Home/Where we build/Topanga
Hillside home builder in Topanga, for canyon lots the County looks at closely.
Steep ground, septic, a fire road for a driveway, and a coastal plan over all of it. Addition Building & Design is a family-run design-build firm with forty years as a builder in Los Angeles, and hillside foundations on both sides of this range.
Photograph · a canyon in the Santa Monica Mountains from the air, 2026
Topanga
A canyon is a hillside with fewer ways in.
Topanga is unincorporated, so the County of Los Angeles permits it, not the City, and the rules are the County's: its building and planning departments, its fire department's say on access, water and defensible space, and its coastal plan for the Santa Monica Mountains over much of the canyon. Most lots are on septic. Many are reached by a road the fire department has an opinion about. The house you can build here is decided by those reports before it is decided by taste.
We have not built in Topanga yet. We have built the same ground next door: hillside and canyon lots in Pacific Palisades and Malibu on the coastal side of this range, the Hollywood Hills and Mount Washington on the city side, Bel Air between them. Mike Ross holds the license, signs the contract, settles the design with our design partners, has it engineered by our structural engineers, pulls the permit and walks the site. Christine Ross is the first call and the standing one.
The hillside work
The same slopes, on either side of the ridge.
Caissons and grade beams
What a canyon house stands on. Engineered to the soils report, inspected before the pour.
Mount Washington hillside
A terraced canyon lot on the city side of the mountains.
Palisades canyon, under way
A rebuild on a canyon lot above the bay, framed in August 2026. Ask and we will walk you through it.
What a Topanga build involves
Four reports before a floor plan.
The County path
County building and planning, the fire department's review, and the coastal plan where it applies. The forms, fees and timing differ from the City's, and the sequence matters. We file in the right shape for the right office.
Septic
The septic feasibility can set the size of the house and where it sits on the lot. The engineers settle it first, not after the floor plan is something you love.
Access and water
The fire department reviews the driveway's grade and width, the turnaround, and the water available for fighting a fire. On a canyon lot those reviews can reshape the site plan, so they come early.
The ground and the code
The soils report decides the foundation; the wildfire code decides the assemblies, the vents, the glazing and the decks. We design to both from the first sketch. Rebuilding in Topanga after fire.
A family firm
Canyon owners want a builder who will actually drive up.
Four to five projects a year, because that is how many the family can personally be present for. A builder with forty years in Los Angeles, a daughter carrying the firm forward, and one phone number: 310.617.2722.
Questions Topanga owners ask us
Before you buy the lot.
Topanga is unincorporated, so the County of Los Angeles does, through its building, planning and fire departments, and much of the canyon falls under the County's coastal plan for the Santa Monica Mountains. We confirm which reviews your lot triggers before the design starts.
Our hillside work is next door and across the city: Pacific Palisades, Malibu, the Hollywood Hills, Mount Washington, Bel Air and the canyons above the valley. Ask us and we will walk you through a canyon lot we are building on now.
Usually, and the answer comes from three reports before any drawing: the soils report, the septic feasibility and the fire department's access review. We order them first, because they set the size of the house and where it can sit.
Every home we build in Topanga is detailed to California's wildland-urban interface standard, and the County fire department reviews access, water and defensible space alongside it. It is the floor, not an upgrade.
After we have stood on the lot and read the survey, the soils report and the septic feasibility. Then a line-item, fixed scope, a date when the price locks, and every change in writing before it happens.
Elsewhere on the coast and in the hills
Hillside construction
Caissons, grade beams, soils reports and the ten hillside projects behind them.
Private Consultation
Begin with a conversation.
We take on a select number of significant projects each year. If you are considering a custom estate, a hillside build, or a full transformation, we would be glad to walk the property with you.