Chapter 5 Quiz: Windows and Doors

Multiple Choice

1. The U-factor of a window measures:

a) The resistance of the glass to heat flow b) The rate of heat transfer through the whole window assembly per square foot per degree of temperature difference c) The fraction of solar radiation that passes through the glass d) The amount of visible light transmitted through the glass

2. A homeowner notices foggy, cloudy glass between the panes of one double-pane window. The most appropriate and cost-effective repair is:

a) Replace the entire window including frame, sash, and glass b) Drill a hole in the glass, inject desiccant, and seal the hole c) Replace only the insulated glass unit (IGU) while keeping the existing frame and sash d) Install an interior storm window over the existing fogged window

3. In a cold climate (Climate Zone 5), which SHGC specification would be most appropriate for a large south-facing window?

a) SHGC 0.20 — minimize solar heat gain b) SHGC 0.40 — allow solar heat gain to reduce heating load c) SHGC must always be below 0.25 regardless of orientation d) SHGC does not matter for north-south oriented windows

4. A homeowner feels a draft near a double-hung window on a cold day. After investigation, the draft appears to come from behind the interior trim, not through the window sash. This most likely indicates:

a) The IGU seal has failed and gas is leaking b) The window glass has become porous with age c) Air is bypassing through the rough opening gap between the window frame and the wall framing d) The window's low-e coating has degraded and must be replaced

5. Which window frame material provides the best thermal performance (lowest thermal bridging) and is also highly resistant to moisture and dimensional change?

a) Aluminum with thermal break b) Standard vinyl (PVC) c) Fiberglass d) Clear-finished solid wood

6. The "simple payback" calculation for a $16,000 full window replacement project that saves $200/year in energy is:

a) 8 years — within the typical warranty period b) 32 years — longer than the expected service life of the windows c) 80 years — far longer than the expected service life d) Cannot be calculated without knowing the R-value of the original windows

7. Why can standard double-pane windows sometimes perform worse for noise reduction than single-pane windows at certain sound frequencies?

a) Double-pane windows allow more air infiltration, which carries sound b) The two panes can vibrate resonantly at certain frequencies, amplifying transmission c) The argon gas fill transmits sound better than air d) The low-e coating reflects sound back into the room, creating echo

8. Proper window installation flashing must be lapped in which order to correctly manage water?

a) Head (top) first, then sides, then bottom pan b) Bottom pan first, then sides lapping over the pan, then head flashing lapping over the sides c) Side flashing first, bottom pan second, head flashing third d) The lapping order does not matter as long as all four sides are flashed

9. A homeowner in a humid climate is considering installing a "high SHGC" window on the east side of their home to admit morning light. What caution should they consider?

a) High-SHGC windows are not available in double-pane configurations b) East-facing windows receive low-angle morning sun that can create significant solar heat gain and glare, particularly in summer c) High-SHGC windows condensate more in humid climates d) SHGC only affects south-facing windows and has no effect on east-facing orientations

10. For a pre-1940 wood single-pane window in good structural condition, which of the following represents the best cost-benefit approach for improved energy performance?

a) Full window replacement with a modern fiberglass triple-pane unit b) Restoration of the existing sash (reglaze, repaint, new weatherstripping) plus addition of an interior storm window c) Replacement of the glass panes with double-pane IGU units fitted to the existing sash d) Application of window insulation film to the interior glass surface

Short Answer

11. A window salesperson claims that replacing your 1988 aluminum double-pane windows with new triple-pane vinyl windows will "reduce your heating bills by 35%." What questions would you ask and what calculation would you do to evaluate this claim? What finding from building science is the salesperson most likely ignoring?

12. Explain why proper head flashing at a window installation is critical, and describe what happens when head flashing is installed incorrectly (tucked behind the housewrap rather than lapped over it). How long might it take before the error becomes visible as water damage?

13. A homeowner near a busy highway complains that their recently replaced windows "do nothing for the noise." The new windows are standard double-pane low-e vinyl, U-0.28. What are the likely explanations for why noise is still getting through, and what would you recommend they investigate or do differently?

Answer Key

Multiple Choice: 1-b, 2-c, 3-b, 4-c, 5-c, 6-c, 7-b, 8-b, 9-b, 10-b

Short Answer Guidance:

11. Key questions to ask: What is the current U-factor of the existing windows vs. the replacement? What fraction of my total heat loss do windows actually represent? Is the "35% savings" based on replacing single-pane or double-pane originals? What is the total project cost, and what is the simple payback in years?

The key calculation: Estimate current window heat loss (U × area × degree-days × fuel cost conversion) vs. new window heat loss at the lower U-factor, and find the annual savings. Divide project cost by annual savings for payback years.

Building science finding being ignored: In a home with existing double-pane windows, windows typically represent 10–20% of total heat loss. Air infiltration and ceiling/wall conduction are usually larger. A 35% reduction in heat loss through the windows translates to only 3.5–7% reduction in total heating cost — not 35%. The 35% figure likely refers to the percentage reduction in heat loss through the glass alone, not total heating costs.

12. Head flashing correctly laps outward over the drainage plane (housewrap or building paper) below the window, ensuring that water running down the wall from above is directed outward — over the window, not behind it. If the head flashing is tucked behind the housewrap, water running down the wall is directed behind the flashing and into the rough opening behind the window frame. This water wets the rough opening framing, the window sill framing, and the window frame itself. Because this all occurs behind finished surfaces, it may not be detected for 2–5 years until the wetting has accumulated enough to rot the rough opening framing and stain the interior drywall or sill. By that point, the repair requires full window removal, framing replacement, and reinstallation.

13. Likely explanations: (1) Standard double-pane windows are not optimized for acoustic performance — their STC is typically 26–28, barely better than single-pane. The window may be performing exactly as specified while still transmitting significant noise. (2) The windows may be air-tight at the glass but have poor weatherstripping or unsealed rough openings — sound travels through air paths, not just through the glass. (3) Other noise paths exist besides the windows — walls, the soffit/eave area, adjacent doors, HVAC penetrations.

Recommendations: First, investigate and seal any air leakage around the window frames and at rough opening penetrations. Second, evaluate whether noise is also entering through adjacent walls, as this would persist regardless of window quality. Third, if glass performance is truly the issue after air sealing is complete, consider interior storm windows or purpose-built acoustic laminated glass products rather than a second replacement.