Home Additions

There’s no honest single per-square-foot price for an addition, because an addition almost always touches the whole house, not just the new space. Adding 700 sq ft to a 1,400 sq ft home usually means reworking much of the existing house too: tying in the roof, structure, electrical, plumbing, HVAC and finishes. The real budget depends on how much of the home changes, and that takes plans and a clear picture of your goals to pin down.

Why two additions of the same size can cost very different amounts:

• Front additions usually cost more than rear ones. They change the street-facing look, often get more planning review, and need more finish work.
• Second stories are their own category: reinforcing or adding foundations below, a new roof, stairs.
• Additions on more than one side multiply the tie-in work.
• Lot and site conditions: soil, hillsides, access, and utility upgrades like a new electrical panel or PG&E service.

Design and plans run about $12–$18 per square foot of the proposed floor plan, including both architectural and structural plans. Some architects charge considerably more.

The best way to get a real number: have a general contractor walk the house with you. We’ll look at the existing structure, talk through what you want, and give you a ballpark. Call (650) 801-2699 or request a free consultation.

Yes, but only for the new construction, not the whole house. Under California’s Proposition 13, the county assessor adds the market value of the new construction (for example, the added square footage) to your existing assessed value. Your original base year value on the rest of the home stays the same, so you don’t lose your Prop 13 protection by building.

• Usually reassessed: added square footage, and converting space into something new, like a garage or attic into a bedroom.
• Usually not reassessed: normal maintenance, repairs and like-for-like replacements, such as a new roof, cabinets or fixtures.
• Excluded by law: solar panel systems, qualifying seismic retrofits, and accessibility improvements for a disabled occupant (which require filing with the assessor).

The assessor values the addition at what it adds to the home’s market value, which isn’t always the same as what you paid to build it. Your county assessor’s office can answer questions about a specific project.

For most homeowners, yes. An addition is a one-time capital expense. Moving to a bigger house comes with ongoing costs that never go away:

• A new mortgage at today’s rates, which may be well above the rate on your current loan, carried for the life of the loan.
• A higher property tax bill, because the new home is assessed at its full purchase price. With an addition, only the new construction is added to your assessed value.
• Selling and buying costs: agent commissions, transfer taxes and closing costs.

Our rule of thumb: in the Bay Area, where many homes sell for around $2.5 million, a 25–30% down payment on a bigger house is $625,000 to $750,000. That’s a lot of money, and it goes a long way toward improving the house you already own. For homes priced over $2 million, a 25% down payment usually equals at least 75% of the construction cost of an addition.

Even after budgeting for a rental while you’re out of the house during construction, keeping your existing cost basis low and making a one-time upgrade is usually cheaper than moving, and you keep your neighborhood, schools and lot.

Yes. Most neighborhoods are priced by the square foot. As a simple example: if homes in your neighborhood sell for about $1,000 per square foot, adding 500 square feet adds meaningful value on its own. Renovating the existing house at the same time (new kitchen, bathrooms, countertops, flooring) adds more on top of that. A local real estate agent can pull comparable sales for an estimate specific to your home.

• Cash is ideal if you have it.
• A HELOC (home equity line of credit) can be a good option.
• A cash-out refinance at a higher rate than your current loan can be expensive to carry over time, so run the numbers carefully.
• Construction loans are fine, but be careful with how you get one.

Keep the loan and the contractor separate. Get your price from the contractor, then arrange financing yourself through an independent loan broker. Be wary of all-in-one offers where the contractor or a company tied to them also provides the loan. If the same party controls both the project and the financing, a project that drags on can earn them more interest, and that’s a conflict of interest you don’t want. We’d also steer most homeowners away from using a reverse mortgage to fund a remodel. We’re builders, not financial advisors, so talk to a lender or broker about your situation.

It depends on the city, and especially on how that city runs plan check. For a typical addition, expect roughly 6–8 weeks to prepare architectural and structural plans, about 10 working days for the city’s intake, then one or more 30-day review cycles until the plans are approved.

• Design (6–8 weeks): architectural and structural drawings are prepared for submittal.
• Intake (about 10 working days): the city checks that the submittal is complete before review starts.
• Plan review (30-day cycles): every project goes through the two core departments, Planning (zoning, setbacks, height, design) and Building (structural, energy and code). Depending on your lot and the scope of work, they may route the plans to other reviewers, such as Fire, Civil/Public Works (grading, drainage, utilities), Geotechnical (hillside and soils), an arborist for protected trees, or historic review in older neighborhoods. Reviews often happen one department after another, and each round of comments and fixes can add another 30-day cycle.

Why cities differ: large cities like San Jose review plans in-house, so the queue is long, but San Jose offers fast tracks. One-story additions under 500 sq ft can qualify for same-day Residential Express permits, and ADUs have their own dedicated service. Smaller cities often send plan check to a private third-party firm, which is frequently faster.

What adds review cycles: the more work you’re doing, and the closer the project gets to the line where the city treats it as new construction, the more comments to expect.

A full-house remodel with an addition typically takes about 7 to 13 months of construction. Two things decide where you land in that range:

• Scope of work: the bigger the scope, the longer the build.
• Who’s making the decisions on finish materials: this is the most underestimated factor. When a licensed professional handles the shopping and selections for tile, fixtures, cabinets and finishes, the project moves much faster. The more the homeowner is handling and organizing the moving parts, the closer the project gets to the high end of that range.

Yes, you need both: an architect for the plans and an engineer for the structural design. What matters is who coordinates them. You have two good options:

• The contractor coordinates everything, using in-house or partner architects and engineers. This is usually the easiest path, as long as the contractor has done it before and can show you finished work.
• An architect leads, coordinating the engineer and later the contractor.

Either way, the person in charge of all of it should be a licensed professional, the architect or the contractor, not the homeowner. At Build Better Properties we handle that coordination for you; design and plans typically run about $12–$18 per square foot of the proposed floor plan, architectural and structural together.

There are two meanings, and the second one surprises most homeowners:

1. The obvious one: the house is demolished, the foundation is pulled out, and a new home is built from scratch.
2. The one people get confused about: even an addition or a remodel can be tagged as new construction if it crosses a city’s threshold for square footage added, walls altered, roof altered and so on. Once that happens, the whole project has to meet the codes for a new house, which can add requirements like fire sprinklers and full energy compliance, plus more cost and review time.

We design additions to stay clearly on the addition-and-remodel side of that line whenever possible. That’s one of the biggest ways we save clients time and money.

They solve different problems. An addition makes your main house bigger. An ADU gives someone else a separate place to live. A second story adds the most space without touching your yard.

• Addition: expands your existing home, such as a bigger kitchen or dining room, or more bedrooms and bathrooms. If your house itself feels too small, an addition is the answer; an ADU in the backyard won’t fix that. Additions also tend to add more value than ADUs, because they add square footage to the primary home.
• ADU (accessory dwelling unit): a separate home with its own kitchen, bathroom and entrance, either detached in the backyard or attached to your house. Best for rental income, or for family living with you who want their own privacy.
• Second story: the largest option. The whole roof comes off and a new floor goes on top. It usually only makes sense when you need a lot of space, think 1,000 sq ft or more, and your lot is tight or you don’t want to give up the backyard. A second story isn’t necessarily the most expensive choice, but it is the most involved, and it’s harder to do one without the project being treated as new construction. If you need less space than that, an addition or an ADU is usually the better fit.

For most homes in good condition, adding on wins. A teardown really only makes sense in two cases:

• You want new construction for your own reasons, such as a completely different layout or a brand-new home.
• Fixing the existing house would cost more than building new, for example when the structure or foundation is in poor shape.

If the house is in good shape and you need a modest amount of space, say 400 to 800 sq ft, an addition is usually the better choice. You keep the existing foundation and much of the structure, the project stays in the addition-and-remodel category for permits, and only the new construction is added to your property taxes.

Most houses can, but the foundation almost always needs to be reinforced. How much foundation work is needed depends on the existing structure, the soil, and whether the house sits on a hillside. A structural engineer evaluates all of this during design.

The amount of foundation and structural work also shapes the first floor. The new second story’s weight has to come down through posts, beams and walls below, so the more support the engineer needs, the less wide-open space you can keep on the ground floor.

On our Fremont second-story addition, for example, we retrofitted the entire home with 15-foot-deep drilled piers to handle the area’s expansive soil. The engineering assessment is part of our design phase, so you’ll know what’s required before construction is priced.

It depends on your city’s floor area ratio (FAR): how much total house you can have compared with the size of your lot. Every city calculates it differently, and some count more than just the house. A few examples:

• San Jose: single-family homes up to about 45% of the lot area get standard review; going bigger triggers an extra Single-Family House Permit.
• Los Altos: about 35% of the lot on typical lots, with lot coverage also capped at 35%.
• Saratoga: besides limiting floor area, the city counts impervious surfaces like paving and driveways toward site coverage, so landscaping and hardscape plans affect how much you can build.

Setbacks (how close you can build to property lines) are fairly standard on typical single-family lots: about 5 ft from each side property line, about 25 ft from the street, and a larger rear setback that varies by city and zoning district.

Check for easements first. A land or utility easement on your property can push the buildable area in further than the setbacks alone. Easements are usually recorded on your title from when you bought the house, so check your title report, and a licensed land surveyor can map them for you.

Height limits and, in many Peninsula and South Bay cities, daylight plane rules for second stories also shape the final size. Your city’s planning website lists its rules, and we check your lot against all of them at the start of design, so the plan is sized to what your city will actually approve.

We strongly recommend moving out. Living in a house during an addition is extremely difficult and, more importantly, unsafe:

• Utilities get shut off. Water, power and gas are cut periodically during construction for safety.
• Parts of the house are held up by temporary supports. While walls and framing are being changed, sections of the structure are supported by temporary shoring.
• The house is open to the weather. An addition usually means removing part of the existing house, so it’s open to the elements for part of the build.

At Build Better Properties, we don’t build additions with people living in the house. It’s too dangerous. Plan to be out for about the length of construction, typically 7 to 13 months for a full remodel with an addition, and we work as fast as we safely can to get you back home.

Smaller projects are different. Kitchen and bathroom remodels have workarounds that let families stay home. On one Campbell project, we renovated all 3.5 bathrooms while the family lived there.

Yes, but usually by updating the existing house to match the new addition, not the other way around. The addition is the newest part of the home, so it makes more sense to bring the older rooms up to it than to build new space that imitates old finishes.

Nobody wants a visible seam where the old flooring meets the new, or where fresh paint and trim stop. So most additions include upgrading the existing house at the same time, with flooring, paint and finishes carried through the whole home for one seamless look. That’s a big reason additions cost more than the new square footage alone, and why so much of the work on an addition happens inside the existing house.

Outside, we design the addition around the existing rooflines, siding and windows so it looks like it was always there. And because we build our cabinetry in our own shop, new kitchens, built-ins and storage can be carried through the whole house for a unified look.

Plan for them up front. It’s far cheaper to handle these systems during construction than to come back for them afterward.

• Roof: it’s your call, but often worth doing all at once. If the addition already means replacing or modifying 50% to 60% of the roof, and the older section has been up for 20 years or so, it makes a lot of sense to redo the whole roof now.
• Kitchen: it can often be kept as is if it sits in an area the addition doesn’t touch. If the kitchen moves or grows, plumbing and venting get rerouted too.
• HVAC: depending on how much square footage you add, your existing system may be too small for the new house. Include heating and cooling in the plans and budget from the start.
• Electrical: the panel may need an upgrade, and larger projects can require a new PG&E service.

We plan these tie-ins in the design phase so they’re in the budget from day one, not discovered during construction.

A change order is a written change to the contract’s scope and price after work begins. On additions and remodels they usually come from four places:

• Hidden conditions: once walls and floors are opened, older homes can reveal dry rot, termite damage, outdated wiring or plumbing, or past unpermitted work that has to be corrected.
• City or inspector requirements: an inspector or plan reviewer can require something that wasn’t on the approved plans.
• Selections over allowance: if the contract includes an allowance for tile, fixtures or appliances and the chosen items cost more, the difference becomes a change order.
• Homeowner changes: moving a wall, adding a window or upgrading a finish mid-project.

How we keep change orders down: complete plans and a detailed scope before pricing, clear allowances, and finish selections made early. When a change is needed, it’s priced and signed in writing before the work happens, which California law requires for home improvement contracts.

Choose someone who explains the process clearly, has good references, and tells you the bad news along with the good. A good contractor will walk you through where the difficulties will be, what’s hard, and what will be easier. If everything you hear is good news, be careful.

• Check references and visit a job site. Ask to see a project in progress, not just photos of finished work.
• Pick someone you get along with. You’ll be working together for months.
• Watch out for prices that swing with bargaining. If a contractor bids $100,000 and drops to $50,000 as soon as you push back, that’s a major red flag. Good contractors know their costs and don’t have that kind of margin to play with.
• Get proof of insurance with the contract, before you sign: general liability and workers’ compensation.
• Check the license on the CSLB website.

Other good questions to ask:

• Have you built projects like mine in my city, and can I see them or talk to those clients?
• Who runs the job day to day, and how will we communicate?
• What’s the payment schedule? In California, a home improvement down payment can’t be more than $1,000 or 10% of the contract price, whichever is less.
• How are change orders handled and priced?
• What’s the realistic timeline for permits and construction?

Use the Contractors State License Board’s free Check a License search at cslb.ca.gov. Enter the license number or business name to confirm the license is active, see its classifications, and check bond and workers’ compensation status and any public complaints. Build Better Properties is CSLB license #1077286, Class B General Building.

For most homeowners, design-build is the way to go. One company handles design, engineering, permits and construction under one contract, so one person is in charge of everything. The contractor works with architects and engineers they already know and trust, which streamlines the process, and the builder checks cost as the plans are drawn, so the design stays within budget.

When to hire a separate architect: if you have a very specific need or a very particular design in mind, an architect can be the right choice. Keep in mind that clients who go this route often end up paying more for construction, because nobody is checking cost while the plans are being drawn. Architects are great at creating beautiful designs, and beautiful, intricate details take more time and money to build.

Build Better Properties is a design-build firm.