Alterpex
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Alterpex is a California-based design and documentation firm that has narrowed its focus to a single residential niche: accessory dwelling units. The company is headquartered in Valencia, California, with additional offices in Los Angeles and San Francisco, giving it genuine reach across the state's three major metros. Alterpex's deliberate positioning as ADU-only designers sets them apart from generalist architectural firms that offer ADU work as one of many services. They explicitly state on their website that they focus only on ADU design and do not build, manage construction, or act as a general contractor, which removes any ambiguity about what you're buying.
The core offering is a full design workflow from site evaluation through permit-ready construction documents. When you start a project with Alterpex, they begin with a site evaluation and feasibility study to understand your lot, zoning constraints, and what's realistic. From there, they move into custom floor plan development, 3D modeling and visualization, and code compliance review. The output is a complete set of permit-ready construction documents that you can use to submit to your municipality for approval. They also coordinate with structural engineers and MEP consultants as needed, which is important because ADU permits often require engineer stamps on the structural and systems drawings, not just architectural documents. If you need it, they can provide construction supervision to oversee the build once you've hired a contractor, though this is additional to the core design work and they do not act as the general contractor themselves.
The pricing baseline is a $2,000 minimum project cost, which is on the lower end of the ADU design market and signals they're willing to work on smaller, simpler projects. The final price depends on project scope and complexity, but they indicate most ADU design projects complete in three to six weeks depending on the complexity and number of revisions required. They also mention faster timelines if you select one of their pre-designed ADU plans rather than commissioning a fully custom design. This matters if your schedule is tight. Alterpex's service area covers multiple California regions including Los Angeles, San Diego, San Jose, San Francisco, Sacramento, Beverly Hills, Malibu, Santa Barbara, and Palo Alto, which means they have both breadth across the state and deeper familiarity with multiple regional jurisdictions and their specific ADU regulations.
What distinguishes Alterpex beyond the ADU focus is their background in BIM (Building Information Modeling) and construction technology. Their main business includes 3D laser scanning, as-built documentation, drone services for site inspection, and coordination of complex construction documents. This technical foundation carries through into their ADU work. When they produce a 3D model of your ADU, it's not a pretty rendering alone, it's a coordinated model that helps catch conflicts between architecture, structure, and mechanical systems before drawings go to permit. This reduces the risk of resubmittals due to clashing disciplines.
The service area advantage is real. ADU regulations vary significantly by city and county even within the same metro area. Los Angeles County cities have different unit size limits than San Francisco, Sacramento has different standards than San Diego. Alterpex's multiregion presence means they've worked within multiple jurisdictions and can advise on what's achievable in your specific location. This is more valuable than a firm that operates in just one or two cities and may have less familiarity with your local rules.
Like most design firms, Alterpex doesn't publish detailed pricing for specific design packages or plan sizes. You contact them with your project address, scope, and square footage target, and they provide a customized quote. This approach is standard for architectural work and reflects the genuine variation in complexity between projects. A simple garage conversion is dramatically simpler than a new detached ADU with full mechanical systems. The lack of transparent tiered pricing is a practical trade-off for accuracy, though it does mean you'll need to reach out for a quote rather than seeing an instant number online.
Compared to marketplace-based plan sellers like those that operate at the national level, Alterpex is a design firm for hire, not a plan catalog. This means your drawings are custom to your lot, your jurisdiction, and your needs, not an off-the-shelf template. For permit approval, this is a meaningful difference. A template plan may not match your setback requirements, your site's slope, or your city's specific details. A custom design from Alterpex accounts for all of those from the start, which typically means faster permit approval and fewer rounds of corrections.
The construction supervision option is worth noting. Many design firms offer it as a premium service to oversee quality and catch problems during framing, MEP rough-in, and other critical stages. Alterpex positions this as available but optional, which means you can hire a design firm and supervise the build yourself, or hire a project manager or construction overseer separately, or use their supervision. Having the option without being forced into an upsell is practical.
The feasibility study that launches every Alterpex project is a concrete value-add. Many homeowners approach an ADU designer with fuzzy goals, half-baked lot measurements, and no clear picture of what the city actually allows. Alterpex's initial study forces clarity: they measure, map zoning setbacks, research local ADU ordinances, and produce a written assessment of what's possible. This document protects you from spending months and money on a design that turns out to violate local rules. It also anchors the design process because both you and the designer start from shared, verified facts about the property instead of guesswork or outdated information.
Alterpex works well for homeowners in California's major metropolitan areas who want a full-service design firm with genuine ADU specialization and deep knowledge of multiple jurisdictions. Their commitment to design-only means you retain control of the permitting and construction phases, and their BIM background suggests rigorous coordination of design disciplines. At the lower end of pricing in this category, they're accessible even for modest accessory unit projects. If your location is outside their current service region, they indicate they provide services nationwide, though their strongest presence and expertise is in California where they're based. For a first-time ADU designer in Los Angeles, San Francisco, Sacramento, or San Diego, Alterpex combines local jurisdiction expertise with the efficiency of a firm that has streamlined its entire workflow around accessory units.