My clients purchased a site in a well-established neighborhood in a Seattle suburb.
Managing the runoff is a matter of great concern and may affect the safety of hundreds of people nearby. Since the footprint of every house (and its driveway and sidewalks) replace permeable (absorbent) ground surface with impermeable surface, water running off the impermeable surfaces can cause the soil to become over-saturated, weaken, and slide. In these environments, special care must be taken to ensure that foundations are supported by more stable soil or bedrock and that the foundations are designed with adequate strength to resist the forces of shifting soil around them. The steeper the slope, the greater the danger.Īny disturbance to the ground during construction- excavation and backfilling, especially during spring or any rainy period - disturbs the site’s static state and may pose a real and sudden danger to construction crews. Landslides occur when these soils become saturated and heavy, and gravity beckons. Soft soil not retained by ledge or deep-rooted trees on steep slopes is prone to dangerous landslides that can affect areas tens of times larger than a single home site and may impact hundreds of lives. What are the issues of building on steep slopes? This is a long post, so if you don't have the time to read this over a nice cup of tea, go directly to the last section, “Tips for building site hunters regarding steep slopes” … and please return later to read the entire piece! What are the concerns with building on a steep slope how are they addressed and what is the cost of addressing them? Building on steeper slopes often presents challenges, and this type of construction is carefully regulated by local jurisdictions that vary, as do local soil types.Ĭodes that restrict building exist to protect the environment and the people who share it.
The ideal slope for in-ground building is a slope of 5 to 7 feet through the width of the house, or 15% to 20%. A more measurable benefit of building into a slope is often reduced heating and cooling expenses -and added comfort- that result from the temperature of the soil five feet below grade (the “outside air temperature” of these spaces) is a constant 52 degrees year-round. And if properly designed, the in-ground living area can be bright and spacious.Įnvironmentally responsible site design begins with minimizing disturbance to any site, and working with the existing topography is an essential ingredient. Building into a gentle slope can enhance the efficiency of a design by providing living space inside the foundation and requiring less additional material and labor than the same amount of space above grade.
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