How to Order Windows

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How to Order Windows

Things to consider before you choose windows for your new home

Posted on May 20 2016 by Martin Holladay
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Anyone who needs to choose windows for a new home has a lot of decisions to make. In this article, I’ll try to provide an overview of some of the factors to keep in mind when ordering windows.

Egress requirements

Most building codes require that every bedroom include at least one window that meets emergency egress requirements — in other words, a window that is large enough to allow a person to escape during a fire. These requirements can be found in 2012 IRC Section R310.1.

If any part of a basement has been turned into habitable space, then that area also needs at least one egress window.

To meet emergency egress requirements, a window:

  • Needs to be operable (not fixed).
  • When opened, needs to have an opening that begins no higher than 44 inches above the flooring.
  • Needs to have an opening that is at least 20 inches wide.
  • Needs to have an opening that is at least 24 inches high.
  • Needs to have an opening that measures at least 5.7 square feet (unless the window is located on the ground floor, in which cast the minimum opening area is 5.0 square feet).

Note that a window that barely meets the minimum width and height requirements is not large enough to meet the minimum area requirement.

Fixed or operable?

Once you’ve specified at least one operable window for each bedroom and, if necessary, for the basement, you can think about how many of the remaining windows in your house should be operable.

For example, let’s say that your living room will have four windows. Should you buy four operable windows? Or should you instead consider buying two fixed windows and two operable windows?

In most cases, it makes sense to resist the temptation to make every window operable. Look around your house and think about which windows really get opened on a regular basis. Most don’t.

Fixed windows have several advantages: they’re less expensive than operable windows and they are almost always less leaky. So whenever it makes sense, choose fixed windows rather than operable windows.

Cross ventilation and light from multiple sides

Any room with more than one exterior wall should probably include windows on different walls. There are at least two reasons for this rule: rooms are more pleasant when natural light enters the room from more than one direction; and operable windows on two different walls provide more effective ventilation than operable windows on just one wall.

Glazing area

Your designer will probably be determining the area of windows facing north, east, south, and west. If you are designing your own house, here are some points to remember:

  • Traditional cold-climate advice called for placing more windows on the south side of a house than any other side, and for minimizing north-facing windows. Recent studies question the validity of some of these passive solar principles, especially the idea that cold-climate homes need very large areas of south-facing glazing. In most homes, it doesn’t make sense for designers to treat windows as if they were space-heating appliances. For more information on this topic, see Reassessing Passive Solar Design Principles.
  • In most climates, large areas of unshaded west-facing windows can lead to overheating.
  • Getting the right amount of window area is tricky. This is one area of design where experience and judgment are extremely valuable. If the glazing area is too low, rooms can be dark and depressing; if the glazing area is too high, the glare can be overwhelming.
  • If you are building on a narrow urban or suburban lot, think about privacy. You probably don't want your house to include large windows that allow your neighbors to observe your daily activities. One way to preserve privacy while still admitting natural light is to include a horizontal band of fixed windows near the ceiling, between about 6 feet and 7 feet above the floor.

Solar heat gain and exterior shading

Solar heat gain through windows is usually desirable during the winter but undesirable during the summer. Designers use several methods to reduce undesirable solar heat gain:

  • Roof overhangs on the south side of a house are usually sized to shade south-facing windows at the summer solstice.
  • West-facing windows should usually be minimized or should be protected by a deep porch. In hot climates, this advice applies to east-facing windows as well.
  • Exterior shading devices like awnings are more effective at reducing solar heat gain through windows than interior shading devices like blinds.
    • Glazing specifications

      The two most important metrics that determine glazing performance are U-factorMeasure of the heat conducted through a given product or material—the number of British thermal units (Btus) of heat that move through a square foot of the material in one hour for every 1 degree Fahrenheit difference in temperature across the material (Btu/ft2°F hr). U-factor is the inverse of R-value. and solar heat gain coefficient(SHGC) The fraction of solar gain admitted through a window, expressed as a number between 0 and 1. (SHGCSolar heat gain coefficient. The fraction of solar gain admitted through a window, expressed as a number between 0 and 1.). For an in-depth look at glazing specifications, see All About Glazing Options.

      When it comes to glazing specifications, here are important points to remember:

      • In all climate zones, a lower U-factor is better than a higher U-factor.
      • If you live in a hot climate and are worried that solar heat gain will lead to overheating, any windows that will receive direct sunlight should be equipped with glazing that has a low SHGC.
      • In cold climates, most designers assume that south-facing glazing should have a relatively high SHGC. However, the advantages of this type of solar gain have probably been overstated. Some designers now specify glazing with a low SHGC for all orientations.
      • Not all low-eLow-emissivity coating. Very thin metallic coating on glass or plastic window glazing that permits most of the sun’s short-wave (light) radiation to enter, while blocking up to 90% of the long-wave (heat) radiation. Low-e coatings boost a window’s R-value and reduce its U-factor. windows have a low SHGC. It’s possible to buy a low-e window with either a low SHGC or a high SHGC. Again, check the NRFC label.
      • All other factors being equal, a triple-glazed window will have a lower U-factor than a double-glazed window. That said, low-e coatings are available that allow a well-designed double-glazed window to have a lower U-factor than a poorly designed triple-glazed window. A well-designed triple glazed window will beat any double-glazed window, however. When in doubt, compare U-factors. (When you do this, make sure that all U-factors are calculated according to the same standard; in the U.S., this means according to the requirements established by the National FenestrationTechnically, any transparent or translucent material plus any sash, frame, mullion, or divider attached to it, including windows, skylights, glass doors, and curtain walls. Rating Council, as reported on the ubiquitous NFRC label.)
      • In cold climates, a well-designed triple-glazed window will save energy, and will be more comfortable for people to sit beside, than a double-glazed window. The colder the climate, the more likely that the upcharge for triple-glazed windows can be justified by anticipated energy savings.
      • Very expensive windows probably won't save enough energy to justify their high cost. For more information on this issue, see Study Shows That Expensive Windows Yield Meager Energy Returns.

      Avoid sliders and double-hungs

      Windows can be ordered as fixed windows, horizontal sliders, double-hungs, casements, awnings, or tilt/turn units. Of these six types of windows, four — fixed, casements, awnings, and tilt/turns — are amenable to weatherstripping and latching systems that result in low levels of air leakage. The other two types — horizontal sliders and double-hungs — almost always leak more air than fixed windows, casements, awnings, or tilt/turns.

      In the U.S., casement windows usually open outward. European tilt/turn windows, on the other hand, almost always open inward. If you’ve never lived in a house with tilt/turn windows, consider how these windows interact with curtains, blinds, and knickknacks on your window stool before you decide to embrace the European lifestyle.

      Martin Holladay’s previous blog: “Domestic Hot Water: No Perfect Solution.”

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  1. Michael Henry

1.
May 21, 2016 10:27 AM ET

don't always avoid double hungs
by Gilbert Fulford

Great article. Just thought I would add that in many towns and cities there are areas where double hung windows are required because of historic zoning. If you install anything other than double hung windows the historic zoning commission will make you remove them and they don't want to hear about air leakage rates or triple pane european style windows. It is important to know your local ordinances/zoning before you order anything.


2.
May 21, 2016 2:41 PM ET

Edited May 21, 2016 2:43 PM ET.

It's past time for convenient exterior movable shading
by Derek Roff

The effect of natural light on human enjoyment of a space is very large. Changes in light through the course of a day, from season to season, and in different weather patterns make a fixed window and overhang design sub-optimum. The design profession has done much too little in addressing the needs for control over natural lighting, especially via movable exterior shading. While interior shades are also useful, only exterior shading can preserve most of the view and emotional connection with the outdoors, while significantly modifying the amount of light entering the room.

When I last visited high-efficiency houses in Europe, several years ago, I saw a variety of moveable exterior shade options, that the home owners said were satisfying and effective. Most were electric, and all could be operated conveniently from inside the house. Only a few were integrated with the thermostat/heating system. The owners said the prices were reasonable, and the reliability high. The USA market seems to have few of the options that I saw, and we tend to be erratic in our approach to what price we will call reasonable.

Given the huge role that windows play in the owners' satisfaction with a building, I think we are long overdue for the incorporation of convenient exterior movable window shading. It's a chicken and egg problem. People contemplating building a home aren't aware to the advantages. Designers see few products available. Manufacturers don't see a market. I hope this will change in the next decade.


3.
May 21, 2016 4:06 PM ET

Emulating double-hungs
by James Morgan

Historic District committees will often accept casements with center bars to emulate the look of double-hungs. This is also useful when meeting egress codes.


4.
May 21, 2016 5:41 PM ET

Edited May 21, 2016 5:42 PM ET.

I know that both Zola and
by Jonathan Lawrence CZ 4A New Jersey

I know that both Zola and Klearwall have windows that have been approved by historic districts in NYC. They are typically a fixed sash on top and a TnT on the bottom.

There are providers of external shading systems in the US, although most of their products are actually sourced from Europe. Not a lot of folks in the US like the look of external shades so that may be part of the reason you don't see a lot of designers making provisions for them. New homes rarely have shades pre-installed and trying to retrofit with external shades can be a nightmare at that point.


5.
May 21, 2016 8:32 PM ET

Codes and Windows
by Malcolm Taylor

Our code isn't as concerned with the size of the window used for egress, as the clear area available to escape through when the window is open. In practice this excludes awning windows and some others where the mechanisms impede egress.

Another consideration when designing, is that the area of glazing on exterior walls is often limited by the distance from the lot line. Under our code walls closer than four feet may be precluded from having any windows at all.

In buildings with more than one occupancy, like an apartment over a garage or shop, there are also limitations on where windows can be located so that a fire in the lower occupancy can not spread or impede exiting from above.


6.
May 22, 2016 4:27 AM ET

Response to Derek Roff (Comment #2)
by Martin Holladay

Derek,
Like you, I've seen electrically operated exterior shading devices in Europe. By far the most common of these are roll-down metal shutters. These effectively shut out light (and solar heat gain), and provide improved security for homeowners worried about burglary. But they aren't very subtle, and I imagine that you are talking about more aesthetically pleasing options.

You noted that when you were visiting high-efficiency houses in Europe, "The owners said the prices [of their electrically operated exterior shading devices] were reasonable." I'd just like to point out that "reasonable" for the owner of a new home in Germany is different from "reasonable" for an American.

I imagine that the cost of an electrically operated shading device is at least as much as, and in some cases more than, the cost of the window.


7.
May 22, 2016 6:32 AM ET

Retractable awnings
by Reid Baldwin

Retractable patio awnings are popular in the U.S. Most people don't buy them for the purpose of shading their windows, but they do accomplish that.


8.
May 22, 2016 2:30 PM ET

Motorized Canvas Awnings
by Pat Kiernan

A Passive House in Maryland has:

"Motorized canvas awnings at all main west windows, capable of 100% shading when required"

I could imagine using something like this over south facing glass to provide adjustable shading here in Colorado.

See: http://www.phius.org/phius-certification-for-buildings-and-products/case...


9.
May 22, 2016 2:39 PM ET

Motorized canvas awnings
by Martin Holladay

Thanks for the link, Pat.

Anyone know what these cost? Or how much an electrician charges per window to install them?

.

Motorized canvas awnings 1.jpg


10.
May 22, 2016 3:10 PM ET

Tempering
by David Gadbois

Do most windows generally come with tempered glass nowadays? Or does that incur additional cost as an option?

Also, I'd anyone offering windows with advanced features like electronic dimming or frosting (for privacy) or anti-intrusion glass?


11.
May 22, 2016 3:41 PM ET

David
by Malcolm Taylor

The companies I buy from will supply any type of glazing I request, but their basic glazing only differs in thickness depending on how large the window is. Tempered glass is expensive and generally reserved for where it is mandated by building codes, such as on stairs, windows extending close to the floor and some locations in bathrooms. Similarly security glass or fire rated glazing can be installed but at a considerable premium. I would imagine that none of these specialized glazings are included as part of any company's basic packages because they are unnecessary.


12.
May 22, 2016 8:05 PM ET

Edited May 22, 2016 8:07 PM ET.

What is the cost of tempered glass?
by Derek Roff

Malcolm says, "Tempered glass is expensive". I've been trying to find out how much more it costs than regular glass. The only site that offered an overview said regular glass costs $12-$64 per sq ft. and tempered glass costs $14-$70 per sq ft. A minor difference. Other sites that would give me online quotes for a sample window in either tempered or regular glass showed a price difference from 10%-20%. My favorite glass supplier will only make double-pane windows in tempered glass, and their price was about 10% above the cheapest standard glass quote that I found, and 20% below the highest standard glass quote that I found.

There are so many variables, but my previous experience and my current online search both indicate that tempered glass is not very expensive, averaging something like 10% more. Does anyone else have specific cost comparisons?


13.
May 22, 2016 10:39 PM ET

Edited May 22, 2016 10:41 PM ET.

Double hungs vs Casements
by Jim Baerg

I've never read anything about what type of windows to use in high wind areas. Some years ago I replaced old wooden double hungs on a few upstairs windows. The new vinyl casements had heavy duty Truth hardware, multi-point locks and triple weatherstripping. All well and good, except that we like the windows cracked while sleeping. There is enough play in the hardware when the wind is howling that the open sash flops back and forth. I'm sure we'll have to replace the hardware at some time. I could have used good quality double hungs (Marvin maybe) and achieved the same amount of air leakage. Also, my daughter left a casement wide open all summer and the sash frame sagged such that we couldn't close and lock the window. Double hungs don't suffer from these issues.
I don't recall ever reading an article on GBA about variations in DH weatherstripping. Which brands and models work the best?


14.
May 22, 2016 10:54 PM ET

Derek
by Malcolm Taylor

I'll call my glass supplier and get an exact amount. It's a holiday here tomorrow so it won't be until Tuesday.


15.
May 23, 2016 4:46 AM ET

Edited May 23, 2016 5:16 AM ET.

Response to Jim Baerg
by Martin Holladay

Jim,
Q. "I don't recall ever reading an article on GBA about variations in double-hung weatherstripping. Which brands and models work the best?"

One of the possible ratings that appear on an NFRC window label is the AL (air leakage) rating. For manufacturers, AL testing is optional -- but it is required for any window seeking an Energy Star designation.

If you are shopping for double-hung windows, you might want to compare AL ratings.

For more information on the topic, see this Q&A thread: "What's the range of window air leakage values for good-quality US windows?"


16.
May 24, 2016 2:26 PM ET

Reply to Derek
by Malcolm Taylor

For a 2 ft x 3 ft double glazed unit with 1/2" spacer, I was quoted $90 for regular glass and $145 for tempered. That is quite a difference, but depending on what portion of the window price is glazing and what part frame and hardware, it may well be closer to the 10% to 20% you cite.


17.
May 24, 2016 3:06 PM ET

Operable panels instead of windows?
by Ethan T ; Climate Zone 5A ; ~6000HDD

I've been trying to figure out why it is necessary for the location of light penetration (windows) to be the same as the location for ventilation and/or egress. Is it out of convenience? Habit? Why not install very well insulated and thermally broken fixed windows and then create fully functional ventilation/egress panels (doors?) which, could be cheaper, and much easier to insulate, while actually providing a safe means of egress? Maybe the combination window/egress is cheaper in the long run? But by asking the window to perform so many functions, we are sacrificing design, and ultimately, function.


18.
May 24, 2016 3:11 PM ET

Doors?
by Ethan T ; Climate Zone 5A ; ~6000HDD

I guess another way to ask my question is... how does the best door compare to the best window when it comes to cost, thermal performance, etc? Perhaps egress doors, where applicable, would be more cost effective than egress windows?


19.
May 24, 2016 3:48 PM ET

Doors for egress
by Reid Baldwin

Ethan, unless you needed a door anyway, then you are proposing an incremental penetration. The fixed window would be a little better than the egress window, but the door would be much worse than uninterrupted wall. Comparing the best door to the best window isn't the right comparison.


20.
May 24, 2016 3:55 PM ET

Response to Ethan T
by Martin Holladay

Ethan,
In addition to Reid Baldwin's point, here are a few more:
1. Most people don't want an exterior door in their bedroom. They'd rather use the wall space for book shelves or a dresser. Moreover, rightly or wrongly, an exterior door in a bedroom makes people feel insecure and more vulnerable to burglars.

2. A second-floor door is dangerous.


21.
May 24, 2016 7:26 PM ET

William Shurcliff
by Malcolm Taylor

Back in the 1970's William Shurcliff, one of the pioneers of both thermal solar and super-insulation, experimented with separating the glazing and ventilation functions by using fixed windows and installing small insulated openings in the walls nearby. I don't know how he dealt with egress. Perhaps it wasn't in the code at that time?


22.
May 24, 2016 7:31 PM ET

Thermal Shutters and Shades By William Shurcliff
by Ethan T ; Climate Zone 5A ; ~6000HDD

Thanks everyone for helping me think through the insulated opening/window question. It has led me to Thermal Shutters and Shades by William Shurcliff, which I'll add to the reading list (http://www.builditsolar.com/Projects/Conservation/ThermalShades/intro.htm).


23.
May 25, 2016 4:56 AM ET

Edited May 25, 2016 11:14 AM ET.

Response to Malcolm and Ethan
by Martin Holladay

Malcolm and Ethan,
I have a soft spot in my heart for William Shurcliff, the author of several pioneering books on superinsulation. That said, his ruminations on movable insulation for windows sound dated.

He's right, of course, that covering windows with movable insulation every night, and removing the insulation every morning, saves energy. The problem is that no-one (except Ven Sonata and his Buddhist community members in British Columbia) wants to take on the twice-daily chores to ensure that the insulation is in the right position.

So his advice makes me smile with nostalgia rather than alter my plans for my next passive solar house.

William Shurcliff wasn't the only voice advocating small doors to admit ventilation air, and other doors to allow the ventilation air to leave the house. The idea was popularized by Rex Roberts in the early 1960s, in his widely read book, Your Engineered House. I read the book and built the house. The ventilation doors were fussy to build and hard to weatherstrip, and they leaked boatloads of air. I never opened them. But the doors, even when closed, ensured that the thermal envelope was leaky, winter as well as summer.


24.
May 25, 2016 10:34 AM ET

Martin
by Malcolm Taylor

His enthusiasm was infectious. I secretly still want to load my attic with hundreds of carboys filled with water. Luckily I have a sensible wife.
Good operable windows simply don't represent enough of an efficiency drop from fixed units to warrant worrying about them.


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