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CGI Home Additions & ADU: The San Jose Owner's Guide
For homeowners in San Jose planning a CGI home addition or ADU, installed projects typically run $53,100 to $153,400 depending on square footage, foundation work, and finish level. A detached ADU sits higher, usually $106,200 to $259,600, because it means running new utilities, pouring a separate slab, and building a full second structure. When owners call us about a CGI addition that is not going well, the problem is almost always the same: a contractor who started without a fixed number, or a sub who walked off after framework. We fix both by writing the price and the scope down before a single board gets ordered.
We're an independent San Jose remodeling company, not affiliated with CGI. We do stock and install the same trade-grade materials used in CGI home additions, and our crews build additions and ADUs to California Title 24 energy code and Santa Clara County setback rules. The guide below tells you what to look for, what it costs, and when to call us at (669) 274-2362.
Which CGI Models This Applies To
CGI home additions and ADUs are not like swapping a cabinet pull. The compatibility question is not about a model number on a box. It is about the structural and permitting path: attached versus detached, existing foundation match, roof tie-in, and utility stub distance. If you have a CGI addition that is already framed, we match the existing stud spacing, ceiling height, and roofline pitch rather than forcing new work into old dimensions.
One gotcha we see regularly in San Jose: attached additions built in the 1990s and early 2000s often have 2×4 exterior walls with no continuous air barrier. California energy code now requires 2×6 exterior walls or continuous insulation on most addition permits. If your CGI plans are older than about 2016, the permit package may need updating before inspection. We identify this during the estimate and price the correction up front, not as a change order after demo.
For materials inside the addition, we work with the same trade brands many CGI specs call for: KraftMaid and Wellborn cabinetry, Cambria, Silestone and Caesarstone countertops, Kohler and Moen fixtures. If your CGI addition package included these lines, we can match the existing finishes so the new space does not look tacked on.
Styles & brands we work with
Signs Your CGI Home Additions & ADU Is Failing
- Cracked drywall at the seam where the addition meets the original house. This usually means differential settling or an improper foundation tie. The two structures move at different rates, and the seam cracks first. We saw this repeatedly in Willow Glen additions where the footing was not doweled into the existing slab.
- Doors or windows that stick at the addition end of the house. When the addition shifts even 1/8 inch, door corners bind. It is a pressure point, not a warped door panel.
- Water staining on the ceiling near the roof tie-in. The valley where new roof meets old roof is a classic leak point. San Jose's winter rain exposes this within one season.
- Electrical flicker when the addition's circuits load up. Some older additions were wired with shared neutrals that do not meet current code. If you run a space heater and the kitchen lights dim, the panel and subpanel need attention.
- Floor slope you can feel in the addition but not the original house. More than 1/4 inch drop over 8 feet indicates a foundation that was poured too thin or on uncompacted fill, which is common in San Jose's East foothills where clay soil moves.
See the difference
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After
Before
After
Before
AfterReplacement Cost & What's Included
For a grounded plan, here are the San Jose ranges we quote from, including labor, materials, permits, and our written guarantee:
- Home Addition (attached, 400–800 sq ft): $53,100–$153,400
- ADU Construction (detached, 600–1,000 sq ft): $106,200–$259,600
- Garage Conversion to living space: $35,400–$94,400
What moves the number up? A second bathroom in the addition, a kitchen rough-in with gas line, upgraded electrical panel, or pier-and-grade foundation instead of a slab. What moves it down? A simple bedroom bump-out with no plumbing, no subpanel, and standard finishes. We give you a line-item written price before any work starts, so you see exactly where the dollars go. Every addition and ADU we build in San Jose carries our 365-Day Done Right Promise: if something we touched fails inside a year, we come back and fix it at no charge. In writing.
DIY or Call Us?
You can safely do two things yourself: document the problem with photos and measurements, and pull your original permit packet from the San Jose building department online portal. That record tells us what was approved versus what got built, which often shows the failure point. But do not open up a load-bearing wall, touch roof framing, or re-run electrical. A sagging tie-in or a cracked footing is a structural and safety issue. Trevor Nash will tell you the same thing on the phone: give him the real problem and he will give you the real number. For anything beyond paint-level fixes, call (669) 274-2362 and we will come look.
FAQs
A properly built addition or ADU in San Jose should last 50 to 80 years for the structure, with periodic maintenance on the roof and exterior siding every 15 to 20 years. The weak points in our climate are UV exposure on the west-facing walls and seasonal clay soil movement, not the framing itself.
Yes, in most cases. Foundation cracks can be epoxy-injected, roof tie-ins can be re-flashed, and failing drywall seams can be cut back and re-taped with flexible joint compound after the movement source is fixed. Rebuilds are only necessary when water damage has reached the framing or the foundation has shifted beyond repair tolerance. Call (669) 274-2362 for an honest inspection, not a sales pitch.
A targeted repair, like a roof tie-in leak or a cracked seam, usually takes one to three days once materials arrive. A full rebuild or a new detached ADU runs four to eight months in San Jose because of the permit review timeline at the county level plus construction.
We stock common framing lumber, sheathing, roofing underlayment, and fasteners in our San Jose yard, and we order cabinet lines, countertops, and fixture packages from local suppliers who keep KraftMaid, Cambria, Silestone, and Kohler in regional warehouses. Most materials for a repair are on hand within three to five business days.
Need an honest number for your San Jose addition or ADU project? Call (669) 274-2362 to schedule a free estimate. We answer the phone with a real person, every time. We will write the price down, put the guarantee in writing, and show up when we say we will.
Written by Trevor Nash, Owner, Penhallow Remodeling San Jose at Penhallow Remodeling San Jose, serving San Jose and nearby areas.
