How We Fixed a Shifting Foundation at our Home on Carriage Dr.

The following story is about a subject that has bedeviled and been costly for residents of Rose Hill and neighboring communities for more than 50 years. Side and rear walls of homes have collapsed because of shifting clay in developments that were zoned in the 1960s and before. Properties that were zoned then but not developed until later have resulted in slides, particularly those home built at the bottom of a hill. That is apparently what happened in this case when the upper slope was developed after the approval of engineers, both public and private, that were involved in the process. I was a member of the Fairfax County Planning Commission from 1975 to 1995 and tried, along with then Supervisor Joe Alexander and many interested citizens, to avoid development on marine clay and steep slopes. We weren't always successful because of land values and engineers' reports that the clay issue could be contained. This story should be required reading for all engineers and residents who are involved with properties that include marine clay.  

- Carl Sell, President, Rose Hill Civic Association

Creaking floors at night? Unexplained knocks in the wall? Who you going to call? For Peter and Rhiannon on Carriage Drive, the answer was not Ghostbusters, but a foundation specialist. Soil in our area has large amounts of clay. When wet, this clay expands; when dry, it contracts. Over time this process pushes on walls and causes sinkage below foundations.

The couple's house had classic signs of foundation damage: doors and windows that were stuck, cracks in the drywall at the corners of window and doorways, and squeaky, uneven floors. There were three problems: 1) the foundation in two corners had sunk, 2) the back wall built into the hill was pushed inward, and 3) and the grading around the house had deteriorated, preventing water from running away from the house. The couple spent a year planning the work, obtaining quotes, and evaluating contractors, eventually signing a contract with Structural Repair & Renovations.

The first step was to stabilize the foundation. Work began in November 2024, when the crew excavated the perimeter of the house to access the concrete footing. To prevent the foundation from sinking, twenty-six piers were driven into the soil around the house and secured to the footing. To keep the back wall from moving inward, ten composite straps were installed inside from the footing to the sill plate.    Exposing the back wall showed the damage was greater than anticipated, and rebar and concrete columns were cast into a portion of the back wall to strengthen it.

The next step was to prevent water buildup around the foundation. The crew applied heavy, multi-layered waterproofing around the house to direct water down along the walls to an exterior French drain at the base. Then the excavation was backfilled with gravel to allow water to filter down to the drain, preventing the hillside from expanding and contracting into the walls.

Lastly, to direct water away from the house, the entire property was regraded, and downspouts were buried and directed away from the house.

Exposing so much of the structure of the house was an opportunity to add a personal touch and prepare for future additions. A slab was poured along the   entire length of the front to provide a concrete porch. The side exit into the hillside was expanded to prepare for a mudroom and kitchen expansion addition. The air conditioner was moved away from the bedrooms to reduce noise at night. Two windows were added to the lower level to increase natural light. Walls from a previous remodel that overly divided the lower level were removed. Finally, the structure of the rear deck, which had deteriorated, was rebuilt.

The project spanned three months, and the couple spent two and a half weeks out of the house while the inside portions of the work (removal of walls and drywall, installing new windows, and reinforcing the back wall) were underway. While it was a large undertaking, the house is better for the work and the bumps in the night have disappeared.

(Photos: Peter Knudtson)