ADU Construction in Manhattan Beach
ADU construction in Manhattan Beach that starts with level readings and soil probes, with fire-rated walls where the unit sits near a property line.
Before any sketch, we run a level from the curb to the rear fence of a Manhattan Beach lot. That reading shows how much the ground rises or falls across the yard and how the back corner compares with the sewer main in the street. Those readings settle whether a detached unit can drain by gravity and how deep its footings need to go, so they come ahead of any talk about size or layout.
Probing where the footings land
With the levels recorded, a probe rod or hand auger goes down at the corners of the proposed footprint. Firm soil close to the surface keeps the foundation to a simple slab with thickened edges. Loose fill or soft layers push the design toward deeper footings, and the engineer may ask for a soils report before sizing them. We also look at any retaining walls along the property lines. A new unit set close to one adds load behind it, and an old wall that was never engineered may need its own repair before the unit goes up beside it.
Walls close to the property line
Under state ADU law, the side and rear setbacks for a detached unit can shrink to 4 feet. That spacing is tight enough that the residential code treats those walls as fire-separation walls, so they get a rated assembly, often Type X gypsum inside and a rated exterior finish outside. Openings on those sides are limited in size, which shapes where windows can go. We plan the bedroom and bath around that rule early, so daylight comes from the yard side and the plan check comments stay short.
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ADU Construction in Manhattan Beach: questions
That comes down to the cross-slope and the setbacks together. A unit at the low corner may need a sewage ejector if its drains end up under the street main. A unit near the high side may need a cut and a retaining wall. Our level readings show which trade-off is smaller on the particular parcel.
It does, provided the footprint stays at or under 500 square feet on one level. Manhattan Beach plan check reads the wall sections along the property lines closely, so those details are drawn out in full in the set. A larger plan, a second story or a site that needs special engineering is priced on its own.
Grade change sets the foundation scope, with stepped footings on a gentle rise and piers tied by grade beams where the drop is steeper. Shoring or a retaining wall at a cut adds more. Hand-carrying materials past a house with no side access also adds labor, which the walk to the rear makes clear early.
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