An Accessory Dwelling Unit (ADU) is a secondary habitable structure that shares a lot with a primary home, often used as a short- or long-term rental. ADUs effectively increase housing density and provide workforce housing in communities facing housing shortages. Typically small and efficient, ADUs can be socially, economically, and environmentally sustainable housing options. When it is detached from the main house, it is called a detatched accessory dwelling unit (DADU).
Airtightness is the practice of designing and constructing a building’s envelope, which includes exterior walls, roofs, and slabs, to prevent uncontrolled air leakage. Achieving high airtightness is verified by a blower door test, and is one of the most impactful, effective, and low-cost energy reduction strategies. It also improves comfort and reduces moisture-related durability and air quality problems. It is critical for buildings with high airtightness and low air leakage to have continuous, filtered fresh air delivered through an energy recovery ventilation system (ERV). Airtightness is measured in Air Changes per Hour (ACH), a measure of how many times the air in a building is replaced with outdoor air in one hour, when a building is pressurized to a specific relative pressure (typically 50 pascales for residential). A higher ACH value indicates a leakier building, while a lower value signifies a more airtight one. 2018 code mandates airtightness of 3.0 ACH50, while Passive House buildings must meet an airtightness of 0.6 ACH50 or less (five times more stringent than code).
Biophilic design is an approach that connects people with nature in buildings through natural light, outdoor views, natural materials, nature-derived patterns, and greenery. These connections enhance well-being, comfort, and productivity while fostering a stronger bond with the natural environment.
A blower door is specialized equipment that is used to measure airtightness by using a powerful fan to pressurize or depressurize a building to a specific target pressure. Once pressurized, the equipment measures the rate of pressure loss in Air Changes per Hour (ACH). Code requires maximum 3 ACH at 50 Pascals pressure; Passive House requires 0.6 ACH50. While a building is pressurized, leaks can be detected using infrared cameras or smoke machines.
Building science is the physics of how buildings perform as systems, focusing on the interaction between materials, energy, moisture, air, and people. It examines the movement of heat, air, and moisture through walls, roofs, and floors, how indoor air quality and comfort are maintained, and how to use energy efficiently. In simpler terms, building science helps architects, engineers, and builders understand why buildings stay warm or cold, dry or damp, quiet or noisy, and how to design and construct them to remain safe, healthy, comfortable, and energy-efficient over time.
Climate zones are regions established by the International Building Code, defined by temperature, humidity, and heating/cooling demand, used in building design to guide energy efficiency strategies.
Zone 5: Cold with significant winter heating demands, moderate summer cooling.
Zone 6: Very cold winters with short mild summers and high heating demand.
Zone 7: Subarctic or severe cold with extremely high heating demand, short summers, often snow-covered.
These zones help determine insulation, window performance, and HVAC requirements for energy-efficient homes.
An Energy Recovery Ventilator (ERV) is a mechanical ventilation system that runs continuously, 24 hours a day, exhausting stale indoor air and supplying fresh, filtered outdoor air. In the process, exchanging heat and latent energy between the warm and cold air streams with efficiencies of up to 90 percent (so, if indoor temperature is 70°F and outdoor air is 0°F, the delivered fresh air would be about 63°F). This mechanical ventilation system improves indoor air quality by constantly exchanging stale, indoor air with fresh, outdoor air, removing particulates, carbon dioxide, and reducing concentrations of water vapor. Additionally, the system prevents pressure-driven air exchange through cracks in walls or windows, which often contain contaminants. ERVs are required in Certified Passive House buildings, but are critical to maintaining indoor air quality and are essential components of any healthy home.
Energy Use Intensity (EUI) is the measure of a building’s energy consumption per square foot per year. The metric quantifies efficiency, allowing performance to be compared between buildings. It guides design decisions and ensures energy goals such as Passive House or net-zero targets are met.
Heat Recovery Ventilators (HRVs) use the same core technology as ERVs, but do not transfer latent heat (energy contained in moisture). As a result, HRVs can have higher energy transfer efficiencies than ERVs; however, in dry climates, they often lead to overly dry indoor air.
Mold forms when moisture enters wall systems through infiltration, condensation, or vapor diffusion, creating conditions where mold can grow unseen inside the structure. Mold growth can damage building materials, reduce indoor air quality, and cause an array of health issues. Controlling moisture, managing ventilation, and sealing leaks prevents mold growth in homes. Mold spores and fragments can irritate the nose, throat, and lungs and are associated with respiratory conditions such as asthma, allergic reactions, coughing, and wheezing. Prolonged exposure to moldy indoor environments has been linked to cognitive issues, anxiety, and other systemic effects.
Passive House is a voluntary building performance standard for ultra-low-energy, healthy, and comfortable buildings. Requirements include very low heating and cooling demand, exceptional airtightness, continuous insulation, and controlled ventilation with heat recovery. These performance targets are verified through modeling and testing to ensure comfort, durability, and minimal energy use. See our page with more in-depth information here.
PHI stands for Passive House Institute, the original standards-developing and adjudicating authority, based in Darmstadt, Germany. PHIUS is the Passive House Institute of the U.S.; this group branched off from the European organization in the 1990s in order to create more climate-specific adjustments to the metrics better suited to North America's much more widely varied climates. The underlying building science, energy savings, and health benefits are consistent between the two standards.
PHIUS CORE ensures a building meets strict energy efficiency, comfort, and airtightness standards appropriate for its local climate. PHIUS ZERO includes all CORE requirements as well as net-zero energy, meaning the building must generate as much renewable energy on-site annually as it consumes.
R-value is a measure of the resistance of a material to heat transfer. The higher the R-value, the less energy will transfer through the material. Think of it like a blanket for your house. A thicker or more insulating blanket has a higher R-value and keeps the house comfortable and reduces energy use. Unlike the U-Factor, R-value applies only to individual materials or layers.
Solar heat gain is heating energy provided by the sun's radiation. In cold-climate regions dominated by heating needs, like most of North America, harnessing the free energy from the sun can provide around one-third of the total heating energy, significantly reducing the size of heating systems. Proper building orientation, high-performance windows, and calibrated shading overhangs are critical to optimize solar heat gain while preventing overheating during hot months.
Solar Heat Gain Coefficient (SHGC) is a measure of how much of the sun's heat is allowed through a window, on a scale from 0 to 1. The lower the number, the lower the heat gain. In cool climates, windows in single-family homes should ideally have a high SHGC and carefully calibrated shading overhangs to capture solar heat in winter while blocking unwanted sun in summer. The impact of SHGC on energy demand is nuanced and should be modeled individually for each window, taking orientation, shading, and other factors into account.
A thermal bridge is a thermally conductive building element that "bridges" between the interior and exterior of a building, creating a weak point in the thermal envelope. Thermal bridges create pathways for rapid heat loss and can also create cold spots on the interior of the envelope that can result in condensation and lead to water damage or mold. Examples include cantilevered beams, balcony supports, and even structural framing elements that break cavity insulation. Thermal bridges can be minimized by providing continuous exterior insulation, detailing junctions carefully, and using materials with low thermal conductivity.
U-Factor is a measure of the thermal conductivity of an assembly, such as a window or wall. It is the inverse of R-value (thermal resistance). The lower the U-Factor, the better the thermal performance. The U-Factor measures the overall performance of assemblies composed of multiple materials, whereas R-value refers only to single-material layers. For example, a U-Factor can describe the performance of a window, including its frame, glass, and spacers.
An Accessory Dwelling Unit (ADU) is a secondary habitable structure that shares a lot with a primary home, often used as a short- or long-term rental. ADUs effectively increase housing density and provide workforce housing in communities facing housing shortages. Typically small and efficient, ADUs can be socially, economically, and environmentally sustainable housing options. When it is detached from the main house, it is called a detatched accessory dwelling unit (DADU).
Airtightness is the practice of designing and constructing a building’s envelope, which includes exterior walls, roofs, and slabs, to prevent uncontrolled air leakage. Achieving high airtightness is verified by a blower door test, and is one of the most impactful, effective, and low-cost energy reduction strategies. It also improves comfort and reduces moisture-related durability and air quality problems. It is critical for buildings with high airtightness and low air leakage to have continuous, filtered fresh air delivered through an energy recovery ventilation system (ERV). Airtightness is measured in Air Changes per Hour (ACH), a measure of how many times the air in a building is replaced with outdoor air in one hour, when a building is pressurized to a specific relative pressure (typically 50 pascales for residential). A higher ACH value indicates a leakier building, while a lower value signifies a more airtight one. 2018 code mandates airtightness of 3.0 ACH50, while Passive House buildings must meet an airtightness of 0.6 ACH50 or less (five times more stringent than code).
Biophilic design is an approach that connects people with nature in buildings through natural light, outdoor views, natural materials, nature-derived patterns, and greenery. These connections enhance well-being, comfort, and productivity while fostering a stronger bond with the natural environment.
A blower door is specialized equipment that is used to measure airtightness by using a powerful fan to pressurize or depressurize a building to a specific target pressure. Once pressurized, the equipment measures the rate of pressure loss in Air Changes per Hour (ACH). Code requires maximum 3 ACH at 50 Pascals pressure; Passive House requires 0.6 ACH50. While a building is pressurized, leaks can be detected using infrared cameras or smoke machines.
Building science is the physics of how buildings perform as systems, focusing on the interaction between materials, energy, moisture, air, and people. It examines the movement of heat, air, and moisture through walls, roofs, and floors, how indoor air quality and comfort are maintained, and how to use energy efficiently. In simpler terms, building science helps architects, engineers, and builders understand why buildings stay warm or cold, dry or damp, quiet or noisy, and how to design and construct them to remain safe, healthy, comfortable, and energy-efficient over time.
Climate zones are regions established by the International Building Code, defined by temperature, humidity, and heating/cooling demand, used in building design to guide energy efficiency strategies.
Zone 5: Cold with significant winter heating demands, moderate summer cooling.
Zone 6: Very cold winters with short mild summers and high heating demand.
Zone 7: Subarctic or severe cold with extremely high heating demand, short summers, often snow-covered.
These zones help determine insulation, window performance, and HVAC requirements for energy-efficient homes.
An Energy Recovery Ventilator (ERV) is a mechanical ventilation system that runs continuously, 24 hours a day, exhausting stale indoor air and supplying fresh, filtered outdoor air. In the process, exchanging heat and latent energy between the warm and cold air streams with efficiencies of up to 90 percent (so, if indoor temperature is 70°F and outdoor air is 0°F, the delivered fresh air would be about 63°F). This mechanical ventilation system improves indoor air quality by constantly exchanging stale, indoor air with fresh, outdoor air, removing particulates, carbon dioxide, and reducing concentrations of water vapor. Additionally, the system prevents pressure-driven air exchange through cracks in walls or windows, which often contain contaminants. ERVs are required in Certified Passive House buildings, but are critical to maintaining indoor air quality and are essential components of any healthy home.
Energy Use Intensity (EUI) is the measure of a building’s energy consumption per square foot per year. The metric quantifies efficiency, allowing performance to be compared between buildings. It guides design decisions and ensures energy goals such as Passive House or net-zero targets are met.
Heat Recovery Ventilators (HRVs) use the same core technology as ERVs, but do not transfer latent heat (energy contained in moisture). As a result, HRVs can have higher energy transfer efficiencies than ERVs; however, in dry climates, they often lead to overly dry indoor air.
Mold can occur when moisture enters wall systems through infiltration, condensation, or vapor diffusion, creating conditions where mold can grow unseen inside the structure. Mold growth can damage building materials, reduce indoor air quality, and cause an array of health issues. Controlling moisture, managing ventilation, and sealing leaks prevents mold growth in homes. Mold spores and fragments can irritate the nose, throat, and lungs and are associated with respiratory conditions such as asthma, allergic reactions, coughing, and wheezing. Prolonged exposure to moldy indoor environments has been linked to cognitive issues, anxiety, and other systemic effects.
Passive House is a voluntary building performance standard for ultra-low-energy, healthy, and comfortable buildings. Requirements include very low heating and cooling demand, exceptional airtightness, continuous insulation, and controlled ventilation with heat recovery. These performance targets are verified through modeling and testing to ensure comfort, durability, and minimal energy use. See our page with more in-depth information here.
PHI stands for Passive House Institute, the original standards-developing and adjudicating authority, based in Darmstadt, Germany. PHIUS is the Passive House Institute of the U.S.; this group branched off from the European organization in the 1990s in order to create more climate-specific adjustments to the metrics better suited to North America’s much more widely varied climates. The underlying building science, energy savings, and health benefits are consistent between the two standards.
PHIUS CORE ensures a building meets strict energy efficiency, comfort, and airtightness standards appropriate for its local climate. PHIUS ZERO includes all CORE requirements as well as net-zero energy, meaning the building must generate as much renewable energy on-site annually as it consumes.
R-value is a measure of the resistance of a material to heat transfer. The higher the R-value, the less energy will transfer through the material. Think of it like a blanket for your house. A thicker or more insulating blanket has a higher R-value and keeps the house comfortable and reduces energy use. Unlike the U-Factor, R-value applies only to indivitual materials or layers.
Solar heat gain is heating energy provided by the sun’s radiation. In cold climate regions dominate by heating needs like most of North America, harnessing the free energy from the sun can provide around one-third of the total heating energy, significantly reducing the size of heating systems. Proper building orientation, high-performance windows, and calibrated shading overhangs are critical to optimize solar heat gain while preventing overheating during hot months.
Solar Heat Gain Coefficient (SHGC) is a measure of how much of the sun’s heat is allowed through a window, on a scale from 0 to 1. The lower the number, the lower the heat gain. In cool climates, windows in single-family homes should ideally have a high SHGC and carefully calibrated shading overhangs to capture solar heat in winter while blocking unwanted sun in summer. The impact of SHGC on energy demand is nuanced and should be modeled individually for each window, taking orientation, shading, and other factors into account.
A thermal bridge is a thermally conductive building element that “bridges” between the interior and exterior of a building, creating a weak point in the thermal envelope. Thermal bridges create pathways for rapid heat loss and can also create cold spots on the interior of the envelope that can result in condensation and lead to water damage or mold. Examples include cantilevered beams, balcony supports, and even structural framing elements that break cavity insulation. Thermal bridges can be minimized by providing continuous exterior insulation, detailing junctions carefully, and using materials with low thermal conductivity.
U-Factor is a measure of the thermal conductivity of an assembly, such as a window or wall. It is the inverse of R-value (thermal resistance). The lower the U-Factor, the better the thermal performance. The U-Factor measures the overall performance of assemblies composed of multiple materials, whereas R-value refers only to single-material layers. For example, a U-Factor can describe the performance of a window, including its frame, glass, and spacers.
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