Free written scope consultation - allowances, timeline, and change-order rules on paper before a single trade is scheduled
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After
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AfterFast, Reliable Home Additions & ADU Across Seaside
A home addition or ADU in Seaside typically runs $45,000 to $220,000 depending on whether you’re converting a garage, adding a second story, or building a detached unit from the slab up. Crews from Barrett & Sons Construction serve the entire 93955 zip code, and Tom Barrett’s sons are on-site most days, not dispatched strangers. If you’re planning an addition on a former Fort Ord parcel, call (877) 610-1318 before you sign anything, because Seaside has a permit wrinkle no other Monterey Peninsula city does, and it changes your timeline and your budget.
We’ve been building in Seaside long enough to know what opening up a 1950s military tract home actually turns up. Outdated wiring. Galvanized pipes past their service life. Slab foundations with minimal rebar by modern seismic standards. The good news is none of it surprises us, and none of it should surprise you, because every scope, allowance, and price change at Barrett & Sons arrives as a written change order before a single nail moves.
Why Barrett & Sons Construction Is Seaside’s Preferred Home Additions & ADU Company
Barrett & Sons is owner-operated and has been since Tom Barrett founded the company in 1998. Tom publishes his name, his address, and his license number, the way a contractor who lives twenty minutes away and will see you at the hardware store on Saturday does. His sons run the crews. When you call, a live person answers, 24/7, not a voicemail box or an out-of-state call center.
Seaside homeowners repeatedly tell us the same story. A national outfit quoted one price on the phone and handed them a different bill at the door. That does not happen here. Every job starts with no-hassle upfront pricing in writing, and every change arrives as a written change order before work proceeds. Tom’s 90-Day Done Right Promise is written on every contract, not buried in fine print. If something’s not right, one call brings him back.
We work regularly in Seaside neighborhoods from the older enlisted tract streets near Canyon Del Rey to the redeveloping parcels on the former base. We know the housing stock, the fog, the salt air, and the permit office. That local knowledge is the difference between a quote that holds and a quote that burns its contingency halfway through the job.
Our Home Additions & ADU Services in Seaside
ADU Design & Permitting
An ADU in Seaside starts with the question of where you’re building it. If the parcel sits on former Fort Ord land, the Fort Ord Reuse Authority, FORA, may require environmental review and soil-disturbance protocols before the city issues your permit. We handle that coordination directly, including the paperwork. We also handle the design, the structural drawings, and the energy code documentation so your permit application moves without a back-and-forth stall. A typical Home Additions & ADU design and permit package in Seaside includes allowance line items for soil testing, architectural fees, and city plan check, all in writing.
Garage Conversion ADU
Converting a garage to an ADU in Seaside usually runs $30,000 to $80,000, and the older the tract home, the more the final number leans toward the upper end. Most of the garages we convert were built in the 1950s and 60s as part of Fort Ord’s standardized enlisted housing. Slab foundations are thinner than modern code, walls are often uninsulated, and the electrical service rarely supports a second dwelling without a panel upgrade. We write those allowances into your contract from the start, so the only surprises are the ones on paper.
New Detached ADU
A new detached ADU in Seaside runs $90,000 to $220,000. The range is wide because site conditions vary dramatically from one block to the next. A flat backyard lot with clean soil and easy utility access is one job. A former-base parcel in a UXO risk zone is something else entirely, and that’s before we count the cost of running new water, sewer, and electrical service. Barrett & Sons handles ADU site prep and utilities as a core part of the job, with written allowances for trenching, panel service, and any FORA-required soil work.
Junior ADU & Interior Conversion
A junior ADU, generally under 500 square feet, is the fastest path to rental income or a place for family. These conversions typically use an existing bedroom or attached space, which means the work is mostly interior: partition framing, a kitchenette, a private entrance, and a dedicated heating source. What makes Seaside different is the age of the walls we open. Original galvanized plumbing and early-aluminum wiring are common in these 1950s and 60s tract homes, and when they’re exposed, code says they get replaced. Our contracts include those allowances from day one.
What happens when you call
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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 Seaside
Barrett & Sons carries premium brands across every trade, and that matters when you’re spending five figures on an addition in a salt-heavy climate like Seaside’s. We install GAF roofing on second-story additions and sunrooms because the Monterey Bay marine layer shortens the life of cheaper underlayments. For bathroom work inside a new ADU or junior unit, we’re thorough with Schluter waterproofing systems, because the fog in Seaside is persistent, and moisture moves through walls differently than it does ten miles inland. On windows and exterior envelopes, we lean on Andersen and Marvin, because aluminum-clad frames hold up to coastal air better than vinyl alternatives. When you’re in our showroom or talking with Tom, ask about the brands by name. A contractor who installs materials you can look up is a contractor who stands behind them.
Common Home Additions & ADU Problems We See in Seaside Homes
- Undersized electrical panels from original tract construction. Most 1950s and 60s Seaside homes were built with 60-amp service. A second-story addition or ADU with a kitchenette and heating will usually require a 200-amp upgrade. If you’re on a former Fort Ord parcel, the city and FORA both weigh in on the permit, so we pull the electrical permit correctly the first time.
- Galvanized supply lines at or past their service life. We find this constantly. Opening a wall for an addition means seeing what’s behind it, and original galvanized pipe in Seaside is often corroded to half its original inside diameter. Once exposed, code requires replacement. We write a plumbing rough-in allowance into every addition contract so this is not a surprise.
- Slab foundations with minimal rebar for modern seismic code. Fort Ord-era tract homes sit on slabs that were fine in 1958 and are not fine for a second-story addition in 2026. Structural reinforcement is a line-item allowance on our contracts, not a change order that appears after demolition.
- Coastal fog and salt air attacking the new envelope. Seaside sits directly in the Monterey Bay marine layer corridor. Untreated sill plates and generic fasteners start corroding before the final inspection. Our crews specify corrosion-resistant flashing, properly treated lumber, and exterior coatings rated for salt exposure on every addition and ADU shell.
Pricing for Home Additions & ADU in Seaside, CA
| Project | Price Range |
|---|---|
| Second Story Addition | $45,000-$130,000 |
| Garage Conversion ADU | $30,000-$80,000 |
| New Detached ADU | $90,000-$220,000 |
A second-story addition in Seaside costs more than the same square footage in Monterey proper when the lot is on former Fort Ord land, because FORA’s site-prep requirements add testing, documentation, and sometimes weeks before excavation. A garage conversion costs more when the original 1950s slab needs structural work or the panel needs upgrading. Call (877) 610-1318 for a free estimate, and we’ll give you a written line-item quote with allowances, not a round number that shifts later.
We Also Serve Cities Near Seaside
Barrett & Sons works throughout the Monterey Peninsula. If you’re in Marina, Monterey, Pacific Grove, or Salinas, our crews serve those communities too, with the same written change orders and the same 90-Day Done Right Promise. The permit rules change from one city to the next, but the way we quote and build does not.
Serving Seaside, CA - Our Local Coverage Area
We’re based in the Seaside 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 Seaside
Does a garage conversion ADU in Seaside need extra environmental review if it’s on former Fort Ord land?
Yes, often. Parcels on former Fort Ord land fall under FORA jurisdiction, and if your garage conversion requires soil-disturbing work like trenching for utilities or foundation repair, a UXO risk screen may be required before excavation starts. We coordinate that review directly with FORA and include the allowance in your written quote. Call (877) 610-1318 and we’ll check your parcel’s status before you commit to anything.
What code upgrades should I expect when a Seaside home addition opens up an original 1950s wall?
Typically an electrical panel upgrade to 200 amps, plumbing replacement if original galvanized supply lines are exposed, and structural reinforcement if the foundation predates modern seismic standards. Once a wall is open, the city requires any exposed deficiency to be corrected to current code. That is why we write allowances for panel replacement, plumbing rough-in, and framing reinforcement into every Seaside addition contract before we start.
Why do second-story additions on flat-roof Seaside tract homes cost more here than in Monterey?
Two reasons. First, original Fort Ord housing stock is standardized 1950s and 60s construction, and nearly every exterior wall we frame onto requires structural work the original slab was never built for. Second, if the parcel is on former base land, FORA soil-disturbance protocols can add testing, documentation, and days or weeks before we cut the first footing. A mile into Monterey proper, neither condition typically applies. Call (877) 610-1318 for a quote that accounts for your actual parcel, not a neighborhood average.
How long does FORA environmental review add to an ADU project on former base land in Seaside?
It depends on the parcel’s UXO risk classification and the depth of the soil disturbance, but in our experience the review and any required testing usually add two to six weeks before excavation begins. We submit the paperwork early and keep the rest of the permit process moving so that the wait does not stall your whole schedule.
If my Seaside home addition finds damaged original framing, will my contract protect me from an open-ended bill?
Yes. Our contracts include line-item allowances for structural reinforcement, so if we open a wall off Canyon Del Rey and find framing the 1950s never built for a second story, the cost is already scoped in writing. Nothing gets approved verbally and nothing gets billed that you have not seen on a written change order first. That is the whole point. Call (877) 610-1318 for a free estimate.
Call Barrett & Sons Construction for Home Additions & ADU in Seaside
If you’re planning a second-story addition, a garage conversion, or a new detached ADU in Seaside, call (877) 610-1318 and we’ll schedule a free estimate. We’ll walk the property, check the parcel’s FORA status if it applies, and hand you a written line-item quote with allowances, a scope in writing, and the 90-Day Done Right Promise on the contract. Tom Barrett’s name, address, and license number are published and verifiable. Look us up before you sign anything.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving Seaside and the Monterey Peninsula since 1998.