Collection: Glossary of Building Terms

Welcome to the Polycarbonate Store's Glossary of Building Terms! Whether you're a DIY enthusiast or a seasoned builder, understanding the right terminology can make any project smoother and more successful. This glossary is here to help you navigate common building terms related to polycarbonate installations and greenhouse construction. From "Anchor Bolts" to "Weep Holes," you’ll find clear explanations to help you plan, build, and maintain with confidence. Let's get started!

Anchor Bolts
Bolts to secure a wooden sill plate to concrete, or masonry floor or wall.

Btu (British Thermal Unit)
The amount of heat required to heat 1 lb. of water by 1° F. Used to describe the power of heating and cooling systems in a structure like a sunroom or greenhouse, e.g. 17,000 Btu Output Gas Heater.

Bar Cap System, Aluminum
Capping used externally to hold polycarbonate or glass to framework. Includes rubber gasket to seal out moisture.

Bar Cap System, Poly
UV protected plastic forms used to join Multi-Wall polycarbonate panels while attaching them to the frame. See “Poly End Cap” and “Poly Joiner Cap” below.

Brace
An inclined piece of framing applied to wall or floor to strengthen the structure. Often used on walls as temporary bracing until framing has been completed.

CFM (Cubic Feet per Minute)
The cubic feet of air moved by a fan within 1 minute. Used to describe the power of circulation and exhaust fans.

Caulk / Caulking
(1) A flexible material used to seal a gap between two surfaces; e.g., between pieces of siding or the corners in tub walls. (2) To fill a joint with mastic or asphalt plastic cement to prevent leaks.

Collar Beam / Collar Tie
Nominal 1" or 2" thick members connecting opposite roof rafters. They serve to stiffen the roof structure.

Door Drop
The distance between floor level and the top of the foundation.

Eave Height
Measurement to where the top of the sidewall meets the lowest point of the roof.

Eave Plate
The uppermost (top) plate in a sidewall.

Exhaust Fan
A fan that expels air from a structure like an attic, sunroom or greenhouse. The power of the fan is rated in CFM.

Extrusion
Framing bar formed by pressing or squeezing aluminum or steel through a form. Also used to describe non-specific framing pieces in a greenhouse.

Fascia
Horizontal boards attached to rafter/truss ends at the eaves and along gables. Roof drain gutters are attached to the fascia.

Flashing
Sheet metal or other material used in roof and wall construction to protect a building from water seepage. Step flashing: Flashing application method used where a vertical surface meets a sloping roof plane. 6" x 6" galvanized metal bent at a 90° angle and installed beneath siding and over the top of shingles. Each piece overlaps the one beneath it the entire length of the sloping roof (step by step).

Footer / Footing
Continuous 8" or 10" thick concrete pad installed before foundation. Supports the foundation wall or monopost.

Foundation
The supporting portion of a structure below the first floor of construction, or below grade, including the footings.

Framing
The structural members of a building, such as studs, joists and rafters.

Furring Strips
Strips of wood – often 1 x 2 – used to shim out and provide a level fastening surface for a wall or ceiling.

GFI or GFCI Outlet (Ground Fault Interrupt or Ground Fault Circuit Interrupt)
An electrical outlet that will shut off automatically when a short is sensed, turning off the current to the outlet and any outlet wired after the GFI outlet.

Glazing
The wall, roof or window covering that transmits light into a structure; i.e., glass, polycarbonate, acrylic, plastic.

Glazing Bar
Aluminum framework to which polycarbonate or glass is attached.

Glazing Gasket
A flexible seal used to prevent water from entering between the glazing and the frame.

Glazing “H” Channel
A piece of aluminum or plastic shaped like a lower case “h” used for the bottom and/or top of MultiWall polycarbonate panels, and glass.

Glazing “J” Channel
A piece of aluminum or plastic shaped like a “J” used for the bottom and/or top of 4 mm MultiWall polycarbonate panels, and glass.

Glazing “U” Channel
A piece of aluminum shaped like a squared-off “U” used for the bottom and/or top of 6 mm MutiWall polycarbonate panels.

Glazing Tape - Foam Tape
Used to prevent water from entering between the polycarbonate or glass glazing and the frame. It has a closed-cell structure that cannot absorb moisture.

Glazing Tape - Foilastic Tape
Flashing tape designed to waterproof exterior seams.

Glazing Tape - Vented Tape
A tape that is designed keep insects out and airflow through the flutes (channels) in a polycarbonate sheet.

Hardware
All the “metal” fittings that go into the home when it is near completion. For example, doorknobs, towel bars, handrail brackets, closet rods, house numbers, door closers, etc. The Interior Trim Carpenter installs the “hardware.”

Hardware – Bar Cap Screws
Stainless steel or powder-coated screws are used to secure glazing materials.

Hardware - Washer Head Screws
Roofing crew with a rubber gasket under the washer used to attached roof glazing materials.

Hardware – Gasket Washers
Washers that have a rubber gasket under the washer and is used to attach glazing materials.

Humidity
The amount of water vapor in the air. The air’s capacity to hold vapor is limited but increases dramatically as the air warms. Relative humidity is the amount of vapor in the air divided by the air's vapor-holding capacity at that temperature. This is the most common measure of humidity used in a building structure or greenhouse.

Joist
Wooden 2 x 8’s, 10’s, or 12’s that run parallel to one another and support a floor or ceiling; and supported in turn by larger beams, girders, or bearing walls.

Joist Hanger
A metal “U” shaped item used to support the end of a floor joist and attached with hardened nails to another bearing joist or beam.

Kerf
A groove in the framework designed to receive glazing material.

Knee Brace
A structural component securing the angle between the rafter and the wall.

Lineal Foot
A unit of measure for lumber equal to 1" thick by 12" wide by 12" long. Examples: 1" x 12" x 16 ft. = 16 board feet, 2" x 12" x 16 ft. = 32 board feet.

Load Bearing Wall
Includes all exterior walls and any interior walls that are aligned above a support beam or girder. Normally, any wall that has a double horizontal top plate.

Mastic
A gooey sealant/adhesive used to attach or waterproof a joint.

MultiWall Polycarbonate – 6 mm TwinWall
Double-walled polycarbonate panel that is UV protected. An insulating glazing with an “R” value of 1.6.

MultiWall Polycarbonate – 8 mm or 16 mm TripleWall
Three-walled polycarbonate that is UV protected. An insulating glazing. Comes in 8 mm with an “R” value of 2.1 and 16 mm with an “R” value of 2.5.

MultiWall Polycarbonate – 16 mm 5-Wall
Five-walled polycarbonate that is UV protected. An insulating glazing. Comes in 16 mm with an “R” value of 2.78.

Multi-Wall Polycarbonate – mm to inch conversion
Used to order the correct MultiWall thickness to fit into your building structure or aluminum extrusions. 4 mm = 3/16", 6 mm = 1/4", 8 mm = 5/16", and 16 mm = 5/8".

Organic
Agricultural and horticultural practices that favor the use of naturally occurring fertilizers, pesticides and other growing aids. It can also refer to produce or plants that have not been exposed to synthetic chemicals.

OC / On Center
The measurement of spacing for studs, rafters and joists in a building from the center of one member to the center of the next.

Outside-to-Outside Foundation Dimensions
The measurement from the outermost edge of the foundation to the outermost edge of the foundation on the opposite wall. The size of the foundation should be made to fit the building structure such as a gazebo, atrium or greenhouse.

Poly End Cap
“U” shaped plastic forms are used to seal the top and bottom of MultiWall polycarbonate panels when attaching panels to the frame.

Poly Joiner Cap
“H” shaped plastic used to join MultiWall polycarbonate panels when attaching panels to the frame.

Polycarbonate
Shatter resistant plastic that is lightweight and flexible while maintaining high impact strength. Comes in many different styles.

Pony Wall / Knee Wall
A pony wall, sometimes referred to as a split wall or knee wall, is a single wall composed of two separate wall types; one built above the other. A pony wall is often solid material (wood or stone), with a glazing wall installed above it.

Post
A vertical framing member usually designed to carry a beam. Often a 4" x 4", a 6" x 6", or a metal pipe with a flat plate on top and bottom.

Purlin
An aluminum bar in the roof that runs the length of the building structure to provide support to the rafters or roof glazing bars.

“R” Value (Resistance Value)
A measure of insulation. A measure of a materials resistance to the passage of heat. The higher the R value, the more insulating “power” it has. For example, typical new home walls are usually insulated with 4" of batt insulation with an R value of R-13, and a ceiling insulation of R-30.

Rabbet
A rectangular longitudinal groove cut in the corner edge of a board or plank.

Rafter / Roof Joist
Framing members used to support roof sheeting and roof loads. The rafters of a flat roof are sometimes called roof joists.

Rebar (reinforcing bar)
Ribbed steel bars are installed in foundation concrete walls, footers, and poured in place concrete structures designed to strengthen concrete. Comes in various thicknesses and strength grades.

Ridge
The horizontal line at the junction of the top edges of two sloping roof surfaces.

Roof Bar Length
The measurement from the point of the eave to the ridge along the rafter.

Rough Opening
The horizontal and vertical measurement of a window or door opening before drywall or siding is installed.

Sealant / Caulk
Waterproof filler for cracks and seams to make watertight. Silicone Sealant is a type of sealant used with glass, fiberglass, MultiWall polycarbonate, masonry, aluminum and wood. Some sealants and caulks may not be well suited for certain building materials, check for compatibility issues.

Shade Cloth
Material used to provide shading by blocking some percentage of sunlight. Density and life of shading fabric materials varies.

Shed Roof
A roof containing only one sloping plane.

Shutter
A cover for a vent that is fitted with hinged louvers.

Sill
The horizontal frame forms the base of the building structure and attaches to the foundation.

Sill Plate
A horizontal member anchored to a concrete or masonry wall.

Slope
The incline angle of a roof surface, given as a ratio of the rise (in inches) to the run (in feet). (See also “pitch.”)

Soffit
The soffit is the area below the eaves and overhangs. The underside where the roof overhangs the walls. Usually the underside of an overhanging cornice.

Solar Vent Openers
Non-electric, automatic vent openers. The most popular vent openers operate thermally and have a mineral wax cylinder that expands and contracts due to the temperature in the room.

Square
To make the foundation such that all four corners are at right angles.

Stud
A vertical framing member – also referred to as a wall stud – attached to the horizontal sole plate below and the top plate above. One of a series of wood or metal vertical structural members placed as supporting elements in walls and partitions.

“Two ft on center”
A term often used to describe the practice of building a wall or roof by placing studs or rafters on two-foot centers. Thus, the sheeting or glazing materials can be attached with this knowledge, as work commences.

UV Protected
Material that has a coating or is impregnated with a substance that blocks UV (ultraviolet) light is considered “UV protected.”

Vent
An opening in the building structure to provide ventilation.

Ventilation
To circulate fresh air in a greenhouse or sunroom.

Weep Holes
Small holes in storm window frames that allow moisture to escape.