Comparing Houses With and Without Roof Ventilation - Attic Condensation, Moisture, & Ice Dam Leaks
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This roof ventilation and ice dam leak prevention article compares Two Identical Houses, With and Without Roof Ventilation and Insulation to Understand Attic Moisture Problems. Both homes, located in "the Bleachery" in Wappingers Falls, NY were built in the late 1800's overlooking Wappingers Lake.
This article is part of our roof ventilation & attic condensation article series.
These articles describe inspection methods and clues to detect roof venting deficiencies, insulation defects, and attic condensation problems
in buildings. It describes proper roof ventilation placement, amounts, and other details. The photograph at page top shows the author's introduction to roof ice dams at 25 King Drive in Poughkeepsie, NY in 1970.
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Comparing Two Identical Houses, With and Without Roof Ventilation and Insulation to Understand Attic Moisture Problems
One of these pre-1900 homes (at below left) was renovated by the author (DJF) to include effective soffit intake and ridge exhaust under-roof venting along wtih insulation and air leak sealing throughout the structure. The second home (below right) had a drafty attic that had avoided attic condensation and moisture troubles but the design sucked so much heat out of the home in winter that combined with little attic insulation the house suffered from extensive ice dam formation.
 
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On two identical 1860's Wappingers Falls NY "Bleachery" historic houses shown in these photos, the one with no melted snow was renovated to include continuous soffit and ridge venting and good attic insulation. Look at the difference in the two roofs on the same winter day.
These homes, located on West Street in the village of Wappingers Falls, New York, were built to house workers at nearby mills powered by water from Wappingers Creek. When the homes were built they lacked central heating, storm windows, siding, caulking, and insulation. They were drafty. Interior moisture and condensation were less likely to damage the structure than today, nearly 130 years later, when the energy improvements listed have been added to the homes, making them tighter but also providing indoor moisture sources such as from bathing or cooking.
The house whose roof shows melted snow and bare roof slates (beware of nasty owner) has inadequate venting and inadequate insulation, giving rise to snow melt and ice damming, and almost certainly to attic condensation and moisture.
The house whose roof is covered with a uniform blanket of un-melted snow, (renovated by the author) was improved to add attic insulation in the attic floor as well as continuous soffit intake venting and ridge outlet venting.
After these vents were added we also closed-off the gable end vents (not shown) to assure that airflow moved over the desired pathway.
The builders of this house had blocked the soffits with boards on edge between each rafter pair in an effort to "warm up" the cold attic. We removed these blocking boards to assure a proper airflow. |
Global warming and building ice dam leaks? Venting of roof cavities helps reduce the effects of hot weather associated with global warming
In a 1996 version of this article in the Journal of Light Construction we paraphrased Stephen Jay Gould, a Harvard scholar who said "The world is currently enjoying a brief warm spell in the midst of a basically cool period.
Gould said that the glaciers that covered our region might return in another 10,000 years or so. We added that the sheets of ice we see creeping down buildings in freezing climates are not due to global freezing but due to poor building ventilation and insulation.
That conservative view of climate change has since proven to be mistaken, as very rapid global warming is, in 2008, a fact accepted by virtually every qualified scientist. But global warming does not mean that we can blithely ignore attic ventilation. Not only will the risk of ice dam leaks continue to occur on poorly-insulated and poorly-ventilated building roofs, but more, the benefits of proper under-roof ventilation are present in hot weather as well.
A properly ventilated building roof cavity or attic means that the roof surface as well as the attic will be cooler in hot weather, reducing indoor cooling costs and extending the life of the roof covering.
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
- Building Research Council, BRC, nee Small Homes Council, SHC, School of Architecture, University of Illinois at Urbana-Champaign, brc.arch.uiuc.edu. "The Small Homes Council (our original name) was organized in 1944 during the war at the request of the President of the University of Illinois to consider the role of the university in meeting the demand for housing in the United States. Soldiers would be coming home after the war and would be needing good low-cost housing. ... In 1993, the Council became part of the School of Architecture, and since then has been known as the School of Architecture-Building Research Council. ... The Council's researchers answered many critical questions that would affect the quality of the nation's housing stock.
- How could homes be designed and built more efficiently?
- What kinds of construction and production techniques worked well and which did not?
- How did people use different kinds of spaces in their homes?
- What roles did community planning, zoning, and interior design play in how neighborhoods worked
- "Energy Savers: Whole-House Supply Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Supply_Vent.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11880?print
- "Energy Savers: Whole-House Exhaust Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Exhaust.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11870
- "Energy Savers: Ventilation [copy on file as /interiors/Energy_Savers_Ventilation.pdf ] - ", U.S. Department of Energy
- "Energy Savers: Natural Ventilation [copy on file as /interiors/Energy_Savers_Natural_Ventilation.pdf ] - ", U.S. Department of Energy
- "Energy Savers: Energy Recovery Ventilation Systems [copy on file as /interiors/Energy_Savers_Energy_Recovery_Venting.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11900
- "Energy Savers: Detecting Air Leaks [copy on file as /interiors/Energy_Savers_Detect_Air_Leaks.pdf ] - ", U.S. Department of Energy
- "Energy Savers: Air Sealing [copy on file as /interiors/Energy_Savers_Air_Sealing_1.pdf ] - ", U.S. Department of Energy
- Humidity: What indoor humidity should we maintain in order to avoid a mold problem?
- "Weather-Resistive Barriers [copy on file as /interiors/Weather_Resistant_Barriers_DOE.pdf ] - ", how to select and install housewrap and other types of weather resistive barriers, U.S. DOE
- ...
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
 The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
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