The Building Envelope is the physical separator between the interior and the exterior environments of a building.

Another term is "Building Enclosure". It serves as the outer shell to help maintain the indoor environment (together with the mechanical conditioning systems) and facilitate its climate control.

Considering the 'building envelope first' means that we're making improvements to the enclosure that could reduce heat loss, manage moisture and control airflow from the interior to exterior and vice versa. We do as much as we can to enhance the passive control layers BEFORE we add technology. This approach opens the potential for simplification and greater energy effectiveness of HVAC systems and heat recovery ventilation appliances.

WHAT IS THE BUILDING ENVELOPE?

The Building Envelope is made up of:

• Structural Layers - foundation, framing, trusses, panels and sheeting, engineered products (i.e. OSB, PSL, LSL, etc..)
• Control Layers - Insulation, air barrier(s), vapour barrier(s) and retardants (i.e. VDR paint), sealants, gaskets and caulking. Flashing and drainage on the exterior are also part of the control layers.
• Finish Layers - Drywall, wood flooring and wall panels, trim elements, exterior finish, doors and windows.

The structural elements in a building envelope are doing the job of carrying loads and resisting the many forces that come from the natural environment.

In a deep energy retrofit, it may be necessary to deal with the structure in order to add insulation, replace windows or to run ductwork for ventilation.

SAFETY NOTE: Any structural change to a building must be treated with caution. Always hire professional contractors to do this kind of work.

The main structural components and their functions are as follows:

• Foundations are the part of a building structure that acts as an anchor the ground and transfers loads from above down to the earth below. They may be constructed of stone, brick, solid concrete or concrete blocks or preserved wood.
• Floor systems are horizontal structures made of beams and floor joists. They carry the load of occupants, furniture, appliances and some of the weight of upper structure. Floor systems may be made of dimensional lumber, engineered wood, timber or logs and metal.
• Wall Systems are made of vertical studs, long horizontal 'plates' and beams that span the tops of openings. A wall may be load bearing or non-loadbearing, meaning that it may carry loads from floors and walls above. Wall systems may be made of dimensional lumber, engineered wood, timber or metal.
• Roof Systems are the uppermost structure in a building. They can be sloped or flat, and will transfer loads from snow, rain and wind to the walls, floors and foundation below. A roof can be framed with metal, timber, dimensional lumber and engineered trusses.

Making a more effective building envelope mainly deals with alterations to the CONTROL LAYERS - elements of air sealing, insulation and moisture management. By doing this, we are most likely forced to upgrade mechanical systems, while also working around structure and finishes.

Treating the building envelope first includes the following types of strategies for improved control layers:

• Increased levels of INSULATION all around the building
• Increased AIR TIGHTNESS
• Improved MOISTURE management and bulk water control
• Upgraded WINDOWS and DOORS

With these changes and the addition of MECHANICAL VENTILATION, the energy performance of a building may be significantly improved. This improvement can be measured by comparing...

• The baseline energy audit and blower test results done BEFORE the retrofit, and...
  
• The post-retrofit test or 'commissioning' AFTER the work is done, to ensure that the new layers and systems are doing what they're supposed to be doing.
  

The FINISH LAYERS on the interior and exterior of structure and control assemblies provide the aesthetic or "look" of a building. They may also be pulling double duty in some situations:

• Airtight Drywall - A drywall layer may form a part of the continuous air barrier on the interior of a building. The material itself is air tight and the seams between sheets can be sealed to create a uniform layer. The challenge of this approach comes when there are changes in direction and structure, such as at floor intersections.
• Exterior Drainage Planes - When combined with metal flashing, rain gutters and weather barriers, some exterior finishes may also act to protect under layers from bulk water. Roofing, wall cladding and parging on foundations are some examples.