Trouble in the Attic?
Air Leaks Create Attic Moisture Problems

In colder climates, inspectors often find moisture issues in attics. Warm air leaking into the attic causes most of these problems, as well as ice dam issues. By understanding how this happens, you can help your customer and the seller correct these problems, and youʼll be a star with REALTORS®, too.
Moisture Stains in the Attic
As excessive moisture enters the attic from the heated space, the attic ventilation system is overwhelmed; it canʼt remove all the moisture. This moisture condenses on the cold roof deck.
Photo 1 shows significant signs of condensation on the underside of a pitched roof deck. Moisture has caused mold growth and some delamination of the plywood. Cracks indicate the start of delamination.

Air Leaks Bypass the Chimney
Illustration I019C depicts a typical air leak within the homeʼs thermal envelope. As a fire prevention measure, clearance is allowed between a masonry chimney and the wood framing. If this gap isnʼt blocked with non-combustible material, air will flow freely between the basement and the attic.

Air Leaks in Framing
Air also leaks at other gaps in the heated space to the attic. Illustration I032 depicts typical gaps at the top of a partition wall. Framing shrinks; there is no vapor barrier wrapping the framing; and air leaks into the attic. The illustration also shows a fix with foam sealant.

Framing gaps caused the serious moisture problem shown in Photo 2. Would you believe this home was just five years old? I lifted the insulation, exposing the top of the partition wall framing.
On the left is the clear plastic vapor barrier over the drywall. Darkened insulation indicates air leaks: Insulation filters the air and leaves black stains. Note the clean insulation, where framing protected it from air movement.

Serious Moisture in a Small Apartment Building
I investigated moisture dripping from an attic in a small five-year-old, two-story apartment building. Photo 3 shows water stains on the truss framing and the pink blown-in insulation.
I moved the insulation and found a 1- to 2-inch gap in the framing extending to the basement. The framing had been built in sections and butted together with no air sealing between sections.

Air Leaks Create Ice Dams, Too
A house in a cold climate faces another problem due to attic air leaks. In winter, attic heat warms the roof deck, causing rooftop snow to melt. The slushy melted snow flows down the roof and into the gutters. Since gutters and overhangs arenʼt warmed by the escaping heat, they remain cold, and the slush refreezes there. As the process continues, the ice gets thicker, forming a dam.
Eventually, water ponds behind the ice (the same way water pools behind a river dam), and this water can leak through an asphalt shingle roof. Roof shingles are designed to shed water but will not resist ponding water. Leaks will occur just above the ice dams, penetrating the overhangs.
The Takeaway
Many older homes donʼt have attic moisture issues because back then there was little insulation to the attic. When the attic is warm, condensation and stains donʼt occur (although ice dams may still form).
As we do a better job of insulating areas between the attic and heated spaces, attics have become cold. Add a warm-air leak to a cold attic and youʼll have significant moisture and condensation problems.
When you identify these issues, suggest a professional evaluation and repair that includes insulation and air sealing of the heated space.
To learn more, attend Tomʼs technical presentations at educational sessions for ASHI chapters and local groups. Tom can also provide his knowledge for your educational event; contact him at Tom@htoyh.com. Tom will give presentations on Water, Vapor and Dew Point for Home Inspectors and Basement Inspections at ASHI Inspection World 2023.
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In this Issue
Coming Home: A letter from ASHIʼs new president
Mock Inspections
Errors & Omissions Insurance
A Good First Impression
Seeing Is Believing
Survey Says
Postcards from the Field
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