![]() ![]() Tim Healey Secured by helical tie-backs driven to refusal into the strong, rocky soil under the house, the steel-reinforced shotcrete retaining wall had the strength to hold gravel backfill, support the soil under the house footings, and serve as a foundation for a new wood deck to be constructed later in the house rehab project. ![]() After extensive back and forth with the structural engineer (considering concrete piers, steel reinforcement cages for the garage, or garage replacement), we concluded that a three-sided retaining wall-doweled into the existing structure, with helical tie-back soil anchors for supplemental strength-above the garage could support the house and the soil above the garage, and provide a foundation for a front-yard deck-triple duty. While hillside houses in our area typically rest on concrete piers, they would not be able to support the soil cut above the garage, leaving that structural problem unsolved. Meanwhile, I considered how best to support the house. With proper drainage and upwards of 20 cubic yards of soil removed from the roof, the garage will be far more robust. Our plan is to remove the torchdown material, correct the roof slope with lightweight concrete, and restore the roof’s waterproofing. The slope of the garage roof was inadequate in several parts of the area we uncovered, allowing water to pool on it. With the soil removed, we learned that the garage had previously been unearthed and reroofed with torchdown material, and the soil replaced as loose fill-which provided little or no structural support for the house above it. When soil on top of the concrete garage roof, downslope of the house, was excavated, the garage roof was found to be in need of repair to restore effective drainage and waterproofing. In order to waterproof the garage and to relieve some strain, we dug the back half of its roof out of the hillside, leaving a 7-foot-tall-by-12-foot-wide soil cut above the back wall of the garage and tapering cuts on either side. The garage had significant water leaks at the back and was showing signs of stress. Because I was concerned about settling in what looked like loose fill, we dug the footing of the foundation to 24 inches below grade (rather than the typical 12 inches permitted by code). We raised the corner of the house by 6 inches to level the floors trimmed and raised the bottom of the cripple wall to remove rot and increase separation from grade and replaced large portions of the foundation. In the vicinity of the garage, the house foundation had settled noticeably, with the wooden cripple wall between the foundation and the framed floor nearly submerged into the soil. The existing home’s shallow foundation was lightly built in the 1920s, and the building’s floor system and cripple walls had been buried in accumulated soil and were damaged by dry rot. ![]()
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