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Technical Reference

Building Envelope Glossary

Plain-language definitions of every technical term used in building envelope inspection reports, moisture diagnostics, and BC building science documentation.

A

Air Barrier
A continuous layer of materials designed to control uncontrolled air movement through the building envelope. Effective air barriers are critical for moisture management, energy performance, and occupant comfort.
Air Leakage
Uncontrolled movement of air through openings, gaps, or cracks in the building envelope. Air leakage carries moisture vapour and is a leading cause of condensation, mold growth, and energy loss.
Airtightness
A measure of how much uncontrolled air passes through the building envelope under standardized pressure conditions, typically expressed as air changes per hour at 50 Pascals (ACH50).

B

Blower Door Test
A diagnostic procedure using a calibrated fan mounted in a door frame to depressurize or pressurize a building, quantifying total air leakage and identifying leakage locations.
Building Envelope
The physical boundary between the conditioned interior of a building and the exterior environment. It includes the foundation, walls, roof, windows, doors, and all interfaces between these elements.
Building Wrap
A weather-resistant barrier (WRB) material installed over exterior sheathing to resist water penetration while allowing water vapour to pass outward. Also called housewrap.

C

Capillary Action
The movement of liquid water through small pores or channels in building materials without the assistance of gravity or external pressure. A significant moisture pathway in masonry, concrete, and wood.
Cladding
The exterior finish material applied to the outside of a building frame. Common cladding types include fibre cement panels, metal cladding, stucco, brick veneer, and wood siding.
Condensation
The process by which water vapour in air changes to liquid water when the air cools below its dew point. Condensation within wall assemblies causes wood decay, corrosion, and mold growth.

D

Dew Point
The temperature at which air must be cooled at constant pressure for water vapour to condense into liquid water. When surfaces within a wall assembly reach the dew point, interstitial condensation occurs.
Drainage Plane
A designed pathway within a wall assembly that allows any water that penetrates the cladding to drain away from the building. A continuous drainage plane is essential in BC's high-rainfall climate.

E

Envelope Failure
A breakdown in one or more components of the building envelope allowing uncontrolled water, air, or vapour intrusion. Envelope failures range from localized cladding breaches to systemic moisture accumulation.
EIFS (Exterior Insulation Finishing System)
A cladding system using foam insulation board covered with a reinforced base coat and finish coat. Legacy EIFS systems without drainage cavities have been a significant source of envelope failures in BC.

F

Façade
The exterior face of a building, particularly the front or principal elevation. Façade inspection evaluates cladding condition, joint integrity, penetrations, and drainage.
Flashing
Thin impermeable material (typically metal or flexible membrane) used at joints, transitions, and penetrations in the envelope to direct water away from the building structure.
FLIR (Forward Looking Infrared)
A brand of professional thermal imaging cameras widely used in building envelope diagnostics. FLIR cameras detect infrared radiation emitted by surfaces, rendering temperature variations as visible images.

G

GPR (Ground Penetrating Radar)
A non-invasive scanning technology that uses radar pulses to detect subsurface anomalies. Used in building envelope inspection to detect moisture in flat roof assemblies and below-grade structures.

H

Hygrothermal Analysis
Computer-based simulation of heat and moisture movement through building assemblies over time. Used to predict condensation risk, drying potential, and long-term durability of wall designs.

I

Infrared Thermography
The use of infrared cameras to detect and visualize surface temperature differences on building components. Temperature anomalies indicate moisture, air leakage, or insulation deficiencies.
Interstitial Condensation
Condensation that forms within the layers of a wall, roof, or floor assembly when warm, moist air contacts cooler surfaces. Often invisible until structural damage has occurred.

M

Moisture Content
The amount of water in a material expressed as a percentage of the material's oven-dry weight. Building materials have damage thresholds above which decay, mold, and structural deterioration accelerate.
Moisture Meter (Resistance Type)
An instrument that measures electrical resistance between two probes inserted into a material to determine moisture content. Most accurate for wood-based materials.
Moisture Intrusion
The unwanted entry of liquid water or water vapour into a building envelope or its components. Sources include rain penetration, rising damp, condensation, and plumbing leaks.

P

Parapet
A low wall at the edge of a roof, terrace, or balcony. Parapets are high-risk areas for moisture intrusion due to complex flashing requirements and exposure to standing water.
Penetration
Any element that passes through the building envelope, including pipes, conduits, fasteners, windows, and doors. Every penetration is a potential moisture pathway requiring proper sealing and flashing.

R

Rain Screen
A wall assembly where the outer cladding is separated from the moisture-resistant barrier by a ventilated air cavity, allowing water that bypasses the cladding to drain and evaporate.
Remediation
The repair or replacement of building components that have been damaged by moisture intrusion. Remediation scope is often determined by the findings of a professional envelope inspection.

T

Thermal Bridge
An area of the building envelope with significantly higher thermal conductance than the surrounding assembly, resulting in locally elevated heat loss and increased condensation risk.
Thermal Imaging
See Infrared Thermography. Thermal imaging is the practical application of infrared cameras to detect temperature anomalies in building envelopes associated with moisture, air leakage, and insulation failure.

V

Vapor Barrier
A material with very low water vapour permeability used to control vapour diffusion through a building assembly. Placement relative to the insulation layer is critical — incorrect placement can trap moisture.
Vapor Diffusion
The movement of water vapour through solid materials driven by differences in vapour pressure. Unlike air transport, vapour diffusion is a slow process but can cause significant long-term moisture accumulation.

W

Weather-Resistive Barrier (WRB)
A material installed over exterior sheathing to resist bulk water penetration while allowing the assembly to dry. Also called building wrap or housewrap. Must be continuous and properly lapped.
Weep Hole
Small openings at the base of a cladding system or window sill that allow accumulated water to drain out of the wall cavity. Blocked weep holes are a common cause of moisture entrapment.

Term not listed? Call our specialists at (604) 239-9934 for technical clarification.

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