Free written scope consultation - allowances, timeline, and change-order rules on paper before a single trade is scheduled
Before
After
Before
After
Before
AfterFast, Reliable Home Additions & ADU Across San Lorenzo
A home addition or ADU in San Lorenzo typically runs $45,000-$130,000 for an addition and $90,000-$220,000 for a detached ADU, with garage conversions landing between $30,000 and $80,000. The bigger variable here isn’t the square footage, it’s the approval path. In San Lorenzo, virtually every project passes through the San Lorenzo Village Homes Association’s Architectural Control Committee before Alameda County will finalize permits. Skip that step and the job stalls, even with county approval in hand. Barrett & Sons Construction has steered dozens of San Lorenzo projects through the SLVHA review and county permitting in sequence, so the work never sits half-finished waiting on a committee. Call (877) 610-1318 for a free estimate and a straight answer about your property.
Key Takeaways for San Lorenzo Homeowners:
- SLVHA architectural approval and Alameda County permits must run in the right sequence, or you get a cease-and-desist.
- Nearly every home addition touches framing, wiring, and foundations from 1944-1952 Bohannon tract construction.
- Written change orders protect you from surprise invoices when the original rough-ins don’t match the as-builts.
- Free estimates, a 90-Day Done Right Promise, and permits pulled and inspections signed on every eligible job. Call (877) 610-1318.
Why Barrett & Sons Construction Is San Lorenzo’s Preferred Home Additions & ADU Company
We’re the owner-operated option in San Lorenzo, the crew whose name is on the truck and whose owner’s sons run the job sites. Tom Barrett founded Barrett & Sons in 1998, and the company has spent 29 years doing exactly what San Lorenzo’s housing stock demands: opening up 70-to-80-year-old Bohannon tract homes and making them work for the next 50 years. We’re not a franchise dispatching strangers. Tom Barrett publishes his name, his address, and his license number. Look it up before you sign anything.
San Lorenzo homeowners repeatedly tell us the same story: a national outfit quoted one number on the phone, then handed them a different bill at the door. That doesn’t happen with us. Every scope, every allowance, and every price change arrives as a written change order before work proceeds. The permit inspector works for you, not for me - that’s why I like him. Permits are pulled and inspections signed on every eligible job. And every completed project carries the 90-Day Done Right Promise, written on the contract: if it’s not done right, Tom comes back and makes it right, one call.
We answer the phone 24 hours a day with a live person - not a voicemail box, not an out-of-state call center. For San Lorenzo residents, that matters when a rough-in gets opened and the 1948 wiring isn’t what the plans showed. You need an answer, not a ticket number.
Our Home Additions & ADU Services in San Lorenzo
Our Home Additions & ADU team handles everything from a 400-square-foot garage conversion to a full second-story addition. Here’s how each major service works in San Lorenzo specifically.
ADU Design & Permitting
In San Lorenzo, the design and permitting phase is where most projects win or lose months of delay. We sequence SLVHA Architectural Control Committee approval against Alameda County permits so nothing stalls mid-construction. The submittal packet for the committee needs exterior elevations, material and colour samples, setback compliance, and a written description of the proposed work. We prepare that packet, file it, and attend the review on your behalf. About three to six weeks later, the committee issues its determination, and only then do we finalize the county permit application. This sequencing is the single most important fork in the road for any San Lorenzo ADU.
Garage Conversion ADU
Garage conversions are the most common ADU path in San Lorenzo because the 900-1,100-square-foot Bohannon lots rarely have room for a detached structure. The conversion itself runs $30,000-$80,000, but the condition of the original garage matters. Many of these garages were built with minimal framing, no insulation, and electrical service never intended for living space. When we opened up a 1948 Bohannon tract home on Paseo Grande for a garage-conversion ADU, our crew found original knob-and-tube wiring and undersized 2×4 framing that never appeared on any as-built. We isolated the scope of work, filed a change order for the rough-in replacement, and got the SLVHA committee sign-off before the county inspection so the project didn’t sit half-finished waiting on a committee. That’s how it’s supposed to go, and that’s how we run every job.
New Detached ADU
A detached ADU in San Lorenzo runs $90,000-$220,000, with the range driven largely by foundation requirements and flood-zone location. Sections near San Lorenzo Creek sit within FEMA-designated flood zones, which triggers elevated foundations and floodproofing requirements for new accessory structures. Additionally, the East Bay’s expansive clay soils shrink and swell dramatically between the dry summer and wet winter. Any detached foundation needs soils work beyond what a standard slab would require in neighboring towns. We account for that in the original estimate, not in a change order at the end.
Junior ADU & Interior Conversion
A Junior ADU (JADU) is the most budget-conscious option in San Lorenzo: converting existing interior space, typically a bedroom or den, into a self-contained unit with its own entrance, efficiency kitchen, and bathroom. The 70-year-old homes in San Lorenzo lend themselves to this because the original floor plans often include a rear bedroom with direct access to the yard, which becomes the JADU’s separate entrance. The county and the SLVHA both allow JADUs in most residential zones here, and the approval path is considerably shorter than a detached ADU. Interior conversions also tend to surface fewer surprises around framing and foundation, because you’re working inside an existing envelope.
What happens when you call
- 1
A real person answersNo phone trees - you reach a local pro.
- 2
You get an upfront price rangeHonest numbers before anyone is dispatched.
- 3
A background-checked tech heads outLicensed & insured, dispatched right away.
- 4
You approve before work beginsNothing starts until you say go.
Trusted Brands We Service in San Lorenzo
We stock Simonton and Ply Gem windows for San Lorenzo additions, and we use PGT impact-rated products where flood, wind, or exposure conditions call for them. Our San Lorenzo customers don’t get mystery brands off the back of a van. When you ask what’s going into your addition, we hand you a cut sheet with a product name you can look up. And because we run our own materials purchasing, we can get replacement sashes, hardware, and trim packages to a San Lorenzo job site faster than a crew crossing the Bay Bridge from a distant yard. If a window arrives wrong or a frame member shows up twisted, we reorder it and keep the job moving. That’s what the 90-Day Done Right Promise means in practice.
Common Home Additions & ADU Problems We See in San Lorenzo Homes
When we walk a San Lorenzo property for the first estimate, we’re looking for the same failure modes over and over. Here’s what we see.
- County permits pulled before SLVHA approval. This is the most expensive avoidable mistake in San Lorenzo. The San Lorenzo Village Homes Association’s Architectural Control Committee must approve exterior work before, or concurrent with, Alameda County permitting. Skipping this step gets a cease-and-desist letter from the HOA even after the county has issued permits. The project stalls mid-construction, and the homeowner is left with an open trench or torn-off wall waiting on a committee calendar. We file the SLVHA packet first, every single time.
- Original 1940s framing that can’t support the planned load. Bohannon tract homes were built fast, between roughly 1944 and 1952, and the framing reflects that speed. Undersized 2x4s, non-standard spacing, and original subfloors that were never meant to carry a second story. When homeowners assume the original framing is fine and plan a second-story addition, the county requires engineered fixes once the walls are opened. That delay and added cost is avoidable with a structural assessment before the permit package is filed.
- Expansive clay soil movement cracking new slabs. San Lorenzo sits on East Bay expansive clay that swells in wet winters and shrinks in dry summers. New additions and ADUs need foundation design that accounts for this movement, or the slab cracks and the foundation ties fail. The cracks typically show up after final inspection, when the contractor is long gone. We spec foundation reinforcement and soil preparation in the original scope of work.
- Flood-zone requirements caught late. Portions of San Lorenzo near San Lorenzo Creek fall inside FEMA-designated flood zones. A garage conversion or ADU in these zones triggers elevated foundation and floodproofing requirements that a homeowner only discovers when the county comments on the permit. We identify flood-zone status during the first site walk, so the estimate reflects it from the start.
Pricing for Home Additions & ADU in San Lorenzo, CA
Here are the realistic ranges for San Lorenzo, based on our recent jobs in 94580 and the surrounding streets.
| Project Type | Typical Range in San Lorenzo |
|---|---|
| Home Addition | $45,000-$130,000 |
| ADU Construction | $90,000-$220,000 |
| Garage Conversion | $30,000-$80,000 |
Those ranges aren’t inflated, and they aren’t teaser numbers. A 500-square-foot room addition with a simple gable roof, standard windows, and no structural surprises will land near the lower end. A second-story addition over an existing 1948 footprint, with load-bearing upgrades, engineered foundation ties, and SLVHA-mandated exterior finishes, will land near the upper end. The only way to pin down the real number is to look at the property. We offer free written estimates, and we encourage you to compare our line-item scope against any other bid. A free second opinion on any written estimate is a standing offer. Call (877) 610-1318 to schedule yours.
We Also Serve Cities Near San Lorenzo
Our crews work throughout Alameda County. Beyond San Lorenzo, we regularly run additions and ADUs in Ashland, San Leandro, Cherryland, and Castro Valley. If your property is in 94580 or a neighboring ZIP, we can get to you fast, and no trip charge applies inside the county. Call (877) 610-1318 and we’ll schedule the site walk.
Serving San Lorenzo, CA - Our Local Coverage Area
We’re based in the San Lorenzo 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 Lorenzo
Yes. In San Lorenzo, the SLVHA Architectural Control Committee must approve exterior work before, or concurrent with, Alameda County permitting. Skipping this step has caused homeowners to receive cease-and-desist letters from the HOA even after the county permit was issued, stalling the project mid-construction. We file the SLVHA packet first and sequence the county permit around the committee’s calendar so the work doesn’t sit half-finished. Call (877) 610-1318 to confirm your property’s path.
The original foundations under San Lorenzo’s Bohannon tract homes were poured quickly, often without the reinforcement modern code requires. More importantly, the expansive clay soils beneath them shrink and swell between seasons, which means any new addition needs foundation ties built to absorb differential movement. We assess the existing stem wall and footings before we spec the addition, and we include engineered fixes in the original scope. Call (877) 610-1318 for a foundation assessment on your San Lorenzo property.
It may. Portions of San Lorenzo near San Lorenzo Creek fall within FEMA-designated flood zones, and new or substantially improved structures in those zones must meet elevated foundation and floodproofing standards. A garage conversion that changes the use from storage to living space can trigger those requirements. We check the flood map on your specific parcel during the first estimate, and we’ll tell you what it means in dollars before you commit to anything. Call (877) 610-1318 to find out your flood-zone status.
Expect roughly three to six weeks for the SLVHA Architectural Control Committee review, plus whatever time is needed to revise and resubmit if the committee raises questions. The key is sequencing: we file the SLVHA packet first, prepare the county permit in parallel, and schedule the construction start around the committee’s determination. Done this way, the review doesn’t add real time to the overall project. Done out of sequence, it can add months of stalled work. Call (877) 610-1318 to get a realistic timeline for your San Lorenzo addition.
Yes, in most cases. The SLVHA Architectural Control Committee reviews exterior materials, colours, and styles against the original Bohannon character of the neighborhood, and fiber-cement lap siding is commonly approved when presented in a colour and profile consistent with the surrounding tract homes. We prepare elevation drawings and material samples for the committee as part of our permit package. If you’re considering fiber-cement siding, we’ll walk you through the submittal requirements at no charge. Call (877) 610-1318.
Call Barrett & Sons Construction in San Lorenzo
If you’re planning a room addition, a garage conversion, or a detached ADU in San Lorenzo, start with a site walk and a written estimate. We’ll tell you what the SLVHA will need, what the county will need, and what the real number looks like in writing before you sign anything. Ring (877) 610-1318 to schedule your free estimate. Ask anyone on your street, or look up the license number yourself. We’ll be here when you call.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving San Lorenzo since 1998.