Window Know-How
A Guide to Going Green
By Magazine Editors | From Preservation | March/April 2009
To live green at home, and reduce your monthly energy bills, it's important to evaluate windows. If you live in an older residence, don't assume that replacement windows are the only option. Historic wooden windows are remarkably efficient as long as they're well maintained. (And there's nothing greener than preserving what you already have.) Conversely, manufacturing and installing replacement windows consumes enormous amounts of energy. Keep these tips in mind as you consider your options:
Older is Better: Old windows were fabricated from old wood. It's generally denser and lasts longer than the new wood used for modern windows.
Caveat Emptor: Some salespeople promote replacements as cure-alls, but even the highest-quality replacement units can fail. In addition, experts note that new vinyl or PVC replacement windows can release toxic byproducts into the atmosphere.
Watch Your Pennies: Tearing out existing windows to install replacements is expensive and wasteful.Although you may achieve some energy savings, it will take decades (or centuries) to recoup your investment. Plus, you'll have to dispose of the old windows, adding to the nation's waste management woes.
Maintenance is Key: A well-sealed, tight-fitting window saves energy.
Check for Condensation: It can rot window sills and rails.
Use Storm Windows: They increase energy efficiency. Monitor them for clues about your house. Cold air leaking in through a storm window can create condensation on your window panes. Warm air escaping from your house can cause a storm to fog up.
Insulate: More heat is typically lost through the roof and walls than through windows. Adding just 31⁄2 inches of insulation to your attic can save more energy than new windows.
Install Window Treatments: Something as simple as a conventional window shade mounted inside the frame and touching the sill, with no more than a 1⁄4-inch gap at the sides, can reduce heat loss by as much as 27 percent. A shade with a reflective coating will provide even more protection.
Remember to. . .
1. Keep all exterior surfaces painted A coat of paint protects wood. Pay particular attention to horizontal surfaces, such as window sills, where water collects.
2. Replace glazing compound (the putty that holds panes in place) when it dries out. Missing or cracked compound results in air infiltration. Always paint glazing after it has cured.
3. Maintain window locks Functioning locks hold rails tightly in place. A tight fit reduces air exchange.
4. Keep movable surfaces free of paint buildup so that sashes slide freely.
5. Replace any cracked or broken panes promptly.
6. Add or renew weather stripping where it makes sense. When correctly installed, weather stripping can increase a window's efficiency by as much as 50 percent.
7. Watch for water Whenever you use storm windows, remember to clear the weep holes at the base to allow condensation to drain away.
8. Check seals around exterior storms and caulk well.
9. Test for air leaks On a windy day, hold a lighted birthday candle or incense stick near the window frame to detect drafts.
10. Think about safety Evaluate emergency exit routes before sealing windows with caulk or adding storms.
Sum of Its Parts
A. Jamb Vertical or horizontal member that frames the window opening
B. Rail Horizontal part of sash
C. Pane or Light Glass held in place by glazing putty and metal glazing points
D. Top Sash Upper section of window, may slide down to open
E. Stile Vertical part of sash
F. Meeting Rail One of the two horizontal members of a double-hung sash which come together
G. Muntin Strip that separates the panes of a window. The shape, or profile, of a muntin provides a clue to the window's age.
H. Bottom Sash Lower section of window, typically slides up to open
I. Casing The finished, often decorative, framework around a window
J. Stool Interior shelf-like board at the bottom of a window against which the bottom rail of the sash rests
(Illustration by mckibillo)
Sources: Forum Journal, 20, no. 2 (2006), National Trust for Historic Preservation; Historic Home Works, historichomeworks.com, calculations by Keith Heberem; Cornell Extension Service
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Comments
Submitted by crtpwd at: May 13, 2009
I am also interested in what people think about steel casement windows c.1935.? I am trying to convince someone not to tear them out, and that the winter coldness in the bedroom is not due to the windows, but no insulation. Is there a storm window for push-out casments?
Submitted by kazbern at: April 22, 2009
How would the editors assess old steel casements, c. 1956? Most of them close well enough, but the mechanisms are worn and they are not safe in a fire (cannot be opened quickly). Very few contractors will refurbish steel casements (like 1 in the whole USA?).
Submitted by BENMURPHYONLINE at: April 17, 2009
We have old single pane glass windows + storms on our old 1860 house - and the energy efficiency is phenomenal! You really don't have to replace your old windows - just maintain properly... -B
Submitted by Collingswood NJ Historic Preservation Commission at: March 30, 2009
Do the math - don’t rely on exaggerated sales pitches Investigate what improvements will save real energy and be a good return on your investment? A homeowner's easiest energy saving investment may be a programmable thermostat. Used properly, the thermostat can pay for itself in less than a month! Next, check your roof insulation and caulking. Beef-up your home’s insulation! It is important to insulate your roof; remember heat rises. This will cost far less and yield more energy savings than replacing windows. Check your home heating system. Older homes often have very inefficient furnaces and boilers. Want to save 30% to 40% on your heating bill? It is not what those advertising campaigns lead you to believe. Although not as visible and as highly marketed as replacement windows, a high efficiency boiler or furnace can save you thirty of forty percent on your heating bill. This is a far higher savings than you could ever expect from replacement windows at a fraction of their cost. Often utility companies will give you grants to help with this improvement. Check the statistics. Only 10% of you energy loss is from windows, while a much larger share is heat excaping through your uninsulated or underinsulated roof. Advertising from replacement window companies are filled with claims that replacing your windows is the best way to save energy; however if you do the math, window replacement may be the last improvement you should consider. If you already have storm windows, those replacement windows will often actually use more energy. Engineer calculations for the combination of a storm window and a wood window is better than normal insulated glass. So add a storm window and tighten up original wood windows. The newer high performance glass energy savings are so small that an engineering energy-use and expenditure calculation indicates new windows are an extremely bad investment savings compared with the combined wood and storm windows. It takes 240 years for payback on low-e replacement windows and about 40 years to recoup the cost of standard replacement windows . Those payback years do not take into account the considerable amount of energy to make, deliver and install new windows and transport the old windows to the landfill. Includiing added embodied or life cycle costs, it is questionable if there ever will be any energy savings given that the lifespan of most replacement windows is less than 20 years. Considering the life-cycle, a replacement window will consume more of our precious energy resources than maintaining your original wood windows made with dense "old grouth" wood. People often claim that their old windows are “drafty”. Drafts often come from cracks in the woodwork around the window assembly. Drafts around the actual window sashes can be stopped by making sure the seals on the storm windows are tight. Stopping outside air infiltration is important, but the number one reason for window drafts will occur even with a perfectly sealed window. As cold air is heavier than warm air, the relative cold surface of a window will cause the room air to drop in front of the window and set up air currents within a room. This is why you feel drafts even on windless winter days. Even the best insulated windows will do little to stop this. The long time solution was the placement of heating vents and radiators below windows to counteract this effect. Cracks will not be addressed by a replacement window either. Gaps should be caulked regardless if a window is replaced or not. Keeping and maintaining what you have leaves the smallest carbon footprint. A beautiful properly maintained antique wood window (when combined with a storm window) may be far “greener” and therefore more environmentally responsible than that expensive clunky plastic replacement.
Submitted by John Leeke at: March 10, 2009
Thanks for listing Historic HomeWorks as a source. >>Install Window Treatments: Something as simple as a conventional window shade mounted inside the frame and touching the sill, with no more than a 1⁄4-inch gap at the sides, can reduce heat loss by as much as 27 percent. A shade with a reflective coating will provide even more protection.<< I know this is true from my own experience and it’s fascinating to have the facts on roller shade performance. What is your source for this info? John
Submitted by Old houses at: March 9, 2009
You are going to put fiberglass or vinyl windows in your historic house.....Wow There is nothing green with plastic windows Please stay away from period houses with that product
Submitted by dknuckey at: March 5, 2009
I disagree with the premise that a well maintained old window is just fine. While well maintained old windows may be somewhat efficient compared to run-of-the-mill replacement windows, the bottom line ins that most windows offer little insulation compared to walls. A single paned window has an R-Value of only 1.2, a double paned of 2.8 - compared to a typical wall with an R-Value of 13. The one window I have found that leaves all the others in the dust are Serious Windows which go as high as an R-Value of 11. (No, I don't work for them, but next time I'm changign out windows, I'll certainly be a customer).