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Home addition roof framing tied into an existing house in San Jose

Structural Work

Home Additions

More square footage, added properly — foundation, framing and roof tied into what's already there, so the new part and the old part behave like one house.

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  • Licensed CA General B #1112902
  • Fully Insured
  • Santa Clara & San Mateo Counties
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The short answer

Home additions in Santa Clara and San Mateo counties run $130K–$490K, driven by how much square footage you add and how much structure has to change to carry it. The question that moves the number most is whether you are adding footprint or rearranging what you already have. Adding footprint means new foundation, new framing, a structural engineer and a full plan check — which is why a budget that comfortably covers a reconfiguration often will not cover an addition of the same room count. A second storey adds a further question: whether the existing foundation and walls can carry it, which is an engineering answer, not an estimate.

Licence
CA General B #1112902
Bond & insurance
$25,000 bond, insured
Permits
We pull and close them
Where
Santa Clara & San Mateo

The hard part is the seam

Anyone can frame a box. What separates a good addition from a bad one is where it meets the existing house: how the new foundation ties to the old one, how the roof lines meet without creating a leak, whether the existing structure can actually carry what you're adding.

That's structural work, and it's why an addition belongs with a builder rather than a remodeler. We open it up, find out what's really there, and tell you early — old houses are full of surprises, and the honest move is to show them to you rather than absorb them quietly and hope.

Scope

What an addition involves

Structural assessment

What the existing framing and foundation can carry, and what has to be reinforced before anything is added.

Permits & engineering

Additions almost always require engineering and plan check. We carry the submittal and the corrections.

Foundation

New foundation properly tied to the existing one, so the two don't move independently.

Framing & roof tie-in

Framing, and the roof connection — the single most common place a bad addition leaks years later.

Systems extension

Electrical, plumbing and HVAC extended into the new space, including whether the existing panel and equipment can carry it.

Finish to match

Interior and exterior finished so the addition reads as part of the house, not as an obvious bolt-on.

Adding footprint versus reconfiguring inside it

Adding footprint versus reconfiguring inside it
Addition (new footprint)Reconfiguration
New foundationYesRarely
Structural engineeringEffectively alwaysOnly where walls come out
Permit pathFull plan checkOften simpler
Setback & lot coverage limitsGoverns what is even possibleNot usually triggered
Typical timeline8–14 months incl. design and permit3–6 months
Cost driverSquare footage plus structureHow many walls move
Ask firstDoes the lot allow it?Is the wall load-bearing?

Common Questions

Straight answers

Will my electrical panel handle an addition?
Often not — and it's better to find out at proposal than at inspection. We check panel capacity as part of pricing. A service upgrade is a real line item and we'd rather show it to you early than surprise you with it mid-build.
Can I live in the house during an addition?
Usually yes, though it depends on the scope and where the work meets the living space. We'll be straight with you about which weeks are genuinely disruptive so you can plan around them.
Is an addition cheaper than an ADU?
Not automatically. An addition avoids a second utility connection but adds structural tie-in work to an existing building — and existing buildings hide problems. Which one makes sense depends on your lot, your goal and what we find. We'll give you an honest read on a call.
Is it cheaper to add on or to reconfigure what I have?
Reconfiguring is almost always cheaper, and the gap is bigger than people expect. Adding footprint means a new foundation, new framing, a structural engineer and a full plan check. Moving interior walls within the existing footprint often means framing and finishes only. This is the single most useful question to settle before anyone draws anything, because a budget that comfortably covers a reconfiguration may not cover an addition delivering the same room count.
Can my house take a second storey?
That is an engineering answer, not an estimating one. It depends on whether the existing foundation and walls can carry the load, and older houses frequently cannot without reinforcement. A structural engineer makes that determination — we coordinate and price that work, and we will not guess at it. Where the answer is no, the reinforcement cost is often what decides between going up and going out.
How long will I be without part of my house?
For most additions the existing house stays livable, because we build the new structure and only break through at the end. The disruptive window is the tie-in: roof, framing and the wall that opens between old and new. Where the addition includes the kitchen or the only bathroom, plan for a temporary arrangement — and plan for it at proposal, not the week it happens.
Will an addition trigger other upgrades?
Sometimes, and it is better to know up front. Depending on scope and jurisdiction, adding conditioned square footage can trigger Title 24 energy requirements, smoke and carbon monoxide alarm updates throughout the house, and occasionally an electrical service upgrade. These are code-driven, not optional, and they belong in the proposal rather than arriving as a change order.
Are you licensed, bonded and insured?
Yes — California General Building (B) license #1112902, a $25,000 contractor bond, and an active workers' compensation policy with The Hartford. Verify the license on the CSLB registry. Certificates of insurance are available on request.
Do you handle the design?
We build your vision — we're not designing the place with you. But "we don't design" does not mean "you're on your own for plans." We coordinate the architect and structural engineer who produce your stamped permit set, including Title 24, and they submit to the city portal. That is a line item we price and manage — on an ADU it runs about $10,000 and it is in the estimate, not a homework assignment we hand you.

On ADUs we can also start from a standard design and give you a materials list, which is usually the faster and cheaper route.

What we won't do is sit and choose your layout, cabinet doors and finishes with you. That is interior design, it is a real skill, and it isn't ours — if that's the help you want we'll say so up front rather than three weeks in.
How do allowances work?
An allowance covers work nobody can honestly price until something is opened up. Those are billed at actual cost, and whatever isn't spent comes off your final invoice. We'd rather show you the unknowns than bury them in a padded fixed price.

Process

How an addition actually runs

  1. The footprint question

    First we settle whether you are adding footprint or reconfiguring inside it. That single answer changes the foundation, the engineering, the permit path and usually the budget bracket.

  2. Design and structural engineering

    An addition ties new structure into old, so a structural engineer is effectively always involved. On a second storey they determine whether the existing foundation and walls can carry it — an engineering answer, which we coordinate and price rather than estimate.

  3. Permit and plan check

    Full review, because you are changing the building envelope. Setbacks and lot coverage govern what is even possible, which is why they get checked early.

  4. Foundation and framing

    New foundation, then framing tied into the existing structure. The house usually stays livable through this, because we build the new structure before breaking through.

  5. The tie-in

    Roof, framing and the wall that opens between old and new. This is the disruptive window, and it is scheduled deliberately rather than stumbled into.

  6. Trades, finishes, close-out

    Rough-in and inspections, then finishes throughout, then final inspection and a punch list walked together.

Deposit is capped at $1,000 by California law. Milestone draws follow the work — see how payments work.

Before you sign anything

Worth reading first

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Service Area

Where we build

Permit process, plan check and utility requirements change at every city line. Each page covers what's actually true where you're building.

Tell us about your project

Book a 30-minute discovery call and we'll tell you what's realistic — scope, budget and timeline — whether or not we're the right builder for it.

Book a Project Discovery Call Call (408) 597-2733