Building Science Glossary

Backdrafting (sometimes called Combustion Spillage)
Combustion appliances – for example, fuel fired heating and stove tops – create exhaust gases that must ventilated to the outdoors. When airtightness measures are planned for a new home or added to an existing home, it’s possible to pull exhaust gases from a furnace or fireplace back into the home if proper ventilation is not included. This is sometimes also called “combustion spillage” and it can be very dangerous. Always consult with HVAC technicians to avoid back drafting with combustion appliances.

Below Grade Assemblies
Construction elements that are touching or below ground. This includes elements like foundation walls and basement slabs.

Building Envelope
Building materials and assemblies that separate indoor conditioned spaces from the outdoor unconditioned spaces make up the building envelope. This includes structure, insulation, barriers, and finishes.
Why it matters: The building envelope is the first line of defense against heat loss, moisture, and weather damage.

Blower Door Test
A diagnostic test that uses a specialized opening cover, variable speed fan, and an air pressure gauge (manometer) to measure the pressure difference between inside a building and the outside environment. Results from blower door tests are fed into energy modelling programs like HOT2000 and PHPP.

Capillary Action
Water always wants to move from areas of high pressure to areas of low pressure, and it will move in almost any direction through surface tension and gravity. When water moves through porous building materials (like concrete or wood), this is called capillary action.

Cladding
Exterior finish layers that provide the aesthetic or “curb appeal” of a building. Cladding materials include trim and broad coverage products like wood, vinyl, metal and composite siding, masonry, brick, or stucco. Cladding layers also include elements of flashing and weather resistant substrates to direct water down and away from a building.

Climate Zone
A geographic classification based on temperature and weather conditions that informs building code requirements for insulation, windows, and HVAC design. Canada’s climate zones are classified by Heating Degree Days, or HDD.

Compliance
When your building follows all the rules and meets all targets laid out in the building code, this is called compliance. A building may follow one of two paths to demonstrate compliance – the prescriptive path or the performance path, both of which are laid out in the building code.

Component
These are the parts of an assembly or a fixture in construction. For example: glass, spacers, frames and coatings are components of a window assembly.

Condensation
Water vapour condensing from a gas back to a liquid when the ambient temperature falls and air can no longer hold the moisture AND where it meets an impermeable surface. The most common type of condensation happens on windows. Condensation is related to the “dew point” in air and how it should be managed when designing assemblies in our climate. Failure to account for condensing surfaces may lead to mold, mildew, or rot.

Conditioned Space
When we heat, cool or regulate humidity in the interior spaces of a building, this is called conditioned space. Spaces in a building that are not heated, cooled or ventilated are called unconditioned space.

Conductive Heat Loss
Heat that escapes through solid materials, such as walls or windows, due to temperature differences. Heat energy will always move from warm to cold, and conductive heat loss shows up in buildings most often as “thermal bridging”.

Continuous Insulation
Insulation layers that cover a surface completely without interruptions from structure or finishes. Modern building code requirements will often specify continuous insulation on the exterior of a building. Additionally, renovation contractors will often use continuous insulation for energy retrofits. Because it is relatively uninterrupted, continuous insulation optimizes the effectiveness of thermal materials and eliminates thermal bridging.

Dew Point
The temperature at which air becomes saturated and changes from a gas (vapour) back to liquid form. The building code describes the importance locating the dew point relative to impermeable materials and insulation, to prevent condensation forming inside wall, floor and roof assemblies.

Drainage Plane
When bulk water like rain and melting snow is directed to down and away from a building, the sloped surfaces and elements like flashing and cladding are sometimes called “drainage planes”. These surfaces include “control layers” in the building envelope, such as weather resistant barriers (WRB), rain gutters, roof and wall finishes and parts of exterior trim.

Dwelling Units
When a building has separate individual living spaces, such as apartments, those spaces are called dwelling units. You may see dwelling units in houses, duplexes, low-rise multi unit residential buildings (MURBs), hotels, or high-rise MURBs.

Effective (Thermal Resistance)
Measuring the effective thermal resistance of an assembly means that you’re adding together the R-Value or RSI of each material to get an overall thermal resistance for all the parts together. Effective thermal resistance also factors in losses from “thermal bridges” and openings. The building code lays out methods for calculating the effective thermal resistance of common built assemblies.

Embodied Carbon
The greenhouse gas emissions associated with manufacturing, transporting, and installing building materials. A material with intensive energy requirements in its creation may be described as having “high embodied carbon”. Although measurement of embodied carbon is still new to construction and renovation, future building codes may include references to material “life cycle assessments” and “environmental product declarations”, which consider embodied carbon.

Energy Advisor (EA)
A building science professional who helps plan energy efficiency measures and improvements, for both new and retrofit construction projects. An EA will conduct an “energy audit”, which is diagnostic testing (blower door) on buildings, logging results by using software like HOT2000 and then to create a performance plan that improves comfort and energy efficiency. Energy advisors are registered through EnerGuide at Natural Resources Canada.

Energy Audit
A professional assessment of a building’s energy performance, identifying areas for efficiency improvements. This process is done by a registered energy advisor.
Why it matters: An energy audit is the first step to understanding where your home is wasting energy and how to fix it.

Energy Efficiency 
All buildings use energy for heating, cooling, hot water and operating appliances – for maintaining comfortable living conditions. When an assembly, system or appliance is good at conserving energy during its operation, we call this “energy efficiency”. The ability to use less energy to maintain occupant comfort is the primary target for energy efficient buildings.

Energy Model
By entering information and data about a building into a computer program like HOT2000 or Passive House Planning Package (PHPP), an Energy Advisor can create a virtual representation of the building to show how it will use energy. This is called creating an energy model.

Energy / Enthalpy Recovery Ventilator (ERV)
A mechanical ventilation device with the same function as an HRV but with the addition of recovering humidity from exhaust air. SEE HEAT RECOVERY VENTILATOR (HRV).

Fenestration
This is the technical word for windows, taken from the Latin word “fenestrare” which means “opening for light”. In the building code, fenestration refers to windows that are in vertical walls. Windows in ceilings and roofs are called “skylights”.

Heat Loss
Heat energy always moves from warm to cold and through three main methods: conduction, convection and radiation. Because we heat our buildings in winter, some of that heat energy escapes through one or all those methods – this is heat loss. Insulation is the primary material used to reduce heat losses, though air barriers are equally important – air leaks are the most common form of heat loss.

Heat Recovery Ventilator (HRV)
A ventilation appliance used to bring in fresh air and exhaust stale air from a building. The heat recovery happens as the outgoing, warm exhaust air passes by in the incoming, cooler fresh air in the core of the appliance. While the primary function is fresh air supply, an HRV may also reduce the energy required to maintain comfortable indoor temperatures, extending the useful life of heating and cooling equipment.
(diagram maybe?)

HOT2000
An energy modelling software created by Natural Resources Canada that helps designers and energy advisors to map out energy efficiency measures for buildings. Basic information about the size and geometry of a building are entered into HOT2000, along with data obtained by blower door testing.

HVAC
Stands for Heating (H), Ventilation (V), and Air Conditioning (AC) and includes all mechanical systems that control the temperature, air quality and humidity of indoor conditioned spaces.

Insulation
Material that slows the transfer of heat, keeping buildings warmer in winter and cooler in summer. All insulations work by using tiny air pockets or bubbles of inert gases to trap heat energy as it passes through the material.
Why it matters: Proper insulation reduces energy costs, improves comfort, and can extend the life of your HVAC system.

Indoor Air Quality (IAQ)
The condition of the air inside a building, influenced by ventilation, pollutants, humidity, temperature, environmental, or other factors. 

Load-Bearing Assembly
Elements in a building that support structural weight (dead loads), occupants and furniture (live loads). Examples of load bearing assemblies are roofs, exterior walls, beams, window and door headers, and floor systems – these structures transfer dead and live loads to the building foundation and the ground.

Moisture Barrier
A material that resists water and other moisture penetration, protecting the building structure from damage. In the building code, a ‘moisture barrier’ is commonly referring to membranes and liquid coatings used on the exterior of a building, especially on foundations. For example, a peel-and-stick membrane used on a foundation wall or footing is a moisture barrier.

Net Zero Energy Home
A home designed to produce as much energy as it consumes over the year, through efficiency and renewable energy. A Net Zero Energy Home will aim to have an annual energy consumption of 40 gigajoules or less (40 GJ), through the optimization of building envelope and power systems in the building. 

Opaque Assembly
When we put building materials together that you can’t see through – like a wall or ceiling – this is called an opaque assembly. This is a common way that the building code refers to construction assemblies.

Partition Wall
An interior wall that divides spaces but, in most cases, does not carry structural loads. A partition that transfers weight from above and to the foundation is called “load bearing”, and you’ll likely see this type of partition in homes built before 1980. In modern construction, partition walls will likely be located beneath floor and roof trusses that have long span capability. Partition walls will also not usually have insulation installed unless they intersect with exterior assemblies. However, using thermal insulation in partitions to reduce sound transmission between rooms is a practice often used between living and sleeping areas.

Passive Survivability
The ability of a building to maintain safe indoor temperatures for longer during a power outage or extreme weather event. Currently, hours and/or days of safety are used to qualify the passive survivability of a household.
Why it matters: This means a home can stay more comfortable and livable without active heating or cooling, which is critical during emergencies.

Performance Path
When we deviate from or exceed the minimum requirements in the building code, this is called following the performance path. Insulation, air sealing, quality windows, and doors and elimination of thermal bridges are part of a high-performance design. This path requires the creation of an energy model and consultation with a registered Energy Advisor.

Permeance
Materials that have vapour, moisture and air resistant properties can be classified by ‘permeance’, or how much (or how little) they will allow the passage of water or air. The rates of permeance in materials range from very permeable (e.g. crushed stone) to impermeable (e.g. polyethylene). Permeability is affected by temperature and relative humidity, and the building code describes the proper sequencing of materials that are used for creating impermeable layers. This is especially important in mapping out the location of “dew point” in an assembly.
Unit of measurement:
Imperial: grains of water vapour per square foot per hour per inch of mercury (gr*ft2*hr*inHg)
Metric: nanograms of water vapour per second per square metre per Pascal (ng*sec*m2*Pa)

Prescriptive Path
If you follow the minimum requirements in the building code exactly to the letter, this is called using the prescriptive path. This path provides pre-engineered boundaries for structure, systems, control layers and openings.

Proposed vs. Reference
The house we want to construct is called our proposed building. A. virtual version of that same building, built to the minimum level of code is called our reference building. This scenario is used mainly for buildings following the performance path – the proposed building will meet or exceed the performance of the reference building.

R-Value (Imperial) and R.S.I. (Metric)
A measure of a material’s ability to resist heat flow, used almost exclusively for insulation materials. The higher the R-value / RSI, the better the performance. SEE THERMAL RESISTANCE.

Rainscreen
Adding an airspace behind masonry veneers has been common practice for many years, as it allows for air flow and drying potential. This method of ensuring air flow behind finish layers on a building is now common in modern residential construction and renovation and is called the “rain screen” layer. This air space allows for drying potential to the exterior, and may be constructed with wood strapping, plastic mesh roll fabrics or brick ties. The rain screen will incorporate into the “drainage planes” on a building.

Radiant Heat Transfer
Heat that travels in electromagnetic waves and is absorbed by surfaces and objects in line-of-sight to the heat source. The most common example of a radiant heat source is the sun.

Resilience 
A building’s ability to withstand and recover quickly from extreme weather events.
Why it matters: A resilient home stays safer and more comfortable during power outages, storms, or extreme temperatures.

Retrofit
The process of renovating an existing building to upgrade energy efficiency, comfort or resiliency of the structure and property.

Sheathing
Engineered wood panels in thicknesses from 3/8” (9.5 mm) to 3/4” (19 mm) that cover exterior walls, roofs, or floors, providing horizontal shear strength / racking resistance and a base for exterior control layers and finishes. Building code specifies what type and thickness are required for elements of structure.

Smart Thermostat
A programmable thermostat that adapts to occupancy and temperature patterns.

Smart Air and Vapor Retarder
A roll-type synthetic fabric that changes its permeability depending on humidity levels, allowing walls to dry while still controlling airtightness.

Stack Effect
Warm air is lighter than cold air and will rise to upper floors in a building. Without sufficient air movement (i.e. ventilation), the warm air can remain trapped in higher floors with colder air on lower floors, creating a “stack” of temperature variation in a building.

Soffit Vent
In residential construction, an insulated attic space above flat ceilings needs passive ventilation at the lower and the upper parts of the roof. The overhanging eaves or ‘soffits’ on a roof will receive vented panels, strip vents or circular puck vents to accommodate the required amount of ventilation according to building code.

Solar Heat Gain Coefficient (SHGC)
Windows and doors with glazed portions (glass) will allow sunlight into a building. This is most pronounced on the South facing parts of a building, with daily gains on East and West sides at sunrise and sunset respectively. Window and door units are rated for their capacity to allow or prevent the entry of heat energy from sunlight as it shines on a building – this is called ‘solar gain’ and it accounts for shading, coatings on the glass, location of glazing on the building and the insulation in the building envelope. In colder climates, windows and doors with a higher capacity for solar gains are desirable, while hotter climates would go for lower solar gain. The Solar Heat Gain Coefficient is the metric we use to define the amount of gains a window or glazed door unit will allow.
Measurement: A dimensionless number between 0 and 1. For example: an SHGC of 0.4 means that the window allows 40% of the sun’s heat to pass through it. An SHGC of 1 means that 100% of the sun’s heat can pass through.

Thermal Bridging
When heat moves through a material that is more conductive than surrounding materials, creating weak spots in the insulative ability of an assembly. This is a common problem in buildings where structural elements interrupt insulation layers (i.e. in cavities), and where assembly elements span the distance from warmer interior to colder exterior conditions. The heat energy that travels across these conductive ‘bridges’ may contribute to the overall heat loss in a building and may lead to problems like condensation inside assemblies.

Thermal Characteristics
All materials used in construction are measured for how well they function as an insulator or conductor of energy. Slowing the passage of heat energy is expressed as a material’s thermal resistance capacity and is measured as RSI (Metric) or R-Value (Imperial). When we combine materials to create assemblies like foundations, floors, walls and roof structures, the collected RSI or R-Values of those materials will describe the thermal characteristics of the entire assembly. For example, a well-insulated and airtight attic assembly may have positive thermal characteristics, whereas an uninsulated, leaky crawlspace foundation would have poor thermal characteristics.

Thermal Comfort
The condition of mind that expresses satisfaction with the indoor environment, influenced by temperature, humidity, air movement, activity, clothing, metabolism and radiant heat. Thermal Comfort is further defined by ASHRAE Standard 55, “Thermal Environmental Conditions for Human Occupancy”.

Thermal Resistance
A number that describes how well a material can resist or slow down the passage of heat energy. Imperial measure of thermal resistance is “R-value”, and the Metric measure is “R.S.I”.
Units of measurement:
• Imperial R-value = square feet per degree Fahrenheit per hour over British Thermal Units (ft2*F*h/BTU)
• Metric R.S.I = square metre per degree Kelvin over Watts (m2*K/W)

Unconditioned Space
Any space in a building that is not heated, cooled or ventilated. When we heat, cool or regulate humidity in the interior spaces of a building, this is called conditioned space.

U-Value
The thermal conductivity of an assembly of materials – U-value is used to quantify the performance of window and door units and is used frequently in measuring thermal conductivity of built assemblies in Passive House construction. U-value is the opposite of effective R-Value.
Units of measurement:
• U-Value = Watts / metre squared per degree Kelvin (W/m2*K)

Vapour Barrier
An impermeable or semi-impermeable material that limits water vapor movement through a wall, ceiling, or floor. A common vapour barrier material is polyethylene plastic.
NOTE: many contractors use polyethylene material as both a vapour AND air barrier. This is achieved by taping or applying acoustic sealant to seams and penetrations. SEE SMART AIR AND VAPOUR BARRIERS.

Vapour Diffusion
The slow movement of water vapor through materials due to vapor pressure differences- also called osmosis. SEE PERMEANCE.

Vapor Permeability
The rate at which water vapor passes through a material. SAME AS PERMEANCE

Ventilation
The exchange of stale indoor air (exhaust) with fresh outdoor air (supply) to maintain good indoor air quality and to allow for drying potential of materials. Ventilation in buildings can be passive (natural) or mechanical (using powered ventilation equipment, such as an HRV or ERV).

Weatherstripping
Materials that are used to seal air leaks around windows, doors and other penetrations in the building envelope. This may include caulking, electrical outlet gaskets, or adhesive foam and neoprene strips on window and door jambs.