A free site visit, a check of what your lot allows and a written, line-item price.
Get your free estimateTrusted Home Addition Contractor for San Francisco Homeowners
Adding square footage to a San Francisco home means dealing with soft story retrofits on older Victorians, steep lots that climb 30 degrees or more, and a Planning Department that reviews every inch of a setback. A home addition in this city is not a weekend project, and the contractor you hire matters as much as the design. Lodgewick ADU San Francisco has been doing this work since 2010, led by Russ Delmar, who knows what it takes to pull permits in the Sunset, Richmond, and Noe Valley without burning six months of a homeowner’s patience. If you want straight numbers, a written price before any work starts, and a crew that shows up when they say they will, call (707) 760-0502 and let’s talk through your lot.
What you get with us: a written price before a single nail is driven, a defined arrival window for every work day, a clean job site at the end of each day, and a written guarantee on the full project. We call it the 365-Day Done Right Promise. If it’s not right, we come back and make it right. That commitment is in writing, every time.
How Much Does a Home Addition Cost in San Francisco?
A home addition in San Francisco typically runs $350 – $650 per square foot depending on foundation work, structural upgrades, and finish level. A simple ground-level bump-out of 200 square feet might land between $70,000 and $130,000. A full second story on an existing single-story home starts around $250,000 and often reaches $500,000 or more when you factor in seismic retrofitting and a new roofline. Below are the realistic ranges by project type we see across the city.
- Sunroom addition: $45,000 – $120,000 depending on glazing, foundation type, and whether it’s a conditioned or three-season space.
- Room addition (single room bump-out): $70,000 – $180,000 based on size, site access, and structural work.
- Second story addition: $250,000 – $600,000 depending on square footage, roof complexity, and whether the existing foundation needs reinforcement.
- Garage addition: $60,000 – $200,000 for a functional attached or detached garage with livable space above, depending on slab work and finishes.
- Bathroom addition: $35,000 – $95,000 when adding a full bath to existing floor plan or as part of a bump-out.
- Bedroom addition: $60,000 – $160,000 depending on whether it’s a ground-level addition or part of a second story.
Those are the numbers Russ Delmar puts in writing before work begins. No door-knock price changes. No “while we’re in there” upcharges. Call (707) 760-0502 for a free estimate and we’ll walk the site, measure, and hand you a line-item quote you can take to the bank.
Sunroom Addition
A sunroom addition is a glazed living space built onto the side or rear of a home, designed to bring in natural light while protecting you from San Francisco wind and fog. In neighborhoods like West Portal or the Marina, homeowners choose a sunroom when they want year-round reading space, a plant room, or a breakfast nook that feels outdoors without sitting in the cold. Lodgewick ADU San Francisco builds sunrooms with proper thermal breaks in the frame, low-E glass, and a foundation that ties into the existing structure instead of floating like a patio cover. Expect to spend between $45,000 and $120,000 depending on glazing package and whether the space is heated.
Three-Season vs. Conditioned Sunrooms
A three-season sunroom saves money up front but will sit unused during December and January when the outside temperature drops into the 40s. A conditioned sunroom with a dedicated mini-split or tied-in HVAC runs higher on the front end but functions as real square footage you can use every day of the year. We’ll price both so you can decide with actual numbers in hand.
Permitting and Setbacks in San Francisco
San Francisco treats a sunroom as habitable space, which means it counts toward your rear yard setback and requires a building permit. On a 25-foot-deep lot in the Outer Sunset, the rear yard requirement often limits how far you can project. Russ and his team check the zoning before you spend a dollar on plans.
Room Addition Contractor
A room addition contractor builds new single-room living space onto an existing home, typically a family room, office, or flex space that extends the footprint of the house. When a San Francisco family outgrows their living room but doesn’t want to move, a room addition is often cheaper than a second story and far less disruptive than a full remodel. Lodgewick ADU San Francisco handles everything from foundation and framing through drywall, paint, and trim, with the same written-price guarantee we put on every job. A single-room bump-out in this city runs $70,000 to $180,000 depending on size, access, and what’s hiding under the existing floors.
Foundation and Seismic Considerations
Most San Francisco homes built before 1940 sit on perimeter concrete foundations with little to no rebar, which means any room addition triggers a seismic upgrade to that section of the home. This is not an optional add-on. It’s code, and it protects the new room and the old house from moving independently in an earthquake. We include the retrofit in your written price, not as a surprise change order.
Site Access on Hill Lots
If your home is on a hill in Diamond Heights or Glen Park, getting materials and equipment to the rear of the lot changes the entire bid. We plan for crane or conveyor delivery, permit parking, and even neighbor notifications before mobilization. The written price accounts for access up front so the number we hand you is the number you pay.
Second Story Addition Contractor
A second story addition contractor adds a full or partial upper floor to a single-story home, which is often the only way to double living space on a tight San Francisco lot where front and rear setbacks already squeeze the footprint. This is the most involved type of addition because it requires opening the roof, reinforcing the first-floor walls, and often upgrading the foundation to carry the new load. Lodgewick ADU San Francisco plans second story additions with structural engineering, seismic bracing, and a written price that includes all of it. Expect a full second story to run $250,000 to $600,000 in this city, with partial second stories landing lower.
Living Through a Second Story Build
Adding a second story to a home you’re still living in is a different animal than a rear addition. The house gets opened to the sky, and there will be a period where water intrusion protection consists of temporary tarping and meticulous sequencing. We walk you through the schedule week by week so you know exactly when the roof is off, when the framing is up, and when you can sleep under a finished roof again.
Structural Engineering We Use
Every second story in San Francisco requires stamped structural drawings. We work with licensed structural engineers who specialize in soft-story retrofits and vertical additions on older wood-frame construction. The cost of that engineering is in the written estimate, not billed separately after the fact.
Garage Addition Contractors
Garage addition contractors build new attached or detached garage space, often with a livable room above, for homeowners who need parking, storage, or a workshop and an extra bedroom or office. In San Francisco, where street parking is a daily negotiation and lots are narrow, a well-built garage addition solves two problems at once. Lodgewick ADU San Francisco constructs garage additions from the slab up, including engineered footings, shear walls, and finished interiors above. A garage addition in this city costs $60,000 to $200,000 depending on whether it’s attached, detached, and what goes above the garage.
Garage-to-Living Space Sequencing
If the plan is a garage with a bedroom or ADU above, the slab and first-floor framing have to be designed for that future load from day one. Pouring a 4-inch slab today means ripping it out in three years when you’re ready to build up. We design for the full structure on the first set of plans, even if you phase the build.
Drainage and Side Hill Garages
San Francisco’s hills in neighborhoods like Miraloma Park and Forest Hill create drainage challenges that flat suburban garages never face. We grade the apron, install trench drains where needed, and write the waterproofing details into the plan rather than treating them as an afterthought after the first winter rain.
Bathroom Addition Contractor
A bathroom addition contractor builds a new full or half bath where one doesn’t exist, either by capturing underused space inside the existing footprint or extending the home outward. In San Francisco’s older homes, many of which have one bathroom serving three bedrooms, adding a second bath is one of the highest-return projects a homeowner can do. Lodgewick ADU San Francisco handles planning, supply and drain lines, waterproofing, and finish plumbing, with the written price before work starts. A new bathroom addition in this city runs $35,000 to $95,000 depending on whether you’re building inside the existing envelope or adding square footage.
Plumbing Stack and Venting
The two things that drive bathroom addition cost more than anything are where the main stack sits and whether the new bath can reach it without cutting through load-bearing framing. We map the plumbing path before pricing, so your written bid reflects the actual work, not a best-case scenario.
Waterproofing on Upper Floors
A second-floor bathroom addition over existing living space needs a watertight pan, proper subfloor preparation, and a continuity of waterproofing that a ground-floor bath doesn’t demand. We’ve torn out enough failed upper-floor bathrooms in Noe Valley and the Richmond to know exactly where leaks start and how to build so they never do.
Bedroom Addition Contractor
A bedroom addition contractor adds sleeping quarters to a home’s footprint, whether by extending the ground floor, building above an existing room, or converting an awkward existing space into a code-compliant bedroom. San Francisco homes built in the 1920s and 1930s often have two small bedrooms and a family that needs three or four. Lodgewick ADU San Francisco designs bedroom additions that meet egress requirements, minimum room dimensions, and window area rules the city enforces. A bedroom addition in San Francisco typically runs $60,000 to $160,000, with the final number driven by square footage and whether the foundation needs seismic work.
Egress and Legal Bedroom Requirements
A legal bedroom in San Francisco needs a specific window size for fire escape, a closet, and minimum square footage. Call a room a bedroom on a listing and the building inspector will check. We make sure your new bedroom is legal the first time so appraisal and resale value hold up.
Closet and Storage Planning
Bedroom additions that skip closet planning end up with armoires and dressers eating the square footage you paid for. We design storage into the framing from the start, including reach-in closets, built-in wardrobes, and window seat storage where the lot orientation makes sense for it.
Brands We Service
We work directly with the major prefab and panelized building systems homeowners ask for by name. James Hardie siding and trim shows up on the majority of additions we build in San Francisco because it holds up to the wet, salty air in the outer neighborhoods better than wood and doesn’t need repainting every four years. We have crews trained in Hardie’s installation specs for rainscreen applications, which matters when the inspector asks about drainage plane details.
For homeowners who want a faster build, we have hands-on experience with Boxabl and Plant Prefab systems, including their panel connections, foundation interface, and finish sequencing. A Boxabl addition or Plant Prefab module can cut on-site framing time significantly, though San Francisco’s crane access and narrow streets still drive logistics that we plan for up front. Whether you want a prefab system or stick-built framing, we can help you price both and choose with your eyes open.
Signs You Need a Pro Right Now
- Your foundation shows new cracks or movement. If you’re planning an addition but the existing foundation is shifting, adding load on top accelerates the problem. A professional structural assessment now costs far less than underpinning later.
- Your family has outgrown the bedroom count. Kids sharing a room works until it doesn’t. If someone is sleeping in a dining room or the basement, you’ve already answered the question of whether an addition is worth it.
- You’ve been quoted widely different prices by different contractors. A spread of $100,000 between bids usually means one contractor is leaving out scope. Get a written, line-item quote from someone who walks the site and includes permits, engineering, and seismic work.
- Your home was built before 1940 and hasn’t had a seismic retrofit. Adding square footage to an unretrofitted San Francisco house without addressing the foundation is like adding a second layer to a cake sitting on a paper plate. Get the retrofit priced with the addition.
- You want to stay in the neighborhood but can’t find a bigger house. In neighborhoods like West Portal, Glen Park, and the Sunset, just moving to a larger home often means leaving the area entirely. An addition keeps you where the school, the commute, and the neighbors are.
Our Process, Step by Step
- 1
Call and talk to a real person. We answer the phone 24/7 at (707) 760-0502. No voicemail tree, no chatbot. You’ll talk to someone who can book your free on-site visit and answer basic questions about your lot and scope.
- 2
Free on-site walkthrough with Russ. Russ Delmar comes out, walks the property, checks access, foundation, roofline, and zoning setbacks, and asks questions about how your family actually uses the space. This is where the written price starts taking shape.
- 3
Written, line-item estimate. You get a document that breaks down foundation, framing, electrical, plumbing, finishes, and permits. This is the price. It doesn’t change when we open the walls unless you ask for a change and we price it in writing first.
- 4
Permit and engineering package. We handle the drawings, the structural engineering, and the permit submittal to the San Francisco Department of Building Inspection. You don’t chase the city. We do.
- 5
Build, clean, and stand behind it. Crews show up in the window we gave you, clean the site at the end of every day, and finish with a written guarantee covering the work for 365 days. If something isn’t right, call and we come back and fix it.
Our Service Area Near San Francisco
We serve homeowners across San Francisco and the surrounding Bay Area, including Oakland, Hayward, Richmond, Daly City, San Leandro, San Rafael, Hillsborough, Martinez, San Bruno, San Carlos, and Millbrae. If you’re in one of these cities and planning an addition, the process is the same: free on-site visit, written price, and the 365-Day Done Right Promise. See our San Francisco home addition services for more on how we work in the city proper.
Serving San Francisco, CA - Our Local Coverage Area
We’re based in the San Francisco area and know this community well. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
Frequently Asked Questions About Home Addition Contractor in San Francisco
A home addition contractor plans, permits, and builds new living space onto your existing home, handling everything from foundation and framing to electrical, plumbing, drywall, paint, and finish trim. At Lodgewick ADU San Francisco, that includes the structural engineering, the permit submittal, and the written price before work starts. Russ Delmar runs every project with the same guarantee: if it’s not right, we come back and make it right.
A single-room ground-floor addition typically takes 3 to 5 months from permit approval to final inspection. A second story addition usually runs 6 to 10 months depending on scope and weather. San Francisco’s permit review adds time that contractors can’t control, but we submit complete, stamped packages that reduce back-and-forth with the Department of Building Inspection.
Home additions in San Francisco run $350 to $650 per square foot depending on whether you’re building out, building up, and what the existing foundation can carry. A 300-square-foot room addition might cost $105,000 to $195,000. Call (707) 760-0502 and we’ll walk your lot and give you a written number for your specific project.
Yes, we have direct experience with Boxabl and Plant Prefab systems including their panel connections and foundation interfaces. We’ll price a prefab addition alongside stick-built so you can see the real difference in cost and schedule. We also use James Hardie siding and trim on most exterior work because of how it handles San Francisco’s marine climate.
We serve the broader Bay Area including Oakland and Hayward, with the same written-price guarantee and 365-Day Done Right Promise. Each city has its own permitting and zoning quirks, and we handle those locally. If you’re in Oakland or Hayward and planning an addition, call us and we’ll schedule the same free walkthrough.
If any work we performed fails within 365 days due to workmanship or materials we installed, we’ll come back and fix it at no charge. This is delivered as a written guarantee on every project, before work begins. Most contractors won’t put the guarantee in writing. We do, on every job, no exceptions.
Start by gathering anything you know about your home: original construction year, any past remodels, foundation type if you know it, and a rough budget range you’re comfortable with. Then call (707) 760-0502 to book a free on-site visit. Russ will walk the property, check access and setbacks, and give you a written price so you can make the decision with real numbers in hand.
Schedule Your Home Addition Contractor Service in San Francisco Today
Call (707) 760-0502 and talk to a live person right now. We’ll schedule your free on-site visit, walk the property with you, and hand you a written, line-item price before any work begins. The estimate is free, the guarantee is in writing, and the number we quote is the number you pay. If you’ve been burned by a contractor before, this is the way it should work. Reach us 24/7 at (707) 760-0502.
Written by Russ Delmar, Owner at Lodgewick ADU San Francisco, serving San Francisco since 2010.
