A design-build firm handles design, permits, and construction under one contract. A general contractor builds from plans you get from a separate designer or architect. Design-build is usually simpler for a first ADU. Hiring a designer and bidding the plans to general contractors gives you more control and more price competition, but you coordinate the pieces.
Both models build good ADUs. Here’s how to choose.
How does design-build work?
One company takes the project from feasibility through design, engineering, permits, construction, and final inspection.
Pros
- One point of accountability, with no designer-versus-builder finger-pointing
- Pricing is based on the builder’s own design, so surprises are less likely
- Design and construction planning can overlap, which can save time
- Less coordination for you
Cons
- Less head-to-head bidding on one set of plans
- Your design options are limited to the firm’s style and experience
- The convenience may be priced in, so compare carefully
How does the general contractor model work?
You hire a designer or architect to produce permit-ready plans, then get bids from several general contractors on those same plans.
Pros
- Competitive bids on identical plans make comparisons easy
- Full control over who designs your ADU
- Design and construction costs are transparent and separate
Cons
- You coordinate between designer and builder
- Bidding starts only after design is done
- Anything missing from the plans becomes a change order
Which costs less?
It depends. Bidding plans to several general contractors can produce a lower construction price, but gaps between the plans and the build can turn into change orders. A design-build price may look higher at first while covering more risk. Compare total project cost, including design, engineering, permits, and likely change orders.
Which should you choose?
Choose design-build if: this is your first ADU, your lot has complications such as a slope, septic, or overlays, or you don’t want to manage the project.
Choose a designer plus general contractor if: you have an architect or a clear design vision, your project is straightforward, or you’ve managed construction before.
Consider prefab as a third path. Prefab companies are a kind of design-build with factory construction. See prefab vs. site-built ADUs.
What should you check either way?
- Licensing. The builder needs an active CSLB license, usually a B (General Building) license. Structural calculations are typically prepared and stamped by a licensed engineer.
- ADU history. Ask for finished ADUs, not just remodels.
- The contract. Scope, price, schedule, change-order process, and the California down payment limit of 10% or $1,000, whichever is less.
- References. Call them.
See how to choose an ADU contractor and ADU contractor red flags.
What should you ask each bidder?
For design-build: “For your last three ADUs, what was the promised timeline and cost, and what did they actually come in at?”
For general contractors: “On your last three projects built from someone else’s plans, how many change orders were there, and why?”
Want to talk to a local ADU contractor?
Call (661) 486-8393. If no one answers, leave a voicemail with your name, phone number, address, and the type of ADU you want. You can also use the contact form. We’ll pass your details to a local ADU contractor, who will follow up with you directly. There’s no obligation to hire.
Design-build vs. general contractor FAQs
Is design-build more expensive?
Not necessarily in total. It can cost more up front but may reduce change orders. Compare total project cost.
Do I need an architect for an ADU?
Not always. California doesn’t require a licensed architect for most wood-frame single-family dwellings up to two stories, which typically includes ADUs. You’ll still need structural engineering where calculations are required.
Can a design-build firm handle my permits?
Yes. Most design-build firms prepare and submit the permit application and respond to corrections.
How many bids should I get with the general contractor model?
Getting more than one bid on the same plans lets you compare price and exclusions directly.