Golden State ADUs is a full-service accessory dwelling unit (ADU) design-build specialist serving Cool, California. We specialize in ADUs and nothing else. We are your ADU builder and your ADU contractor in one company: architectural design, structural and civil engineering, county permitting, and construction all happen under one agreement with one accountable team.
Here is the short version for any homeowner deciding who to hire. We are licensed and bonded (LIS. #1125656), trusted by 100+ happy customers, and every ADU project we complete carries a 10-year structural integrity warranty plus a 1-year fit-and-finish warranty. Cool is an unincorporated community in El Dorado County with no municipal building department of its own, so the permit for your accessory dwelling unit goes to the El Dorado County Planning and Building Department. We prepare that submittal, answer the county’s comments, and carry construction through to final sign-off. Permits, paperwork, compliance, done for you.
The easiest first step is a free consultation: a 1-hour project walkthrough on your property. You get a parcel-specific read on what your land can support, with no obligation to build. See our full ADU services or book a consultation.
Accessory Dwelling Units for Cool Properties: Design, Permitting and Construction
Every ADU type below is designed, engineered, permitted, and built by the same team. You will not hire a separate architect, a separate engineer, and a separate permit consultant, then spend your weekends keeping them in sync. One ADU contractor owns the entire building process from first sketch to final inspection, and we walk you through the ADU options that actually make sense for your lot.
Detached ADUs, Attached ADUs and Custom Living Space
A detached ADU is a standalone house on your own land, built for rental income, guests, or a quiet workspace away from the main house. Detached ADUs average around 750 square feet of additional living space, which comfortably holds a full kitchen, a bathroom, a bedroom, and a real living area. Attached ADUs share a wall with the primary house, and an attached ADU can be the smarter build when septic location, slope, or long utility runs make a standalone structure expensive. Building detached ADUs on foothill acreage often comes down to where the usable ground is rather than how many acres you own. Whether the right answer is detached, attached, or a conversion, every layout we produce is drawn for your parcel and your finish level, from cabinetry and flooring to exterior materials that suit a foothill property.
Garage Conversions and Accessory Structure Conversions
Many Cool properties already carry a structure worth evaluating, and garage conversions are often the shortest route to finished living space. Housing around Auburn Lake Trails includes ranch-style homes, wood cabins, custom homes, and properties with equestrian facilities, which means garages, barns, shops, and outbuildings are common. Before we design a garage conversion ADU, we check permit history and whether the existing structure can reasonably meet local building codes for foundation, framing, egress, insulation, and utilities. Garage conversions also raise a parking question, and California ADU law has narrowed when replacement parking can be required, so we confirm what applies to your property during design rather than at plan check. Sometimes the honest answer is that new ADU construction is the better value. We will tell you that early.
ADU Models: Studio, 1, 2 and 3 Bedroom Units for Family or Rental Income
Our ADU models run from compact tiny homes and studios through three-bedroom accessory dwelling units, and the right configuration usually follows the purpose rather than the square footage. A studio or one-bedroom is efficient space for rental income. Two and three-bedroom units suit a grown family member or a long-term tenant. Senior-friendly ADUs are planned for aging in place, with level entries, wider doorways, curbless showers, and a layout that works with a walker. Call it a granny flat or a parents ADU, it remains one of the most popular reasons homeowners build, giving aging parents independence on the same property and keeping a multigenerational family close without anyone losing privacy.
ADU Plans, Pre-Reviewed County Plans and Custom ADU Design
El Dorado County offers pre-reviewed ADU plans, and we will tell you plainly whether one suits your parcel or whether a custom ADU serves you better. Either path, the county’s checklist still requires project-specific documentation covering the site plan, solar, fire, and related items, so a pre-reviewed plan shortens drafting rather than erasing the submittal. Most single-family and multi-family residential lots in California are eligible to build an ADU under state law, part of a broader push to expand affordable housing supply, which is why the real question is almost never “am I allowed” but “what fits here.”
Permitting and Compliance, Done for You
Permitting is the part of an ADU project homeowners dread most, so we absorb it completely. We assemble the permit application, submit it, own every county comment and correction, and schedule inspections. We handle permits start to finish, including coordinating fire, solar, and septic review, all three of which El Dorado County identifies as possible ADU requirements. The county also warns that parcels in historic, medium or high fire-hazard, flood, or airport-review areas may require additional documents. We confirm zoning and setback compliance against local codes, plan for any electrical, water, or sewer upgrades the new unit triggers, and handle the distinct secondary address every new California ADU needs.
Interior Design Bundles and Post-Project Support
Our interior design bundles cover curated furniture layouts, material selections, and finishing details, so a rental unit is ready to list and a family unit is ready to live in. After handover, construction administration keeps us reachable, backed by the 1-year fit-and-finish warranty.
Why Cool Homeowners Choose Golden State ADUs as Their ADU Builder
The single biggest advantage we offer is that nothing gets handed between firms. Our ADU design and engineering come from our in-house arm, Golden State Design & Engineering, so the person who assessed feasibility on your slope is connected to the person who stamped the structural drawings and the person answering the county’s correction notice. When one ADU builder owns all of it from concept to completion, there is nobody to point at. You work with a dedicated project manager who knows your file.
The proof behind that promise: licensed and bonded under LIS. #1125656, trusted by 100+ happy customers, 18 Google reviews, a 10-year structural integrity warranty, and a 1-year fit-and-finish warranty on every project. Responsiveness is something we treat as a deliverable. We answer calls and emails quickly and send regular construction updates rather than waiting to be chased.
On budget, the antidote to surprises is a complete estimate you can actually read. Hold any ADU builder to these standards:
- Architectural plans, engineering, and permitting soft costs itemized separately from construction costs
- Named allowances for finishes and clear written exclusions
- Site work called out specifically: grading, retaining, drainage, utility runs, septic, fire requirements, access
- A payment schedule tied to completed construction milestones, not to the calendar
- An advance deposit no greater than 10% of the project cost or $1,000, whichever is less, as California law requires
Compare itemized estimates from more than one ADU contractor before you sign anything, and expect design and consulting work to represent roughly 10% of a total project budget. Review portfolios and ask for references from past clients. We are glad to walk you through our completed projects and put you in touch with homeowners who have been through the ADU process with us. Years of building accessory dwelling units have taught us where budgets break, and innovative solutions on a difficult site are usually what keep a project whole. A well-built accessory dwelling unit adds meaningful value to a property and can be legally rented for income, which is exactly why the estimate behind it deserves scrutiny.
Request a walkthrough and an itemized estimate and see the detail for yourself.
Our ADU Construction Process, From Free Consultation to Certificate of Occupancy
Four steps, with honest planning ranges attached: typically 3 to 5 months for design and permitting, then 3 to 4 months for construction. Whole-project timelines of roughly 5 to 11 months are common for ADU builds, and a foothill parcel with grading or septic work sits toward the longer end.
- Free consultation and feasibility review. During the 1-hour walkthrough we look at slope, driveway access, septic location and capacity, utilities, fire requirements, easements, trees, and the genuinely usable buildable area. You leave knowing whether the project makes sense before you have spent a dollar.
- Design, engineering and budget analysis. We draw the unit to your life and your parcel, run the structural and civil work in-house, and apply value engineering where it protects the budget without cheapening the result.
- County permit submissions and approval. A complete application starts a 60-day review period with El Dorado County. We respond to corrections, and when corrections are issued we return documents at least 15 calendar days before the review period expires, or request tolling, so the clock does not work against you.
- Construction, inspections and sign-off. We build with high quality materials and sequence inspections carefully: foundation, exterior shear, roof sheathing, framing, plumbing, electrical, mechanical, insulation, gypsum board, and finals. Where grading is required, rough-grade clearance has to happen before the foundation inspection, and final grading approval is required before occupancy. We sequence the job around that, not into it.
What Building an ADU in Cool Actually Involves
Who issues the permit when there is no city hall
Cool is unincorporated, so there is no city counter to visit. Permitting runs through the El Dorado County Planning and Building Department, with the west-slope Building Division at 2850 Fairlane Court in Placerville. The county does not publish a single Cool-specific total for typical ADU permit fees, because charges depend on valuation, district, school, fire, septic, and other agency variables. That is why we carry permits as itemized soft costs in your estimate rather than dropping in a round number and hoping.
What Cool properties are actually like
Local building splits roughly into two worlds: Auburn Lake Trails, a gated residential and equestrian community using Cool addresses, and the rural acreage parcels spread out from the junction of State Routes 49 and 193. Auburn Lake Trails began developing in the 1970s and holds everything from small residential lots to parcels of five or more acres. Survey-derived data puts about 94.9% of its housing in detached single-family homes with a median structure built around 1985, which usually means an older house with older electrical service, older septic, and a driveway that was never designed for a concrete truck. The message we repeat most often here: acreage is not the same as usable buildable area, and ADU construction costs move with ADU size, finishes, and the site conditions you have to solve before framing ever starts.
Slope, wildfire and the October 15 deadline
Terrain drives the budget on most Cool parcels. The Auburn Lake Trails wildfire plan documents steep slopes, ridges, drainages, dense vegetation, and substantial fuel loading around the community, and the county listed Auburn Lake Trails as a completed proactive defensible-space inspection area for 2024 and 2025. Fire, solar, and septic review are all live considerations, and defensible space belongs on the site plan from the first sketch. Season matters too: when grading extends into the winter period, temporary erosion controls must be in place before October 15, so early planning buys you a full construction window. Parcel-level fire designation and insurance questions should go to the appropriate authority or an insurance professional.
How we serve Cool from our Roseville office
Our office at 1001 Enterprise Way #100 in Roseville is a practical drive from Cool via Interstate 80 and Highway 49, and we build ADUs throughout California, from foothill acreage to valley communities such as Elk Grove. Cool has no contractor supply yard of its own, so we plan material procurement, delivery routing, staging areas, concrete access, and gated-community coordination before mobilization rather than improvising at the gate.
Frequently Asked Questions
How much does it cost to build an ADU in Cool, CA?
ADU construction commonly runs about $250 to $300 per square foot, with a frequently cited national average near $128,000 and prefabricated units starting around $30,000. On a foothill property, slope, grading, driveway access, septic work, and fire requirements move that number significantly, which is why ADU cost for a 1,000 square foot unit in California spans such a wide range. Our ADU Cost Estimator is a reasonable starting point, and we price a project only after a site review. Ask us for a real estimate.
Do I need a permit to build an ADU in Cool, and who issues it?
Yes, a permit is required, and because Cool is unincorporated the permitting comes from El Dorado County rather than a city department. The west-slope Building Division handling these projects is at 2850 Fairlane Court in Placerville. Your ADU must meet local zoning and setback rules, and most single-family and multi-family residential lots are eligible to build one under state law.
How long does an El Dorado County ADU permit take?
The county begins a 60-day review period once it receives a complete application. That is a review window, not a finish line: corrections, septic review, fire review, or grading can extend the real schedule. Corrected documents should go back at least 15 calendar days before the initial period expires unless tolling is requested, and we manage the submittal and every round of corrections so those deadlines are met.
What are the ADU setback requirements and property line distances on a Cool acreage parcel?
The county’s posted zoning ordinance allows detached ADUs up to 1,600 square feet on lots of at least one acre, subject to current parcel and code verification. For attached units, allowable square footage can also be tied to the primary home’s size. The practical limit is usually smaller. Distance to the front property line, side yard and rear yard setback rules, slope, septic field and reserve area, and fire access determine what genuinely fits, and we map all of it during the walkthrough before a single line of design is drawn.
Can I build an ADU inside Auburn Lake Trails?
Association-governed gated communities can carry recorded restrictions and design-review steps, so the answer depends on what applies to your specific parcel. We help identify those requirements and prepare the submittal accordingly. Request current association documents directly from the association so you are working from what is in force today.
Will an ADU increase my property taxes, and can I rent it out?
Completed ADU construction is assessed as new improvement value rather than triggering a reassessment of your unrelated existing land and improvements. Confirm your own situation with the county assessor or a tax professional. The upside is that new livable space adds real property value and can be legally rented, which is how many homeowners generate rental income from underused land and turn it into passive income and long-term wealth.
Let’s Find Out What Your Cool Property Can Support
One ADU builder, from the first sketch to the certificate of occupancy. The free consultation gives you a parcel-specific read on slope, access, septic, fire requirements, and usable buildable area, plus an itemized estimate with clear allowances and exclusions, so you leave with clarity whether or not you build with us.
We serve Cool and the surrounding foothill communities from our Roseville office. If grading is likely on your site, starting now puts you ahead of the October 15 erosion-control window instead of behind it. Call (916) 909-2387, email office@gsadus.com, or book a consultation.
