Definitions and Answers to Frequently Asked Questions
Replacement Window Terms
- Double Pane: Nearly all windows manufactured today are double pane. These are built with two panes of glass bonded together to a spacer or super spacer that insulates the inside glass surface from the outside glass surface. The air gap and lack of contact between the glass is what leads to most of the benefits such as reduced sound transfer, and reduced heat transfer. The glass unit (both panes and the spacer) is called an IGU or insulating glass unit.
- SHGF or SHGC: Solar Heat Gain Factor or Solar Heat Gain Co-efficient. This is a rating given to windows indicating the amount of protection the window provides from direct sun heat gain. If you feel the sun through your current windows, they have a high SHGC. For Houston replacement windows, a low number of .20 is really good.
- UF or U-Factor: The UF is a rating given to windows to indicate their ability to keep your home insulated from the cold. In the Houston area, UF is not as important as the SHGC. A rating around .30 to .25 would suffice here because we really don’t use the heater on very many days.
- Energy Star: The US Government lab that rates a product’s energy efficiency. Energy Star rates all kinds of products so this is considered a minimum standard for windows.
- UV Rays: Ultra-Violet rays consist of light waves that are not visible to our eye but, they have a damaging effect on our skin and our home’s flooring and furnishings. UV light will fade carpet , flooring, furniture and any other surfaces or fabrics exposed to it.
- Low-E: Low-E or Low Emissivity comes from a thin, invisible to us layer of silver oxide material coated to the inside of glass to prevent the passage of UV light.
- Double Strength Glass: Double strength glass is really “double the strength” of glass most of us grew up with. It is thicker and heat treated to resist being easily broken. It’s not unbreakable it’s just more versatile and stable.
- Tempered: Tempered glass is also known as safety glass. It is treated with High heat and slower cooling times so that it will resist some impacts. When it does break it will usually break out completely in very small and somewhat dull pieces. This makes it ideal for shower doors and any high traffic area in your home. City building codes will indicate where tempered glass is required. All glass installed in doors must be tempered as a general rule.
- Laminated: Laminated glass is another type of strengthened glass. This is accomplished by pressing (laminating) two sheets of glass together with a thin, clear vinyl sheet in between. This process results in the opposite of tempered glass. Laminated glass will stay intact when broken because it is fused to the plastic sheeting in between the panes of glass.
- Argon Gas: Argon gas is an inert, non-harzardous gas that is heavier than air. Filling the chamber between two panes of glass (called the air gap) with argon gas significantly increases the replacement window’s insulating factor (see UF).
- Egress: This term comes from building code and refers to a window’s ability to become an exit in an emergency such as fire. Generally, 9 square feet of exit is required in all bedrooms for example. That’s one of the reasons in Real Estate that a room must have a window in order to be called a bedroom.
- NFRC: The NFRC or the National Fenestration Rating Council is an independent lab that specifically tests and rates windows, doors and skylights. They are specialized and go into much more detail and depth rating products than the Energy Star does. Every new window and door will have the NFRC label affixed to it showing how the window fares on it’s testing.
Replacement Window Styles
- Single Hung: Windows that open vertically but only the lower sash opens upward. The upper sash is fixed.
- Double Hung: Windows that open vertically. Both sashes operate enabling you to vent the room from the top of the window (for safety and security) or the bottom sash.
- Slider: Windows that operate horizontally. One window slides past the other and in some cases, both sliders operate.
- Picture: These windows do not open. They are full glass from corner to corner.
- Casement: Casement windows are the type that operate with a crank handle. Mostly, these open out and open horizontally. There are other types of casement that hinge at the top or bottom and they have specific names like hoppers and jalousies.
- Mullion: With large window openings, mullions are used to connect two or more windows together. The windows can be mulled vertically for very wide openings or horizontally for very tall openings. More that one type of window can be mulled together and one common style is a double hung window on each side of a single picture window, called a triple.
- Geometric Generically, any shaped window other than square or rectangular.
- Eyebrow: A shaped window that is curved with one side taller and the other side narrow or to a point.
- Round Top: Mostly, tall, rectangular windows with a rounded top…rounded meaning that the curve is nearly half a complete circle. Concentric.
- Arch Top: A curved top window that is not concentric. The curve radius may or may not be consistent within it’s length of run.
