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passive house
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what is passive house
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Passive House is a building standard that is truly energy efficient, comfortable and affordable at the same time.
Passive House is not a brand name, but a tried and true construction concept that can be applied by anyone, anywhere.
Yet, a Passive House is more than just a low-energy building:
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Passive Houses allow for space heating and cooling related energy savings of up to 90% compared with typical building stock and over 75% compared to average new builds. Passive Houses use less than 1.5 l of oil or 1.5 m3 of gas to heat one square meter of living space for a year – substantially less than common “low-energy” buildings. Vast energy savings have been demonstrated in warm climates where typical buildings also require active cooling.
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Passive Houses make efficient use of the sun, internal heat sources and heat recovery, rendering conventional heating systems unnecessary throughout even the coldest of winters. During warmer months, Passive Houses make use of passive cooling techniques such as strategic shading to keep comfortably cool.
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Passive Houses are praised for the high level of comfort they offer. Internal surface temperatures vary little from indoor air temperatures, even in the face of extreme outdoor temperatures. Special windows and a building envelope consisting of a highly insulated roof and floor slab as well as highly insulated exterior walls keep the desired warmth in the house – or undesirable heat out.
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A ventilation system imperceptibly supplies constant fresh air, making for superior air quality without unpleasant draughts. A highly efficient heat recovery unit allows for the heat contained in the exhaust air to be re-used.
Passive House – building for energy efficiency, comfort and affordability
Typical heating systems in Central Europe, where the Passive House Standard was first developed and applied, are centralised hot water heating systems consisting of radiators, pipes and central oil or gas boilers. The average heating load of standard buildings in this area is approximately 100 W/m² (approx. 10 kW for a 100 m² apartment). The Passive House concept is based on the goal of reducing heat losses to an absolute minimum, thus rendering large heating systems unnecessary (see image 1). With peak heating loads below 10 W per square meter of living area, the low remaining heat demand can be delivered via the supply air by a post heating coil (see box below). A building that does not require any heating system other than post air heating is called a Passive House; no traditional heating (or cooling) systems are needed.
Passive Houses around the world
The Passive House concept itself remains the same for all of the world’s climates, as does the physics behind it. Yet while Passive House principles remain the same across the world, the details do have to be adapted to the specific climate at hand. A building fulfilling the Passive House Standard will look much different in Alaska than in Zimbabwe.
For a 90 second tutorial on how Passive House works click here.
Courses are available online for Passive House:
passive house requirements
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For a building to be considered a Passive House, it must meet the following criteria ( for detailed criteria, please see the building certification section):
1. The Space Heating Energy Demand is not to exceed 15 kWh per square meter of net living space (treated floor area) per year or 10 W per square meter peak demand.
In climates where active cooling is needed, the Space Cooling Energy Demand requirement roughly matches the heat demand requirements above, with an additional allowance for dehumidification.
2. The Renewable Renewable Primary Energy Demand (PER, according to PHI method), the total energy to be used for all domestic applications (heating, hot water and domestic electricity) must not exceed 60 kWh per square meter of treated floor area per year for Passive House Classic.
3. In terms of Airtightness, a maximum of 0.6 air changes per hour at 50 Pascals pressure (ACH50), as verified with an onsite pressure test (in both pressurized and depressurized states).
4. Thermal comfort must be met for all living areas during winter as well as in summer, with not more than 10 % of the hours in a given year over 25 °C. For a complete overview of general quality requirements (soft criteria) see Passipedia.
Passive House buildings are planned, optimised and verified with the Passive House Planning Package (PHPP).
All of the above criteria are achieved through intelligent design and implementation of the 5 Passive House principles: thermal bridge free design, superior windows, ventilation with heat recovery, quality insulation and airtight construction.
The following five basic principles apply for the construction of Passive Houses:
Thermal insulation
All opaque building components of the exterior envelope of the house must be very well-insulated. For most cool-termperate climates, this means a heat transfer coefficient (U-value) of 0.15 W/(m²K) at the most, i.e. a maximum of 0.15 watts per degree of temperature difference and per square metre of exterior surface are lost.
Passive House windows
The window frames must be well insulated and fitted with low-e glazings filled with argon or krypton to prevent heat transfer. For most cool-termperate climates, this means a U-value of 0.80 W/(m²K) or less, with g-values around 50% (g-value= total solar transmittance, proportion of the solar energy available for the room).
Ventilation heat recovery
Efficient heat recovery ventilation is key, allowing for a good indoor air quality and saving energy. In Passive House, at least 75% of the heat from the exhaust air is transferred to the fresh air again by means of a heat exchanger.
Airtightness of the building
Uncontrolled leakage through gaps must be smaller than 0.6 of the total house volume per hour during a pressure test at 50 Pascal (both pressurised and depressurised).
Absence of thermal bridges
All edges, corners, connections and penetrations must be planned and executed with great care, so that thermal bridges can be avoided. Thermal bridges which cannot be avoided must be minimised as far as possible.
To find out which of our products are suitable for Passive House requirements click here.
Our Passive House performance data pack can be downloaded from our members library here.