Introducing the Passive House system: A new standard for building green

Space heating energy demand
Space heating energy demand cannot exceed 15 kWh/m² (4.75 kBtu/sf) of net living space
(i.e. treated floor area) per year or 10 W/m² (3.17 Btu/sf) per hour of peak heating demand. In climates where active (mechanical) cooling is needed, the space cooling energy demand requirement roughly matches this, with a slight additional allowance for dehumidification.

Primary energy demand
The total energy to be used for all domestic applications (i.e. heating, hot water and domestic electricity) must not exceed 120 kWh/m² (38 kBtu/sf) of treated floor area per year.

Airtightness
In terms of airtightness, a maximum of 0.6 air changes per hour at 50-Pa pressure (ACH50) must be verified by an onsite pressure test, with results given in both pressurized and depressurized states.

Thermal comfort
Thermal comfort must be met for all living areas during both winter and summer, with not more than 10 percent of the hours in a given year over 25 C (77 F).

Five basic principles
Passive House does not provide prescriptive details on how to achieve the Passive House standards outlined above, as it is a performance-based set of goals. Designers are encouraged to customize building envelope details to their climate, building typology, and construction needs, allowing for innovative building techniques.

There are five basic Passive House principles at the core of achieving the properly designed envelope to earn Passive House certification:

• a thermal bridge-free design;
• superior windows (which can be Passive House-certified products);
• ventilation with heat recovery;
• high-quality insulation; and
• airtight construction.

These five principles guide the architect and engineer design process throughout, beginning from concept to construction, to ensure the project meets Passive House goals.

Thermal bridge-free design
Eliminating thermal bridges prevents heat from flowing through a building envelope. Heat follows the easiest path from warm to cold surfaces. When not detailed correctly, construction materials such as metal studs, steel headers, and metal fasteners can cause severe thermal bridging and increase energy usage due to heat loss. Various construction alternatives using such techniques as insulating porous concrete masonry units (CMUs) and insulation stops can help minimize thermal bridging.

An important tool for the design and engineering team to identify the existing conditions of thermal bridging is the infrared (IR) camera—a device that produces visualizations by detecting heat as IR energy and then converting it into electronic signals processed to produce thermal images. The images allow designers to read where heat loss is occurring in the building envelope, often revealing surprising conditions invisible to the naked eye.