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What is “Low E” and how does it work?

“Low E” is short for “low emissivity” and is a thin metallic coating that helps improve the thermal efficiency of windows. There are two main types of Low E coating: hard coat and soft coat.

Hard coat Low E, also known as pyrolytic coating, is sprayed on during the float glass process and is easier to manufacture and handle than soft coat Low E. Hard coat has average performance compared to other products available, but offers high passive solar heat gain (which is desirable in our climate to keep your home warm in winter).

Soft coat Low E, or sputter coating, is produced in a vacuum chamber by applying multiple layers of silver between layers of metal oxide. Soft coat Low E provides the highest performance, with a virtually invisible coating.

Low E primarily targets ways that heat can escape your house in winter, and invade during summer by reflecting radiant heat back toward its source (i.e. the sun in the summer and the warm interior of your home in the winter). This translates to added comfort and energy savings (Cardinal Glass claims that your energy bills can be reduced by 30% by switching to Low E glass).

In a 68° F room, the glass in a single pane window will be 30° F when the outside temperature is 20° F.  The inside pane of glass in an insulated glass unit featuring Cardinal LoĒ³-366 will be 61° in the same situation!

As technology improves, glass manufacturers are producing specific Low E coatings to help you take advantage of local climates. For instance, the south and southwest United States want to minimize solar heat gain, to reduce the amount of energy spent on cooling, while here in the Pacific Northwest, we want to select glass that has a high insulating value (or a low U-Value), while allowing as much passive solar heat gain as possible during the winter. Stop by one of our locations to consult with us to determine the right Low E coating for your project.


What are jamb extensions?

Originally indicating the vertical members of the frame, the term “jamb” has come to mean the frame in which a window or door sits.  Jamb depth varies between window manufacturers — vinyl windows typically are 2 5/8” to 3 3/8” thick while wood windows range from 3 1/2” to 4 9/16”.  In turn, jamb extensions refer to wood or another material that adds width to the jamb so that the window fills the entire opening depth from the exterior to interior sheathings (often plywood or oriented strand board on the outside and drywall on the inside).  In this way, casing or trim material simply needs to be added to the vertical wall surfaces after the windows are installed.  Without jamb extensions, a skilled trim carpenter or drywall installer is required to fill the unrequited space with wood, drywall, or another material before the window can be trimmed, so having jamb extensions applied by the window manufacturer can save labor expenses on the jobsite.


What is a “DP” rating? Is it like a “PG” rating?

A “DP” or “design pressure” rating is a numerical value given to a building component that represents its ability to withstand a given amount of wind load.  DP ratings represent three performance elements — structural load, water resistance, and air infiltration resistance.  A higher DP value indicates a window or door that can withstand more wind, water, and/or structural load than a window with a lower DP.

In practicality, a window or door with a structural DP rating of 50 has passed a structural test pressure of 75 pounds per square foot (equal to a 200 mph wind).  A product with a 50 DP rating for water performance has passed testing under conditions of 8” of rain driven at 50 mph, while a 50 DP rating for air performance has withstood air infiltration at 25 mph.

Misrepresentation or partial disclosure of DP testing within the window and door industries has led to a “watering down” of the DP rating.  An advertised DP rating had to meet two out of three components of the testing.  While some manufacturers advertised the lowest DP rating passed by a product in the interest of full disclosure (thereby demonstrating the high-grade quality of their product), many other manufacturers used the highest value attained in two out the three tests (allowing their product to appear higher in quality).

As a result, to be able to accurately compare one brand’s product to another, the “Performance Grade” or “PG” rating system is being implemented.  PG Ratings will be given to products that meet all elements of the testing (the air infiltration, water, and structural loading components) while DP will merely refer to the structural loading aspect.  Stop into any of our locations to consult regarding which windows or doors meet the ratings needed for your project.


Why is moisture forming on or in my window?

It depends on where the condensation is forming:

Inside your window – When condensation forms between panes of glass in an insulated glass unit, the seals have most likely failed and the glass might need to be replaced. We can help you determine if replacement can be covered under the manufacturer’s warranty, and are happy to stop by and give you a free quote for replacing your window.

On the window exterior  – Exterior condensation results from dew, and since the window glass is usually slightly cooler than other materials around it, dew forms on that surface first.  In fact, exterior moisture can demonstrate that your windows are working properly and retaining heat inside your house.

On the window interior – This often means that your windows are preventing air leakage. For the best explanation on why interior condensation forms and how to minimize it, check out this video by Anderson:

Interior condensation may also indicate that your house has excessive humidity. Window glass is usually cooler than the rest of your room, so when warm air laden with moisture comes in contact with the glass, the moisture condenses on the glass. Signs of excessive humidity can include a damp feeling in the air, mold or mildew on surfaces, a “musty” odor, sweaty pipes, blisters in interior or exterior paint, or warped wooden surfaces.

How to prevent interior condensation – Many daily activities (such as showering, cooking, laundry and breathing) put moisture in the air, but humidity can be controlled. Simple things, like running exhaust fans during showering and cooking, cut down on moisture in the air. You can also reduce interior window condensation by leaving window coverings (like blinds) open to allow air flow, or occasionally leaving doors to closed-off rooms open for a while.


Even accounting for the difference between western and eastern windows manufacturers, many windows have odd sizes. Why is that?

The “rough opening” is the framed opening in your wall for the window to fit in. Rough openings are usually sized 1/2” larger than the height and width of the window’s frame size to allow room to shim the window in case the opening is not perfectly square. However, some manufacturers recommend a rough opening size different from this rule of thumb — consult with any member of our sales staff to verify the proper rough opening for the window you are planning on using.


Why do standard window sizes vary by manufacturer?

On the west coast, architects have a common practice of using “nominal” sizing for windows where the rough opening (the framed wall opening for the window fit into) is a standard size, such as 5’ wide by 4’ tall. Following World War II, there was a major building boom in west coast states and high aluminum supply (used for the production of bombers and fighter planes during the war). These two factors led to the installation of standard size, easily-produced aluminum windows in our area.

However, in the east and Midwest, window manufacturers historically produced windows with a different sizing scheme; their window sizes were based on standard “daylight” or visible glass sizes, not the window’s rough opening. Architects and builders everywhere but the west built their rough opening to accommodate the window manufacturers’ specifications.

As window and door sales become less regionalized, interference between the two sizing systems has developed. In our area, many architects will still design houses with nominally sized windows and doors. This works well with the sizing flexibility of aluminum, vinyl, and fiberglass windows.

However, if you choose to use a wood window from a Midwest manufacturer such as Andersen (Bayport, MN),Marvin (Warroad, MN), Integrity (Grand Forks, ND), or JELD-WEN Premium Wood (Hawkins, WI), the manufacturer’s rough opening may be a different size than the rough opening framed in your house.

Changing over existing production processes to accommodate “standard” sizing is a difficult endeavor for manufacturers of wood windows, however many of the top companies are introducing new nominally sized windows that allow you to choose custom sizes. These can be costlier, and if you decide to use wood windows and doors, we can provide you with a list of rough opening sizes so that your contractor can accurately frame your window and/or door openings.


Can I have my windows replaced to take advantage of new energy-efficient technologies while maintaining my home’s historic appearance?

Absolutely!  Many of the windows we sell keep the appearance of historic windows and have features such as:

  • insulated glass units (some filled with inert noble gasses, such as argon),
  • Low E coatings,
  • tight-fitting components, and
  • improved weather-stripping to seal out the weather.

Simulated divided lites (SDLs) use applications to the exterior and interior of insulated glass units to give the appearance of divided sash windows.  Cottage style sashes (where the top sash of a double hung window is smaller than the bottom sash) match the look of many Victorian era homes, and exquisite arched top windows compliment the  Victorian homes dotting our towns and countryside.  Stop by one of our showrooms, or request an appointment for a member of our sales staff to come to your home and discuss possibilities!


What does it mean to have a “clad” wood window?

A wood window’s “cladding” is the material applied to the exterior of the window frame to improve its ability to resist corrosion and rot, and to provide a low maintenance exterior. Aluminum, vinyl, and fiberglass are all used as cladding, and each offers pros and cons that we are happy to discuss with you.

As an alternative to cladding, JELD-WEN offers pine wood windows and doors treated with their unique AuraLast process. AuraLast penetrates the interior of the wood and provides superior resistance to decay, water saturation, and termites. It also acts as a wood conditioner, so stain applies much more evenly.


How often do you recommend that I clean my windows?

Cleaning the glass of windows and doors is occasionally necessary for clarity and exceptional performance. When cleaning, avoid using abrasive materials that might scratch the glass. See your manufacturer’s website for specific details on cleaning methods.


How do I care for my new windows?

We recommend that you follow the care and maintenance recommendations of your window manufacturer: