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Building Near a Fault in Lehi: Setbacks, Hillside Rules and Your Lot

If you're building on a sloped lot in Lehi, or near a mapped fault, the city can require a geologic report before it approves the home, and that report can set a no-build area across the lot. A setback rarely makes a lot unbuildable, but it can change where the house goes, how big it is, and how the basement works. The time to find out is before you buy or finish a design.

What a fault setback is

A fault setback is an area on either side of a fault where homes are not built, because the ground there can break and shift in a large earthquake. The distance is not a fixed number. Under the Utah Geological Survey's guidance, it comes from a site-specific study and is based on how wide the zone of ground movement is and how much and which way the fault has moved in the past.

Why it matters in Lehi

The Wasatch fault zone runs along the base of the mountains through northern Utah County, and the Utah Geological Survey and U.S. Geological Survey have mapped fault traces and surface-fault-rupture hazards in the Lehi area. Mapped faults sit inside special study areas, and a site inside one needs a fault study before building.

You can check whether a lot is inside a mapped study area on the Utah Geologic Hazards Portal. Being outside one doesn't rule out other hazards, which is where Lehi's hillside rules come in.

Lehi's hillside rules

Lehi's Development Code (Chapter 12-A, Hillside Preservation) applies to any property with slopes of 10 percent or more. Its stated purposes include limiting exposure to geologic hazards such as surface fault rupture, landslides, rock fall and groundwater problems. Under it:

Anyone grading, excavating, filling or building on a slope over 10 percent submits a soils report and a geologic report to the city for review.
The geologic report and map are prepared and stamped by a licensed geologist, and cover hazards including fault rupture and other seismic hazards, landslide potential and groundwater.
Slopes over 30 percent can't be disturbed unless engineering measures recommended by an engineering analysis are accepted by the city.
Homes on steep slopes follow the building code, unless the soils or geologic report recommends something stricter.

Lehi's Building Division takes geotechnical reports with the permit submittal. Rules change, so confirm the current requirements with the Lehi Building and Inspections department early.

When to get the study

Get the geologic and soils work done before the design is finished. If the report moves the buildable area, every drawing based on the old footprint has to change, and redrawing costs more than ordering the study first. A fault study can involve trenching across the suspected fault, so allow time for it.

How a setback changes the home

The footprint. The house may need to be narrower, shifted or shaped differently to stay out of the setback.
The basement. A full-width basement may not fit, which affects plans for a theater, gym or suite. A basement bedroom still needs a code-compliant egress window, placed inside the approved area.
The garage and driveway. A no-build strip can change where the garage sits and how the driveway reaches it, especially on a slope.
Suites and ADUs. A setback can limit where a separate entrance goes. Keeping kitchens, baths and laundry close together over the main plumbing helps a compact suite fit.

Questions to ask before you buy a sloped lot

Is the lot inside a mapped fault special study area?
Does it have slopes over 10 percent, and any over 30 percent?
Was a geologic or soils report done when the subdivision was approved, and does it set any no-build areas?
Where can the house, garage and driveway actually go once those are drawn on the plat?

For what drives the cost of building, see cost to build a house in Utah. Planning a walkout? See can your lot handle a walkout basement?

Looking at a lot in Lehi? Contact us and we'll help you check what it can support before you commit to a design.