Things to Consider When Building a House on a Sloped Building Site

How the Right Planning Can Make Building a House on a Steep Site a Success

A client of mine asked me the other day if I found designing houses for sloped building sites challenging. It was at that moment that I realized I had only designed one house on a flat site since starting to work in the Cincinnati/Northern Kentucky area 6 years ago after I relocated from the mountain west. All of the other dozens of home I’ve designed have been on varying degrees of sloped sites.

 Our region is made up of a series of rolling hills and meadows making flat lots a rarity for those currently building homes. Many sloped building sites in our region are safe to build on and can make for an interesting backdrop for your dream home. Some building sites make the design and construction process a little more challenging, which is when a geotechnical investigation may be required. Your architect will do a preliminary assessment to determine if a geotechnical report will be required for your property. Some local jurisdictions require a geotechnical report with the building permit drawings if the area is known to have problems that could impact the foundations of the building.

 Kentucky and Ohio’s oldest rocks were formed during the Ordovician Period that lasted 45 million years. Throughout the following Paleozoic period shallow seas covered the area, depositing marine sedimentary rocks such as limestone, dolomite and shale. This why we find so many fossils in rocks at the earth’s surface. Fun trivia fact: Kentucky was the first state to be fully geologically mapped. During the Middle Devonian period, massive limestone formations took shape which now form much of the state’s Karst topography which is prevalent farther south in the Louisville area and beyond. Karst topography generally refers to an area where limestone and bedrock have eroded beneath the earth’s surface in an irregular way.  It is important to know if your site has Karst topography as it can have huge implications for building on the site. If you suspect you have Karst topography on your building site you will need to hire a geotechnical engineer who will determine if it is safe to build on your site and will guide the architect to locate the house in a safe zone, as well as guide the structural engineer to design for the type of foundation you will need. If you have any caves on your property this could be a sign that Karst topography and sinkholes could be present. It is also sometime best practice before purchasing property to create a clause in the purchase agreement that purchasing the lot will be pending the findings in a geotechnical investigation. Sidebar: Most architects are available for hire on an hourly basis as a consultant to help you find the perfect building lot.

 Once you’ve found your perfect sloped building site you will work closely with your architect to start developing the program (*Protip #1) for your home. When designing a home on a sloped site your architect will start by assessing the best way to get a driveway to the home while studying the site grading (the slope of the earth/dirt) needed to achieve access to the house that is not too steep for a car or the builder’s equipment. Oftentimes the best location for the driveway and garage will dictate the initial concept for the home design.

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After the access to the site has been located your architect will work with you to start arranging different rooms in your program and do bubble diagrams of desired adjacencies (*Protip #2). We will study stacking: for example, you might not want the kids’ rumpus room above the master suite unless you like the sound of an elephant stampede while trying to sleep in on Saturday mornings. The bubble diagrams will inform the next phase of design where real walls and windows begin to be placed. Here at PCA Architecture we study adjacencies with a series of massing models that can show you the approximate size and location of the rooms in your house without getting too specific with the form.

 

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During the programming phase your architect will also need to know how long you plan on being in the home. I always like to ask people if they plan on going out “feet first”. If so, we will need to make accommodations for potentially maneuvering into and through the house with a wheelchair or walker which will make for aging in place a lot easier. If your garage is located on a lower level, as sometimes makes the most sense on a sloped lot, we can easily make space for a small elevator chase in the preliminary design phase. Even if you choose not to install the elevator in the first phase of your construction project, we can design the elevator chase and have it built when the home is initially built. This will make the installation of an elevator in the future when you need it fairly simple.

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An important item we consider during the initial design phase happens while we study the house in a site section. We try to keep all of the foundation walls 10’-0” tall or less. Once a concrete foundation wall gets over 10’ tall the cost rises exponentially. By limiting the site work and height of foundation walls though thoughtful site design it allows you, the homeowner, to save a lot of money. One of the most commonly requested and erroneous solutions to building on a sloped site is to “create a flat area to build the house on in the middle of a hill”.  This is a very expensive option due to the amount of earthwork required.

 

One of the biggest ways we bring value to the project and work to save our client’s money is by working with the land, not fighting it. We allow the land be our guide for the design. We never recommend taking a home that was designed for a flat building site and plopping it onto a sloped site. This rarely works out well. One huge cost for building on a sloped site is the site development cost. The site development costs include:

  • Grading (moving of the earth) done by an excavator on large machinery.

  • Cutting in and building the driveway

  • Constructing swales to divert water away from the home

  • Constructing retaining walls

  • Getting utilities: water, gas, sewer, electricity to the home.

 

The less we try to modify the slope of the site, or create a hill where there wasn’t one before, the more cost effective it will be to build your home. And more importantly, your home will be authentically influenced by its unique building site and be more architecturally significant and interesting. The more economical the site development costs are, the more money you will have to spend on fun things like rain showers, high-end appliances and that indoor slide you’ve always wanted.

 

*Protip #1: The Program is a list of all the rooms you want in your home with approximate size.

For example:

            Master Suite:

  • 16x16 bed area

  • 8x10 walk-in closet

  • Master Bath:

  • (2) vanities

  • Soaking tub

  • Flush entry shower 3x5

  • Separate toilet room

 

*Protip #2: Bubble Diagrams

  • Bubble diagrams are just what they seem - quick and dirty sketches that show approximate size and adjacency of the home. For example - you prefer for the kitchen and great room to face certain desirable view of the property.

 

Emma Adkisson