FAQ (100+)

A building performance standard where year-round thermal comfort is achieved primarily by conditioning the fresh air required for healthy indoor air quality, without relying on large conventional heating or cooling systems.

The Passive House Institute retrofit standard for existing buildings, with slightly relaxed airtightness (≤1.0 ACH50) and climate-specific heating demand limits compared to new construction.

Passive House Planning Package — the energy modeling software used to verify heating/cooling demand, loads, primary energy, and certification criteria before construction.

Net usable floor area in Passive House modeling, excluding internal walls and certain stair volumes, used as the reference area for energy metrics.

Air changes per hour at 50 Pascals pressure difference during a blower door test. New Passive House buildings must achieve ≤0.6 ACH50.

Thermal transmittance measuring how quickly heat flows through a building component. Lower U-values mean better insulation. Windows use U-factor; opaque assemblies often use R-value.

Thermal resistance of insulation or assemblies (hr·ft²·°F/Btu). Higher R-values reduce heat loss through walls, roofs, and floors.

Linear thermal bridge coefficient (Btu/hr·ft·°F) describing heat loss along junctions such as wall-to-floor connections.

Point thermal bridge coefficient (Btu/hr·°F) for discrete penetrations like structural ties through insulation.

Solar Heat Gain Coefficient — the fraction of solar radiation that passes through glazing as heat. Critical for balancing winter gains and summer overheating.

Heat Recovery Ventilator or Energy Recovery Ventilator — balanced ventilation systems that recover heat (and sometimes moisture) from exhaust air to precondition incoming fresh air.

Primary energy accounting that reflects renewable energy supply factors, used in Passive House Plus and Premium certification classes.

Combined measure of air temperature and radiant surface temperatures that determines perceived thermal comfort per ISO 7730.

A localized area where insulation is interrupted or thinned, creating a path for heat to bypass the thermal envelope.

Total exterior envelope area divided by treated floor area. Higher SAR means more heat-losing surface per unit of living space.

Yes. Passive House buildings are not sealed boxes. Windows open normally; mechanical ventilation provides consistent fresh air when closed.

No. The standard applies to offices, schools, multifamily housing, retrofits, and mixed-use buildings worldwide.

Continuous insulation, airtight construction, high-performance windows and doors, thermal-bridge-free design, and balanced ventilation with heat recovery.

Passive House limits energy demand through the building envelope first. Net zero focuses on offsetting annual energy use, often with renewables. Many Passive House projects also achieve net zero.

Thermal comfort per ISO 7730 should be achievable by post-heating or post-cooling the ventilation air stream alone, without recirculating large volumes of conditioned air.

No. Active systems are sized small and used as backup. The goal is to minimize — not eliminate — mechanical heating and cooling.

68°F with 50% relative humidity is the standard interior design condition for residential Passive House modeling.

Passive House uses exterior envelope dimensions for a conservative, reproducible calculation of transmission losses.

A 1977 Canadian prototype that demonstrated super insulation, triple glazing, heat-recovery ventilation, and early airtightness testing — a direct ancestor of the Passive House standard.

The Passive House Planning Package (PHPP) is the primary certification tool. designPH provides a SketchUp-based interface for PHPP workflows.

Prioritize insulation, airtightness, and window performance before sizing mechanical systems.

Use energy modeling during schematic design to test form factor, orientation, and insulation thickness.

Simpler, more compact massing reduces envelope area and lowers insulation requirements.

Climate and form factor dependent. Cool-temperate single-family homes often need R-38 to R-60+ opaque assemblies; multifamily compact forms may need less.

Lower is better. Multistory apartments can reach 0.08–0.10; single-story homes may exceed 0.30 and require more insulation.

No. Each additional inch yields diminishing returns. PHPP optimization balances cost and performance.

Spray foam insulates well but is not a dedicated air barrier product. Dedicated membranes, tapes, and detailing are still required for ≤0.6 ACH50.

Exterior insulation greatly reduces bridging but fasteners, balconies, and window penetrations can still create bridges if not detailed carefully.

At 68°F and 50% RH, surface temperatures below ~54°F increase mold risk; below ~49°F condensation risk rises sharply on cold surfaces.

Wrap the thermal envelope without gaps so heat cannot bypass insulation layers.

Place vapor control layers on the warm side in heating climates and on the exterior in hot-humid climates.

Add insulation until diminishing returns; PHPP finds the economic and performance sweet spot.

It prevents drafts, moisture damage in assemblies, uncontrolled heat loss, noise infiltration, and undermines ventilation system performance.

Liquid-applied membranes, specialized tapes, and well-cast concrete (when crack-free) — not standard DIY caulk or duct tape.

At a point when the air barrier is accessible — typically after windows are installed and before drywall — and again at final completion.

Treated floor area multiplied by 8.2 ft standard ceiling height defines the reference test volume for most residential projects.

The average of pressurization and depressurization results at 50 Pa, expressed as n50 (ACH).

Buildings over 53,000 ft³ must meet n50 ≤0.6 and should report q50; target q50 <0.034 CFM/ft² is recommended.

Yes — exterior intake and exhaust openings should be sealed during the test to avoid false leakage through ductwork.

Identify the continuous airtight layer on drawings before construction begins.

Conduct blower door tests at rough-in and again at completion to catch leaks when they are accessible.

A 1-inch air leak moves far more moisture than vapor diffusion through intact materials.

Installed U-values often need to be ≤0.14–0.17 Btu/(hr·ft²·°F) in cold climates, depending on climate and orientation mix.

Three glass panes with low-emissivity coatings and argon or krypton gas fill, reducing conduction and radiation heat transfer.

A simplified metric where lower U and appropriate SHGC together indicate climate-suitable glazing performance.

Frames conduct heat differently than glass. Uf, spacer psi-values, and frame-to-glass ratio all affect comfort and energy.

Exterior shading blocks solar gain before it enters the building and is far more effective for summer comfort.

Use certified connection details and proper interior/exterior air seals at rough openings.

Cold climates favor lower U and moderate-to-high SHGC on south facades; cooling climates need stronger shading.

Small differences in g-value significantly affect annual energy balance in PHPP.

Natural ventilation is unreliable, causes excessive heat loss in cold weather, and cannot guarantee consistent indoor air quality.

Roughly 0.3–0.4 air changes per hour based on occupant count and humidity control needs, verified in PHPP.

HRVs recover heat; ERVs also transfer moisture. Cold dry climates often use HRV; humid or mixed climates may benefit from ERV.

Often yes in mild climates via supply-air post-heating coils. Disconnected or extract-only rooms may need supplemental heat.

Prevent condensation and heat loss when warm exhaust ducts pass through cold zones or vice versa.

Supply and extract airflows should be balanced with ≥75% heat recovery for certification.

Bedrooms and living areas get supply air; kitchens and baths extract; transfer paths connect zones.

High-quality filters protect occupants and keep heat exchangers clean.

Mini-split heat pumps, ventilation-integrated coils, small hydronic panels, and electric resistance backup sized to low peak loads.

Without active cooling, indoor temperatures should not exceed 77°F for more than 10% of annual hours.

External shading, low SHGC glazing, night ventilation, airtight envelope, insulation, and minimizing internal gains.

Rarely in Passive House. High-performance glazing eliminates cold downdrafts that conventional systems compensated for.

In Passive House, domestic hot water energy can equal or exceed space heating — efficient DHW design matters.

Size to peak load (≤3.17 Btu/hr·ft²), not conventional oversizing rules.

People, appliances, and lighting offset heating demand — account for them in PHPP.

Reduce solar gains and internal loads before adding mechanical cooling capacity.

Upfront costs can run 5–15% higher initially, but energy savings, comfort, durability, and incentives improve lifecycle economics.

A metric comparing incremental investment to annual energy saved — useful for comparing envelope upgrades.

Growing evidence shows lower operating costs, comfort, and certification status attract buyers and reduce vacancy.

30% federal solar ITC, IRA heat pump rebates up to $8,000, EV credits, and state-specific efficiency programs.

Use annuity or present-value methods comparing extra envelope investment to decades of energy savings.

Combine federal tax credits, IRA rebates, and state programs to offset envelope and heat pump costs.

First Passive House projects cost more; teams with repeat experience reduce premiums significantly.

Certification class requiring on-site or nearby renewable generation offsetting higher PER demand thresholds.

The highest class — lowest PER demand and highest renewable generation requirements.

No. Envelope improvements deliver better ROI and reduce required PV capacity.

Minimize demand with the envelope so solar and batteries can cover a larger share of needs.

Size PV and storage based on PHPP primary energy and occupant usage patterns.

Low-flow fixtures reduce hot water energy — often a larger load than space heating in certified homes.

Yes, though they are separate from certification criteria. They reduce potable water use and support sustainability goals.

Mineral wool, cellulose, wood fiber, EPS, and polyurethane each offer different R/inch, vapor, and carbon profiles.

Not for certification, but they support indoor air quality alongside mechanical ventilation.

Detailing that keeps Ψ <0.006 Btu/hr·ft·°F and ΔUTB <0.0018 Btu/(hr·ft²·°F) across the envelope.

Design review in PHPP, construction documentation, blower door test, ventilation commissioning, and independent certifier review.

No. Airtightness is achieved through detailing, crew training, and quality control — not a single product.

Any change to insulation, windows, or ERV specs should be verified in PHPP before installation.

Annual heat loss through opaque or glazed envelope areas. Formula: QT = A × U × ft × Gt. Units: kBtu/yr. A = area (ft²), U = 1/R, ft = ground correction factor, Gt = heating degree hours.

Peak-hour heat loss used to size heating systems. Formula: PT = A × U × ft × ΔT. Units: Btu/hr.

Sum interior film resistance, layer resistances, and exterior film resistance. Formula: R = Rsi + Σ(d × r) + Rse. Units: hr·ft²·°F/Btu.

Annual loss along linear junctions like slab edges. Formula: QT-tb = L × Ψ × ft × Gt. Units: kBtu/yr.

Heat loss from air leakage at resting pressure; e ≈ 0.07 commonly used. Formula: QV-infill = Vn50 × e × n50 × Cair × Gt. Units: kBtu/yr.

Convert CFM at 50 Pa to air changes per hour. Formula: n50 = (V50 × 60) / Vn50. Units: 1/h.

Surface-normalized leakage for buildings >53,000 ft³; target <0.034 CFM/ft² recommended. Formula: q50 = (V50 × 60) / EAn50. Units: CFM/ft².

Weighted U-value including glass, frame, spacer, and installation losses. Formula: Uw = (Ug×Ag + Uf×Af + Ψspacer×Lspacer + Ψinstall×Linstall) / Awindow. Units: Btu/(hr·ft²·°F).

Net annual energy through glazing after solar gains and transmission losses. Formula: QS - QT = (r × SHGC × Aw × G) - (Aw × U × Gt). Units: kBtu/yr.

Residential qi typically 0.67–1.30 Btu/(hr·ft²). Formula: QI = 0.024 × Ht × qi × ATFA. Units: kBtu/yr.