Whether you are talking to your contractor, to the window company, to your electrician or to the geek squad about your computer issues, it really helps when you know the terminology. Before undertaking any aspect of house renovation, familiarize yourself with the jargon associated with the job you are planning. It will make it so much easier to talk to a specialist.


Single glazing: This means there is one pane of glass in the frame.

Double glazing: This means there are two panes of glass in the frame, held apart by a spacer, with a layer of inert gas, such as argon, sealed between them.

Triple glazing: As you would expect, this means there are 3 panes of glass in the frame, held apart by two spacers instead of one and sealed with a layer of gas in between.

Argon or Krypton Gas: Sounds like something Superman might need! These gases are pumped in between glazing layers to increase insulation and slow down heat transfer.

Spacer:  A spacer holds the panes apart creating an insulating air space where gas can be added.

U-Value: The U-value is used to express the insulation value of a window. It measures how well a product keeps heat from escaping a building via thermal conductivity.  This is an important rating during the winter months in colder climes. Windows with a low U-factor indicate better insulation.

Low-E: E is for Emissivity. The term low-emissivity means that a layer of fine metallic particles has been applied to the glass in order to reduce heat transfer. A Low-E coating is designed to reflect heat back to the source. So if you are perspiring in Palm Springs, the coating will reflect the heat back to the sun. If you are shivering in Chicago, your heating bounces back into your home.

Solar Heat Gain Coefficient (SHGC): This measures how much heat from the sun is blocked. It is expressed as a number between 0 and 1.  The lower the number, the more heat is blocked.  It will depend on your climate whether you should look for a high or low number.  If you live in the hot south, look for a low number to keep the heat out. If you live in the chilly north, you may want to feel the warmth of the sun and would therefore choose a higher number.

Visible Transmittance: This measures the amount of light a window lets through. It is expressed as a number between 0 and 1. A lower number means the room will be dimmer; a higher number means the room will be brighter. Choose a lower number if you want to reduce glare, but bear in mind that a very low number may mean you have to use artificial lighting even during the day.

Air Leakage: This measures how much outside air comes into a building through a product. Rates fall in a range between 0.1 and 0.3. The lower the air leakage number, the better the product is at keeping air out.

Condensation Resistance:  This measures how well a product resists the formation of condensation, which can drip onto wood and cause mold and damage. The measurement is expressed as a number between 1 and 100. The higher the number, the better the resistance.

Water infiltration: This measures the amount of water and pressure that a window can resist before water leaks through it. The higher the water infiltration measurement, the better the window is able to withstand leakage.

Structural Performance Rating: This rating measures the amount of air pressure or wind a window can resist before it fails. The higher the structural performance rating, the more wind a window can resist.

Acoustic Performance Rating: This measures the amount of sound transmitted through a window. The higher the acoustic performance rating, the better the product is at blocking noise. You may also see this measurement referred to as the Outside-inside Transmission Class (OITC) or Sound Transmission Class (STC).

Security Performance Rating: This measures the ability of a window to resist forceful entry. The higher the rating, the harder it is to break in. Ratings range from 10 to 40.

Who would have thought windows were so involved?