If you live anywhere that sees real winter—hard freezes, surprise thaws, and that muddy shoulder season that seems to last forever—you’ve probably heard some version of this advice: “Make your footings deep, or your deck will move.” That’s not scare talk. In freeze-thaw climates, the ground can literally grab a footing and lift it, then let it drop unevenly later. The result can be a deck that feels bouncy, slopes toward the yard, or develops gaps where it used to sit tight against the house.
So how deep should deck footings be in freeze-thaw areas? The practical answer is: deep enough to get below the frost line, plus built in a way that resists frost heave. The more complete answer includes soil type, drainage, deck loads, and the kind of footing you’re using. Let’s walk through it in a way that actually helps you plan (or sanity-check) a deck project—especially if you’re dealing with a climate like Michigan’s.
Freeze-thaw 101: why the ground messes with your deck
Frost heave isn’t just “the ground expands when it freezes.” The real culprit is water. When temperatures drop, moisture in the soil freezes and forms ice lenses—thin layers of ice that can grow by pulling in more water from surrounding soil. Those ice lenses can lift soil (and anything in it) upward. Then, when things thaw, the soil doesn’t always settle back evenly, especially if it’s been disturbed or if drainage is poor.
This is why two decks built the same way can behave totally differently. One might sit perfectly for decades, while the other starts to twist after a few winters. It’s not only the cold—it’s cold plus moisture plus soil conditions plus how the footing interacts with all of that.
Deck footings are basically your deck’s “anchors.” In freeze-thaw zones, anchors need two qualities: they must be deep enough that frost can’t get under them, and they must be shaped/installed so frost can’t grab and pull them upward along the sides.
Depth basics: the frost line is your starting point
In most cold regions, building codes require footings to extend below the local frost depth. That depth is often called the frost line (or frost depth). The logic is simple: if the bottom of the footing is below where the ground freezes, frost can’t form beneath it and jack it up from underneath.
In Michigan, frost depth is commonly around 42 inches in many areas, but it can vary by region and local code. Some municipalities may require 48 inches or have specific guidance based on historical freezing patterns and soil conditions. If you’re in a different freeze-thaw region, your number may be 30 inches, 36 inches, 48 inches, or even deeper.
Here’s the key: “below frost line” usually means the bottom of the footing is below frost depth—not just the top of the concrete or the post base. If you’re using a poured concrete pier, you’re thinking about the bottom of the bell (or base) of that pier. If you’re using a different system, you still want the bearing point below frost depth.
Not all soils behave the same in winter
Soil type can make frost heave either a minor annoyance or a major structural bully. The soils most prone to frost heave are those that hold water and allow capillary action to feed ice lens growth. Silty soils are often the biggest troublemakers, and certain clays can also be problematic because they retain moisture and drain slowly.
Sandy and gravelly soils tend to drain better, which means less water available to form ice lenses. That doesn’t mean sand is “safe” no matter what—if the area is saturated or drainage is poor, you can still see movement. But as a general rule, better drainage equals less heave pressure.
If you’re not sure what you have, pay attention after rain or snowmelt. Does water linger? Does the yard stay squishy for days? Do you see puddling near where footings would go? Those are clues that your deck needs extra attention around drainage and footing design, not just depth.
How deep is deep enough in Michigan and similar climates?
For a typical residential deck in a Michigan-like freeze-thaw climate, footings often need to extend to roughly 42 inches or deeper, depending on local code. Many builders will go a little deeper than the minimum to account for soil disturbance during excavation and to create a more stable bearing surface. It’s not uncommon to see holes dug to 48 inches to ensure the bottom is truly below frost depth after cleanup and leveling.
But depth isn’t the only variable. A slender, straight-sided pier that goes deep can still be vulnerable if frost grips the sides and pulls upward (especially if the surrounding soil is wet and fine-grained). That’s why footing shape and surface interaction matter almost as much as the tape-measure number.
If you want to compare notes with people who build for these conditions every day, it can be helpful to see how experienced deck builders in Michigan think about frost depth, drainage, and long-term stability. The best crews don’t just “dig to the number”—they build a system that behaves well over many winters.
Footing shapes that fight frost heave (and ones that invite it)
Bell-shaped footings: wider at the bottom for a reason
A bell-shaped footing (sometimes called a “belled pier”) flares out at the bottom, creating a wider bearing area. This does two things: it spreads the load over more soil, and it makes it harder for frost to lift the footing because the bottom is mechanically “locked” below the frost zone. Frost can tug on the sides, but it’s fighting a larger base that’s anchored below.
Bell footings are especially useful when soil bearing capacity is questionable or when the deck carries heavier loads (think: hot tubs, masonry fireplaces, big gatherings, or multi-level designs). They can also help reduce settlement because the load is distributed more gently.
The tradeoff is excavation complexity. Digging a clean bell shape by hand is harder than digging a straight hole, and it can require specialized tools or forms. Still, in many freeze-thaw areas, the extra effort is worth it for peace of mind.
Straight piers: common, but they need the right details
Straight-sided concrete piers are common because they’re straightforward to form with cardboard tubes. When they’re deep enough and installed with good drainage and proper bearing at the bottom, they can perform well. The problems usually show up when one or more details are skipped: shallow depth, muddy bottom, no gravel base, or poor site drainage.
Another issue is “skin friction.” In heave-prone soils, frost can grab the sides of the pier and pull upward. Some builders mitigate this by using smooth forms, ensuring the surrounding backfill drains well, and avoiding conditions where water sits around the pier.
If you’re using straight piers, it’s smart to focus on a clean, compacted base (or appropriate gravel layer), consistent depth across all footings, and a plan for moving water away from the deck area.
Helical piles: a different approach for difficult sites
Helical piles (screw piles) are steel shafts with helix plates that are literally screwed into the ground to a specified torque. They can be a great option where excavation is difficult, access is tight, or soils are challenging. Because they’re installed deep and anchored by the helix plates, they can resist uplift and settlement well when designed properly.
They’re not a universal solution, and they aren’t always the cheapest option. But for some sites—especially those with high water tables, lots of roots, or limited room for digging—they can be a clean, engineered path to stability.
If you’re considering helical piles, make sure the installer is experienced and that the pile selection is based on actual site conditions and loads, not guesswork.
Drainage is the quiet hero of stable footings
Even if you hit the perfect depth, water management can make or break your deck’s long-term performance. Remember: frost heave needs moisture. If you reduce the amount of water in the soil around your footings, you reduce the “fuel” for ice lenses.
Start with surface drainage. Does the grade slope away from the house? Are downspouts dumping water near where a footing will sit? Is there a low spot that collects meltwater in March? Small fixes—like extending downspouts, regrading a bit, or adding a swale—can dramatically improve footing behavior over time.
Then think about subsurface drainage. In some cases, a gravel layer at the bottom of the hole (where allowed by code and used correctly) can help create a more stable bearing surface and improve drainage. The goal is to avoid a muddy, waterlogged base that can settle or freeze unpredictably.
What “below frost line” really means when you’re building
Measuring from finished grade (not from where you happen to be standing)
Footing depth is typically measured from finished grade—the final ground level after landscaping and grading—not from the temporary grade during construction. If you dig footings before final grading, it’s easy to accidentally end up shallower than required once the yard is leveled out.
This matters a lot on sloped lots. One side of the deck might be close to the ground while the other side is high on posts. Each footing still needs to reach the required depth below the local frost line, measured from the grade at that footing location.
A good practice is to mark intended finished grade at each footing location before digging. It’s a small step that prevents a surprisingly common mistake.
Clean bearing at the bottom: no loose soil, no mud soup
The bottom of the hole should be clean and undisturbed. If you over-dig and then toss loose soil back in, you’ve created a soft layer that can compress over time. That can lead to settlement, which can be just as annoying as frost heave.
If you do over-dig, the fix is usually to bring the bottom back up with appropriate compacted material (often gravel) or to pour additional concrete, depending on the design and local requirements. The point is to avoid leaving the footing sitting on fluff.
Also, if the hole fills with water, don’t ignore it. Pump it out and figure out why it’s happening. Pouring concrete into a waterlogged hole can compromise the footing and create long-term movement.
Loads change the footing conversation more than most people expect
Depth protects you from frost, but size protects you from sinking. The heavier the deck (and everything you plan to put on it), the more bearing area you may need. That’s why codes and engineering tables don’t just specify depth—they also specify diameter or footing size based on tributary area and soil bearing assumptions.
Hot tubs are the classic example. A filled tub with people in it can add thousands of pounds in a small footprint. If the footings under that area aren’t designed for the load, the deck can settle unevenly even if every footing is below frost depth.
Other “weight multipliers” include outdoor kitchens, large planters, pergolas with heavy roofs, and any deck that’s significantly elevated (because taller posts can amplify movement and make small shifts feel bigger).
Attached vs. freestanding decks: different risks, same frost rules
Attached decks (with a ledger board at the house) are common, but they can introduce an extra layer of complexity in freeze-thaw regions. Houses often have deeper foundations than deck footings, so if the deck moves even slightly while the house stays put, you can get stress at the connection point.
Freestanding decks avoid ledger issues, but they rely entirely on their footing system for stability. That means consistent depth and consistent performance across all footings becomes even more important. If one corner heaves and the others don’t, you’ll feel it.
Either way, the frost line still matters. The difference is how movement shows up: attached decks can rack against the house; freestanding decks can rack within their own frame. Both are avoidable with good design and installation.
Real-world warning signs that footings weren’t deep enough
If you’re evaluating an existing deck (or a deck you’re thinking of buying with a home), there are a few clues that footings may be too shallow or that frost heave is already at work. Look for posts that seem to have “risen” out of the ground, gaps under beams, or post bases that look stressed or tilted.
On the deck surface, pay attention to doors that suddenly rub, railings that feel slightly out of plumb, and stairs that no longer sit evenly on their landing. These can be signs of seasonal movement that’s accumulating year over year.
Also check for drainage issues: downspouts dumping near posts, soil that slopes toward the deck, or areas where snowmelt pools. Often, the fix isn’t only “dig deeper next time,” but “stop feeding water to the soil around the footings.”
Deck stairs and landings: the sneaky frost-heave hotspot
Stairs are often where frost problems show up first. Why? Stair stringers and landings sometimes get built on small pads, shallow piers, or even patio blocks. In a freeze-thaw region, those shallow supports can move dramatically compared to the main deck footings.
When stair supports heave, the stairs can pull away from the deck or push into it. You may see cracked stringers, loose connections, or a bouncy bottom step. It’s not just annoying—it can become a safety issue quickly.
If you want stairs that feel solid every season, treat their supports like first-class structural elements: below-frost footings, proper bearing, and thoughtful drainage. The goal is for the stairs and the deck to move together (ideally, not at all).
Concrete, forms, and hardware: small choices that matter in winter
Using the right concrete mix and placement habits
Most residential deck footings use standard concrete mixes, but placement matters. Pouring into a wet, muddy hole can weaken the bottom and create voids. Pouring in cold weather without protection can also affect curing and long-term strength.
If you’re pouring late in the season, pay attention to overnight lows and follow local best practices for cold-weather concreting. Sometimes that means using warm water in the mix, insulating blankets, or scheduling pours when temperatures are stable.
Good concrete is part material, part method. A well-planned pour can be the difference between footings that last decades and footings that start shifting after the first tough winter.
Post bases and keeping wood out of the ground
Even if your footing is perfect, you can still shorten the life of your deck if wood is too close to soil or sitting in water. Post bases that elevate the post above the concrete help prevent rot and make the connection more durable.
In freeze-thaw areas, hardware also goes through a lot: moisture, salts, and constant expansion/contraction cycles. Using appropriate connectors and corrosion-resistant fasteners is a quiet investment in a deck that doesn’t get wobbly over time.
And if you’re in a region where de-icing salts are common, consider stepping up corrosion protection. It’s one of those details you’ll be grateful for years later.
When your yard is a sponge: high water tables and heavy clay
Some properties are just naturally wet. Maybe you’re near a lake, the soil is heavy clay, or the water table rises during spring melt. In those cases, even deep footings can be exposed to a lot of moisture, which increases frost-heave potential.
For these sites, the strategy often becomes layered: deeper footings, better drainage planning, and sometimes alternate foundation systems like helical piles. It can also mean rethinking where the deck sits so you’re not building in the wettest part of the yard.
This is also where experience really shows. Builders who regularly work in wet, freeze-thaw conditions tend to spot red flags early—like where water will collect, how snowmelt travels, and which corners of the deck are most likely to move.
Covered decks and wind protection: how add-ons affect footing needs
Add a roof, a pergola, privacy walls, or a big screen system, and you’ve changed the forces your footings must handle. It’s not only weight; it’s wind uplift and lateral loads. A covered structure can act like a sail in strong gusts, especially in open areas.
This matters in freeze-thaw zones because a footing that’s marginal on uplift resistance can be stressed by both frost action and wind forces. The combination can loosen connections and amplify movement.
If you’re dreaming about outdoor living that extends your season, options like screened gazebos in Michigan can be amazing—but they should be planned with the right footing design from the start. It’s much easier (and usually cheaper) to build the foundation correctly now than to retrofit later.
Permits and inspections: what they catch (and what they don’t)
In many areas, a permit and inspection process helps ensure footings meet minimum depth and sizing requirements. Inspectors often want to see footing holes before concrete is poured, verifying depth, diameter, and sometimes soil conditions.
That’s a good thing, but it’s important to understand what “minimum compliant” means. Code minimums are a baseline, not a guarantee of perfect performance on every property. If your site has unusual soil, drainage issues, or heavier loads, you may need more than the minimum.
Also, inspections can’t always catch workmanship issues like muddy hole bottoms, poor compaction, or water management problems that happen after the inspector leaves. That’s why choosing a careful builder (or being a careful DIYer) matters so much.
DIY vs. pro install: where people most often go wrong
DIY decks can be great projects, but footings are where small mistakes get expensive. The most common DIY footing problems in freeze-thaw zones are: digging “close enough” to frost depth, inconsistent depths across footings, pouring on loose soil, and ignoring drainage because it doesn’t seem urgent in summer.
Another common issue is underestimating how long it takes to dig deep holes, especially if you hit rocks, roots, or dense clay. When fatigue sets in, people start compromising: a few inches shallow here, a smaller diameter there. Unfortunately, winter doesn’t care how tired you were in August.
If you’re hiring out, look for teams that talk comfortably about frost depth, soil, and drainage—not just decking boards and railing styles. The foundation is the part you won’t want to redo.
Smart questions to ask before anyone starts digging
If you’re interviewing a contractor, you don’t need to sound like a structural engineer. A few practical questions can tell you a lot about how they think:
Ask what frost depth they build to in your municipality, and whether they go beyond the minimum. Ask how they handle wet holes or high water. Ask what they do if they over-dig, and how they ensure the bottom is stable before pouring. Ask how they route downspouts and surface water away from the deck area.
And if your project includes heavier features—like a roof, a hot tub, or a big screened structure—ask how that changes footing size and reinforcement. A confident, experienced answer is a good sign you’re in capable hands.
Designing for decades: footings as part of the whole deck system
A deck that feels solid year after year is rarely the result of one single “magic” detail. It’s usually a chain of good decisions: correct depth, correct sizing, proper drainage, quality connectors, and a frame that’s braced appropriately for lateral movement.
In freeze-thaw climates, bracing can be especially important for taller decks. Even tiny footing movement can feel bigger when posts are long. Diagonal bracing and thoughtful framing reduce sway and help the deck feel planted.
If you’re building something custom—multi-level platforms, integrated seating, curved stairs, or a covered entertaining space—it’s worth working with specialists who build these systems all the time. Partnering with Michigan custom deck builders can help ensure the design choices you make for looks and lifestyle still play nicely with frost depth, soil behavior, and structural realities.
A quick depth checklist you can keep in your back pocket
If you want a simple way to sanity-check a footing plan in a freeze-thaw area, here’s a practical checklist to run through before concrete shows up:
Verify the local required frost depth and make sure the bottom of each footing will be below it. Confirm depth is measured from finished grade at each footing location. Ensure the bottom of each hole is clean and stable, not loose or muddy. Confirm footing diameter (or bell size) matches the deck loads and layout. Make a plan for surface water and downspouts so the area around footings doesn’t stay saturated.
If those items are handled, you’re already ahead of many projects. Freeze-thaw climates are demanding, but they’re not mysterious. Build below frost, manage water, size for loads, and your deck has an excellent chance of staying level and sturdy through many winters.
