What does a custom home actually cost to build here?

Methodology

How we price a custom home in Altadena

Most builders will not put numbers on a website. We think that is backwards. Below is the actual logic behind the calculator above: the five categories that move a custom home budget in the San Gabriel foothills, and roughly how much each one moves it. The estimator applies these same factors to your answers — nothing is hidden behind the form.

1. Home size and the base cost per square foot

Every estimate starts with conditioned square footage multiplied by a base rate tied to your level of finish. Our working bands are approximately $425 per square foot for a refined standard build, $575 for elevated custom, $750 for high custom and $950 and up for architectural, ultra-custom work. Those rates cover the shell, structure, systems and interior finishes at that quality level.

Square footage is not linear in your favor. Fixed-cost rooms — kitchens, bathrooms, mechanical rooms — carry a disproportionate share of the budget, so a 2,400 sq ft home rarely costs two-thirds of a 3,600 sq ft home. Growing a plan usually adds the cheapest square feet in the house; the expensive ones were already there.

2. Architectural and structural complexity

Complexity is the quietest budget driver, because it never appears as a line item a homeowner recognizes. Multiple roof planes, cantilevers, long clear spans, exposed structure, curves and non-rectilinear geometry all mean more engineering, more steel, more framing labor and slower weather-sealing. In our data a highly sculptural design runs roughly 12 to 22 percent above a comparable simple form, and a genuinely simple rectilinear plan with one roof pitch can come in about 6 percent below.

A second story adds around 6 percent over a single-story home of the same size — stairs, taller framing, second-floor plumbing and drainage, and more expensive access for every trade.

3. Windows, doors and glass

Glass is the single largest swing available to a homeowner in Southern California, because the climate invites it. A conventional punched-window package sits slightly below our base rate. Oversized aluminum-clad units add roughly 5 percent. Multi-slide and lift-and-slide walls of glass add roughly 14 percent, and thermally broken steel or minimal-frame systems can add 26 percent or more.

The cost is never only the unit price. Big openings mean headers, moment frames, larger foundations, specialized installers, flashing details that cannot be improvised, and lead times that shape the entire schedule.

4. Kitchens and bathrooms

These rooms are priced as dollar adders, not percentages, because their cost tracks the program rather than the house size. In current Altadena-area pricing we carry roughly $65,000 for a semi-custom kitchen, $135,000 for fully custom cabinetry with integrated appliances, and $235,000 for a chef's kitchen with a scullery.

Bathrooms carry about $42,000 each beyond the first two. Every additional bath is plumbing, waterproofing, tile labor, glass, ventilation and fixtures compressed into a small footprint — the highest cost per square foot in the house.

5. Site conditions, access and approvals

Two identical houses on two Altadena lots are not two identical projects. A flat lot with easy street access comes in about 3 percent under our base rate. A steep hillside site adds around 15 percent for excavation, caissons, retaining and crane work. Add a narrow street with nowhere to stage material and it approaches 24 percent.

Approvals matter too. Hillside and fire-severity overlay requirements add roughly 5 percent in hardening, access and compliance work, and a discretionary or historic review path adds about 9 percent along with months of schedule. Exterior scope — driveway, hardscape, planting, pool and outdoor living — is carried separately, from about $45,000 for a minimal program to $315,000 and up for a full outdoor build.

Why the range is ±15%

Before drawings exist, twelve inputs cannot produce a single defensible number. A ±15% band around the midpoint reflects the real accuracy of pre-design estimating: material and labor movement, unknowns below grade, and the dozens of selections that have not been made yet. As drawings develop and we price real scopes with real subcontractors, that band narrows.