Free written scope consultation - allowances, timeline, and change-order rules on paper before a single trade is scheduled
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AfterFast, Reliable Home Additions & ADU Across San Marino
A room addition or ADU in San Marino runs $45,000-$130,000 for most projects, with detached ADUs starting around $90,000 on the estates near Huntington Drive and Lacy Park. The Design Review Board is the real gatekeeper here, and pulling permits on a 1920s Spanish Colonial is a different job than on a newer build. We’ve worked this city long enough to know exactly what the DRB rejects and what it approves. If you’re weighing an addition, a second story, or a garage conversion in San Marino, our Home Additions & ADU team can walk you through costs, timelines, and the review process before you spend a nickel. Call (877) 610-1318 to schedule a free estimate.
Why Barrett & Sons Construction Is San Marino’s Preferred Home Additions & ADU Company
Tom Barrett founded this company in 1998, and he put his name on the truck for a reason: if something goes wrong, you’ll see him again, not a call center in another state. His sons run the crews, and they’ve spent the last 29 years learning what San Marino’s housing stock demands. Old-growth Douglas fir framing doesn’t behave like modern lumber. Lath-and-plaster walls need a different touch than drywall. These aren’t things you learn from a franchise operations manual.
San Marino homeowners don’t ask us for the lowest bid. They ask whether we know the difference between Ludowici clay tile and generic concrete tile before we submit drawings. We do, and the DRB notices. That’s why our name keeps coming up on Lacy Park blocks and in the neighborhoods south of Huntington Drive.
Every scope, every allowance, every price change arrives as a written change order before work happens. Permits get pulled, inspections get signed, and every job carries our 90-Day Done Right Promise in writing. One call brings Tom back if anything is not done right.
Our Home Additions & ADU Services in San Marino
New Detached ADU
A new detached ADU in San Marino is the most involved project we handle, typically $90,000-$220,000 depending on size, materials, and site work. On a 1920s Spanish Colonial near Huntington Drive, we designed an ADU with a Ludowici clay tile roof, matching the main house’s 4:12 roof pitch and hand-troweled lime plaster exactly. The DRB approved it because every material echoed the original. We sequenced the rough-in and inspections so the owner’s builder warranty on the original structure stayed fully intact, and the final sign-off came six weeks after the DRB’s conditional approval.
ADU Design & Permitting
San Marino design and permitting work is not a paper-pushing exercise. The city’s Design Review Board scrutinizes every roofline pitch, window trim profile, and exterior finish material against the home’s original character. Our design team starts with photographs and measurements of your existing house, then builds the plan from period-appropriate specifications. This phase typically runs $45,000-$130,000 depending on complexity, and it can add months to your timeline. But the alternative, submitting drawings that get rejected, costs far more in redesign fees and lost time.
Second Story Additions
Adding a second story to a San Marino estate means opening up framing that’s been settling since the 1930s and working with old-growth lumber that predates modern building codes. We brace, reinforce, and match the existing structure before we build upward. The DRB will reject second-story plans that copy generic suburban profiles; the new roofline has to continue the original home’s pitch, and window trim must match the period. Expect $45,000-$130,000 for a well-executed second-story addition.
Garage Conversion ADU
A garage conversion in San Marino typically costs $30,000-$80,000. The older homes here often have detached garages with original siding and roof profiles that date to the 1920s and 30s. Converting one into living space while preserving the exterior usually satisfies the DRB, but you’ll need to address the slab, the electrical service, and possibly the foundation before anyone moves in. We’ve converted garages in the 91108 and 91118 zip codes where matching the original clapboard or stucco was the difference between approval and another review cycle.
What happens when you call
- 1
A real person answersNo phone trees - you reach a local pro.
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You get an upfront price rangeHonest numbers before anyone is dispatched.
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A background-checked tech heads outLicensed & insured, dispatched right away.
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You approve before work beginsNothing starts until you say go.
Trusted Brands We Service in San Marino
When a San Marino addition calls for a paver walkway, a patio, or sitework around the new structure, we work with Techo-Bloc and Cambridge Pavers because the DRB recognizes their profiles as compatible with San Marino’s historic palette. We also handle slab work with Quikrete and other specified materials where the structural engineer requires it. We don’t stock mystery brands, and we don’t substitute materials after approval. Anything we specify in a change order is what shows up on the job site.
Common Home Additions & ADU Problems We See in San Marino Homes
- DRB rejection after full architectural drawings. The roofline pitch or window trim didn’t match the original period style, and the owner burned months and thousands in redesign fees. We reverse-engineer the existing house before we draw anything.
- Voiding a new-home builder warranty. Cutting into load-bearing walls or altering a foundation without a written change order approved by the original general contractor kills the warranty. We coordinate with the original builder where needed and put everything on paper.
- Modern cement stucco on a historic addition. Cement stucco doesn’t breathe like original lime plaster, which traps moisture and leads to cracking. The DRB’s material compatibility review will flag it, and worse, the crack spreads into the original wall assembly.
- Unreinforced masonry and cripple wall failures after the fact. San Marino sits on the alluvial fan below the San Gabriel Mountains, near the Sierra Madre fault zone. If seismic retrofitting isn’t sequenced into the addition plan early, you’ll retrofit after the fact at a much higher cost.
Pricing for Home Additions & ADU in San Marino, CA
A home addition in San Marino runs $45,000-$130,000 for most attached room or second-story projects. Detached ADUs go higher, $90,000-$220,000, because they require separate foundations, utilities, and more DRB scrutiny. Garage conversions are the most economical at $30,000-$80,000. What moves the number? Matching historic materials is the biggest driver in San Marino. Ludowici clay tile costs far more than standard concrete tile, and lime-based stucco trades cost more than a modern cement crew. Seismic work on older unreinforced structures adds to the total, as does DRB-requested revisions. Here is what we bill most often:
| Project Type | San Marino Price Range |
|---|---|
| New Detached ADU | $90,000-$220,000 |
| ADU Design & Permitting | $45,000-$130,000 |
| Second Story Additions | $45,000-$130,000 |
| Garage Conversion ADU | $30,000-$80,000 |
Every line above is a starting point. You’ll get a written, line-item quote after we walk the site and check the existing structure. Call (877) 610-1318 to schedule your free estimate. We never quote one number on the phone and hand you another at the door.
We Also Serve Cities Near San Marino
Our crews work throughout the San Gabriel Valley. We frequently handle additions and ADU projects in San Gabriel, East San Gabriel, Alhambra, and East Pasadena. If you’re in one of those areas and weighing a room addition or ADU, the same written-change-order standards and period-material knowledge apply. Read more about our work in San Marino to understand how we approach historic neighborhoods.
Serving San Marino, CA - Our Local Coverage Area
We’re based in the San Marino area and know this community well. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
FAQs - Home Additions & ADU in San Marino
For a 1930s Spanish Colonial, San Marino’s DRB typically takes 3 to 6 months from initial submittal to conditional approval. Several factors stretch the timeline: the completeness of your materials documentation, whether your roofline and window trim profiles match the original, and how many revision cycles the board requests. A well-prepared application with period-correct Ludowici tile profiles and lime-based plaster specifications moves faster. Call (877) 610-1318, and we’ll tell you honestly where your project stands.
Yes, but not with a generic design. Attached second-story additions in San Marino’s historic districts must continue the original home’s roofline pitch, replicate window trim and exterior finishes, and avoid adding visual mass that the DRB deems incompatible. We’ve done it on Spanish Colonial Revival and Mediterranean Revival estates by copying the existing pitch and material palette exactly. Get the design right the first time, and the review goes much faster. Call (877) 610-1318 to talk through your house.
Your builder warranty stays intact only if the conversion is done with written approval from the original general contractor and no structural work happens outside that approved scope. Cutting into load-bearing walls or altering the foundation without a written change order voids the warranty. We sequence rough-in and inspections so the original builder’s work remains untouched where it matters. We’ll put every scope change on paper before work begins. Call us about your project and we’ll walk you through the warranty risk.
A new detached ADU in San Marino must meet current seismic code on its own foundation; that’s the law. The bigger question is whether the original house needs retrofit work, and in many older San Marino estates the answer is yes. Cripple walls, unbraced foundations, and unreinforced masonry are common in 1920s-to-1940s construction. If the addition shares a wall or foundation with the existing structure, retrofitting often gets sequenced into the same permit. Call (877) 610-1318 and we’ll have a structural engineer look at your specific site.
The first upgrade in most newer San Marino homes is replacing builder-grade windows with period-consistent Andersen or Marvin units, and upgrading hollow-core doors to solid wood with period millwork. It improves energy performance, reduces noise, and gives the house a visual weight that helps the DRB view the subsequent ADU or addition more favorably. It’s a $4,500-$15,000 window project on most homes, and it sets the right tone for the rest of the work. We’ll give you a line-item quote before anything gets ordered.
Ready to talk? Call Barrett & Sons Construction at (877) 610-1318 for a free, no-pressure estimate on your San Marino home addition or ADU. We’ll walk the site together, tell you what the DRB wants to see, and put your price in writing before any work begins.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving San Marino since 1998.