Key Terms and Definitions


Measures the insulation’s ability to resist heat flow. The higher the R-value, the better the insulation’s effectiveness. On batt insulation, R-Values are generally found on one side. These values should be shown when installed.

Batt Insulation

Pre-cut sections of fiberglass or rock wool insulation that fit between studs and beams in walls and floors.

Blown-In Insulation

Loose-fill insulation, such as fiberglass, cellulose, or mineral wool, that is blown into building cavities or attics using special equipment.

Foam Board

Rigid panels of insulation that can be used to insulate walls, floors, and ceilings. They are made of polystyrene, polyisocyanurate, or polyurethane.

Perm Rating

A perm rating is the unit telling us the mass rate of water vapor flowing through one square foot of material.

Vapor Barrier

Material used to prevent moisture from passing through the insulation, which can lead to mold growth and structural damage. (Class I vapor barriers have a perm rating of 0.1 or less)

Vapor Retarder

Material that reduces the rate at which water vapor can move through a material. (Kraft Facing has a perm rating of 1.0 perm. Perm ratings of 1.0 – 0.2 are considered class II vapor retarders)

Thermal Bridge

An area or component of a building that has a significantly higher heat transfer than the surrounding materials leading to energy loss, such as a metal stud in a wall.

Spray Foam Insulation

A chemical product that expands and hardens into foam to insulate and seal gaps. It comes in open-cell and closed-cell varieties. (Respirators are needed during installation of this material)

Reflective Insulation

Insulation that reduces heat transfer by thermal radiation. It often consists of layers of foil-faced material.

Air Sealing

The process of sealing gaps and cracks to stop air leakage, which can significantly improve a building’s energy efficiency.

IC Rated

Insulation Contact Rated; refers to light fixtures that are safe to be in direct contact with insulation without posing a fire risk. (You can find “IC” on the inside or back side of light fixtures)

Kraft-Faced Insulation

Insulation with a paper facing that acts as a vapor retarder, typically used in exterior walls to control moisture. (Kraft facing will burn and must be installed in substantial contact with an approved ceiling, floor or wall material.)

Clear Poly/Fire Poly

Plastic sheeting used as a vapor barrier; “Fire Poly” is flame retardant. (Fire Poly can be installed in areas where it has no contact with ceiling, floor, or wall meterial….dead spaces)


Fabric or synthetic material is used to hold loose insulation material in place. (Used on BIBS/net & blow applications)

BIBS/Blow In Blanket System

A system where loose-fill fiberglass or cellulose insulation is blown into walls or cavities behind a special breathable fabric to create a seamless insulation blanket. (Also called Net & Blow)


Typically acrylic-based and white in color, this sealant is used to fill vertical stud gaps or seal bottom plates to subfloor. It can also be used for post-drywall air sealing. Silicone type must be used when caulking windows is called out.

Canned Foam

Sealant materials used to fill cracks and gaps for air sealing and insulation. Window and Door or Fireblock types are used on job sites.

Window and Door Foam

Sealant typically used on windows and doors and does not cause bowing on window or door frames. White in color and can be used for sealing other areas where fireblock foam is not needed.

Fireblock Foam

Sealant typically used on vertical and exterior penetrations where building code requires a UL/ASTM rated foam. Orange in color and not meant for windows or doors.

Vinyl/Basement Blanket

Insulation wrapped in vinyl used in basements to improve thermal performance and include a finish look. (The white facing is normally perforated to allow moisture to escape)

Split Wires

The practice of installing insulation around wires of a wall cavity to maintain full R-value of the insulation material. Gas and water drain lines are also insulated around.

Electrical Boxes

Plastic or metal boxes housing electrical connections. (Air sealing and insulating behind exterior boxes may be required prior to insulating the wall)

Water Lines

Pipes that carry water throughout a building. (These lines should left exposed to the warm side if insulating around in an exterior wall)

California Corner

An energy-efficient framing technique where three studs form a corner pocket, allowing more space for insulation.

Air Seal

The process or material used to reduce air leakage in buildings.

Top/Bottom Plates

Horizontal framing members in wall construction; top plates are at the top of the walls, bottom plates are at the base.

Double Studs

Two studs placed together in a wall for added structural support.

Building/Thermal Envelope

The physical barrier in a building that controls heat flow, airflow, and moisture. (Insulation is installed along this barrier of the home or building to maintain indoor temperature and comfort)

Roof Truss

The framework supporting the roof, typically made of triangular structural units.

Web/Scissor Truss

Types of roof trusses; “Web” has interconnected triangles, “Scissor” allows for a vaulted ceiling.

Gable end/Hip Roof

Roof styles; “Gable” has two sloping sides that meet at the top, “Hip” has sides that slope down to the walls.

Floor Under/Porch Under

Insulation installed under the main floor or under porches.


The space between each floor of a home or building. Normally insulated for sound or filled to prevent the spread of a fire when sprinkler lines are not present within the floor system.

Mechanical Room

A room housing HVAC equipment, water heaters, etc.

Bonus Room

An extra room that doesn’t fit into the standard layout, often over a garage.

Dead Spots/Space

Areas in a building where finished drywall does not come in direct contact with the inside. Duct work or plumbing are usually found in these spaces.

Boxsills/Rim Joist

Areas around the perimeter of a floor, are particularly vulnerable to air leaks.

Roof Deck

The foundation layer of the roof onto which roofing materials are applied.


Exterior features; “Soffit” is under the roof eaves for ventilation, “Fascia” is the vertical finishing edge connected to the ends of the rafters.


Installed in attic insulation to maintain ventilation pathways between insulation and roof sheathing. These also help prevent wind washing where wind will blow into the soffit and move around the attic insulation causing damage.


Spaces between the top plate and the roof deck that require insulation and/or air sealing.


Areas at the top of rooms, often challenging to insulate due to their height.


A tray ceiling (also sometimes called a recessed ceiling) resembles a large upside-down tray that is set into the ceiling of a room.


A ceiling space that is angled vs flat.


Cathedral ceilings are tall, central, and symmetrical. These types of vaulted ceilings originated in churches and cathedrals, hence the name.


A short wall and/or ceiling height change used to support rafters in attics.


A type of insulation material with an R-value of 38, indicating its thermal resistance.


Vertical structures that define rooms and support the roof.


A type of basement with one or more sides exposed to daylight; also refers to windows or other openings providing natural light.


A basement with a door providing direct exit to the ground level outside.


Installation techniques to improve sound or thermal insulation, often involving layers or staggered placement.


A building or area for storing vehicles, often insulated differently from living spaces.


Walls that separate different living spaces or rooms within a building. These walls separate units within an apartment building or townhome.

House to Garage/Common Wall

The boundary or connection area between a house and its garage, often a focus for air sealing.


Refers to the inside or outside parts of a building or its components.


A material, device or construction installed to restrict the movement of air within open spaces of concealed areas of building components such as crawl spaces, floor/ceiling assemblies, roof/ceiling assemblies and attics.


Fireblocking involves the use of field-installed building materials to prevent the movement of undetected flames to other areas through such concealed spaces. (fireblocking is intended to resist the movement of flames, whereas draftstopping is intended to resist the passage of smoke and gases.)


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