground and the concrete will be protected.

When to dig in winter is a judgment call, and sometimes waiting for spring is the right one. If you have a problem that cannot wait, our excavation team can tell you what is realistic for your site.

Common questions

This article explains general rules and common situations in Chicago. It is not legal advice, and City rules change. For a specific property, check with the Chicago Department of Buildings or a licensed professional.