A whole-home Passive House retrofit in Los Gatos, designed and built to certified Passive House performance — using roughly 90% less energy than a code-built California home, with continuously filtered fresh air, a near-airtight envelope, and a non-combustible exterior engineered for the wildland-urban interface.
Continuous insulation, an airtight shell, and triple-pane windows mean almost no heat escapes. The whole home stays warm with a fraction of the energy a typical house needs.
A typical winter's heating runs on roughly 1/4 to 1/7 the energy of a code-built home.
Heat doesn't escape because there's almost nowhere for it to go. The home is built like a thermos: continuous insulation outside the structure, with no thermal bridges through framing, no leaky penetrations, and high-performance triple-pane glazing.
The Passive House "high" envelope targets work out to R-35 walls, R-65 roof, R-20 slab — roughly 2× the effective R-value of a code-built California assembly.
| Assembly | U-value | ≈ R |
|---|---|---|
| Wall to exterior (PH 'high' tier) | ~0.162 W/m²K | R-35 |
| Ceiling / roof (PH 'high' tier) | ~0.087 W/m²K | R-65 |
| Slab on grade (PH 'high' tier) | ~0.284 W/m²K | R-20 |
| Windows installed (Uw) | ~0.86 W/m²K | ≈ U-0.15 |
Most homes have hundreds of small gaps in their walls and ceilings. Each is a path for drafts, energy loss, and — in California — wildfire smoke. This shell is sealed, taped, and pressure-tested.
About 10× tighter than the same house built to current code.
Every joint, every penetration is sealed against air movement. A vapor-permeable air-barrier membrane wraps the structure on the outside; tapes and gaskets close every seam; cans, ducts, and electrical penetrations get airtight sealing kits.
It isn't taken on faith — the house is pressurized to 50 pascals with a blower door, and any leak above target is hunted down and fixed before drywall closes the wall.
| Detail | Spec |
|---|---|
| Primary air barrier | Vapor-permeable WRB, taped & sealed |
| Window/door rough openings | Liquid-applied flashing + tape |
| Penetrations | Airtight gaskets & sealants |
| Test method | Blower door @ 50 Pa |
| Target leakage rate (n50) | ≤ 0.6 ACH₅₀ |
| Code-built baseline (CA) | ~ 3 ACH₅₀ |
| Older homes (typical) | 5–10 ACH₅₀ |
An airtight house breathes through one place: a continuously running, filtered heat-recovery ventilator. Pollen, traffic soot, and wildfire smoke get filtered out before they reach a bedroom.
During wildfire season, most smoke enters homes through the same cracks that leak heat: sill plates, recessed lights, attic penetrations. Sealing the envelope means sealing out smoke.
Combined with a filtered HRV that gently pressurizes the interior with clean outdoor air, the family inside has a refuge of breathable air — even when the sky is orange.
Outdoor air is filtered to MERV-13 (F7) — pollen, traffic soot, and wildfire PM 2.5 are removed before air ever reaches a bedroom.
The ERV/HRV runs continuously at 23 cfm per occupant, capturing most of the heat in the leaving air on its way out — so fresh air doesn't mean cold air or a big bill. An automatic summer bypass mode allows free night cooling when outside conditions favor it.
The HRV runs continuously at a low rate, replacing roughly the entire air volume of the home every 2–3 hours with filtered fresh air — quietly, efficiently, and balanced.
Stale air from kitchens and baths leaves through one duct; fresh outdoor air enters through another, passing through the filter and the heat exchanger on the way to bedrooms and living spaces.
| Parameter | Spec |
|---|---|
| Ventilation system | ERV/HRV continuous, balanced |
| Fresh-air supply rate | 23 cfm/person (24-hr average) |
| Supply filtration | F7 / MERV-13 |
| Summer bypass | Automatic — free night cooling when conditions favor |
| Supply locations | Bedrooms · living areas · office |
| Return locations | Kitchen · bathrooms · laundry |
| Auxiliary | No range hood recirculation; sealed make-up air |
Triple-pane windows with two argon-filled cavities aren't only thermal insulators — they're sound insulators. Street traffic, neighbours, the lawnmower next door: all quieter from the inside.
Each ~10 dB drop sounds about half as loud to the human ear.
The same triple-pane glazing that drives down heat loss is also a heavy, dense barrier to airborne sound. Each cavity de-tunes a different frequency band; argon damps mid-range traffic; the laminated outer pane handles high-frequency noise.
Frames are insulated and thermally broken — not aluminum, not vinyl — so they don't become a path for either heat or noise around the glazing.
| Spec | Value |
|---|---|
| Glazing makeup | Triple-pane, two argon cavities, 2× low-E coatings, 1.8" overall |
| Center-of-glass U-value (NFRC) | 0.113 BTU/h·ft²·°F (≈ 0.642 W/m²K) |
| Window U-value installed (Uw) | ~0.86 W/m²K (≈ U-0.151) |
| Solar heat gain (g-value / SHGC) | 0.22 |
| Frame grade | phC-Grade Windows/Doors · insulated, thermally broken |
| Estimated outside-noise reduction (OITC) | ~38–42 dB |
Because the envelope is so efficient, the entire home — heat, cooling, hot water, induction cooking, EV charging — runs on a modest rooftop solar array. The grid acts as a battery: surplus power flows out in summer, and comes back in winter.
Annual solar generation is sized to match annual whole-house electricity demand. With Passive House construction cutting heating/cooling loads 80–90%, the panels needed are roof-friendly, not roof-covering.
All-electric end-uses: heat-pump heating & cooling, heat-pump water heating, induction cooking, EV charging — no gas line, no combustion in the home.
Because Passive House construction collapses heating and cooling demand by ~80–90%, the residual electricity load is mostly water heating, plug loads, lighting, induction cooking, and EV charging. A right-sized rooftop array balances that annual load.
Operating cost: essentially the cost of being grid-connected, after accounting for net-energy metering. No gas line, no combustion appliances, no CO from cooking.
| Energy use | Approach |
|---|---|
| Heating & cooling | Air-source heat pump · all-electric |
| Domestic hot water | Heat-pump water heater |
| Cooking | Induction (no gas service) |
| EV charging | Level 2 — wired in |
| Backup | All-electric · no combustion in the home |
| Generation | Roof PV — sized for net-zero annual electricity |
| Net annual energy | ≈ 0 kWh / year |
Wildfires destroy homes mostly through wind-blown embers finding flammable surfaces and unsealed openings. This exterior is built almost entirely from non-combustible materials.
Combined with the airtight envelope, the result is a home that resists ignition outside and keeps smoke outside.
The roof is the primary ember target. So it's standing-seam metal — the highest fire rating available (ASTM E108 Class A) — with sealed edges and ember-resistant attic vents.
The walls are stucco and fiber-cement, with mineral wool in critical layers. There's no exposed wood at the ember-vulnerable details: eaves, rake edges, soffits, and decks are detailed for ignition resistance.
| Element | Spec |
|---|---|
| Roof | Standing-seam metal · Class A (ASTM E108) |
| Cladding | Stucco + fiber-cement, ASTM E84 Class A |
| Insulation in fire-critical zones | Mineral wool (non-combustible) |
| Attic / soffit vents | Ember-resistant 1/16" mesh |
| Eave details | Sealed, no exposed framing |
| Decking | Composite or non-combustible substrate |
| Combustible materials at perimeter | Minimized · no wood within 5 ft of structure |
Independent third-party energy modeling using PHPP (Passive House Planning Package).
| Treated floor area (TFA) | 508.65 m² · 5,473 sf |
| Annual heating demand | 11.4 kWh/m²·yr (PH limit ≤ 15) |
| Annual cooling + dehumidification | 13.5 kWh/m²·yr (PH limit ≤ 15) |
| Airtightness · n50 | ≤ 0.6 ACH₅₀ (PH Classic target) |
| Active cooling included | Yes |
| Standalone dehumidification required | No |
| Site energy (heating + cooling, combined) | ~5,600 kWh/yr |
| Wall (PH 'high' R-value tier) | ~0.162 W/m²K · R-35 |
| Ceiling / roof (PH 'high' tier) | ~0.087 W/m²K · R-65 |
| Slab on grade (PH 'high' tier) | ~0.284 W/m²K · R-20 |
| Window U-value, installed (Uw) | ~0.86 W/m²K · ≈ U-0.151 |
| Glazing solar heat gain (g-value) | 0.22 (PH 3-pane spec) |
| Cladding | Stucco, fiber-cement, vertical wood accent |
| Roof | Standing-seam metal · Class A |
| Ventilation | ERV/HRV continuous · MERV-13 (F7) filtration · 23 cfm/person |
| Heating & cooling | Air-source heat pump · all-electric |
| Domestic hot water | Heat-pump water heater |
| Cooking | Induction · no gas service |
| Solar PV | Roof-mounted · sized for net-zero annual electricity |
Independent third-party energy modeling using PHPP — preliminary values from the Passive House design review.
| Parameter | Value | Unit / Note |
|---|---|---|
| Project type | Building Retrofit | Whole-home Passive House retrofit |
| City | Los Gatos, CA | Latitude 37.23°, Longitude −121.95° |
| Site elevation | 174 m · 570 ft | Altitude-corrected climate dataset |
| Treated Floor Area (TFA) | 508.65 | m² · 5,473 ft² |
| Gross envelope area | 1,566.37 | m² · 16,854 ft² |
| Form factor | 3.1 | ft²/ft² (envelope ÷ TFA) |
| Number of units | 1 | Single-family |
| Occupancy | 7 | persons |
| ASHRAE climate zone | 3B | Warm, Dry |
| CA Title 24 climate zone | 4 | — |
| PHI climate zone (site-specific) | Warm | — |
| Hygiene Criterion exterior temp | 9.4 | °C · 49.0 °F |
| Comfort Criterion exterior temp (12 coldest hrs) | 1.2 | °C · 34.2 °F |
| Criterion | PH limit | This house | vs. limit | Pass |
|---|---|---|---|---|
| Annual heating demand | ≤ 15 kWh/m²·a | 11.4 | 24% below | ✓ Yes |
| Cooling + dehumidification demand | ≤ 15 kWh/m²·a | 13.5 | 10% below | ✓ Yes |
| Airtightness · n50 @ 50 Pa | ≤ 0.6 ACH₅₀ | ≤ 0.6 | Meets target | ✓ Target |
| Active cooling included | — | Yes | — | — |
| Standalone dehumidification | — | No | Not required | — |
| Hygiene Criterion (mold/condensation) | 100% units pass | 100% | Met | ✓ Yes |
| Comfort Criterion (interior surface temp) | 100% units pass | 100% | Met | ✓ Yes |
Target wall R-value R-35 (PH 'high' tier).
| Layer (interior → exterior) | Material | Thickness |
|---|---|---|
| Interior finish | Drywall w/ vapor-open paint | ½" |
| Stud cavity | Vapor-open insulation (cellulose, dense-pack fiberglass, or mineral wool batts) | 5½" |
| Sheathing / air barrier | OSB or plywood, taped & sealed at all seams and penetrations | ½" |
| Continuous exterior insulation | Mineral wool, EPS, or wood fiber · metal fasteners | 4–5" |
| Weather barrier | Vapor-open WRB, wind-barrier function | — |
| Vented cavity | Pressure-treated furring strips | ¾" |
| Cladding | Stucco · fiber-cement · vertical wood accent (per architectural) | — |
| Wall assembly target R-value | 2x6 + continuous insulation | R-35 |
| Element | Spec | Target |
|---|---|---|
| Roofing | Standing-seam metal · Class A (ASTM E108) | — |
| Underlayment | High-temp self-adhered membrane | — |
| Sheathing / air barrier | Plywood, taped seams | — |
| Continuous insulation | Polyiso (or equivalent) — sized for target R-value | — |
| Ceiling / Roof target R-value | PH 'high' tier | R-65 |
| Layer | Material | Target |
|---|---|---|
| Slab | Concrete | 4" |
| Sub-slab continuous insulation | XPS or EPS foam (closed-cell) | R-20 |
| Vapor barrier | Reinforced poly, taped to walls | — |
| Capillary break / drainage | Compacted gravel | — |
| Slab on grade target R-value | PH 'high' tier | R-20 |
| Spec | Value | Notes |
|---|---|---|
| Glazing makeup | Triple-pane | Two argon-filled cavities, 2× low-E, 1.8" overall |
| Center-of-glass U-value (NFRC, Ucog) | 0.113 BTU/h·ft²·°F | ≈ 0.642 W/m²K |
| Window U-value installed (Uw) | ~0.86 W/m²K | ≈ U-0.151 in U.S. units |
| Glazing solar heat gain (g-value / SHGC) | 0.22 | Low-gain coating (PH 3-pane spec) |
| Frame grade | phC-Grade | PHI efficiency class for transparent components |
| Frame construction | Insulated, thermally broken | Not aluminum, not vinyl |
| Window units per 100 ft² TFA | 1.5 | Average unit size 32.4 ft² |
| Edge spacers | Plastic (warm) | No metal — avoids thermal bridging |
| Estimated outside-noise reduction (OITC) | ~38–42 dB | vs. ~28 dB code dual-pane |
| System | Spec |
|---|---|
| Heating & cooling | Air-source heat pump (variable speed) · all-electric |
| Active cooling included | Yes |
| Standalone dehumidification | Not required |
| Domestic hot water | Heat-pump water heater (HPWH) |
| Ventilation | ERV/HRV continuous, balanced |
| Fresh-air supply rate | 23 cfm/person (24-hr average) |
| Filtration | F7 / MERV-13 supply filter |
| Summer bypass | Yes — automatic free cooling at night when conditions favor |
| Cooking | Induction · no gas service |
| EV charging | Level 2, hardwired |
| Solar PV | Roof-mounted · sized for net-zero annual electricity |
| Combustion appliances | None — all-electric, no gas service |
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