The gaps around the windows and doors of the average house equal a hole in the wall measuring 3 feet by 3 feet.
Problem Restatement
What is the effective air leakage area of the gaps around doors and windows in the average house?
Governing Equations and Input
Leakage Area [in2] = # doors * door area [ft2] * leakage area per door [in2/ ft2] + # windows * window area [ft2] * leakage area per window [in2/ ft2]
Information Sources, Data, and Measurement
The 2001 ASHRAE Fundamentals Handbook provides data from over 1,000 homes that were tested for air leakage. Table 1 from ASHRAE Chapter 261 shows the effective air leakage area attributed to each building component. The calculations for a sample house are shown in the chart below.
Leakage Area (from ASHRAE tables)
Total Leakage Area
Doors
in2/ft2
ft2/door
# doors
in2
Double, weatherstrip
0.12
20
3
7.2
Caulking
Weatherstrip
Windows
in2/ft2
in2/ft2
ft2/window
# windows
in2
Wood framing: caulked, weatherstrip
0.004
0.012
20
12
3.84
11.04
Final Answer
Summing the areas attributed to windows and doors in a typical home indicates that the claim’s estimate of 1,296 square inches, a 3’x 3’ hole, is over-stated. Other combinations of window and door types and different housing configurations can be input into the governing equation. Most realistic inputs will also yield an effective leakage area below that proposed by the claim.
Deeper Issues
Roll your cursor over the different parts of the house to see the percentage of air leakage attributed to each component.
Windows and doors only account for approximately 15% of total air leakage in a house. Even considering all avenues of leakage in a house, the 3’x 3’ hole is an overestimation of the total leakage area.
Despite the conclusions of this analysis, air leakage constitutes a significant energy loss for a house. Sealing a house’s leaks too tightly, however, may lead to water-related problems. A tightly-sealed wall cavity lacking the ability to dry out may be a suitable home for mold growth and may cause subsequent indoor air quality problems. Additionally, air leakage in houses typically meets the natural ventilation requirements for the residents of the house. Sealing a house’s air leakage should be done in order to conserve energy but should be accompanied by measures to ensure proper ventilation and to prevent water problems and mold growth.
This claim was likely more accurate at the time it was initially published circa 1970 because homes built before then were on average more leaky than those built more recently. The push for energy conservation in houses over the past several decades accounts for this condition.
Other Related Questions
What are methods to ensure proper ventilation in homes without sacrificing energy efficiency?
How does air leakage in commercial buildings compare with that of residential buildings?
If you have a solution to any of these problems, please share it through the Feedback section. It might become the next Myth published on this web site. You can also report any technical issues or take a brief survey
to help us make this site a better teaching tool.
