Comparing Houses With and Without Roof Ventilation - Attic Condensation, Moisture, & Ice Dam Leaks
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A comparison of two homes, with and without working roof ventilation shows the effects of ice dams, leaks, attic moisture, and risk of attic mold
How to detect roof venting deficiencies, attic insulation defects, and attic condensation problems
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This is "Comparing Two Identical Houses, With and Without Roof Ventilation and Insulation to Understand Attic Moisture Problems", part of our discussion of "Attic Condensation".
This article describes 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.
Comparing Two Identical Houses, With and Without Roof Ventilation and Insulation to Understand Attic Moisture Problems
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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Alan Carson Carson Dunlop Associates, Toronto, Ontario. Mr. Carson is a home inspection professional, educator, researcher, writer, and a principal of Carson Dunlop Associates, a Toronto home inspection and education firm. Mr. Carson is a past president of ASHI, the American Society of Home Inspectors
Some great illustrations of the proper under-roof ventilation pathways are offered by Carson Dunlop
. Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. (727) 595-4211 mark@BestTampaInspector.com 11/06
Daniel Friedman - principal author Daniel Friedman, editing, expanding, adding to comments from John Annunziata, P.E. - NY Metro ASHI informal chapter discussions. A version of this material was published as "Case in Point: The Ice Dam Cometh, Dan Friedman, Journal of Light Construction, NE8/JLC February 1996 p. 8.
Technical reviewers are invited to comment or ask questions - contact us
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Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building design, inspection, and repair, and about indoor environment testing, diagnosis, and cleanup are at the InspectAPedia Bookstore.
"Weather-Resistive Barriers", how to select and install housewrap and other types of weather resistive barriers, U.S. DOE
More Information on Building Diagnostic Inspections and Repairs
More Reading about Dealing with Attic Mold, Identifying, Removing, and Preventing Mold in Attics
Be sure to review HOW TO FIND MOLD: How to Inspect Homes and Other Buildings for Mold - the Basics of How to Find Problem Mold Indoors
in our Mold Action Guide. Here are other articles that will be helpful in evaluating attic mold presence, causes, and cures:
How to Clean Moldy Wood Framing & Sheathing How to clean/seal mold from/on exposed lumber or plywood subfloor or roof sheathing indoors - some suggestions based on our field and laboratory research
Lighting, proper use of: proper aiming of a good flashlight can disclose hard to see but toxic light or white mold colonies on walls.
Stuff that is not mold but is often mistaken for it - things you may not want to test. Also, not all "black mold" is toxic - here are examples of harmless black mold.
Humidity: What indoor humidity should we maintain in order to avoid a mold problem?
Mold-Resistant Building Practices, advice from an expert on how to prevent mold after a building flood and how to prevent mold growth in buildings by selection of building materials and by anti-mold construction details.
InspectAPedia® Home & Site Map - Building & Environmental Inspection, Testing, Diagnosis, Repair, & Problem Prevention Advice: In-depth research & advice on diagnosing, testing, correcting, & preventing building defects & indoor environmental hazards. Unbiased information, no conflicts of interest.
The Mold Information Center: What to Do About Mold in Buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems
Environmental Inspection, Testing, & Diagnosis On-Site IAQ, Gas, Air Testing, Mold Investigation, Sick Building Diagnosis, Lab Services, & Remediation Plan Preparation - indoor air quality testing, problem source determination, supporting lab work, written remediation plan addressing removal of environmental and other hazards and prevention of their recurrence.
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