A passive house is a building designed to the Passivhaus standard: through very high levels of insulation, airtightness, thermal-bridge-free detailing and mechanical ventilation with heat recovery, it needs almost no heating system. The standard was developed by the Passivhaus Institut in Darmstadt and is applied internationally.
The hard criteria
The Passivhaus standard works with measurable limits. The main ones are:
- Space heating demand: no more than 15 kWh per square metre of treated floor area per year
- Airtightness: n50 of no more than 0.6 air changes per hour, measured by a blower door test at 50 pascals pressure difference — so at most 0.6 times the internal volume may leak per hour.
- Total primary energy: no more than 120 kWh per square metre per year, including hot water, auxiliary energy and household electricity
- Overheating: only a small share of the year above 25 degrees internal temperature
How those figures are achieved
- Insulation — U-values well below the statutory minimum; in practice often 250 to 400 mm of insulation in roof and wall.
- Glazing — triple glazing with a warm-edge spacer and well-insulated frames.
- Thermal-bridge-free detailing — the insulation envelope runs unbroken around the whole building. Foundation edges, balconies and roof edges are the classic weak points.
- Airtight layer — one continuous, unbroken layer (membrane, plaster or board) with every penetration carefully taped. Test it with a blower door during the shell stage, not at handover.
- Heat recovery ventilation — typically 75 per cent efficiency or better. The standard is not achievable without mechanical ventilation.
- Orientation and shading — solar gain in winter, external shading against summer overheating.
Extra cost and payback
Building to passive standard typically adds a few per cent up to roughly ten per cent over a new building that only meets the statutory minimum; the difference lies mainly in thicker insulation, better glazing and the ventilation plant. The return is a sharply reduced heating demand. On any real project, work with actual quotations and actual consumption — for retrofit (EnerPHit) the cost per kilowatt-hour saved is usually higher than for new build.
Related terms
- U-value
- Airtightness
- Blower door test
- Thermal bridge
- Mechanical ventilation
- Heat recovery
- Triple glazing
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