Glass Glossary of Terms


Annealed glass:
Standard float (plate) glass.

Awning window:
Has a top hinge and swings outward from the bottom for ventilation.

Argon gas:
An inert, nontoxic gas used to fill insulating units for improved thermal performance.

Balance system:
The use of springs or weights to hold a vertical sash in any desired position.

Bay window:
An arrangement of three or more individual window units attached to each other. In a typical three-unit bay, a center section usually remains fixed while the two on either side act as individual casements.

Bent glass:
A glass curved through a special process.

The process by which an edge of glass is finished to an angle so that the edge is not perpendicular to either face of the glass.

A piece of neoprene, silicone, or other suitable material used to position glass in a frame.

Bow window:
A bow window can be arranged with three or more equal width units. They can be fixed or operable or mixed in any combination. They are usually mulled together with a small angle such as 13 degrees.

A synthetic rubber that can be used both as a sealant and architectural glazing tape.

A piece that connects with the keeper mechanism to keep the window sashes together when locked.

Casement window:
A window unit in which the single sash cranks outward to the right or left.

A putty-like compound used to block exterior air or moisture leaks where two surfaces meet and have minimum movement. Large cracks can be stuffed with mineral wood and weather sealed with caulking.

Condensation resistance factor:
A measure of the effectiveness of a window to reduce condensation. A higher number means better efficiency.

Curtain wall:
An exterior building wall which carries no roof or floor loads. It consists entirely of metal, or a combination of metal, glass and other surfacing materials supported by a metal framework.

A piece of glass with a sash around it.

Double glazing:
Two panes of glass enclosing a hermetically-sealed air space.

Double-hung window:
A window consisting of two sashes of glass operating in a rectangular frame, both the upper and lower halves can be slid up and down and usually use a counter balance mechanism to hold the sash in place.

Dry glazing:
A method of securing glass in a frame by use of a dry, preformed resilient gasket, without the use of a compound.

Egress code:
A law requiring a minimum opening of a window for persons to exit or firefighters to enter.

Patterns or designs cut into glass either by acid etching or needle etching techniques.

Fixed window:
A window which is stationary, also known as a picture window. Can also refer to: the part of a sliding window or door which is non-moveable, also known as inactive.

Float glass:
Glass which has its bottom surfaces formed by floating on molten metal, the top surface being gravity formed, producing a high optical quality of glass with parallel surfaces and, without polishing and grinding, the fire-finished brilliance of the finest sheet glass. Float is replacing plate glass.

Flush glazing:
A method of glazing wherein the surfaces of the glass retaining members (stops or beads) are in the same plane normal to the glass as the side faces of the frame members; often achieved by providing pockets in these faces

A deposit of contamination left on the inside surface of the sealed insulating glass unit due to extremes of temperatures. Fogging ultimately resulting in seal failure.

Pre-formed glazing materials used for bedding or securing glass and for separating glass from the frame.

Geometric windows:
Specially designed to create rectangles, triangles, half-rounds, full-rounds, ellipses and more

Buys glass and installs it on a “contractor” basis. Examples: installing the window system in large office buildings, shopping center malls, etc.

The process of installing glass in a frame.

Glazing compound:
A soft dough-like material used for filling and sealing the space between a pane of glass and its surrounding frame.

The horizontal portion at the top of the main window frame.

Head expander:
A u-shaped piece of vinyl placed on the head of a window to be used as filler. This piece will expand or lengthen a unit and fill a gap.

Heat-strengthened glass:
Glass which is reheated, after forming, just below melting point and then cooled. A compressed surface is formed which increases its strength. Used for spandrel glass.

Hermetically sealed unit:
An insulating glass unit made up of two lights of glass, separated by a roll formed aluminum spacer tube (at the full perimeter) which is filled with a moisture absorbing material. The unit is then completely sealed, creating a moisture-free, clean dead air space

Inner pane:
The pane of a double-glazed unit which faces the interior of a building.

Insulating glass:
Insulating glass refers to two pieces of glass spaced apart and hermetically sealed to form a single-glazed unit with an air space between. Heat transmission through this type of glass may be as low as half that without such an air space. It is also called double glazing.

Interior glazed:
Glass set from the interior of the building.

Used around the exterior of a window where the siding fits. It extends beyond the window to the outside edges of an adjoining j-channel.

Made up of horizontally mounted louvered glass that abut each other tightly when closed and extended outward when cranked open.

The vertical parts of the frame on both sides of the window.

Kryton gas:
An odorless and colorless gas that replaces air between two or more glass panes. Krypton is denser than air and works better to deter heat transfers.

Laminated glass:
Two or more sheets with an inner layer of transparent plastic to which the glass adheres if broken. Used for overhead, safety glazing, and sound reduction.

Another term for a pane of glass used in a window.

Lock rail:
The horizontal part of a sash where the cam lock is attached.

Low-e glass:
Low-e coatings are generally neutral in appearance and designed to reduce heat loss through the glass from inside the building. The coating reflects long-wave energy and subsequently reduces the u-value of the glass. Low-e coatings may also be incorporated into solar control coatings to provide both benefits of retaining heat in the building and reflecting heat from the sun providing improved energy control.

Main frame:
Includes the head, sill and jambs of a window.

An intermediate-connecting member used as a means to “join” two or more window products together in a single rough opening.

Muntin bar:
A small bar that divides window or door glass.

Obscure glass:
Any type of glass with uneven surfaces which offers light diffusion and privacy.

Outer pane:
The pane of double-glazed unit which faces the exterior of a building.

A light or sheet of glass.

Patterned glass:
Presents uneven surfaces with different impressed patterns.

Picture window:
Stationary and framed so that it is usually, but not always, wider than it is tall to provide a panoramic view.

Plate glass:
Polished plate glass is a rolled, ground and polished product with true flat parallel plane surfaces affording excellent vision. It has less surface polish than sheet glass and is available in thickness varying from 1/4″ to 1-1/4″. Now replaced by float glass.

Refers to a unit that is vertically level.

Adding or replacing items to existing buildings. Typical retrofit products are replacement doors and windows, insulation, storm windows, caulking, weatherstripping and vents landscaping.

Visible light transmittance:
A percentage of light that is transmitted through glass. The higher the number the more light is transmitted through the window.

Safety glass:
Glass which must have passed an impact test and either must not break or must break safely.

Creating designs on the surface of glass by using high-pressure air mixed with sand applied to the surface of glass to carve texture.

The portion of a window which includes the glass and the framing sections which are directly attached to the glass. Not to be confused with the master frame into which the sash sections are fitted.

Narrow fixed units mulled or joined to door units to give a more open appearance.

A polymeric organic compound offering excellent resistance to cold, heat and water.

Single glazing:
The use of single thickness of glass in a window or door.

Single-strength glass:
A term used to describe glass with a defined thickness (2.16-2.57 mm).

Slider window:
A slider window may have one or two movable panes of glass. Whatever the type, the windows slide horizontally in the frame.

Spandrel glass:
The area of glass panels that conceal structural building components such as columns, floor slabs, heating, ventilating and air conditioning (hvac) systems, electrical wiring and more.

The vertical parts of a sash.

Tempered glass:
Tempered glass is two or more times stronger than annealed glass. When broken, it shatters into many small fragments, thus preventing major injuries. Also known as “toughened glass.”

Triple glazing:
Three panes of glass enclosing two hermetically-sealed air spaces.

Transom window:
A window located directly above a door opening.

Refers to how much heat passes through the glass. The lower the u-value, the better the insulating quality.

UV block:
A measure of the percentage of ultraviolet rays blocked from being transmitted through the glass. A higher uv block indicates that fewer rays are transmitted through the window.

Vinyl glazing:
Holding glass in place with extruded vinyl channels or roll-in type.

Wet glazing:
Uses a silicone-based substance to secure and seal glass to a sash.

Weep holes:
Small openings on the exterior sill designed to allow water that might otherwise accumulate in a window’s sill to escape.

Weep flaps:
Weep holes covered with vinyl to let water escape while keeping bugs out.

Wind load:
The pressure acting on an external surface of a building caused by the direct action of the wind.

Window wall:
A metal curtain wall of the commercial type, in which windows are the most prominent element. Also refers to smallest fixed lights used with wall systems.

Wire glass:
Polished or clear glass that is 1/4″ thick. Wire mesh is embedded within the glass such that the glass will not shatter when broken. The wire pattern is available in many types. It is frequently used in skylights, overhead glazing and locations where a fire-retardant glass is required.

Paul Rabinowitz Glass is a commercial glass installation, maintenance and repair business, located in Philadelphia, PA.


What We Do

  • Storefronts, curtain walls and interior glass partitions
  • Aluminum, glass and hollow metal entrances
  • Revolver Door installation and service
  • Solar and decorative window Films
  • Same Day Glass Replacement
  • Same Day Door Repairs
  • 24/7 Emergency Service

Paul Rabinowitz Glass Sponsors Outward Bound Building Adventure

Paul Rabinowitz Glass company was again a proud sponsor of this year’s Outward Bound Building Adventure held at Commerce Square on Friday October 21, 2016.

Outward Bound is a non-profit, education organization that serves people of all ages and backgrounds through challenging learning expeditions that inspire strength of character, leadership and service to others, both in and out of the classroom.

To raise money and awareness for Outward bound many braved the heights as they rappelled 315 feet down the side of Commerce Square, certainly a great challenge for many!

To learn more about Outward Bound and their mission visit

#outwardboundphl #rabglassgivesback #crazythingsforagoodcause #consideritdone

Paul Rabinowitz Glass Achieves AGMC Certification

Paul Rabinowitz Glass Achieves AGMC Certification

The North American Contractor Certification (NACC), announced that The Paul
Rabinowitz Glass Company has achieved it’s Architectural Glass and Metal Contractor (AGMC) Certification. This ANSI accredited certification audits the company’s operational procedures, quality control specifications, safety guidelines as well as financial standing and record retention.
“This arduous audit/certification process not only showed us how to improve some of our processes, but also confirmed that many of our procedures both internally and in the field already conform to the industries best practices. In the end, attaining this certification took time and hard work, but showed that being an industry leader is ongoing.”
Mark Rabinowitz, President of Paul Rabinowitz Glass Company.
For more information on the NACC please visit


Smoke Baffles a.k.a. Draft Curtains

A smoke baffle is a substantial, noncombustible curtain that is hung tightly against a ceiling. Smoke baffles cordon off sections of a large ceiling for fire prevention purposes. A smoke baffle acts as a partition and “corrals” heat and smoke in the event of a fire within the curtained area. The depth of the heat and smoke contained within the curtained area can affect how quickly sprinklers are activated.

Research has shown that smoke baffles may have an adverse effect on sprinkler activation. In fact, a study published in the February 2008 edition of Journal of Fire Protection Engineering found that a draft curtain has some effect on sprinkler activation, reducing activation time from 8 percent to 15 percent.

Ideally, smoke baffles work in conjunction with vents in the ceiling that pull the smoke out of the building and prevent the spread of fire. Research has shown that the operation of vents is conversely affected if smoke baffles aren’t present. Such systems are intended to maintain a tenable environment until building occupants are able to evacuate in the case of a fire.

Smoke baffles are also known as “draft stops,” “draft curtains” and “curtain boards.” They are generally required by code where moving stairways, staircases or similar floor openings are unenclosed. Pennsylvania fire codes call for “smoke barrier” construction that can withstand a minimum of 1 hour in fire.

Draft curtains are typically used at stair locations and surround the opening to the level above. The purpose is to limit the spread of smoke during a fire and to allow adequate egress, also known as evacuation, as well.

Paul Rabinowitz Glass, commercial glass company,  installs and maintains smoke baffles in the Philadelphia, NJ and Delaware markets.

Skylights: Naturally Lit Interiors Save Energy

Skylights: Naturally Lit Interiors Save Energy

Skylights are one surprising design option for a commercial building that needs to save on energy. Skylights offer many benefits including savings on artificial lighting and heating. One of the largest sources of energy consumption in commercial and industrial applications is artificial lighting.

Skylights impact the building’s energy usage in three ways, two positive and one negative, though the two positive benefits more than make up for the negative one. Skylights save energy by replacing artificial lighting with adequate natural light. This is a positive effect. Another positive effect is the amount of heating energy saved as a result of passive solar gain. (This can be a complex benefit since the design of the building and other construction materials will determine how much passive solar gain there is.) Unfortunately, skylights can lead to some heat loss, though not enough to make skylights a poor decision.

More About Skylights

Current skylights consist of insulating glazing held in aluminum frames in one of many configurations such as single slope, ridge, pyramid and barrel vault. Skylights have been used for more than a century to provide daylight to interior spaces. Early skylights consisted of plate glass — and later, wire glass — in metal frames. They frequently included both an exterior skylight and a second layer on the bottom, a decorative “diffuser” or “laylight.”

Skylights Provide Energy Savings

Some might think that having a surplus of skylights allow more heat to escape than the rest of a roof thereby increasing the running costs of the building. Research from the Institute of Energy & Sustainable Development proves that assumption wrong. Instead, the Institute finds that installing the appropriate number of skylights can reduce overall energy consumption.

Well-designed buildings with abundant natural light experience passive solar gain and need less artificial light. This means that including skylights in building design can offer a dramatic reduction in a building’s total energy consumption as well as reduced CO2 emissions. The benefits of a naturally-lit interior include the reduced energy consumption and reduced emissions, money savings, and a more pleasant environment where people what to spend time.

These are the findings of the study that the National Association of Rooflight Manufacturers (NARM) commissioned from the Institute of Energy & Sustainable Development at Leicester’s De Montfort University.

Daylight has many advantages over artificial light including that it’s an entirely free and unlimited natural resource.

When assessing the overall impact of skylights and glazing on a building’s energy efficiency of a building, there are a lot of factors to consider.

Lux is the measurement of lighting level. A light level of 300 lux is adequate for activities that don’t require the perception of detail; it is suitable for circulation spaces and assembly halls. When a degree of color judgement is required as in many retail, production and office environments, a light level of 600 lux is ideal.

An increase in skylight area, at least within the range of 0 and 20 percent, results in the reduction of total CO2 emissions.

In buildings used primarily during daylight hours during colder months, skylights actually decreases the amount of energy required for heat. For a building that is occupied between 9 a.m. and 5 p.m. for 365 days with a lighting requirement of 600 lux whose roof is 20 percent skylights, there is an impressive 85 percent savings in CO2 emissions from lighting and heat loss over the same building without skylights. When a building with skylights is occupied 24 hours a day, there are no benefits from natural light or passive solar energy.

Yet even at night, skylights can provide a significant energy benefits. When a commercial space requires a lighting level of 600 lux, energy savings are proportionate to the amount of skylight area. The more skylights there are, the better the energy savings. This is especially true for buildings that have a lighting requirement of only 300 lux, which is relatively low. In these low-lit buildings, energy consumption falls even further as the skylight area increases. In buildings that require a lighting level of just 300 lux until it reaches 14 percent.

Get the Most Out of Skylights with Automated Lighting Controls

Because of cloud movement, the amount of sunlight that comes through skylights

Research shows how important appropriate lighting controls are to maximizing the energy savings benefit. Even with skylights, artificial lights are often left on even when not needed. If artificial lights are left on even when sunlight is strong enough that the artificial lighting isn’t needed, the considerable energy savings that skylights offer are lost.

Ensure savings by using simple “on/off” automated lighting controls. These turn on all the artificial lights when sunlight is lost and lighting levels fall below the required lux level. To earn maximum savings, an automated lighting control system that turns on only enough artificial light to maintain the required lux levels is the best choice.

Skylights Provide Numerous Benefits to Commercial Buildings

Skylights have an overall effect of energy savings and reduced CO2 emissions. The bright, natural light let into an interior by skylights help create a pleasant environment, help inhabitants feel better and concentrate better, improve the building’s functionality and reduce energy consumption. All of these make skylights an ideal solution for commercial buildings.

Commercial Door Hardware

Types of Commercial Door Hardware

When a door is needed for commercial offices or a commercial building, several decisions go into one glass door. There are many concerns to take into consideration: amount of traffic through the door, safety concerns and decorative issues like finishes.

All of these considerations lead to choosing among these types hardware: commercial levers, commercial door knobs, commercial door closures, commercial door pulls, commercial push plates, commercial door kick plates, commercial door hinges, commercial door locks and deadbolts and commercial door exits.

Commercial Levers

Commercial lever handles are stronger and more durable than residential locks because they are built to a higher standard than residential hardware. Most commercial locks are made with a heavy duty cylindrical chassis, but there are lighter and heavier duty versions. Light duty versions have a standard tubular chassis, and heavy duty mortise locks. There are several kinds of commercial lever sets: keyed entry levers, privacy levers, passage levers, dummy levers, electronic levers, classroom levers, storeroom levers, dormitory levers, vestibule levers, corridor levers and asylum levers.

There are different levels of durability among commercial locks. Grade 1 locks are the most durable, the heavy duty locks used for such applications as hospitals, public buildings, schools and factories. Grade 2 commercial levers are best for medium duty applications. These Grade 2 levers are best for medical, office, hotel/motel, religious buildings, apartment buildings, retail store and for heavy duty residential use. Keyed function lever sets come with a standard or removable key core.

Commercial Door Knobs

There are several kinds of commercial door knobs such as: keyed entry knobs, privacy knobs, passage knobs, dummy knobs, classroom knobs, storeroom knobs and hotel knobs. Commercial door knobs are constructed to withstand the rigors of use in heavy traffic areas. Commercial locks are graded by ANSI (American National Standards Institute) for strength and durability.

Like with commercial door levers, commercial door knobs come in different gradients to handle varying levels of duty. Grade 2 commercial knobs handle light or medium commercial applications, including professional buildings, hotel/motel, religious buildings, apartment complexes or high traffic residential areas. Grade 1 commercial door knobs handle heavy duty applications. These door knobs are required in places where hard or continuous use is expected, places such as hospitals, schools, public buildings, industrial buildings and factories. Some of the commercial door knobs are available with a standard key cylinder or with removable key core.

Interconnected commercial door knobs are used in apartment buildings or the like where single action egress hardware is required. Door knobs do not meet ADA requirements. If your projects requires ADA compliant hardware, see our commercial lever handles.

Commercial Deadbolts

Usually used with commercial door knobs, commercial deadbolts come in many varieties. The kinds of deadbolts include single cylinder deadbolts, double cylinder deadbolts, one-sided deadbolts, indicator deadbolts, mechanical deadbolts, classroom deadbolts, Bluetooth-enabled deadbolts and deadbolts with key pads.

Commercial Door Closures

Door closures are a great solution to higher traffic doors in commercial applications where spring hinges just won’t do. There are many kinds of door closures such as surface mount door closer, hold open door closures, concealed door closures, delayed door closures and electronic door closures .

Door closures also come with several options such as “hold open,” which is used to keep the door open during high traffic periods, and a “soft close” the door down to avoid a loud slam.

Door Pulls and Door Push Plates

Instead of commercial levers and commercial door knobs, there are commercial door pulls and door push plates.

Commercial Door Kick Plates

Commercial door kick plates come in various sizes and are mounted using screws or magnets. Kick plates are typically ordered 2″ skinnier than the width of the door to avoid interrupting the trim and weather stripping.

Commercial Door Hinges

Commercial grade door hinges are set apart by the use of thicker gauge metal and a sturdier, more secure design. It’s always best, when selecting commercial grade door hinges, to purchase the same brand as the rest of the door hardware chosen to maintain the most consistency in hardware finishes.

Interconnected Door Locks

When the knob or lever is turned to open the door, an internal mechanism in an interconnected door lock deactivates the deadbolt lock. Not only is this type of lock convenient, but it is also required by some retirement homes or some municipalities for certain applications like group.

Commercial Door Panic Devices

Commercial door exit devices, perhaps more commonly referred to as “panic devices,” are the T-shaped bars that lay across a commercial door at approximately elbow height. They have “touch” bars that release the locking mechanism allowing for exit. These are most commonly used on rear doors that are part of a fire exit or emergency exit strategy. There are a few kinds of panic devices such as rim exit devices, rod exit devices and mortise lock exit devices.

All of these types of commercial door hardware come in several types of finishes. The available options include polished brass, antique brass, oil rubbed bronze, satin nickel, antique pewter, satin or polished chrome, aged bronze, satin bronze, white and matte black.

With so many pieces of door hardware to choose from, it can get pretty overwhelming. We’ll help you find the perfect commercial door closures, commercial door locks, commercial door hinges, commercial door knobs, commercial door stops and commercial door push, pull and kick plates. Give us a call (215-425-8600) and let us know what you’re up to. We’re happy to serve you!


The Revolving Door

The first revolving door was invented in 1888 with the goal of preventing wind, snow, rain, dust, or noise from entering buildings. The original patent application was filed by Theophilus Van Kannel of Philadelphia. (He was granted U.S. patent 387,571 for a three-wing “Storm-door structure” on August 7, 1888.)

While Kannel’s design for revolvers featured three wings or chambers that would allow people to pass through, the most often used design is a four-wing revolver. Additionally, revolving doors can feature just two wings or chambers.

Revolving doors provide opportunity for increased traffic while minimizing the ability of people to run into each other. In one hour, a standard four-wing revolving door allows for the movement of up to 4,800 people into and out of a building. Revolving doors are usually seen in large buildings, and it’s these same buildings that account for18.6 percent of America’s total energy costs.

Revolving doors have, over the past two decades, met the security requirements of both Fortune 500 companies and airports.

Revolving doors, or revolvers, have a lot of benefits. Here, we’ll explore some of those benefits, including energy savings, an enhanced user experience, and lobbies that are quieter, cleaner and more beautiful.

Energy Savings

Because revolving doors are both always open and always closed, they provide the least possible amount of air infiltration.Swinging doors exchange eight times more air than revolving doors.

In “Modifying Habits Towards Sustainability: A Study of Revolving Door Usage on the MIT Campus,” MIT researchers considered the effects of revolving doors at several of locations on campus.

Revolving doors are only effective when they are used, and the researchers at MIT found a usage rate of approximately 68 percent. The average daily cost of energy due to air leakage at MIT was $13.10 during the winter, but a 75 percent usage rate of revolving doors drops the cost to $7.66. If the doors saw 100 percent usage, the daily cost of energy would drop to $2.83.

Based on these findings, two revolving doors at one building could save approximately $7,500 per year in natural gas used to heat and cool. That’s a savings of nearly 15 tons of CO2 emissions.

While revolvers have been traditionally considered a cold-climate solution, they’ve become an increasingly popular entryway product in warmer climates, as it’s just as important to keep conditioned air in a building as it is to keep heated air in a building.

More Beautiful, Quiet, Cleaner Lobbies

Revolving doors have other great benefits, including less space usage and better safety. Revolving doors do not require the same kind of space that traditional manual, or “swing,” doors require, and they’re also safer than traditional doors, which can slam closed on users. The chamber style of revolving doors also provide for a cleaner, more quiet lobby since they don’t open directly to wind and street noise.

Increased Safety

Revolvers can be much safer than traditional manual swing doors. Revolving doors that require users to push through max out at approximately 12 revolutions per minute, with canopy- or floor-mounted controls to keep them from spinning out of control. Automatic revolving doors are built with a series of active and passive sensors that keep them safe.

Enhanced User Experience

The ease with which patrons can enter your building when you use revolving doors will make them happy customers. The investment in powered doors demonstrates that your company cares about the patron’s convenience, said Donald Moerbe, president of the American Association of Automatic Door Manufacturers, to These entrances can be especially helpful in positioning your company as a competitor for the business of senior citizens.

The Challenge of Increasing Usage

With as many benefits as revolving doors offer, it’s a no-brainer to install them or retrofit your building with revolvers, but it’s not always such a no-brainer for users to pass through them instead of using a manual or swinging door.

Andrew Shea from Good magazine wrote “How To Hack Big Energy Savings With a Simple Sign and a Revolving Door,” based on his own non-scientific experiments and observations. When there are revolving doors and swinging or manual doors in close proximity, people will follow the flow of traffic unless redirected by someone or something like a sign. Shea observed roughly 28 percent of people using revolvers when most traffic flowed through the swing doors into major buildings in Manhattan. Surely, manual doors are crucial for allowing building access to the disabled and to those bearing large deliveries, but “our country could decrease the $68 billion we spend on heating and cooling every year if the rest of us used revolving doors,” Shea wrote.

Using three different signs, Shea tested the impact of signs on the flow of traffic through revolving doors on Columbia University’s campus. He found that the bigger the sign, and the more closely aligned it is with the building or organization’s branding, the more effective it was. So a two-foot arrow in Columbia’s royal blue that points to the revolving doors and says “Please use revolving doors,” is more effective than a small orange sign with the same script.

Interestingly, the energy savings from using revolvers aren’t linear. You’ll see greater savings when you increase revolving door usage from 50 to 75 percent than you’ll see increasing usage from 25 to 50 percent. And so anything you can do to increase usage of your revolving doors, especially later efforts, will really pay off.

Energy Efficient Windows & Doors

Whether your company is working on plans for a new building or looking to renovate or add onto an existing property, you can find energy-efficient windows, doors and skylights to fit your needs. First, though, you have to understand a few basic principles including how these glass products gain and lose heat, energy performance ratings, and energy performance characteristics such as U-factor, solar heat gain coefficient and air leakage.

Windows, doors and skylights gain and lose heat in three ways:

(1) Direct conduction through the glass, glazing, frame and/or door.

(2) Radiation of heat, typically generated by the sun, into a house, and the loss of heat out of the house through room-temperature objects such as people, furniture and interior walls.

(3) Leaking of air through and around doors, windows and skylights.

That doesn’t mean you can’t reduce the amount of heat loss or increase the amount of heat gain. By choosing and using energy-efficient windows, doors and skylights, you can protect the environment, reduce the costs of heating and cooling your company headquarters, and enjoy a naturally lit work environment.


The energy performance ratings of windows, doors and skylights indicate the product’s potential for heat gain and heat loss. Energy performance ratings also tell you how much potential the window, door or skylight has for allowing sunlight into your home.

How do you know what a window or door’s energy performance rating is? All ENERGY STAR qualified windows, doors and skylights carry labels or stickers from the National Fenestration Rating Council (NFRC). The NFRC runs a voluntary program that tests, certifies and labels windows, doors and skylights based on their energy performance ratings. These NFRC labels enable consumers to reliably determine the product’s energy properties and compare with other windows, doors and skylights.

ENERGY STAR, a government-backed program, provides information on energy efficiency and enables businesses and individuals to protect the environment. ENERGY STAR qualifications are based solely on U-factor and solar heat gain coefficient (more on these later).


You must choose, position and size your windows in a specific way to maximize solar heat gain. In very hot climates, you want big windows facing the south to collect solar heat in the winter, as this is when the sun hangs lowest in the sky. By summer, the sun has risen high overhead. That’s when you’ll want overhangs and other shading devices on those south-facing windows so that you can prevent excessive heat gain, thereby reducing the costs of cooling the house.

On, it’s recommended that you minimize the use of Windows on walls that face north, east and west while still allowing for adequate daylight. This is because it is difficult tocontrol heat and light through east- and west-facing windows when the sun is low in the sky. East- and west-facing windows, doors and skylights should be shaded and/or have a low solar heat gain coefficient. North-facing windows are used solely for light purposes as they collect little solar heat.

In addition to using shading to help control solar heat gain, you can purchase windows with low-emissivity (low-e) glazing.


Using the folloing energy performance characteristics, you can measure and rate the heat loss and heat gain properties of windows, doors and skylights.

– U-factor is usually expressed in units of Btu/hr-ft2-oF. This is the rate at which a window, door, or skylight conducts non-solar heat. A U-factor may refer solely to the glass or glazing, but NFRC U-factor ratings refer to the entire window or door’s performance. This includes frame and spacer material. Windows, doors and skylights with lower U-factors are more energy-efficient.

– The fraction of solar radiation admitted through a window, door or skylight is called solar heat gain coefficient. This solar radiation is either transmitted directly and/or absorbed. It issubsequently released inside the home as heat. The amount of solar heat a window, door or skylight transmits and the greaterits shading ability, the lower the solar heat gain coefficient will be. “A product with a high SHGC rating is more effective at collecting solar heat during the winter,” according to lower the product’s solar heat gain coefficiency rating, the better it will be at reducing the amount of cooling needed in the summer. Your building’s climate, orientation and external shading determine the optimal solar heat gain coefficient for a particular window, door or skylight.

– Air leakage, expressed in units of cubic feet per minute per square foot of frame area (cfm/ft2), is the rate of air movement around a window, door or skylight in the presence of a specific pressure difference. The tighter the product frame, the lower the air leakage will be.


There are two energy performance characteristics that can be used to measure and rate a window, door or skylight’s ability to allow sunlight into a building: visible transmittance and light-to-solar gain.

– Visible transmittance: A fraction of sunlight’s visible spectrum (380 to 720 nanometers) that enters a building through the glazing of a window, door or skylight. The higher the visible transmittance, expressed as a number between 0 and 1, the more visible light flows through a window, door or skylight. The visible transmittance you need for a window, door or skylight is determined by your building’s daylighting requirements. Another consideration is how much reduction of interior glare the space needs.

– Light-to-solar gain is the ratio between the solar heat gain coefficient and visible transmittance, which is a gauge of how efficient different glass or glazing types are at allowing daylight in while blocking heat gains. The higher the light-to-solar gain rating, the more light is allowed in while avoiding excessive amounts of heat. Light-to-solar gain ratings aren’t always provided on products.

Novo Nordisk, Princeton NJ

Paul Rabinowitz Glass completed the new corporate headquarters of Novo Nordisk, a pharmaceutical company located in Princeton, NJ. This fast-paced project was a complete fit-out that included the installation of a new ½” tempered glass entranceway with low profile rails, (200) Dorma Agile 150 interior office sliding glass doors and (10) conference room doors extending over five floors.