Philadelphia Window Company
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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 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.
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.
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.
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
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
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
1. Control the intensity of daylight 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
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. 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
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
SOUND TRANSMISSION
VENTILATION
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.
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.
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
Be compatible with aluminum, wood, or vinyl Hold up mechanically under use Resist air and water leakage Weatherstripping (continued) 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
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
Attic mold under your roof is a serious problem that should be addressed by a |
