Karen asks: We are considering buying a property that’s labeled as “gently rolling”. Do we need a builder to look at it in order to tell us if a walk-out basement is possible? How much slope is required?
Steve Bliss, of BuildingAdvisor.com, responds: Assuming an 8 ft. foundation wall, and assuming your foundation projects one foot above grade at the front of the house, you need approximately a 7 ft. change in elevation from the front of the house to the back for a walkout.
Much more slope than that would be expensive to build on and might require expensive retaining walls. A little less slope (4-6 ft.) is fine as the house can be raised in front, or the grades adjusted a bit in the finished grading. In general, walk-outs are a little more expensive to build in cold climates as deep footings are required on the walk-out section of the basement.
As to whether you have enough slope at your desired house site, you might want to have a builder or house designer take a look. There are often constraints as to exactly where on the lot you can build a house. These include setbacks, septic location, drainage issues, road access, etc. On smaller lots, there are only one or two practical places to site a house, so you would need establish at least a preliminary house site before addressing the walk-out issue.
See also Building On A Slope
Kenny says
Should I Level Sloped Lot or Build Walk-Out?
My wife and I are considering buying a lot that is sloping towards the rear at about 9% by my estimations. My question is will we be required to have a walkout basement, or can leveling be done? Is one option cheaper than the other in general?
buildingadvisor says
That’s a pretty mild slope, so you will not need a walk-out. In fact, a walk-out is much easier to build with a slope of 15-20%. For a typical 8 ft. foundation wall, you need about 7 ft. of drop in grade from front to rear grade.
A moderate slope is good for site drainage. It’s easy to get water away from the foundation and to direct foundation drains to daylight. If you want a level yard, you will need to bring in fill or cut-and-fill with materials already on site. You may want to consider level front and rear yards with a small retaining wall or landscaped slope.
Costs are very dependent on the local availability of fill materials. In cold climates, a walk-out requires additional excavation and concrete on the low side to keep the footings below the frost line. Cost-wise, a walk-out is often cheaper, depending on the grade and cost of fill.
Best to check with a local excavation company for realistic local costs in your area. You can read more on sloped lots at this link.