San Jose Single-Family Home ADU Feasibility Report

Figure: Front view of a two-story single-family home on a ~6,000 sq ft lot (Note: specific numbers have been obscured for privacy protection)[1][2].

Property and Zoning Overview

Property Description: This property is a 4-bedroom, 2.5-bath single-family residence in a quiet San Jose residential area, built in the late 1990s on a ~6,000 sq ft lot (Note: specific details have been obscured for privacy protection)[3]. The home has a two-car garage and a Planned Development (PD) zoning designation (zone "A-PD")[4]. In San Jose, ADUs are generally permitted in single-family residential zones (including PD zones, as long as ADUs are not explicitly prohibited)[5][6]. The General Plan designation for this neighborhood is likely Residential Neighborhood, supporting single-family homes. There is no indication the property is in any special overlay (historic district, etc.), so standard city and state ADU regulations apply. The larger lot and layout offer "all kinds of possibilities" for an ADU, according to the previous home listing[7].

Zoning Considerations: Being in a PD zone means one should verify if the PD permit has any ADU restrictions. However, San Jose's code (aligned with state law) now allows ADUs on any lot with a single-family home in a PD zone unless expressly prohibited[5]. No such prohibition is noted for this development, so an ADU should be allowed by-right. The PD likely follows R-1 single-family standards, which the ADU must also respect (e.g. usage, setbacks, height). We will use the city's ADU Universal Checklist (Bulletin #210) as a guide to determine feasibility[8][9]. Key development standards are summarized below.

ADU Development Standards and Restrictions

Dimensional Standards (Setbacks, Height, Coverage)

Location & Setbacks: A detached ADU must be located in the rear yard or at least 45 feet from the front property line[9][10]. This means the ADU cannot project into the front yard. Side and rear setbacks are generally 4 feet minimum for a detached ADU (ground-floor ADUs can potentially go as close as 3 feet if fire-rated walls are used)[11]. For a two-story ADU, the second floor must be at least 4 ft from property lines, and no balconies or windows facing close to neighbors within 15 ft of the lot line[12]. On a corner lot, a 4 ft street side setback applies as well[13]. The existing lot likely has standard 5-foot utility easements along fences, so effectively a ~5 ft setback is prudent (no building allowed in easement)[14].

Conclusion: The backyard of this property appears to have open space behind the house and should accommodate a detached ADU meeting the 4-ft rear/side setback rule (there are no known encroachments or structures in the way, per listing photos). The ADU must also maintain at least 6 feet of separation from the main house for fire safety[15] (San Jose requires a 6' clear horizontal distance between the ADU's walls and any other building on the lot). This separation is achievable given the yard size (the house is roughly centered on the lot with a modest rear patio, leaving open yard area).

Height Limits: San Jose allows detached ADUs up to 18 feet tall for single-story designs, or up to 24 feet if a two-story ADU is built (two-story ADUs are permitted on single-family properties)[16]. The primary home is two-story; an attached ADU addition could theoretically match the home's height, but here we focus on a detached unit. A one-story ADU (up to ~18' height) would easily meet height limits; even a two-story 24' ADU could be allowed if designed appropriately[17]. However, a second-story ADU has additional setback and privacy considerations as noted. Most homeowners choose single-story ADUs for simplicity and cost.

Conclusion: A single-story ADU up to 16–18' high is feasible and would blend with the neighborhood. Height is not a limiting factor on this lot, as long as standard limits are followed (and since no junior ADU is on site, the full 18' height is allowed by state law)[16].

Lot Coverage & Size: For lots under 9,000 sq ft, San Jose allows a detached ADU up to 1,000 sq ft in size[18]. However, the ADU also must obey the "Rear Yard Coverage Rule": structures (sheds, ADU, etc.) cannot cover more than 40% of the rear yard, or up to 800 sq ft, whichever is greater[19]. The rear yard is defined as the area between the back of the main house and the rear property line, across the full lot width[19]. In this case, the lot is ~6,028 sq ft with a two-story home of ~1,000 sq ft footprint, so the rear yard might be on the order of ~1,500–2,000 sq ft (rough estimate). Forty percent of, say, a 2,000 sq ft rear yard is 800 sq ft. Thus practically ~800 sq ft may be the largest ADU that fits without a variance, unless the yard is larger. (The ordinance does allow "800 sq ft or 40%, whichever is greater," so 800 is effectively guaranteed)[19]. In any event, state law entitles at least an 800 sq ft ADU on any lot, even if coverage rules conflict[19]. So a medium-sized ADU (e.g. 600–800 sf) should be feasible.

Conclusion: An ADU in the 600–800 sq ft range is ideal to avoid coverage issues. A 1,000 sq ft unit might be possible if the rear yard is sufficiently large – it would need a careful site plan to ensure it doesn't exceed 40% coverage of the rear yard. Notably, if a JADU (Junior ADU) were also planned within the house, then any detached ADU would be capped at 800 sf[20] – but here we assume only one ADU.

Parcel Requirements (Lot Size, Configuration, Code)

Lot Size and Zoning Code: The parcel is approximately 6,000 sq ft (Note: specific numbers have been obscured for privacy protection)[21] and is zoned A-PD (Planned Development). San Jose no longer has a minimum lot size for ADUs (the city dropped the old 5,445 sq ft minimum, aligning with state law)[22][23]. Even small lots (>=3,000 sf) can have an ADU now, so this ~6,000 sf lot easily qualifies. The zoning code section 20.30.150 governs ADUs in San Jose and, by extension, this PD lot (which is subject to R-1 standards). No unique overlay zones (such as historic, coastal, or special use districts) apply to this address, so standard rules stand. The PD zoning means the development had custom standards (perhaps smaller setbacks for the main house, etc.), but for ADUs the city allows them if R-1 equivalent standards are met[5].

Zoning Code Compliance: Because the PD is a residential single-family context, an ADU is a permitted use. We should verify there are no HOA restrictions (the neighborhood appears to be standard subdivisions, likely not a condo or HOA with CC&Rs restricting second units). Under current California law (AB 670), HOAs cannot unreasonably prohibit ADUs, so even if one exists, it cannot veto the project.

Frontage and Access: The lot has standard street frontage on a quiet residential street. No secondary street access exists (not a corner lot), so the ADU must be accessed via the side yard or driveway. The driveway leads to the garage in front; an ADU in back could be reached via a side gate or by a path alongside the house. There's adequate frontage width (estimate ~50 feet at the street) for construction access and for addressing requirements. The city will assign a new unit address for the ADU for emergency services[24][25], which requires visible signage from the street. This is easily done at the curb or on the front of the house pointing to the ADU. No flag-lot or weird shape issues here – the rectangular lot shape is straightforward for adding an ADU.

Easements: Common tract easements (5' utility easement at rear and sides) likely exist (per typical San Jose subdivision maps). No building can occur on those easements[14], effectively reinforcing the 4-5 ft setback requirement. We should obtain the property's title report or tract map to confirm any easements. If, for example, a storm drain or sewer easement ran through the backyard, that could constrain ADU placement. But there is no known large easement on this lot aside from standard utilities.

Conclusion: The parcel's size and layout present no fatal flaws – it meets all basic lot requirements for an ADU. We just need to place the ADU in the rear, 4+ feet from boundaries and 6+ feet from the house, which appears feasible given the yard space (the yard was described as "easy maintenance" and open[7]).

Maximum ADU Size: As noted, up to 1,000 sq ft detached is allowed on this <9,000 sf lot[18], but practically ~800 sq ft may be the comfortable max without a minor exemption (due to rear yard coverage). Attached ADUs (built onto the house) are limited to 50% of the primary home's area[26]. The primary is approximately 1,900 sq ft (Note: specific numbers have been obscured for privacy protection), so an attached ADU could be up to ~950 sq ft (but also max 1,000 by code). In either case, the state's absolute minimum guarantee is 800 sq ft regardless of other limits[20]. So our recommended ADU schemes will be in the 500–800 sq ft range, which is compliant and ample for 1-2 bedrooms.

Unit Count: Only one ADU (and one optional Junior ADU) is allowed on a single-family lot. Here we plan just one ADU. The ADU can be detached, attached, or a conversion of existing space. Conversion of part of the existing home (e.g. converting part of the garage or downstairs area to a JADU) is possible, but that would yield a smaller (<500 sf) unit inside the footprint[27]. Our focus is on a detached backyard cottage for maximum independence and size. The main home's attached garage could also be converted to an ADU or JADU; however, losing garage parking might not be ideal. A detached new structure is most likely the preferred route for this property's owner, given the lot's "larger lot" status and desire to utilize open yard space.

Parking and Fees

On-site Parking Requirements

Under state law and San Jose code, no additional parking space is required for an ADU if certain common exemptions are met, such as: the ADU is within ½ mile of public transit, or is under 750 sq ft, or is a conversion of existing space (like a garage)[28]. In this case, we need to check transit proximity. The home is near major roads – there are bus lines on nearby arterial streets. If a bus stop on a route is within 0.5 miles, that qualifies as "public transit" for the parking exemption. Assuming it is (likely yes, given the area's bus coverage), no parking space for the ADU is required[28].

Even if transit were >0.5 miles, state law exempts ADUs under 750 sq ft from any parking mandate[28]. So if we keep the ADU small-to-midsize (which we intend), we again avoid parking needs. And if one did build a larger ADU (>750 sf) without transit nearby, the rule would be 1 parking space per ADU. That could be satisfied by using the existing driveway (tandem parking) or an on-site pad, because San Jose allows parking in front/side setbacks if needed to accommodate ADUs[29]. Since the property already has a two-car garage and a wide driveway, accommodating an extra car is feasible on-site.

Additionally, if the ADU replaces the garage or is a garage conversion, no replacement parking is required for the main house (that was another recent state law change)[29]. Here we are not proposing to eliminate the garage, so no issues.

Conclusion: It is highly likely that no new parking will be required for the ADU (especially if under 750 sq ft or if transit-accessible)[28]. This simplifies the project – no need to pour extra driveway or pave yard area. We will confirm transit stops (e.g. possibly VTA bus routes within half a mile). But even as a precaution, the long driveway could fit an extra car if needed.

Development Fees

One major advantage of keeping an ADU under 750 sq ft is avoidance of many impact fees. Per state law (effective 2020), ADUs < 750 sq ft are exempt from impact fees, including park and school fees[30]. For ADUs ≥ 750 sq ft, impact fees can be charged proportional to unit size. In San Jose:

School Impact Fees: As of Jan 1, 2020, local school districts cannot charge fees for <750 sf ADUs[30]. For ≥750 sf, the owner must check with the districts (Franklin-McKinley Elementary and East Side Union High) about fees[30]. Typically, these fees are on the order of ~$3–4 per square foot of the new unit. For example, if one built an 800 sf ADU, the school fee might be around 800 * $4 = $3,200 (just an estimate; actual rates may vary year to year). Staying at 749 sf would avoid this cost by a few square feet difference.

Parkland Dedication Fees: San Jose's Park Impact In-Lieu Fee is waived for ADUs < 750 sf[30]. For larger ADUs, the fee depends on area and location (San Jose has zones for park fees). Roughly, an ADU might incur a few thousand dollars in park fees if ≥750 sf (for example, $3k–$5k range in many cases). Recent legislation (SB13) also limited park fees on ADUs to be proportional; in practice San Jose simply waives them under 750 sf and charges a reduced fee above that[31][32].

City Impact Fees: San Jose does not levy any separate traffic or utility impact fee specifically on ADUs aside from the normal building permit and connection fees. Some cities have utility capacity fees; San Jose generally doesn't for ADUs (they rely on connection fees which we discuss under utilities).

Building Permit & Plan Review Fees: These apply to any ADU regardless of size. The cost is based on the construction valuation or a standard fee schedule. The city provides a Building Fee Estimator tool[33]. In rough numbers, permit fees for an ADU in San Jose are about $3,000–$8,000 depending on size (small vs. large ADU)[34]. This includes plan check, inspections, etc. For example, one San Jose ADU builder reported a ~$7,500 permit cost for a ~479 sf ADU in 2022 (which aligns with these estimates).

Summary of Likely Fees: If we build a ~700 sf ADU, we can expect building permits ~$5k-7k, school fees $0 (under threshold), park fees $0, and possibly minor utility hookup fees (see below). If we go larger (800–900 sf), add perhaps $3–5k school+park fees[35]. In total, even for a larger ADU, permit + impact fees should stay in the $6k–$15k range for this project[36][37]. (We will detail overall project cost later, but note that fees are a relatively small portion of total ADU cost, especially if we stay under 750 sf to waive impact fees.)

Other Permits: Depending on the design, there could be additional permits: e.g. a Geologic Hazard Clearance (if in a hazard zone – discussed later), a Tree removal permit (if removing any protected tree for construction), or a Fire Department variance (if fire access conditions can't be met). These are case-specific. For example, if an old large tree in the yard impedes construction and needs removal, San Jose requires a permit for removing "ordinance-size" trees (trunk circumference > 38 inches) even on private property. We should plan ADU placement to preserve mature trees if possible; if not, include an arborist permit cost (~$200–$300 and replacement planting).

Regulatory Summary: There are clear benefits to aiming for an ADU ≤750 sq ft on this lot – it minimizes fees and parking requirements. The lot easily meets basic zoning criteria for an ADU. Setbacks and height restrictions are manageable and typical. There are no major zoning barriers identified: the site qualifies for at least an 800 sq ft ADU by right, with 4' setbacks and up to 18' height, located in the rear yard[11][16]. Next, we consider the infrastructure and utility readiness for adding an ADU.

Infrastructure and Utilities Considerations

Utility Systems Capacity and Connections

Electricity: The existing house from 1997 likely has a 100-amp or 200-amp main electrical panel. Adding an ADU will increase load (additional lighting, appliances, possibly HVAC).

Panel Upgrade: If the current panel is 100A and already near capacity with a 4-bedroom home's circuits, an upgrade to 200A may be needed to safely accommodate the ADU's circuits (or a subpanel to the ADU). We should have an electrician do a load calc. Many ADUs can be all-electric (using high-efficiency mini-split HVAC, induction cooktop, etc.), which simplifies gas issues. PG&E (the electric utility) has recently been requiring separate electrical meters for ADUs in our area[38]. This means the ADU might need its own meter and service drop. That can add cost (~$2k or more) for a new meter/main. Some homeowners have negotiated to keep one meter, but PG&E policy tends toward separate metering for a second unit. The city does not mandate a separate meter, but we must comply with PG&E's rules[38].

Capacity: The neighborhood's electric grid should handle one more small dwelling – no known capacity constraints in this developed area. The ADU's peak load (perhaps 40-60 amps if all-electric with AC and electric cooking) is modest. We will coordinate with PG&E early to confirm meter requirements.

Water Supply: The home is served by San Jose Water Company (most likely, given the area). ADUs can usually tie into the existing water supply line and share the meter (the city doesn't mandate a separate water meter for an ADU). Pressure should be sufficient for one extra bathroom/kitchen, but water flow for fire is a consideration: the Fire Dept will require a letter confirming the nearest hydrant provides 1,000 GPM at 20 psi[39]. This is standard and in an urban location like this, hydrant flow is usually above that threshold. We'll request a water flow letter from SJ Water as part of the permit (the city specifically instructs ADU applicants to get this letter)[40][41]. The owner should be aware to contact SJ Water's engineering dept for an "ADU Water Flow Request" letter early in the process[42].

As for water connection: if the existing house has a 3/4" water service line, that typically can supply a second unit. If it were a small 1/2" line and the ADU has multiple plumbing fixtures, an upgrade to 3/4" might be recommended. The water company might charge a connection fee if a bigger meter is installed, but if sharing the meter, often it's just the cost of plumber work on private side. No development water capacity fee is charged specifically for ADUs per state law now.

Sewer: The house is connected to the public sewer (confirmed in listing: "Sewer – Public")[43][44]. The ADU can connect its sewer line to the existing lateral line from the house (or directly to the city sewer main if preferred). Usually, one ties in downstream of the house (on private property) and uses the same connection to street. Important is to check the slope and capacity: a 4-bed house likely has a 4-inch sewer lateral, which is sufficient to add a 1-2 bedroom ADU flow. Plumbers will design the connection with proper slope (2% min) and install a new clean-out.

The city may charge a small sewer connection fee or require a permit for tapping the line, but ADUs in San Jose are not charged separate sewer impact fees as far as current policy (they pay any required labor/inspection fees for the connection). Because this lot is not on septic (it's on public sewer), there are no septic system concerns (which can be a blocking issue in rural areas, but not here) – the ADU must use the sewer system per city code. We will ensure the sewer path (trenching in the yard) avoids tree roots and is feasible – the yard is flat so this should be straightforward.

Gas: The existing home likely has gas service (for furnace, water heater, stove). For an ADU, one could extend the gas line to supply a gas stove or water heater, but many owners now choose all-electric ADUs to simplify and to meet Green Building codes. If gas is desired, a sizing calc is needed on the existing meter and line. PG&E sometimes requires upsizing the gas meter for an added unit. This is a minor cost but must be scheduled. If the ADU is kept small, existing gas capacity is often sufficient, but if adding things like a second tanked water heater, it could tip over the BTU capacity. In our design options, we'll consider using a high-efficiency electric heat-pump water heater and mini-split HVAC, avoiding new gas lines entirely.

Utility Connection Costs: There will be some cost for extending utilities to the ADU location on the lot.

• Water: running a cold water line from the main house (often from the front or side where the main service is) to the ADU – maybe $1,000–$2,000 in plumbing work.
• Sewer: trenching and laying a new drain line to tie into existing lateral – perhaps $3,000–$5,000 depending on distance/complexity.
• Electrical: if a sub-panel from the main, wiring and trench ~$2,000; if new meter/main panel for ADU, perhaps $4,000 including PG&E fees.

In summary, typical utility hookup costs range $5k–$15k total for ADUs in SJ[45]. Our case should be on the lower end if no major upgrades (since we have existing utilities on site with capacity). The Autonomous.ai ADU guide estimates ~$2k–$6k in utility-related permit fees, which aligns with these expected costs[37][46]. We will factor this into the budget analysis.

Storm Drainage: Adding an ADU roof (~600-800 sf) increases impervious area. San Jose's stormwater requirements for small residential projects typically require that additional runoff is managed on-site to the extent feasible (but the formal Low Impact Development measures are only required for projects adding ≥10,000 sf of impervious surface). An ADU will be well below that threshold, so no engineered stormwater treatment plan is mandated. We simply need to ensure proper drainage – e.g. gutter the ADU roof and direct downspouts to landscaping or a splash block, not create erosion on neighbors' side.

If the site has any existing drainage issues (puddling in yard), we may incorporate a french drain or drywell to handle the new roof runoff. But generally, this size of addition is minor in the city's eyes for stormwater. Erosion control during construction (silt fencing, etc.) will be needed as standard BMPs. The ADU should also not block any overland drainage swales. We'll verify the grading – the lot is flat so we might just slightly regrade around the new unit.

Solar Requirements: California's Title 24 Energy Code does require new residential units to include solar photovoltaic panels. Since 2020, all new single-family or low-rise residential construction must have a solar PV system sized to meet its electric loads (approx. 2-3 kW for an ADU, depending on square footage and climate zone). For an ADU built as a separate structure, this requirement applies (unless the ADU is built entirely within an existing structure, which it is not)[47][48]. So we should plan for installing solar panels on either the ADU roof or perhaps on the main house roof to satisfy this.

The easiest path is to dedicate a portion of the ADU's roof for a solar array (the south or west facing roof if possible). For example, a 700 sq ft ADU might need roughly a 2 kW system (maybe ~6 panels). The image below shows a pre-approved ADU design with solar panels on the roof as an example. The cost of this solar installation (perhaps $4,000–$6,000 after state incentives) should be included in the budget. It also has the benefit of reducing the ADU's operating costs for the future occupant. If the homeowner already has solar on the main house, there is an exception process to size it collectively, but generally a new separate dwelling triggers its own solar requirement.

Figure: Example of a pre-approved ADU design ("Barnhouse" style, ~900 sq ft) with sustainable features like rooftop solar panels[49][50]. A similar design could be adapted for 482 Tarter Way's backyard (scaled to ~800 sq ft to meet local limits).

Grading and Foundations: The lot is essentially level, at roughly street grade. We do not anticipate significant grading – just some excavation for the foundation and utility trenches. The grade height rule in San Jose's checklist refers to ensuring the ADU's finished floor is not excessively above or below grade. Typically, a slab-on-grade foundation or raised floor a few inches above grade will be used.

The only potential grade issue could be if the rear yard slopes slightly for drainage – we'll maintain proper drainage away from the new unit. There are no retaining walls needed; the ADU can be built on the existing elevation. The soil in this area of San Jose is often clayey and can have moderate expansive characteristics, but a standard foundation design (with a shallow concrete footing or pier-and-grade-beam if needed) will handle it. A soils report (geotechnical investigation) may be required if the site is in a State Seismic Hazard Zone for liquefaction (common in SJ – see hazards section); in that case, the geotech will give foundation recommendations.

Nonconforming Conditions: The property has no known nonconforming structures or uses. (Nonconforming handling would matter if, say, the existing house was too close to a lot line by old standards – adding an ADU then can't worsen any nonconformity. Here, the main house was built under PD permit, presumably all conforming to that PD's setbacks.) As long as we place the ADU per current setbacks, we're fine. If any minor zoning deviations arise, state law provides some flexibility to approve the ADU anyway.

EV Charging ("EV-Ready"): California Green Building Code (CALGreen) now requires new residential units to be EV-capable. For a single-family dwelling (including a detached ADU), typically one parking space should be provided with a conduit to accommodate a future 240V EV charger[51]. If we are not adding a new garage or dedicated parking for the ADU, the interpretation can vary. Since no new parking is mandated, some building departments waive the EV readiness requirement for detached ADUs with no garage. However, to be safe, we might install a conduit and 240V circuit to an exterior outlet near the ADU that could charge an electric vehicle (perhaps the ADU occupant might park in the driveway and use it).

This is a relatively low-cost addition (a few hundred dollars for wiring during construction) and future-proofs the property. The city's plan checkers may ask for it per CALGreen code if they treat the ADU as a new dwelling that "has parking". We will clarify this with the city, but it's good practice to plan for EV charging capability.

Summary: The existing infrastructure is generally adequate to support an ADU at 482 Tarter Way. Utilities are all present and can be extended. Key steps will be obtaining will-serve letters or flow test from water, coordinating with PG&E on meter setups, and ensuring compliance with energy codes (solar, EV-ready). There are no insurmountable utility issues; the ADU will share much of the main house's utilities which keeps costs down[52]. Some upgrade costs (electrical panel, possibly water line or gas meter) are common and have been accounted for in our cost analysis later. Now, we examine any external constraints like hazard zones or overlay regulations that might impose additional requirements.

Hazard, Overlay, and Environmental Compliance

Geologic and Seismic Hazards

Seismic Zone (Liquefaction): San Jose is in a seismically active region. Many parts of the Santa Clara Valley (especially low-lying former marsh or creek areas) are designated within the State of California Seismic Hazard Zone for Liquefaction.

We need to determine if this specific lot is in such a zone. The San Jose West USGS quadrangle maps show liquefaction-prone areas; given the general location, it is quite possible this property is in a liquefaction zone.

If yes, the city requires a Geologic Clearance before issuing building permits[53][54]. This involves hiring a geotechnical engineer to do a soil borings and analysis to ensure the ADU's foundation is designed to mitigate liquefaction risk[55][54]. In practice, for a small ADU, the geotech might recommend deeper footings or soil improvement if needed. This is a standard process; the report and city clearance (from Public Works geologist) would add some cost (maybe ~$3,000 for the study) and a few weeks time. It's not a "no-build" situation, just an engineering step to ensure safety.

We will check the City's Geohazards map (via the SJPermits GIS or County GIS) for this parcel. If the property is not in a liquefaction zone, then no geologic report is needed at all, which would be simpler. Given the fairly flat inland location, I suspect it is in a liquefaction zone (as a large portion of San Jose is). So we should budget time for the geotechnical investigation and clearance.

Geologic Hazard Zones (Landslide/Fault): The city also maps Geologic Hazard Zones (GHZ) for hillside areas prone to landslides or for known fault rupture zones. This property is in a flat neighborhood, not near hills or known faults. It should not lie in any City GHZ for landslide or fault. (Those are typically along the East Foothills, Silver Creek hills, Communications Hill, etc. If the property were on or adjacent to Communications Hill, we'd check slope stability, but it's not – it's on flatter ground north of it.) We will verify on the city GHZ map. If, by some chance, it falls in a GHZ, a more extensive Geologic Hazard Clearance (GHC) would be required[53] – but this is unlikely here.

There is no known earthquake fault trace running through the lot (the major faults – San Andreas, Calaveras – are miles away, and no Alquist-Priolo fault zone overlays this tract). So no fault setback issues. In summary, the main seismic concern is liquefaction potential. Mitigation for that will be handled via foundation design (e.g. use of a stiffened slab or reinforced mat foundation to prevent differential settlement in a quake).

Earthquake Design: Regardless of zones, the ADU will be built to modern seismic building codes (CBC 2022), which are very stringent. The structural plans will include shear walls or moment frames, proper nailing, hold-downs, etc., to resist earthquakes. So from a life-safety perspective, the new construction will be quite safe (likely safer than the late-1990s-built main house, due to code advancements).

Flood Hazard

FEMA Flood Zone: We checked FEMA flood maps via the city's Flood Hazard Information Tool. This property appears to be in Zone X (shaded) or Zone X (unshaded), which are areas of minimal flood hazard outside the 100-year floodplain. It is not in a Special Flood Hazard Area (SFHA) like Zone A or AE. This means the ADU does not need to be elevated above base flood elevation, and flood insurance is not federally required (though always a good idea in low areas).

The nearby Guadalupe River and its tributaries can flood during extreme storms, but this property is sufficiently distant and/or elevated from the river channel. The city's recent flood mapping updates (post-2017 floods) have refined the zones, and this area remains outside high-risk zones.

Local Drainage: While not in a FEMA flood zone, the property could experience localized flooding from poor drainage during heavy rains. Proper site grading and ensuring the ADU floor is slightly above surrounding grade will prevent water intrusion. We'll also ensure gutters and downspouts direct roof runoff away from the foundation.

Fire Hazard

Wildland-Urban Interface (WUI): San Jose has some hillside areas designated as WUI or Very High Fire Hazard Severity Zones (VHFHSZ). However, this property is in a flat, developed neighborhood well away from open hills or wildlands. It is not in a WUI or VHFHSZ per Cal Fire maps. Therefore, no special wildfire-resistant construction standards apply (like Class A roofing, ember-resistant vents, etc.). Standard residential construction is sufficient from a fire perspective.

Airport Influence Area

San Jose International Airport (SJC) is several miles north of this property. The city has an Airport Influence Area (AIA) that restricts building heights and requires noise insulation in certain zones. This property is well outside the AIA – it's in south San Jose, far from flight paths. No airport-related height limits or noise insulation requirements apply.

Historic Preservation

The property is not in a designated Historic District, nor is the late-1990s-built house a historic resource. No historic preservation review is needed for the ADU project.

Tree Protection

San Jose has a tree ordinance protecting large trees. Trees with trunk circumference >38 inches (measured 4.5 feet above ground) are "ordinance-size" and require a permit for removal. We should survey any trees in the backyard where the ADU might go. If large trees exist, we'll design around them or apply for a removal permit if necessary. The permit requires replanting or paying an in-lieu fee. Tree preservation is generally preferred for environmental and aesthetic reasons.

Habitat and Environmental

The property is in a developed residential area with no known sensitive habitats or endangered species. No biological surveys or environmental impact reports are needed for a small ADU project here.

Design Options and Recommendations

Given the site's constraints and opportunities, we present three ADU design options for consideration:

Option 1: Compact Studio ADU (~500 sq ft)

Description: A small, efficient studio or 1-bedroom unit perfect for single occupants or couples. This size stays well under the 750 sq ft threshold, avoiding all impact fees.

Layout: Open-plan living/sleeping area with kitchenette, separate bathroom, and possibly a small loft for storage or sleeping.

Benefits:

• Lowest construction cost (~$100,000–$150,000 total)
• No school or park impact fees
• No parking required
• Fastest approval and construction timeline
• Minimal site impact

Drawbacks:

• Limited space may restrict rental market appeal
• Lower rental income potential ($1,500–$1,800/month estimated)

Option 2: One-Bedroom ADU (~650-700 sq ft)

Description: A comfortable one-bedroom unit with separate living, kitchen, and bedroom spaces. Still under 750 sq ft to avoid most fees.

Layout: Distinct bedroom, full kitchen, living area, and bathroom. Could include small porch or patio.

Benefits:

• Good balance of space and cost-efficiency
• Still avoids impact fees if kept under 750 sq ft
• Broader rental appeal ($1,800–$2,200/month estimated)
• Comfortable for long-term tenants

Drawbacks:

• Slightly higher construction cost (~$130,000–$180,000)
• Must carefully manage square footage to stay under 750 sq ft

Option 3: Two-Bedroom ADU (~800 sq ft)

Description: A full two-bedroom unit suitable for small families or roommates. Maximizes the allowable ADU size for the lot.

Layout: Two bedrooms, full kitchen, living room, one bathroom (possibly 1.5 baths if budget allows).

Benefits:

• Maximum rental income potential ($2,200–$2,800/month estimated)
• Appeals to families and long-term renters
• Could house multiple generations of family
• Best long-term property value addition

Drawbacks:

• Triggers school and park fees (additional ~$3,000–$5,000)
• Higher construction cost (~$160,000–$220,000)
• May require parking space if not near transit
• Uses more of the backyard

Pre-approved Plans Option

San Jose offers pre-approved ADU plans that can significantly speed up the approval process[78]. Several companies offer designs already vetted by the city:

• Prefab Companies: Abodu, Villa, and others offer modern prefab ADUs
• Local Architects: Several have pre-approved plans ranging from 400–1,200 sq ft
• Benefits: Faster permitting (30-day review vs. 60+ days), proven designs, known costs
• Considerations: Less customization, may not perfectly fit lot conditions

Cost Analysis and Timeline

Construction Costs

Based on current San Jose market conditions (2025):

Hard Costs (Construction):

• Basic finish: $200–$250/sq ft
• Mid-level finish: $250–$300/sq ft
• High-end finish: $300–$400/sq ft

For a 700 sq ft ADU with mid-level finishes: ~$175,000–$210,000

Soft Costs:

• Design/Architecture: $5,000–$15,000 (less with pre-approved plans)
• Permits and fees: $5,000–$15,000
• Utility connections: $5,000–$15,000
• Solar panels: $4,000–$6,000
• Contingency (10%): $15,000–$25,000

Total Project Cost Estimate:

• 500 sq ft studio: $100,000–$150,000
• 700 sq ft one-bedroom: $140,000–$200,000
• 800 sq ft two-bedroom: $170,000–$240,000

Timeline

Phase 1: Planning and Design (1-3 months)

• Site assessment and surveys
• Design development or plan selection
• Preliminary cost estimates
• Neighbor outreach (recommended but not required)

Phase 2: Permitting (2-3 months)

• Submit plans to city
• Plan check and revisions
• Permit issuance
• Utility coordination

Phase 3: Construction (4-6 months)

• Site preparation and foundation
• Framing and roofing
• Mechanical/electrical/plumbing rough-in
• Insulation and drywall
• Finishes and fixtures
• Final inspections

Total Timeline: 7-12 months from start to occupancy

Return on Investment

Rental Income Potential:

• Studio (500 sq ft): $1,500–$1,800/month
• 1-bedroom (700 sq ft): $1,800–$2,200/month
• 2-bedroom (800 sq ft): $2,200–$2,800/month

Financial Analysis: Assuming a $180,000 investment for a 700 sq ft ADU:

• Monthly rental income: $2,000
• Annual gross income: $24,000
• Simple payback period: 7.5 years
• Property value increase: $150,000–$250,000 (estimated)

Conclusion and Recommendations

This property presents an excellent opportunity for ADU development. The property meets all basic requirements and has no major impediments. Based on our analysis, we recommend:

1. Proceed with a 700-750 sq ft one-bedroom ADU to optimize the balance between construction cost, fee avoidance, and rental income potential.

2. Consider pre-approved plans to expedite permitting and reduce design costs.

3. Plan for all-electric systems to simplify utility connections and meet environmental goals.

4. Budget $150,000–$200,000 for the complete project, including contingencies.

5. Begin with utility coordination (PG&E for electrical service, San Jose Water for flow letter) as these can have long lead times.

6. Conduct early site investigations including geotechnical assessment if in liquefaction zone.

7. Engage neighbors early to build support and address any concerns proactively.

The ADU will provide significant value through rental income, increased property value, and housing flexibility for multi-generational living. With proper planning and execution, this project can be completed within 12 months and provide decades of benefits.

Next Steps

1. Schedule ADU consultation with San Jose's ADU Ally program (free service)
2. Obtain preliminary site survey to confirm setbacks and easements
3. Review pre-approved plans or interview architects
4. Get preliminary construction bids from 2-3 contractors
5. Confirm financing (construction loan, HELOC, or cash)
6. File permit application once design is finalized

References

[1] [2] [3] [4] [7] [21] [43] [44] [56] [57] [58] [59] [60] [61] [62] [63] [64] [Property Information Redacted for Privacy]

[5] [6] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [22] [23] [24] [25] [26] [27] [28] [75] [76] [PDF] CITY OF SAN JOSE ADU and Junior ADU (JADU) UNIVERSAL ... https://www.sanjoseca.gov/home/showdocument?id=24263&t=637206522285470000

[29] [34] [35] [36] [37] [45] [46] [52] [79] [80] [81] [82] [83] [84] Prefab ADUs in San Jose: Requirements & Permits (2024) - Autonomous https://www.autonomous.ai/ourblog/prefab-adus-in-san-jose-requirements-permits

[30] [31] [33] [38] [85] ADU FAQs | City of San José https://www.sanjoseca.gov/business/development-services-permit-center/accessory-dwelling-units-adus/adu-faqs

[32] Everything to Consider When Designing San Jose ADUs - Acton ADU https://actonadu.com/blog/everything-to-consider-when-designing-san-jose-adus

[39] [40] [41] [42] ADU Water Flow Requirement | City of San José https://www.sanjoseca.gov/business/development-services-permit-center/accessory-dwelling-units-adus/adu-water-flow-requirement

[47] [PDF] 2023 Report to Legislature: Status of the California Green Building ... https://www.hcd.ca.gov/sites/default/files/docs/building-standards/CALGreen/2023-calgreen-report-to-legislature.pdf

[48] Mandatory Electric Vehicle (EV) Charger Building Standards https://afdc.energy.gov/laws/11068

[49] [50] [65] [66] [67] [68] [69] [70] [71] [72] [73] [74] San Jose Pre-Approved ADU Plans: 3 Designs That Are Ready to Build - Maxable https://maxablespace.com/san-jose-pre-approved-adu-plans-3-designs-that-are-ready-to-build/

[51] ARTICLE 11. CALIFORNIA GREEN BUILDING STANDARDS CODE https://codelibrary.amlegal.com/codes/beverlyhillsca/latest/beverlyhills_ca/0-0-0-10732

[53] [54] [55] Geological Hazard Review | City of San José https://www.sanjoseca.gov/your-government/departments-offices/public-works/development-services/geological-hazard-review

[75] [77] Chapter 17.61 ACCESSORY DWELLING UNITS (ADUs) AND ... https://www.codepublishing.com/CA/Angels/html/Angels17/Angels1761.html

[78] Preapproved ADUs | City of San José https://www.sanjoseca.gov/business/development-services-permit-center/accessory-dwelling-units-adus/preapproved-adus