New Construction in Hermosa Beach: House and ADU in Order
The order of work when a new Hermosa Beach house and an ADU go up together: shared trench, rough inspections, then the house final before the unit's.
A house and an ADU going up together on a Hermosa Beach lot follow a sequence the permits enforce. The shared utility trench goes in before either slab, both frames rise in step, and inspections run side by side. At the end, state ADU law lets a city hold the unit's certificate of occupancy until the main house has its own, so we plan the schedule backward from that last sign-off.
From trench to dry-in
Demolition and utility disconnects clear the lot, then the soils engineer's grading recommendations shape the pad. Water, sewer, power and gas for both buildings go into one trench run, inspected before backfill. Footings for the house and the unit can be poured on the same delivery day. Framing follows, then roofing, windows and the water-resistive barrier, so each shell is dried in before the interior trades arrive. Near the ocean, flashing and fasteners at this stage are chosen to resist corrosion, since they sit behind the finish for good.
Inspections and the last weeks
Rough plumbing, electrical, mechanical and fire sprinkler inspections happen in each building, and insulation is checked before drywall. Finishes then run in parallel. The house reaches final inspection and its certificate of occupancy, and the unit follows. Comparing ADU types matters here too: a JADU finishes with the house because it sits inside it, an attached unit shares many inspections, and a detached unit or a garage conversion keeps its own sequence. Knowing which type is planned lets us book inspectors without gaps.
New Construction in Hermosa Beach: common questions
Building both at once pays off where zoning on the parcel allows a unit: one trench, one concrete schedule and shared inspection visits, which avoids a second round of site work. Adding the unit later repeats mobilization and digging. The City of Hermosa Beach reviews the parcel's allowances, and coastal rules are checked if the lot lies in the Coastal Zone.
Lot lines, soil data and utility capacity are gathered at the start. Design covers both buildings, the coastal permit is handled early where the parcel requires it, and the full set goes to the city building division. Demolition permits and utility disconnects come next, and grading starts once the building permit is in hand.
Solar, sprinklers and water measures for both the house and the unit come from the state's residential, energy and green building codes. City zoning decides height, setbacks and lot coverage. Exterior assemblies are specified for salt exposure, and the parcel's Coastal Zone status decides whether a coastal permit is needed.
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