Published
How steep is too steep to build on? The county has two numbers
Two numbers decide it, and they are not the ones people guess
“Is this lot too steep to build on?” usually gets answered by eye, or by whether a machine can get up it. Fremont County has written answers, and they sit in the Development Code under the heading Critical Areas: Slopes. There are two thresholds and they do different things.
“No building on a steep slope shall be permitted on slopes of one vertical unit in four horizontal units (25%) or more unless a geotechnical engineer certifies that such application creates no significant hazard of slope failure or accelerated soil erosion. Building on slopes of greater than one vertical unit in three horizontal units (33.33%) shall be prohibited.”
— Fremont County Development Code, 2011 Edition (Ordinance 2011-04), section 5.12, Critical Areas: Slopes. Retrieved 19 August 2026
So the shape of it is:
| Slope of the ground | What the code says |
|---|---|
| Under 25 percent | No steep-slope condition from this section |
| 25 percent and over | Building is not permitted unless a geotechnical engineer certifies no significant hazard of slope failure or accelerated soil erosion |
| Over 33.33 percent | Building is prohibited |
| Any slope identified as unstable | The code requires it be put to open space use |
Twenty-five percent is one foot of rise in four feet of run. Thirty-three and a third percent is one in three. Neither is a cliff. Plenty of ground in this country that reads as “a bit of a slope” from the road is sitting in the first band, and a fair amount of what people call a hillside lot is at or past the second.
Why the excavation permit asks about slope
The county's excavation and grading application has three blanks in Section 3 for the FEMA floodplain zone, for slope of 15 to 30 percent, and for slope over 30 percent. Those brackets do not line up exactly with the code's 25 and 33.33, which is worth knowing rather than glossing over — the form is a screening question and the code is the standard.
What the form is doing is flagging the file. Ticking a slope box is what tells the reviewer to look at section 5.12 for your parcel, and it is one of the things that can move an application from a desk decision to a longer review. It is a fair inference, not a stated rule, that a file with a slope box ticked gets more attention than one without.
The setbacks people do not know exist
If your ground is at or over 25 percent, the code adds setbacks measured from the slope itself, on top of whatever property-line setbacks apply. These are proportional rather than fixed, with a cap.
- From the toe of the slope: one half of the height of the slope, but not to exceed 15 feet.
- From the top of the slope: one third of the height of the slope, but not to exceed 40 feet.
Read that on a real lot and it bites. A twenty-foot bank running through the middle of a parcel takes ten feet of buildable ground away at its foot and just under seven at its head, before anyone has drawn a house. A sixty-foot slope hits both caps: fifteen feet at the toe, forty feet at the top. On a narrow lot that can leave a building envelope that does not fit the building.
What a machine can and cannot fix
This is the part that matters commercially, because the instinctive response to a steep lot is to bench it — cut a flat pad and hold the cut with a wall. Sometimes that is exactly right. But three things are worth being straight about before the quote is taken.
- The certification is about hazard, not about flatness. The threshold question at 25 percent is whether a geotechnical engineer will certify no significant hazard of slope failure or accelerated soil erosion. Cutting a pad changes the slope and changes the hazard, and it is the engineer's assessment that governs, not the finished grade.
- Over 33.33 percent the code prohibits building outright, and it does not read as a threshold you engineer your way past. If part of a parcel is over that figure, the honest question is where on the parcel a house can go, not how to make that part work.
- Retaining walls are inside the permit. The excavation and grading application's site plan requirement expressly names construction of a retaining wall, so a benched pad held by a wall is squarely within what the county wants shown and reviewed.
None of that means a sloping lot is a bad lot. Some of the best ground here has fall on it. It means the slope belongs in the diligence before the purchase, alongside the rest of the site prep sequence, rather than being discovered when the first design comes back.
Measuring it before you rely on it
Slope is a ratio, and it is easy to mis-state in a way that flatters a lot. A few practical notes.
- Percent slope is rise divided by run, times one hundred. One foot up over four feet across is 25 percent, not 25 degrees — 25 percent is about 14 degrees.
- The figure that matters is the slope of the ground where the structure goes, not the average slope of the parcel. A gentle parcel can have a steep building site and the reverse is also true.
- A contour map or a survey settles it. An operator's eye is good and is not a certification.
- If the answer is anywhere near 25 percent, get it measured before design rather than after, because the geotechnical certification is a cost and a calendar item, not a formality.
- Ask whoever quotes the earthwork whether their price assumes an engineered wall, and if so, whose engineer.
- Check the slope where the drive has to run as well as where the house sits, since an access that cannot meet the county's grade band at the road is its own separate problem.
- Write the answer down with the date you measured it, so the figure in the file is one you can defend later rather than one somebody remembered.
The related rules that travel with slope
Steep ground rarely arrives on its own. Two neighbouring provisions in the same part of the code catch a lot of the same parcels.
The code requires open space use of all slopes identified as unstable, which is a stronger statement than a setback — it takes the ground out of development rather than pushing a building back from it. And where a parcel is in or adjacent to forested or brushy ground, the code routes the application through its wildfire provisions, which is a separate assessment from the clearing work itself.
The practical summary is short. Under 25 percent, slope is a construction problem. At 25 percent it becomes an engineering problem with a certification attached. Over 33.33 percent the code says no. Knowing which of those three you are in is worth doing before an offer, not after.
Common questions
What slope does Fremont County treat as too steep to build on?
The code sets two thresholds. At one vertical unit in four horizontal units, which is 25 percent, building is not permitted unless a geotechnical engineer certifies that it creates no significant hazard of slope failure or accelerated soil erosion. Above one in three, which is 33.33 percent, building is prohibited.
Is 25 percent the same as 25 degrees?
No, and confusing the two flatters a lot badly. Percent slope is rise over run times one hundred, so 25 percent is one foot of rise in four feet of run, which is about 14 degrees. A slope of 25 degrees would be roughly 47 percent and well past the prohibition.
Can an engineer sign off on ground over 33.33 percent?
The code does not offer that route. The certification path is written into the 25 percent threshold. The sentence covering slopes greater than one vertical in three horizontal states that building shall be prohibited, without a certification exception attached to it.
Are there setbacks from the slope itself?
Yes, for slopes at or over 25 percent, and they are separate from property line setbacks. From the toe of the slope, one half of the slope height, capped at 15 feet. From the top of the slope, one third of the slope height, capped at 40 feet.
Why does the excavation permit ask about 15 to 30 percent and over 30 percent?
Those are the brackets printed on the county's excavation and grading application, and they are screening questions rather than the standard itself. The standard is in section 5.12 of the Development Code, at 25 and 33.33 percent. Ticking a slope box flags the file for that review.
Does cutting a flat pad solve the problem?
Not by itself. At and above 25 percent the question is whether a geotechnical engineer will certify that there is no significant hazard of slope failure or accelerated soil erosion, and earthwork changes that assessment rather than removing it. Retaining walls are also expressly named in the permit's site plan requirement.
What happens to a slope the county considers unstable?
The code requires open space use of all slopes identified as unstable. That is stronger than a setback, because it takes the ground out of development rather than pushing a structure back from it.
How should I actually measure the slope of a lot?
With a contour map or a survey, over the specific area where the structure would sit rather than across the whole parcel. Average parcel slope hides both good building sites on steep ground and steep building sites on gentle ground.