How to Build Above the Frost Line in Wasatch County: Things You Should Be Aware Of

The numbers, by building department

There are two counties and at least five building departments on the Wasatch Back, and they do not all use the same number. These are the adopted frost depths from each department's own design criteria sheet, measured from finished grade to the bottom of the footing.

Kamas does not publish its number online. Call the inspector before you design. Nearby Oakley posts 30 inches to the top of the footing, which works out close to the county's 36 inches to the bottom. For comparison, Salt Lake, Utah, and Davis County builders are used to 30 inches. If you see a blog claiming 48 inches for Park City, it is wrong; the city's own 2026 sheet says 40.

Two details that matter more than the number itself:

• It is measured from finished grade. If you plan to cut the yard down later, or build up a patio against the house, the footing has to be set for where the dirt will end up, not where it is the day we dig.
• Frozen soil is not bearing. The code says footings shall not bear on frozen soil. If we open a trench in January and the bottom is frozen, we wait or we thaw it. We do not pour on it.

What frost heave actually does

It is not just water freezing in place. As the frost works down through the soil, it pulls more water up from below into the freezing zone, and that water freezes into flat layers called ice lenses. The lenses stack, and the ground above them rises. In the right soil it can lift a foot. Then spring comes, the lenses melt, the soil goes soft and wet, and everything settles back, but not evenly, and not to where it started.

It needs three things to happen: cold that reaches the soil, water, and a soil that wicks. Silts and clays wick. Clean gravel does not. That is why the soils report matters so much here and why I put clean gravel under footings and flatwork.

There is a second trick it plays on posts and piers. Frozen soil grips the side of a post the way ice grips a mailbox pole, and when the ground heaves it drags the post up with it. Builders call it frost jacking. It is why deck posts and fence posts around here lean after a few winters when they were not set below frost depth.

A basement handles the house. It does not handle everything else.

Most homes I build on the Wasatch Back have a full basement, and a basement footing is eight or nine feet below grade. Frost depth is not a concern for the main house. Where people get surprised is everything attached to it or sitting next to it. Each of these is inspected against the same 36 or 40 inches on its own:

• The attached garage, if it is slab-on-grade with a thickened edge instead of a full stem wall.
• Front porch and stoop footings.
• Deck piers.
• Retaining walls.
• Detached buildings over 600 square feet. Small sheds are exempt, but a shop or a barn is not.
• Any addition later.

About frost-protected shallow foundations. The code allows a shallower footing if you wrap the edge of the slab in rigid insulation so the ground under it never freezes. It is a real method and it can save money on a slab-on-grade building. But the code only allows it for buildings that are kept heated, and it specifically rules it out for garages, porches, and carports. And no building department on the Wasatch Back publishes a policy on it, so if an engineer proposes one, get the department's acceptance in writing before the drawings are finished.

What is under the lot decides how deep "deep enough" is

The frost depth is the minimum. The soil can push it further. The Utah Geological Survey maps three problem soils in this area that show up in my excavations regularly:

• Collapsible soils on old alluvial fans and debris flows, which are strong when dry and settle the first time they get wet. A lot of the bench lots around the valley are exactly that.
• Expansive clays that swell wet and shrink dry.
• Shallow bedrock, which is great to bear on and expensive to dig through.

Add high groundwater in the valley bottoms and you have the four things a soils report is for. Wasatch County requires a geologic report inside its Geologic Hazards Overlay Zone and recommends one everywhere else. Summit County requires a geotechnical report on any lot with a 15 percent slope or steeper. Park City has a separate soils ordinance about old mine tailings, which is about lead and arsenic, not bearing, and it is its own cost.

A report for a single lot typically runs $2,000 to $3,500, more if the engineer wants extra borings. It tells the structural engineer what the footing can bear on and tells me whether we are over-excavating and bringing in engineered fill, which is the single most common change order on a Wasatch Back foundation. Utah's code even rewards having one: with a geotech report, foundation drainage is only required if the report calls for it.

Your water line goes deeper than your footing

The state plumbing code says a water service line has to be at least six inches below the frost line. The cities go further:

• Heber City: five feet of cover on culinary water. Pressurized irrigation two feet. Hydrants five-foot bury.
• Midway City: five feet of cover, and the house service lateral five feet minimum.
• Park City: five feet minimum, and seven feet on dead-end or snow-plowed lines.
• Jordanelle area (special service district): five feet, with frost-free meter lids.

That trench, and the excavator time to dig it, is part of the site work in The Steps. Two things to plan for on top of it: every outside faucet is a frost-free sillcock, and if you want a yard hydrant for the garden or the horses, its valve sits below frost depth too. If you are on septic, the state wants at least 48 inches of suitable soil under the drain field, which is another reason the soils report comes first.

Snow load and frost depth are related

The same cold that sets the frost depth sets the snow load, and snow load decides how wide the footing has to be. Heber City's ground snow load is 60 pounds per square foot by state statute. Park City and most of the rest of the Wasatch Back are site-specific: the engineer runs your parcel through the Utah State University snow load map, and the published example for Park City comes out around 104 pounds per square foot. Heavier roof, wider footing, more bearing needed from whatever soil is below the frost line. It is all one calculation, which is why the structural engineer's stamp is not a formality here.

The season is short, and winter concrete costs more

The average first fall freeze in Heber is around September 8. Park City, September 15. Kamas, September 9. The last spring freeze is in the first two weeks of June. The soil freezes weeks after the air does and stays frozen for months at these elevations, so the reliable window for digging and pouring is roughly May through October at 5,600 feet and shorter up in Park City.

We can pour in winter. The concrete standard for it is clear: heated water and aggregate, place it warm, protect it under blankets or a heated enclosure until it reaches strength, and never on frozen subgrade. It adds 10 to 30 percent to the concrete cost and slows everything down. If a lot closes in August and the plans take until November, the honest conversation is whether to pay the winter premium or spend the winter on design and permits and break ground the week the frost is out. Missing the fall window usually means four or five months of waiting, so I try to have that conversation before the lot closes.

What the inspector checks

The footing inspection happens after the rebar is in and before any concrete is poured. In Summit County and Midway it is the first structural inspection on the list, right after rough grade. The inspector checks the depth from finished grade to the bottom of the footing against the department's number, that the footing is at least 12 inches into undisturbed soil, that nothing is soft, disturbed, or frozen, that the footing size matches the stamped plans, and the rebar and grounding electrode. Where there is a soils report, they will usually want the engineer's letter confirming the bearing or the over-excavation.

The four-way inspection everyone talks about comes much later, at rough framing, plumbing, mechanical, and electrical. Frost depth is decided long before that, which is why getting the footing inspection right the first time matters. There is no fixing depth after the walls are up.