slope savvy

I recently saw a question in the REtipster forum. A user asked this question.

I'm brand new to the forum/group, and I have been land investing for the past year. I'm 100% remote and have acquired five properties thus far. The issue I've run into several times is topography and slope. It's there a way to circumvent this through LandID, Google Earth or just talking with counties and asking the right question? Does anyone have a slope gradient that they just steer clear from… Like after 29° the property is a wash?

I thought this was an excellent question because the topography of a property can play a BIG role in how easy or difficult it will be to develop and build upon. Consequentially, it can have a major impact on the value of a vacant lot.

It's also very easy to overlook this characteristic when viewing vacant land on a GIS parcel map because parcel maps only look at the property from directly above, which says very little about how flat or steep the property is.

How to Verify a Property's Slope

There are different ways to do this; each approach will give you different degrees of certainty.

The only way to be 100% certain about the terrain of a property is to order a topographic survey.

This type of survey will measure the property from hundreds and, oftentimes, thousands of points to verify the elevations throughout the parcel.

It also costs thousands of dollars, but if you need to be 100% certain about the contours of a property, a topo survey is what you need.

Topo surveys are a vital part of engineering and developing raw land because this data will help the civil engineer determine how much earth needs to be moved so that the excavator can do their job accurately.

…but what if you're not planning to design or build anything on the property yourself? What if you don't need 100% certainty? What if 80% or even 60% certainty would suffice?

If you need a faster, less expensive way to get educated about your property's topography, don't fret! There are other ways to get the job done.

Topo Survey Alternatives

If you're a land flipper, you probably don't want to spend thousands on a topo survey, especially when you need to move faster, and you have no plans to alter the property in any way.

Even so, you don't want to ignore a property's topography altogether.

It's helpful to have some vague idea of how steep the property is so you can be aware of any obvious red flags the future buyer may have to deal with and, more importantly, how it could impact the property's value and saleability.

Here are some other free or relatively inexpensive ways to get these answers.

Free: Google Earth + EarthPoint

Google Earth is an excellent tool because it doesn't cost anything and can reveal a lot of information.

If you're looking specifically for topographic information, it's even more helpful if you get EarthPoint involved, as I'll explain below.

Even though this approach isn't nearly as accurate as a topo survey, it's much better than nothing.

RELATED: 10 Google Earth Hacks Every Real Estate Investor Should Know

Inexpensive: Land id

Land id is like Google Earth on steroids because it integrates many other resources (including the same kinds of topo maps that EarthPoint uses) in one convenient place. It's designed specifically for people who research vacant land.

As you'll see below (starting at 3:07), it offers a more seamless process for checking the topography at any point in the United States.

Land id is also not a substitute for a genuine topo survey from a licensed surveyor, but it's much better than nothing.

The info you'll find in Land ID can often be found from other free sources, but those sources are usually slow and clunky to deal with (if you can find them at all). Land ID offers these answers, as vague as they may be, much faster and easier than other free alternatives.

How Steep Is Too Steep to Build?

Building on sloped land is a mixed bag.

On one hand, you could get awesome multi-level designs and killer views. But, on the flip side, it can be a construction headache and a pain in your wallet.

machu picchu

The earliest known construction on steep sloping land can be traced back to ancient civilizations, such as Machu Picchu, Peru. This famous Incan city, built in the 15th century, is set high in the Andes Mountains atop a ridge nearly 2,500 meters above sea level. The Incas ingeniously terraced the steep slopes around the city to grow crops, prevent erosion, and stabilize the ground for construction.

How steep is too steep? It's not a straight “the steeper, the pricier” answer.

Gentle slopes (0% to 5%) are easy to build on, but once you start hitting slopes above 15% (about an 8.5-degree tilt), your costs are going to climb—pun intended—fast.

If you're looking at steep slopes over 30% (roughly 17 degrees), brace yourself for heavy-duty construction and a heftier bill.

For a ballpark idea:

  • Flat to Gentle Slope (0% to 5%): Easy-peasy. But if it's too flat, you might have drainage issues.
  • Moderate Slope (5% to 15%): Not too bad. You'll get the perks of drainage and maybe some cool design quirks.
  • Steep Slope (15% to 30%): Now it's getting tricky. Expect some extra costs with more engineering challenges.
  • Insanely Steep (>30%): You're in the big leagues now. You'll need top-tier engineering, construction gymnastics, and a fat checkbook.

Other Important Considerations

While the slope is what we're addressing here, it's important to point out some other factors that will play a role.

Soil Type

Certain soil types can create problems on steeper slopes because they can be more susceptible to landslides.

The suitability of soil for construction, especially on slopes, is crucial for the stability of any structure.

Problematic Soils on Slopes:
  1. Expansive clay: Also known as shrink-swell soil, it expands when wet and shrinks when dry. This can lead to ground movement, which can damage foundations.
  2. Loose or unconsolidated sand: This soil type is prone to shifting, especially when wet. It's also susceptible to liquefaction during an earthquake.
  3. Silt and fine-grained soils: These can be problematic when wet because they have low shear strength, which makes them prone to sliding.
  4. Fill soils: These are man-made deposits of soil or other natural materials used to raise the ground level. If not compacted properly, fill soils can be unstable.
  5. Organic soils: These soils contain much organic matter, like decomposed plants. They can compress under load, which is not ideal for supporting structures.
More Suitable Soils for Slopes:
  1. Rock: Bedrock or weathered solid rock can be an excellent foundation, offering stability.
  2. Gravel and coarse sand: These soils drain well, reducing the likelihood of water-induced landslides. They also have good compaction and load-bearing qualities.
  3. Well-compacted soil: Even some soils that aren't ideal naturally can be suitable for construction if they're well-compacted and engineered appropriately.
  4. Sand and clay mixture: A balanced mixture can provide the right balance of drainage and compaction.

If you're curious about what kind of soil is on your property, Land id can help with that, too! The same video I mentioned above explains where and how to find and make sense of the soil maps around the country. Forward the video to the 7:56 mark, and I'll show you!

Retaining Walls

On steeper ground, you might need these to carve out flat spaces to help create the area you need for construction.

The need for a retaining wall in construction largely depends on the site conditions, soil type, and intended use of the area. However, as a general rule of thumb:

  • For slopes greater than 3:1 (about a 33% slope or roughly 18.4 degrees): Some form of stabilization, like a retaining wall, is often required.
  • Slopes steeper than 2:1 (50% slope or around 26.6 degrees): These slopes are considered very steep, and it's more common to see retaining walls or other stabilization measures in these scenarios.

retaining wall

But remember, these are just general guidelines. The need for a retaining wall can also be determined by factors like:

  1. Soil type: Loose, unconsolidated, or saturated soils may need retaining structures even on gentler slopes.
  2. Load near the slope: If you plan to place structures, roads, or other heavy loads near the edge of a slope, you might need a retaining wall to ensure stability.
  3. Drainage: Proper drainage can reduce the need for retaining walls by preventing water from saturating and weighing down the soil. Conversely, poor drainage can exacerbate erosion and increase the need for walls.
  4. Local building codes and regulations: Different regions have their requirements based on local experiences, studies, and historical events.

If you're contemplating building on or near a slope, consult a geotechnical or civil engineer familiar with local conditions and regulations. They can provide the most accurate advice regarding needing a retaining wall or other stabilization measures.

Drainage, Maneuverability, and Other Considerations

Aside from the specific measurables, there are other practical matters to consider.

  • Drainage: Water and slopes can be frenemies. Make sure water drains away from, not into, your home.
  • Getting around: Imagine hauling bricks and beams uphill. It will cost more time and money and could be problematic in the rain or snow.
  • Red tape: Some local councils are fussy about building on slopes. Check the rules before diving in.

Do you have a specific property or situation in mind? An engineer or architect who has done this kind of work before can give you the lowdown on what you're in for.

Anything Is Possible

At the end of the day, any land can be engineered and built upon, regardless of the slope. It's just a question of how much time, money, and effort you want to spend making it happen.

There are plenty of examples around the world of houses built on cliffs.

cliff house

Photo: Modscape

Anything is possible with enough money and dedication to make it happen, but hopefully, the guidelines above will give you an idea of when the costs will be reasonable vs. expensive.

About the author

Seth Williams is the Founder of - an online community that offers real-world guidance for real estate investors.

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