The building envelope is the totality of a building's exterior shell that separates the indoor environment from the outdoor environment. It includes the roof, external walls, cladding, windows, doors, foundation, and all the seals, flashing, and membranes that connect these elements. A well-performing building envelope controls the flow of heat, air, moisture, and light, and serves as the first line of defence against weather, pests, and environmental hazards.
Functions of the Building Envelope
The building envelope performs several critical functions simultaneously. It provides structural support and weather resistance, controls heat transfer to maintain energy efficiency, manages moisture to prevent condensation and water intrusion, regulates airflow and ventilation, reduces noise transmission, and acts as a physical barrier against pest entry. A failure in any one of these functions can cascade into multiple building performance problems.
Common Envelope Deficiencies
During a building inspection, inspectors frequently identify building envelope issues such as failed or missing sealant around windows and doors, cracked or deteriorated cladding, lifting or corroded roof flashing, gaps at wall-to-roof junctions, inadequate weatherproofing of penetrations, and degraded weatherstripping. These deficiencies allow water ingress, air leakage, and pest entry.
Moisture and the Building Envelope
Moisture management is arguably the most critical function of the building envelope. Water that penetrates the envelope can cause timber rot, steel corrosion, mold growth, insulation degradation, and paint failure. Effective moisture management involves multiple layers of defence, including external cladding, building wrap or membranes, cavity drainage systems, flashing, and interior vapour barriers working together as an integrated system.
Inspection and Maintenance
Regular assessment of the building envelope is essential for long-term property protection. Inspectors evaluate the condition and integration of all envelope components and identify areas where maintenance or repair is needed.