A passive house is a building that meets strict energy performance targets defined by the Passive House Institute, a standard developed in Germany and first proven in a 1991 house in Darmstadt. The method has since been applied across every climate zone. The core idea is simple: design the envelope so well that the building needs almost no active heating or cooling. Measured results show passive houses cut space heating and cooling demand by 75 to 90 percent compared with conventional construction, while indoor temperatures stay steady through the year. Indoor air quality improves as well, because the ventilation system filters incoming air continuously.
What the Passive House Standard Requires
The Passive House Institute defines the standard with hard numbers rather than vague goals. Space heating demand cannot exceed 15 kilowatt-hours per square meter per year, roughly 4.75 Btu per square foot per year. Cooling demand follows the same cap. Total primary energy for heating, cooling, hot water, and appliances stays under 120 kilowatt-hours per square meter per year. Airtightness must measure 0.6 air changes per hour or less at 50 pascals of pressure, a level confirmed on site with a blower door test.
Performance Targets at a Glance
| Metric | Passive house limit | Typical conventional home |
|---|---|---|
| Space heating demand | 15 kWh per sq m per year | 60 to 150 kWh per sq m per year |
| Airtightness | 0.6 air changes per hour | 3 to 10 air changes per hour |
| Window U-value | 0.80 W per sq m K or less | 1.6 to 2.8 W per sq m K |
| Ventilation heat recovery | 75 percent or better | None in most homes |
Why the Limits Are Set Where They Are
The 15 kilowatt-hour heating cap is low enough that a small heat source covers the load, often just warm supply air from the ventilation system. That removes the need for conventional furnaces and ductwork in mild climates. The airtightness figure matters because uncontrolled leakage causes a large share of heat loss in ordinary houses. Meeting all four limits together is what separates a passive house from a merely efficient one, and each limit is checked against measured data, not design assumptions. The caps also set an upper bound for energy modeling, so a design team can compare options before anything is built.
- Heating and cooling each capped at 15 kWh per sq m per year
- Total primary energy capped at 120 kWh per sq m per year
- Airtightness at 0.6 air changes per hour or better
- Ventilation heat recovery at 75 percent efficiency or better
The Five Core Principles of Passive House Design
Five design rules deliver those numbers. Continuous insulation wraps the whole envelope. Thermal bridges are eliminated at junctions. The air barrier is sealed airtight. Windows meet high performance glazing specifications. And a mechanical ventilation system recovers heat from exhaust air. The rules work as a system, and designers who want to hear how they play out on real projects can listen to a passive house podcast episode that follows a residential design from concept through detailing.
Continuous Insulation
Insulation wraps the entire heated volume, including slab edges and roof eaves, without gaps. Cold climate walls commonly carry 12 to 18 inches of insulation in double stud walls or insulated concrete forms, reaching R-40 or better, with roofs at R-60. The unbroken layer keeps interior surface temperatures even, which cuts drafts and reduces condensation risk at corners and behind furniture.
Thermal Bridge Free Detailing
A thermal bridge is a spot where insulation is interrupted by a conductive element such as a steel beam or a concrete balcony slab. Passive house rules cap linear thermal transmittance at 0.01 watts per meter kelvin. Detailing choices like cantilevered balcony supports, insulated window frames, and offset wall plates keep heat from short circuiting through the envelope.
The Airtight Envelope
The air barrier is one continuous membrane or board layer, usually placed on the warm side of the insulation. Every penetration, from electrical boxes to pipe sleeves, gets taped or gasketed. The assembly is tested twice: once mid-construction while walls are still open, and once at completion.
Blower Door Testing
A blower door mounts a calibrated fan in an exterior doorway and depressurizes the house to 50 pascals. The test measures how much air leaks through the envelope. A passive house result of 0.6 air changes per hour is roughly ten times tighter than the average existing home, so finding and sealing leaks during framing matters more than chasing the final number.
Windows, Solar Gain, and Ventilation
Windows in a passive house do three jobs at once: they admit daylight, collect solar heat in winter, and keep heat inside at night. Triple glazing with a U-value of 0.80 watts per square meter kelvin or less is standard, with a solar heat gain coefficient tuned to the climate. South facing glass captures winter sun, while overhangs, exterior shades, or deciduous trees block high summer sun. In hot climates the same glazing rules flip: low solar gain glass and deep shading take priority over winter heat collection.
Mechanical Ventilation with Heat Recovery
Because the envelope is so tight, fresh air cannot rely on leaks. A balanced ventilation system with a heat recovery core moves stale air out and filtered fresh air in, transferring 75 to 92 percent of the heat from exhaust to supply. The system runs continuously at low speed and doubles as the primary heat delivery mechanism in many designs. Duct runs are kept short and insulated, and filters are changed twice a year to hold efficiency.
Sizing the Window Package
- Calculate the heating load with the Passive House Planning Package software
- Choose glazing with the right U-value and solar heat gain coefficient for each orientation
- Specify frames and spacers that do not create thermal bridges
- Verify the installation detail for every rough opening before framing is closed
Construction Sequence and Site Practices
Hitting the performance targets depends on the order of work as much as the materials. The air barrier plane is defined before framing starts, insulation is installed without voids, and every trade coordinates penetrations through the membrane. Sequencing mistakes are difficult to correct after drywall goes up.
Step-by-Step Airtight Construction
- Lay out the air barrier plane on the drawings and mark it at the site
- Install the airtightness membrane or boards as framing progresses
- Seal every penetration for wiring, plumbing, and ducts as each trade works
- Run a mid-construction blower door test before insulation and drywall
- Complete the final blower door test and document the result for certification
Where Leaks Hide
- Wall to roof junctions where the air barrier turns the corner
- Window and door rough openings that were not taped
- Electrical outlets and light fixtures on exterior walls
- Plumbing and vent stacks passing through the ceiling
- Slab edges and the top of foundation walls
Cost, Certification, and Retrofits
A passive house typically costs 5 to 15 percent more to build than a code compliant house, depending on climate and design complexity. The premium shrinks when the design team models the building early and keeps the form compact. It is offset by heating bills that drop by roughly 75 to 90 percent, and by smaller mechanical systems that cost less to buy and install. Whole life cost comparisons that include energy, maintenance, and equipment replacement usually favor the passive house within ten to fifteen years.
Certification Pathways
The Passive House Institute certifies buildings under Classic, Plus, and Premium tiers based on energy generation and demand. In North America, PHIUS offers climate specific criteria that adjust insulation and window requirements for hot, humid, and cold regions. Retrofits can pursue EnerPHit, which relaxes the heating demand limit to 25 kilowatt-hours per square meter per year while keeping the same airtightness and ventilation standards. Documentation for certification includes the energy model, blower door results, and photos of every airtightness detail.
Retrofitting an Existing Home
Existing houses rarely reach full passive house performance without major work, but the EnerPHit route applies the same principles in stages. The sequence below shows where the largest gains come from.
- Start with attic and roof insulation, the fastest gain per dollar
- Replace windows with high performance glazing and insulated frames
- Add interior insulation to basement and crawl space walls
- Install a heat recovery ventilator and seal the duct system
- Test airtightness and aim for the best result the structure allows
Passive house is not a single product or a specific architectural style. It is a measurable performance standard that any builder can hit with disciplined detailing and testing. Teams that work through the five principles in order, verify their work with blower door tests, and model the design before construction consistently deliver homes that stay comfortable on a fraction of the energy a conventional house uses.