Understanding Window and Door Terminology

Here at Northern Comfort Windows and Doors, we understand buying new windows and doors can be a bit tricky when there's so much new terminology. We have compiled a list that we hope will help you make the right purchase for your home!

A-D | E-H | I-L | M-P | Q-T | U-Z


Air Chambers
Small honeycomb spaces within the sash and frame which help to insulate and strengthen the window.
Air infiltration
The amount of air that passes between a window sash and frame. In windows, it is measured in terms of cubic feet or air per minute, per square foot of area. The lower the number, the less air the window lets pas through.
Argon Gas
An odorless, colorless, tasteless and non-toxic gas which is six times denser than air. It is used to replace air between the glass panes to reduce temperature transfer.
The center member of a double door, which is attached to the fixed or inactive door panel.


Balance Covers
Covers the balance cavity holding the coil-spring balance system inside the jamb.
Balance System
Device for holding vertically sliding sash in any desired position through the use of a spring or weight to counterbalance the weight of the sash.
A rubber material that seals the glass to the spacer, creating an airtight and watertight IG unit. Butyl has the lowest gas permeability of all rubbers.
The brickmould is on the outside of the window or door and enhances your home's exterior appearance. It attaches to the frame and makes the overall window appear larger. The brickmould also covers the gap between your home's exterior (siding or brick) and the window frame.
Brick to Brick Installation
Frame Out installation, also called Brick to Brick installation, is the recommended solution to your window project. This method removes the entire frame and is taken back to the studding of your home. Insulation is placed around the inside and outside of your new frame.
Advantages: eliminates all rot and mould from wood frames in the building envelope, extremely energy efficient, maintenance brick mould on the outside, fresh trim on the inside of your home. Full window installation can be excellent, and depending on the type of windows you want, this might be your only choice, it's best to work with an experienced window installer to ensure that the job is done correctly.
Bead Stop
The wood strip that a swinging sash closes against, as in a casement window. Also a finishing trim at the sides and top of the frame to hold the sash.
Bottom Rail
Bottom horizontal part of a window sash.


Cam Lock and Keeper
The mechanisms which pull the sash together when placed in the locked position.
Centre of Glass U and R-values
The U- and R-values measured from the centre of the glass to 2-½” from the frame.
Condensation Resistance Factor
A measure of the effectiveness of a window or glazing system to reduce the potential for condensation. The higher the condensation resistance factor, the more efficient the window and glazing system.
Energy transfer from one material to another by direct contact.
Heat transfer by currents that flow from a warm surface to a colder one.
Check Rail
Top rail of the upper sash and the bottom rail of the lower sash on a double-hung or single-hung window where the lock is mounted and meets when closing, also known as meeting rail and lock rail.
All-wood window protected by a beautiful, durable, low-maintenance aluminum-clad exterior in your choice of colours.
Molding of various widths, thicknesses and shapes applied to the framework of window and door units.
A sealant used to seal construction joints, in order to prevent water and air infiltration.


Dead-air space
The space between the panes of glass of an I.G. Unit.
A material used in insulating glass to absorb water vapor which causes fogging.
Double-Strength Glass
Glass with a thickness of approximately 1/8″
Direct Set Side Lite
A direct set side lite creates brighter spaces as light is able to travel through a larger opening. Equally safe as they are beautiful, each direct set side lite glass is custom-made and sealed inside two panes of tempered glass.
Door Lite
Decorative, clear or wrought iron glass inserts that is installed into an entry door when it is manufactured.
Drip cap
A moulding placed on the top of the head brickmould or casing of a window frame.
Dry glazing
A method of securing glass in a window frame with a dry, preformed, resilient gasket, without the use of a glazing component.


Energy Star
Energy Star is an independent government program establishing a standard set of guidelines to recognize the energy efficiency of various products. Energy Star guidelines are used in conjunction with a variety of building materials, including windows and patio doors. Over the past ten years, Energy Star guidelines have helped double the efficiency of windows they endorse.
The relative ability of a surface to reflect or emit heat by radiation. Emissivity factors range from 0.00 to 1.00 and are typically measured in a U-Value (or its inverse R-Value). The lower the emissivity, the less heat that is emitted through a window system.
An ER-Rating is derived from solar heat gain, heat loss through frames, centre and edge of the glass and air leakage heat loss. The combined effect is measured in number of watts per square metre and is either positive or negative. A positive number represents a net heat gain and helps in reducing the home's heating costs. A negative number indicates that the product loses more energy through heat loss and air infiltration than it gains in solar energy absorbed from the sun (i.e. the home's heating system has to work harder in colder weather).
ER-Ratings range widely depending on the type of window and design options. For example fixed windows score better ER-ratings than operating ones. Operating windows and sliding doors typically have a negative ER- number ranging from -30 (indicating weaker energy performance) to -5. Fixed windows can be designed to have positive numbers ranging from -20 to +10.
Edge of glass
The area within 10 cm (2.5 in) of the edge surrounding the perimeter of the glass.
The space in which the operating part of the window requires clearance for fire regulations.
The rate at which a surface of a material radiates long-wave heat energy, usually referring to glass surface properties. Low emissivity results in less overall heat loss.
Extension jambs
Flat wood or vinyl parts that are applied to the inside of the frame to extend it in width, which allows the frame to adapt to a thicker wall.
Exterior glazed
Glass installed from the exterior side of the window.


The process of joining materials by melting them together with extreme heat (over 500° F), resulting in the materials uniting into a one-piece unit.
A thin strip of metal or synthetic material that diverts water away from a window or door.
Foam Spacer
Grilles are permanently bonded to the inside and outside of energy efficient insulating glass with a non-glare foam spacer between the panes of glass to give the illusion of individual panes of glass.
The enclosing box of a window or door that surrounds a sash or sealed unit, consisting of a head, sill and two jambs.


Specially designed windows classified as either Straight line Geometrics such as rectangles, triangles, trapezoid, octagons, pentagons, etc., or Radius Geometrics which include half-rounds, quarter-rounds, full-rounds, sectors, ellipses, eyebrows, etc.
The process of sealing the glass to the sash.
Glazing Bead
A strip of vinyl which surrounds the edge of the glass and holds it in place in conjunction with other sealants.
Decorative horizontal or vertical bars installed between the glass panes to create the appearance of the sash being dividing into smaller lites of glass.
Glazing Stop
Moulding around the interior or exterior of a window sash or door panel that holds the glass in place, also called a glass stop.


The horizontal top portion of the main frame.
Head expander
A vinyl shape cut the width of a product and placed on the head, fitting over it snugly. This piece is used as a filler to expand or lengthen the unit from the head and take up the gap in the opening between the unit and the opening in the unit.
Horizontal framing member placed over the rough opening of a window or door to prevent the weight of the wall or roof from resting on the window frame.
Head flashing
Flashing installed in a wall over a window.


I.G. Unit (Insulating Glass Unit)
Two or more lites of glass separated by a spacer and hermetically sealed at the glass edges.
Intercept Spacer System
Spacer system using a U-channel design to reduce the number of conduction paths.
Insulating glass
Combination of two or more panes of glass with a hermetically sealed airspace in between. May be filled with an inert gas, such as argon to further reduce heat transfer, making a home more energy-efficient and comfortable year round.
Interior glazed
Glass installed from the interior of the building.


Vertical sections of the main frame.


Keeper Rail
The horizontal section of the sash where the keeper is attached.
Keeper Stile
The vertical section of the sash where the keeper is attached.
Krypton Gas
An inert, odorless, colorless, tasteless, non-toxic gas which is about 12 times denser than air. It is used to replace air between the glass panes to reduce temperature transfer and deter convection. Used when a higher performance is desired than that produced with Argon gas.


Lift Handle
A handhold for raising and lowering the sash. Handle implies that the handhold is not continuous across the sash.
Lift Rail
A handhold for raising and lowering the sash. Rail implies that the handhold is continuous across the sash.
A unit of glass in a window.
Low E (Emissive) Glass
Glass with a transparent metallic oxide coating applied onto or into a glass surface. The coating allows short-wave energy to pass through but reflects long-wave infrared energy which improves the U-value.


Main Frame
The head, sill and jambs sections of a window.
Mechanically Fastened Frame
Refers to frames fastened with screws.
Meeting Rail
The horizontal sections of a pair of sash that meet when the sash are closed.
A vertical or horizontal connecting unit between two or more windows.
Multipoint Lock System
Locking system that secures the door at multiple points for added security.
A slot or rectangular cavity cut into a piece of wood to receive another part.
Mortise and tenon joint
Used at the corner of a wood sash to give strength and prevent sagging. Glued and machine squared for perfect fit in frame.
One cam lock lever at the bottom operates multiple locking points to secure the sash to the frame.
Muntin bar (Grille)
Dividing bars or muntins used either on the surface or between panes of glass for a decorative appearance.


Nailing fin
A vinyl or metal flange attached to the perimeter of a window frame for insulation onto the rough opening header, jack studs and rough sill.


Obscure Glass
Glass that has been made translucent instead of transparent.
Refers to a door or a window that has an operable sash or panel that opens to allow passage or ventilation.


Passive Solar Heat Gain
Solar heat that passes through a material and is captured naturally, not by mechanical means.
Parting Stop
Narrow strip, either integral or applied, that holds a sash or panel in position in a window or door frame.
Polyurethane core
Doors are foam injected for higher insulating value.


Resistance a material has to heat flow. The higher the R-value, the greater the resistance, the better the insulation. R-values are the reciprocal of U-values (R-value of 4 is equal to U-value of 0.25).
Wave energy transmitted directly from one object to another through the atmosphere or through transparent or translucent materials. The energy radiated is transmitted, absorbed, reflected or a combination of all three.
Retro-fit Installation
Retrofit windows are great options for those on a tight budget. These windows replace the glass in your old window frames, but leave the frame alone. Retro-Fit installation, also known as Frame-In installation, is the least expensive method of replacing your windows. The Master Frame stays in the opening and so does all your interior trim. The exterior is finished off with maintenance free aluminum capping.
Horizontal top or bottom part of a window sash or door panel.
Reinforced steel
Comes in flat or tubular form that is completely enclosed in the vinyl frame for very large window combinations to structurally enhance the window.
Rough opening
The opening built into a frame wall to receive a window or door unit.


A handhold for raising and lowering the sash. Handle implies that the handhold is not continuous across the sash.
Shading Coefficient
The ratio of solar heat that is transferred through a glazing material relative to the solar heat transferred through 1/8″ clear glass. The lower the number- the more efficient the window is at reducing solar heat gains.
The horizontal, bottom section of the main frame.
Sill Extender
An extrusion that is attached to the bottom of the window to cover the gap between the sill and the rough opening.
Single-strength Glass
Glass with a thickness of approximately 3/32″.
Slider Window
A window in which the sash move horizontally. Sliders are available in a 2- or 3-lite configuration, with the 3-lite having operable end vents.
Sloped sill
The sill of the window that has a downward slope to the outside. This sill has sufficient degree of slope to aid in water runoff.
Solar Heat Gain
The percentage of heat gained from both direct sunlight and absorbed heat. The smaller the number, the greater the ability to reduce solar heat gain.
Material placed between two or more pieces of glass in order to maintain a uniform width between the glass, and prevent sealant distortion.
The vertical sections of the sash.
Sealed Unit
Sealed units can be double or triple glass window panes separated by an air or other gas filled space to reduce heat transfer across a part of the building envelope. The glass panes are separated by a “spacer”. A spacer is the piece that separates the two panes of glass in an insulating glass system, and seals the gas space between them.
Sash Lift
Handle used to assist in raising and lowering the sash of a single-hung or double-hung window.
The horizontal part forming the bottom frame of a window or door opening.
Sound Transmission Class (STC) Rating
Measure of the amount of noise reduction that can be achieved with a given product. A noise reduction of 10 decibels represents cutting the noise level in half, as interpreted by the human ear. So a rating of 25 means that the product reduces the outside noise by approximately 25 decibels, cutting the noise in half 2-½ times, or cutting it by over 80 percent.
Moulding used to hold, position or separate window parts.
Sash balance
A coiled spring or spiral system integrated into the jamb liners to allow double hung or single hung sashes to open and close.
Sealed unit
A combination of two or more panes of glass factory sealed using a spacer bar. Also known as an insulating glass unit (IGU).
Rubber setting blocks used to position the glass into the window to ensure it is level, square and plumb.
Solar transmittance
The percentage of total solar energy that glazing transmits through a window.


Tempered Glass
Glass with a surface compression of not less than 10,000 psi, or an edge compression of not less than 9,700 psi. When broken, the glass breaks into pebbles instead of shards.
Tilt Latch
Mechanism that unlocks the sash and allows it to tilt in from the main frame.
Total Unit U- and R-values
The U- and R-values of the window calculated from the average U and R-values from the center of glass, edge of glass and frame.
Thermal Break
Element of low conductance placed between elements of higher conductance to reduce the flow of heat or cold, often used in nonwood windows to increase energy efficiency.
A window unit combined to the top of a window or door frame.
Triple pane (Triple glazed or Tri-pane)
A sealed unit consisting of three panes of glass separated by two spacer bars.


Amount of heat transferred through a material. The lower the U-value, the slower the rate of heat flow and the better the insulating quality. U-values are the reciprocal of R-values. (U-value of 0.25 is equal to R-value of 4).


Latch mechanism on the interior face of the sash which retains the window in a partially open position for ventilation.
Visible Light Transmittance
The percentage of light that is transmitted through glass in the visible light spectrum (380 to 720 nanometers). The higher the number the higher the percentage of visible light transmitted through the window.
Vent Panel
Panel that moves horizontally on a sliding window or patio door.
Vent Unit
Window that opens and closes.
Visible light transmittance
The percentage of visible light that is transmitted through a glazing combination. The type of sealed unit, coatings and tints will affect the percentage of visible light transmittance.


Material used to form a weather-resistant seal around operable sash.
Weep Holes
Small openings designed to allow water to escape that might otherwise accumulate in a window's sill.
Wind load
The amount of pressure exerted by the wind on a window or door generally expressed in pounds per square foot.

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