Altadena, California
Home Additions & ADUs in Altadena, CA
Garage conversions, attached additions and detached ADUs, priced around the utility runs and the ground, not just the floor plan. Serving Altadena and the surrounding San Gabriel Valley.
The short answer
MKW Homes builds home additions and ADUs across Altadena, and the first thing to know is local. Altadena is unincorporated Los Angeles County, so your permit runs through LA County Public Works on the EPIC-LA portal, not the City of Pasadena. Many lots here slope toward the foothills, which means drainage and retaining, not the framing, often set the budget.
PermitsWho signs off in Altadena.
Permits for Altadena go through Los Angeles County Public Works, Building and Safety.
Local detail
Altadena is unincorporated Los Angeles County, not the City of Pasadena. Permits go through LA County, and the submittal process and review timeline are different. Contractors who work mostly inside Pasadena city limits get this wrong and it costs weeks.
Housing stockWhat we find in Altadena.
Craftsman and ranch homes on larger lots, many on sloping ground against the foothills.
Neighborhoods we work in
The buildHome Additions & ADUs in Altadena.
What actually drives the cost
Start with the type, because it sets the floor. A garage conversion is the cheapest path, since the shell, slab, and roof already stand. An attached addition sits in the middle. A detached, new-build ADU costs the most, because it needs its own foundation and full framing. After type, the money hides in the utility runs: how far water, sewer, gas, and power have to travel to reach the new space. On the sloping lots common here, a new foundation and grading can move the number more than the finishes ever will.
Foundation and finish choices that matter
Foundation type follows the ground. A flat pad can take a slab. A raised floor suits gentler grades and gives you a crawl space for running pipe and wire. A lot that falls toward the foothills often needs caissons, which are concrete piers drilled down to firm soil so the structure does not ride on loose fill. The expansive clay across the San Gabriel Valley swells when wet and shrinks when dry, so footings get sized for that movement. For cladding and roof, matching the existing Craftsman or ranch home keeps the addition from looking bolted on.
The Altadena permit and site reality
Because Altadena is unincorporated, you file with Los Angeles County Building and Safety through the EPIC-LA portal, and county plan check runs its own setback, height, and floor-area rules. California now approves qualifying ADUs ministerially, with reduced parking and set size allowances, but the county still measures every plan against its own standards. On a home built before 1978, disturbing old paint pulls in lead-safe work rules. Slope is the other half of the story: lots in the Meadows and up toward the foothills often need retaining walls and a drainage plan before anyone frames a wall.
How the build actually goes, step by step
It runs in a set order. First a feasibility and zoning check to confirm what your parcel allows. Then design and engineering, followed by plan check and permits through the county. On site we start with foundation, then framing, then rough utilities, with the electrical, plumbing, and mechanical inspections that follow. Next comes insulation and drywall, then finishes like flooring, cabinets, and paint. A final inspection signs it off. In Janes Village and other older pockets, we confirm where the existing sewer and panel sit early.
How long it takes and what living through it is like
Design and permitting usually take longer than people expect, because county plan check has its own queue and slope work can trigger extra review. Once we break ground, a garage conversion moves fastest and a detached ADU takes the longest. During the loud stretches, framing and demolition, you will hear it. The dusty stretch is drywall sanding. We seal the work area off from your living space and stage deliveries so your street parking stays usable. You can stay in the main house through nearly all of it.
How long it lasts and the upkeep it needs
Built right, an addition or ADU lasts as long as the main house, meaning decades. The foundation and framing are effectively permanent. What needs attention is water: keep gutters, downspouts, and the site drainage clear so runoff moves away from the footings, which matters more here because the clay soil moves with moisture. Recaulk wet areas and repaint exterior wood on the usual cycle. If you built caissons or retaining walls on a slope, look them over after heavy winter rain for any new cracking or movement, and call it in early.
The mistake homeowners make
They budget from the floor plan and forget the parts they cannot see on it. The two that bite are the utility runs and the electrical panel. A new kitchen and bath in a detached ADU means trenching water, sewer, and gas across the yard, and that distance is real money. Adding that load often pushes an older 100-amp panel past its limit, so it needs an upgrade before the county will pass it. Neither shows on a rendering, but both are certain costs. Price them up front so the budget holds instead of jumping mid-build.
What to ask any contractor before you hire
Ask for their CSLB license number and check it live on the state board site. Ask if they have run permits through EPIC-LA for unincorporated county work, since that process differs from a City of Pasadena job. Ask how they will handle your slope and drainage, and whether your panel can carry the new load or needs upgrading. Ask for a written scope that names the utility runs, the foundation type, and who pulls the permit. And ask to see a finished ADU they built nearby, then call that owner. A straight builder hands you the number.
QuestionsHome Additions & ADUs in Altadena.
Do I need a permit to build an ADU in Altadena?
Yes. Even with California's ministerial ADU approval, you still file with Los Angeles County Building and Safety through the EPIC-LA portal, because Altadena is unincorporated and the county, not the City of Pasadena, is your permit authority. We handle that filing for you.
Why does my Altadena lot cost more to build on?
Slope. Many Altadena lots fall toward the foothills, so before framing you may need retaining walls, a drainage plan, and caisson piers drilled to firm soil. The local clay swells and shrinks with moisture too, which sizes the footings. That groundwork often moves the budget more than the finishes.
Can I convert my garage into an ADU?
Usually yes, and it is the cheapest route, because the slab, walls, and roof already exist. The real costs are running water, sewer, and gas to it, adding insulation, and often upgrading the electrical panel to carry the new kitchen and bath. We confirm what your parcel allows on the walk.
Will I need to upgrade my electrical panel?
Often, yes. Adding a full ADU or a large addition with its own kitchen and bath can push an older 100-amp panel past what the county will pass. We check your existing panel's capacity early, so the upgrade, if you need it, is in the budget from the start rather than a surprise mid-build.
How long does an Altadena ADU take start to finish?
Plan for design and county permitting to take longer than the build itself, since EPIC-LA plan check has its own queue and slope work can add review. A garage conversion is the quickest build, a detached new ADU the longest. We give you a real schedule once we see the parcel and scope.
Does an addition in a historic part of Altadena need design review?
It can. If an addition changes the roofline or the street-facing exterior in a protected area, the county can require design review before it approves the plans. We flag that in the feasibility check so it does not stall your project later. We confirm the rules for your specific street.
ReviewsWhat clients say.
Hired Mike and his crew to redo our entire backyard and driveway. Removal of the asphalt and existing landscaping, running water lines and electrical, artificial grass, plant borders, a paver driveway, raised the patio gazebo, added a paver patio, landscaped borders, irrigation and outdoor lighting.
Teri CraftLocal Guide · 33 reviewsFrom start to finish the job was handled with the utmost professionalism and attention to detail. What stood out most was their communication. Mr. Ward kept me informed every step of the way.
Angela Adams5 reviewsMKW Homes just painted our home. We are very satisfied with the work. During the process everything was clean and organized.
Jake Baloian3 reviewsMike and his crew were great. They did a wonderful job on the stucco patching and painting, and we were very pleased with the results.
Jen B1 reviewHired Mike and his crew to redo our entire backyard and driveway. Removal of the asphalt and existing landscaping, running water lines and electrical, artificial grass, plant borders, a paver driveway, raised the patio gazebo, added a paver patio, landscaped borders, irrigation and outdoor lighting.
Teri CraftLocal Guide · 33 reviewsFrom start to finish the job was handled with the utmost professionalism and attention to detail. What stood out most was their communication. Mr. Ward kept me informed every step of the way.
Angela Adams5 reviewsMKW Homes just painted our home. We are very satisfied with the work. During the process everything was clean and organized.
Jake Baloian3 reviewsMike and his crew were great. They did a wonderful job on the stucco patching and painting, and we were very pleased with the results.
Jen B1 reviewNearby citiesHome Additions & ADUs near Altadena.
Free estimatesIn Altadena.
Michael usually gets to the property the same week.