High on our list of priorities for the project have been sorting out our sloped lot’s drainage and ensuring that the structure sits on the lot properly. To accomplish this, considerations need to be made in optimizing site excavation to limit engineering requirements and dirt removal from the site.
We sat down with our consultants to review the preliminary concept for the house’s footprint, and made good progress brainstorming and understanding how to address the terrain.
Because of the length of the house and the desire to have backyard space, a large volume of ground will need to be excavated. Once removed, retaining walls will need to be added to shore up the edges of the excavations. In our area, retaining walls lower than 4’ tall do not require an engineering stamp, so the concept of the process was made to include multiple terraced retaining walls, approximately 4’ high and at least 5’ of green area on top before the next step in the terrace. This method also lends itself aesthetically to the property and will allow for nice steps between levels and plus a pleasant water feature.
Once we had the general understanding of the terrain, we began looking at numbers to identify the approximate amount of ground to be removed to achieve the correct elevations for the structure. We used the Primary Terrain Contours from our plan and discussed the location of the floor for the house. The terrain retaining walls and elevations were sketched onto a piece of vellum overlaying our print.
We were able to identify two areas to limit our total cut:
- We decided to move the entire house forward 11 feet. This will reduce the total amount of soil to be removed from the backside of the hill and allow us to use some of the cut soil as fill for the front pad of the house, and it will create flat areas for a small front yard and driveway pad. This approach also means that less soil overall will need to be removed from the site, further reducing costs.
- We will keep grade at the back corners of the house a few feet above the floor platform. In order to achieve this without creating a stepped wall inside the house, due to the differing thicknesses of the framed wall and concrete stem wall, the Architects introduced us to a foundation wall assembly that is a clever and graceful approach. In concept, a 6” concrete retaining wall is constructed from crawlspace footing depth to the top of grade. It has an extra wide footing offset to the interior of the house. A framed load bearing wall is built on the footing to crawlspace height; this supports the platform. The result is a pair of walls with the outer concrete wall shorter and capped 6” above grade, with the framed wall extending the full height to the roof. View the CAD detail
Our changes to the terrain design will add retaining walls in the front and sweep the driveway forward on the lot. The lot has an approximate 22 degree slope; any lot over 18 degrees requires a storm water management plan stamped by an engineer or landscape architect. We will be using a firm to complete this requirement before submitting the site plan to the building department.
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