Designing a House On a Hill or Sloped Site

The house on a hill. It has great connotations: great views; overlooking your lands; impressive when seen from below.

If your wanting to build a house atop a hill or on a sloping site it’s important to understand how to design on them. You need to know how slopes are described on a plan and then how to work the design into the slopes.

Below we will discuss these issues and then review two projects designed on sloping sites.

Understanding sloping sites

When you’re designing a new house you need to know how slopes work on your property. To do this we have to represent slopes using a series of lines called contour lines.

Contours represent how the land rises and falls and how it undulates across the site. This representation uses a pattern of lines on a plan, each line representing a constant elevation (height) above a given reference point. This means that if you could stand at one point on the site then walk perfectly horizontally left and right of that point, you would be tracing a contour line.

To understand how this is done, let’s take a look at the photo of the hill below.

This hill rises around 300 feet above the farmland around it. To show how the form of this would look on plan we need to draw contour lines. Let’s start with one line drawn halfway up the hill.

This red line represents a consistent height above the surrounding land and shows the undulations around the hill. When you transfer that line to a map of the hill you get the plan below showing our red line along with all the other contour lines that represent this hill.

The vertical increment of the contour lines on this map is 10 feet. You figure out heights by counting the number of lines from a start point and then multiplying by the increment.

The map is from a U.S. government service that uses height increments of a given number of feet above sea level. For our red line above you can figure out what the elevation is by starting with the upper left line marked as 1510 feet above sea level. If you count the number of lines from there to our red line, you get an additional 11 lines.

To get the actual elevation of our red line, multiply the number 11 by the 10 foot increment, which gives us 110 feet above the 1510 line. By adding these two numbers we get an elevation of 1620 feet above sea level.

Analyzing a sloping site

Now that we understand what contours are and how they represent slopes we can look at a site we want to build on.

The property survey below shows contours that rise from the lower right up to the top of a hill in the left corner of the site. Each line is marked with a sequential number representing one foot of rise. From the right-most property corner we can see that the property rises 18 feet to the top of the hill.

We see on the plan below the high point of the hill, the creek ravine to the right of the hill, and how water flows downhill shown by blue arrows. The spacing of the lines denotes the relative steepness of slope in relation to other parts of the site, with closer-spaced lines representing steeper slopes than lines spaced further apart.

Modifying the slope for your house

Now that we have a good sense of slopes we need to understand a few concepts of how you can modify slopes to build a building.

Since floors in building are flat a sloping site needs to be modified to create what is called a building pad. This pad is a flat area created by cutting into the slope to get an amount of dirt needed to then create a flat building pad.

The best thing to do is to balance out the amount of soil you dig out (the cut) with how much you need to pile up onto the slope (the fill) to create the building pad. This process, called cut-and-fill, keeps you from having to bring soil to your property from elsewhere, or to take soil from your site to dump off site. This saves you from spending more money than needed to move dirt.

The amount of slope on a piece of property will influence how a house will be designed. Moderate slopes can allow for lower levels that can open onto the ground making them more livable. Extreme slopes create more challenging efforts such as terracing to balance out the cut-and-fill and to make the lowest level accessible from the lower part of the site.

An alternative to cut-and-fill on an extreme slope is to raise the whole house above ground on piers, as shown in the diagram at the bottom.

Locating your house on a sloping site

Let’s go back to the property with the hill we discussed earlier. Let’s say we want to build a single story house just below the top of the hill. The plan below shows the modified contours, show as darker lines, that give us a building pad large enough for the new house.

To get this pad we cut into the hill and then fill in below the hill to get our pad. We also modify contours for the new driveway and the parking area next to the house shown in the plan below.

Controlling rainwater flow on sloping sites

Controlling water on a any building site is important. Controlling water on a sloping site adds additional complications. If you build below the top of the slope you have to deal with water coming towards your home from above. You have to figure out how to get that water around your house.

The site plan below shows the new house, driveway, and the trees on the site. The contours represent how the slopes work now.

The plan below highlights how we cut into the hill and filled in for the building pad creating shallow “ditches”, called swales, at the bottom of the hill that force water from above to split around the house then continue moving downhill. The building pad, shown in yellow, has been sloped so that water drains away from the house.

Beyond the house, reworking of the contours for the new driveway created another swale on the uphill side of the drive, shown as a blue dashed line. This forces any water above the driveway to flow down a path adjacent to the drive so that the water doesn’t overflow onto it. The drive itself is slightly sloped so the water sheds off the driveway to either side of its centerline.

Options to organize your house on a sloped site

Sloping sites offer several design advantages as well as disadvantages over relatively flat sites. Lets take a look at some of these.

Design advantages can include:

• Improved opportunities for views: Nice views can be taken advantage of in ways they can’t with flat sites. The ability to be higher can create views over trees or other buildings that would otherwise be blocked at ground level.
• Opportunities for unique placement of spaces: If your site is significantly sloped downward from the street you could reverse the traditional upper and lower placement of sleeping and living areas. The upper street level could act as the living level while the sleeping rooms could be placed on the lower level that opens out onto the lower lawn. This creates a “rise up in the morning” lifestyle.
• Garages can be placed out of site: Depending on how your site and house design works, you can place your garage at the lowest level out of site from the front of the house at street level.
• Balconies and living terraces are easier to develop: The ability to create multiple levels provides more opportunities to create outdoor living spaces. Upper living areas can easily be extended for terraces and balconies overlooking dynamic views.
• Livable lower levels can be created: Lower levels that can be opened to a lawn can house both living and sleeping spaces that you’d typically not get with a more traditional “dark” basement, expanding the amount of area you can use for day-to-day life.
• Unique opportunities for yard design: moderate to steep slopes allow for unique design opportunities for yards. Terracing yards and gardens adds a dynamic you can’t get with flatter sites.
• More effective means of draining water from the site: With proper site design sloping sites move water more effectively away from the house and across the site.

Design disadvantages can include:

• Higher construction costs: A house built on a moderate to extremely sloping site will have higher construction costs than one built on a mostly flat site. Cut-and-fill and the need for concrete walls to retain soil at the lower level are more costly than for houses built on flatter sites without basements.
• Site access can be challenging: Designing automobile access to the site can be restricted by steep slopes and tight maneuvering spaces depending on the site, its size, and its slope.
• Inclement weather challenges: Snow removal, icy conditions, and extreme rain storms can require more challenging efforts to deal with than with flatter sites.

Two examples of houses on sloping sites

Below we’ll discuss two different houses that I designed on sloping sites. This will provide a better understanding of how house design adapts to sloping sites.

Creekside House

The 5 acre (1.9 hectare) property plan below is for a building site in a rural subdivision with large acreage lots outside of a large city. The contour lines are shown as dashed lines and have a vertical increment of 2 feet. Most of the site is relatively flat, but then drops quickly down to a creek below on the left side of the property.

When visiting the site the owners decided to place their new house in the lower corner of the site. This would allow for the design of a three level home with the lowest level being a walk-out basement and the main level of the house raised up for a nice view down to the creek and of the trees beside it.

The plan below shows the location of the new home including the driveway from the street.

The red lines in the plan below are the modified contours for the house, shown at 1 foot increments for better detail. Note how the garage that projects out across from the house and house itself were raised up above the surrounding flat area. This allows two things: first, it allows for water to drain away from the front of the house and the garage. Second, it allows the first floor of the house to be raised enough to allow for the walk-out basement.

The drawing below shows a section through the three levels of the house. The dashed line running across the lowest level represents the original slope of the property. Note how the basement floor is actually below the ground level at the left. This was done due to the original slope being a bit too shallow to accomplish the full walk-out.

The cut used to create the basement was used to build up the soil at the front of the house and the garage.

The back of the house facing the creek is shown as an elevation drawing below. It shows how the three levels work in relation to the sloping site. The little dashed lines at the bottom represent the steps that go further down to reach the basement level.

Lakeside House

This house is a very large house built on a 30 acre (12.25 hectare) family estate overlooking a lake. The site is relatively flat but then suddenly slopes down to the lake running from top to bottom of the image starting at the left side of the circular driveway in the image below.

The building elevations below show how the slope works as you go from the front of the house in the top drawing to the back (lake side) of the house in the lower drawing.

The slope from the front of the house is enough to allow for a walk-out basement at the left end of the back of the house, which you can see in the drawing above and the photo below.

Sloped stone walls were used for the exterior of the basement level giving the house a strong visual base to sit upon. The slope of the site allows for a raised view of the lake from the main level. The back of the house takes advantage of this view by the use of a veranda and terraces spanning the length of the house and the ample use of windows.

All photos and graphic images are by Cayl Hollis unless noted otherwise.

Featured image photo by Craig Klomparens, courtesy Tilton, Kelly + Bell