WINDOWS AND DOORS

Windows, Phantom Leaks, and the Big Box Stores: This is a horrible story of being ripped off by a major player in the industry.

thanks to CERTAINTEED for the following information:

All windows should be evaluated in terms of their:

•Solar transmittance of visible light (VLT), ultraviolet light (UV), and infrared (IR) radiation

•Ability to control heat loss and gain

•Ability to eliminate air infiltration

•Condensation control

•Ventilation

•Sound transmittance

•Safety

•Durability

SOLAR TRANSMISSION
Sunlight comes to earth in the form of solar radiation. There are three components of solar radiation. Ultraviolet light and infrared radiation are invisible; visible light transmission is what we can see.

Ultraviolet light, which is also known as "shortwave" radiation, makes up about 3 percent of the sun's rays. Although a small amount of UV light is necessary to sustain plant life, ultraviolet light is undesirable because it causes skin to sunburn and carpets, fabrics, and exterior materials to fade.

Infrared radiation is invisible and reaches us as heat. It is the "warmth" of the sun. From the designer's perspective, controlling this component is key to keeping buildings cooler.

Visible light transmission is why we put windows in buildings in the first place!

Measuring Solar Transmission - As you design and specify windows, you'll need to keep in mind that as sunlight reaches a glazing medium, it will interact with that medium in three ways: it is reflected, absorbed, and transmitted (sunlight [100%] = r + a + t). You will naturally be concerned with the percentage of each component.

Absorbed light turns to heat, and the ability of the glass to absorb light will result in the heat flowing either inside or outside the window. This component is not normally a major concern for designers, particularly in residential buildings.

Reflectivity is a concern because it can fundamentally affect the exterior appearance of the structure and significantly reduce the amount of sunlight entering the building. For example, the glass coatings that protect high rise office buildings are highly reflective. Most residential applications demand traditional low reflectance (<16%) applications.

UV block measures the amount of radiated ultraviolet light that is blocked from being transmitted through a pane of glass. Ultraviolet light causes sunburn and fading, so you will want to choose glazing that reduces it.

CONDUCTION

Conduction is the transfer of heat through a solid or liquid (molecule to molecule). For example, conductance occurs when a frying pan is heated on a stove. Window manufacturers have traditionally measured U-Value, or the rate of heat flow through a window (normally from indoor to outdoors). A single piece of 1/8" (3.0 mm) glass has a rating of slightly over 1. For comparison, when other constructions, such as an insulating glass unit, are measured, they typically yield ratings lower than 1.

The lower the U-Value, the better the insulator. The ability of the glazing and the framing material to block or resist this heat flow-its insulating ability-is called
R-Value. U-Value is the reciprocal (1/R) of R-Value and, of course, vice versa.

When evaluating glazing and window U- and R-Value performance, note the test conditions. The NFRC has specified those conditions to be 0°F outdoor temperature and 70°F indoors, with a 15 mph wind speed and no solar load.

CONVECTION

The transfer of heat by convection or through air molecules is the second component of heat transfer. Again, as heat flows to cold, tightly sealed windows and insulating glasses that maintain warmer glass surfaces reduce the effect of cold air blowing through a window crack or cooling the surface of the glazing (wherein conduction would take effect).

RADIATION

The third component of heat transfer is sometimes the least understood. Radiation is the transfer of heat from a warm body to a cooler one without the need of a medium. This is the case in the warmth transferred by sunlight or when standing in front of a fireplace.

Clear glass is transparent to most of the solar radiation that strikes it. This relatively short wave radiation passes through the glass and strikes the walls, floors, ceilings, and furnishings in a room. The solar energy is absorbed and re-radiated as long waves.

The radiation from inside the room is absorbed by the glass and re-radiated. The net effect is to trap heat into the room. In colder climates, heat gain from solar radiation is advantageous. However, when it's 0° outside and 70° inside, single pane glass is not efficient at retarding the heat flow that occurs through convection and conductance. Basic insulating glass units (two pieces of glass separated by desiccated air space) help, but it reduces the U-Value to approximately .5, or an R-Value of 2. In warm climates, heat gain from radiation (the reverse effect of heat flow: hot outside, cool inside) puts extra load on air conditioning systems.

VISIBLE LIGHT TRANSMITTANCE

Visible Light Transmittance (VLT) is a key consideration in windows. By carefully considering VLT, designers can:

1. Control the intensity of daylight
2. Protect specific areas from direct sunlight
3. Avoid glare
4. Ensure that light is distributed uniformly

The shading coefficient measures how much a glazing material transmits heat gain compared to 1/8" glass at a 90° normal ascendant angle. Spectrally selective glazing can affect the shading coefficient because it selectively reflects or absorbs ultraviolet (UV) and infrared (IR) light, while permitting the visible light to pass. Because spectrally selective glazing does not pass the IR and UV portion in the spectrum of light, it can provide a relatively low shading coefficient.

The solar heat gain coefficient is the amount of direct solar radiation that enters through a pane of glass into the home as heat. Its adoption as a measure of glazing systems is relatively new. Similar to shading coefficient, solar heat gain coefficient (SHGC) is preferred because it can be used for solar incidence angles other than 90º. Also, it can be expressed for the glazing SHGC or the total window (SHGCwindow).

Window size, spacing, and location can be used to control VLT. Different types of glass-clear, tinted, and reflective-are available and also provide excellent means of controlling VLT.

NATURAL VIEW

Another consideration, often overlooked, is the view of the environment through the glass and the view of the glass from the outside of the structure. Tinted or highly reflective glass can significantly alter or color an occupant's view by distorting the natural color of objects or making them appear darker. This is because they are not "selective" transmitters of light, and they cut out large portions of natural visible light.

While requirements vary from project to project (some commercial properties require lower visible light), maintaining visible light transmittance is especially important in private residences. And if one follows the lead of the automobile designers, visible light transmittance of 70 percent or above will retain a normal view.

Traditional insulating glass helps control the conduction and convection components of heat transfer, but sophisticated metal coatings, which are known as low-E coatings, combined with inert gas fills (mainly argon) can improve the performance of glazing systems in five ways:

1. Their lower emissivity increases insulating value.
2. Metal blocks UV and IR transmittance.
3. They reduce the potential for condensation.
4. They improve the comfort of the space by keeping homes warmer in winter and cooler in summer.
5. They reduce energy costs.

This is particularly true of spectrally selective glazings (called low-E2), which let in light but significantly reduce unwanted UV light and heat without altering either the natural view of creating unwanted reflections (see Selecting Efficient Windows for Homes in Mixed Climates).

EMISSIVITY

A rating measurement of the amount of long wave radiation or room temperature radiant heat that is absorbed and radiated by a surface. Emissivity varies from 0 (no emitted infrared) to 1 (100% emitted infrared).

LOW-E (low-emissivity)

Glass that is coated with microscopically thin metallic layer(s) that allow visible light to pass through, while blocking ultraviolet and infrared solar energy and reflecting away long-wave room-side heat energy. Different types of Low-E coatings offer varying levels of performance for each of these tasks.

AIR INFILTRATION

Air infiltration can be a major cause of energy loss in the summer as well as in the winter. Cold weather problems are obvious, but in cooled rooms, air leakage puts an extra load on the air conditioner to remove the increased heat and humidity from the air.

Reputable window manufacturers measure the flow of air through a window by subjecting the window to a vacuum and measuring the cubic feet of air that enters the vacuum in a prescribed amount of time. This measurement, in cubic feet per minute (CFM), indicates how much air has leaked. Tight tolerances, good seals, and careful installation can control air infiltration.

CONDENSATION

When the outside air is colder than inside air and the inside relative humidity is higher than the outside, condensation can form on interior surfaces. In colder parts of the country, it can be a serious problem. In a good window design, the U-factor of the framing elements will be equal to or less than the U-factor of the insulating glass.6 If the window is structurally tight, this combination will minimize condensation.

SOUND TRANSMISSION

Noise can be disturbing, distracting, and debilitating. For this reason, you must factor the window's sound transmittance class (STC) into your design considerations. An STC rating indicates the window system's ability to insulate against broadband noise (125-4000 Hertz). Fortunately for the design professional, all the factors that give a window good resistance to water and air leakage also give it good resistance to sound transmission.

VENTILATION

Most people prefer some natural ventilation, so design professionals must include windows that can be opened. Different window styles allow for different amounts of ventilation. Consequently, you must balance ventilation requirements with energy costs and aesthetics as you specify windows.8
Safety
Safety requirements are often spelled out in local codes, and the windows you specify should always meet the requirements of local design codes.

DURABILITY AND MAINTENENCE

Window performance extends beyond manufacturer's test data. To ensure long term satisfactory performance, the materials of construction must have good structural properties, excellent resistance to corrosion, and the ability to withstand deterioration under the climatic and environmental conditions of the area. It should be possible to replace glass and hardware with ease. Material finishes must be attractive, and sealants and gaskets must have high performance even when exposed to the elements.

Aluminum: When new, aluminum has a silvery, bright, and clean-looking finish. Installers often prefer it because it is lighter than wood or vinyl. Aluminum can pit and stain, particularly in certain atmospheric conditions (e.g., salt air), but it can be painted. Aluminum is a natural conductor of heat and cold.

Wood: Wood used in window frames must be kiln-dried to a moisture content no greater than 12 percent at the time of fabrication, and it must be treated for water repellence. Improperly treated wood will deteriorate rapidly. Naturally occurring defects and discoloration in wood can be covered with paint but, in time, paint will fade, flake, and/or peel. Wood is a natural insulator.

Vinyl: Vinyl (PVC) can be used as a cladding for wood, but most often it is extruded and used to fabricate window sashes, frames, and other structural members. Pigment colors the vinyl resin, not just the surface of the extrusion, so vinyl windows do not flake, chip, or rot. Vinyl extrusions are hollow; thus, the frame and sash are efficient insulators. High performance vinyl framing members are sometimes reinforced with aluminum, steel, or fiber glass.

The welds that keep window frames and sashes together are also very important. When welds break down, windows get out of square; sashes do not fit or move easily; air infiltration increases significantly. AAMA and WDMA recommend:

Mechanical joining, brazing, or welding (never soldering) for aluminum. If brazing or gas welding is used, all flux must be removed completely because it can corrode the aluminum. Mechanical joints, even when sealed, can loosen with use.

Finger jointing or edge bonding for wood. The adhesive used in the manufacture of finger-jointed and/or edge bonded parts must comply with the wet set adhesive requirements of ASTM D 5572 and ASTM D 3110. Finger joints and bonded edges may deteriorate as wood expands, contracts, and ages.

Mechanical joining or fusion welding for PVC. Fusion-welding, the high temperature fusion of vinyl corners, creates a weld that is stronger than the profile. Vinyl welds do not deteriorate when exposed to weather and use.

WEATHERSTRIPPING

Weatherstripping seals the opening between the sash and/or the sash and frame. It must be made of high quality materials that meet all performance requirements. Weatherstripping should also:

Be compatible with aluminum, wood, or vinyl

Hold up mechanically under use

Resist air and water leakage

Weatherstripping (continued)
AAMA 701-92 and 702-92 test pile weatherstripping for:

Accelerated weathering (a total of 250 hours)

Compression set: Dry pile must recover at least 86 percent of its original overall height

Shrinkage: Shrinkage must not exceed 1 percent

Construction: Only materials suitable for long-term exposure should be used

Silicone-treated, high density pile double weather-stripping with a Mylar fin affords the best long-term performance.

Replaceable weatherseals (applied by slots, pockets, or other retaining profiles) are only as good as their application and are not, therefore, rated by AAMA for installed performance.

GLAZING

Glazing is the heart of the window. Because it determines performance, careful control of glazing allows you to balance the requirements of the building with its cost. By choosing the proper glazing system you can control heat loss and gain, daylight and shading, UV and IR transmittance, and condensation. Depending upon performance requirements and budget, you can specify any of the following glazing options:

Double-pane glass: Double-pane glass has more insulating ability (lower U-Value) than single pane, but used alone it does not control condensation, infrared and ultraviolet solar energy, or shading.

Low E

(soft coat) is a multi-layer coating using a magnetic sputter vacuum deposition (MSVD) technique. These coatings selectively filter out unwanted heat and ultraviolet light while letting in the visible light. These coatings must be encapsulated in insulating glass units and exhibit a more pristine appearance.

Pyrolyctic

(hard coat Low E) coating is "fired" on as the glass is made and becomes part of the glass. The result is a transparent, hard oxide with improved emissivity but little spectral selectivity. Offer a range of mirror-like appearances.

HARDWARE

From the user's perspective, the most important hardware items are the mechanisms to open, close, and lock the window. The sash must not drift, it should glide easily in the frame, and it should require a minimum amount of manual force to move. The three commonly used mechanisms are:

Gear-type rotary operator

Sash balance

Locks and keepers

Sash balances
These are used in hung (single, double, triple) windows and can be sash balances with jamb-liners or constant force systems. Sash balances must be of corrosion resistant material compatible with the window framing material and, except for stainless steel, coated with a film of corrosion resistant material. There are four basic types of sash balances.

Spiral Balance
A spiral balance is a combination of a tube, coil spring, and a spiral rod. Once tensioned for the weight of the sash, the spiral balance provides positive counter balance by extending and retracting the rod as the sash is moved. This type of balance was used first in aluminum windows and now in vinyl.

Spring Balance
A spring balance consists of an inner torsion spring surrounded by an outer spring. Both are enclosed in a tube. These counter balancing springs function in tandem: The outer extension spring builds up a lifting force as it is extended while the inner torsional spring simultaneously loses tension. These are typically used in heavy commercial windows.

Block and Tackle
A block and tackle balance is a variation of the weighted versions found in old millwork windows; modern versions consist of a spring attached to a block. A nylon cord or metal cable (used in heavier applications) passes around a pulley and over a roller at the top of the frame. It is then attached to the sash.

Tape Spring Balance
The constant force balance spring, sometimes called the tape spring, is the latest technology in sash balances. Fashioned after the same principle as the release in a car seat belt, this coiled stainless steel spring fits into a balance pocket in the head of the jamb and is fastened to the sash. Tape springs are slightly more expensive than those described earlier, but they are more reliable.

Locks and keepers
One of the performance criteria for a window is its resistance to forced entry. To achieve this, locks and keepers must be sturdy and corrosion resistant. They, and their fasteners, must be made of high-quality material (usually aluminum) that will withstand long-term use. In vinyl windows, color matching the painted aluminum surface of the lock and keeper to the vinyl produces the best appearance.