Frost in the Attic

Monday, January 15th, 2018 by Dan McDonald

A recent service call in Doylestown prompted me to re-visit a very common issue that plagues many homes: poor ventilation.

This has been a cold winter so far, and these temperatures help illustrate issues that may not be so obvious in warmer months.

Upon entering my client's attic, I discovered wide areas of moisture on the underside of the roof deck, as well as areas of actual frost from the cold temperature. The customer had uncovered this issue by accident; entering his storage for the holidays. He immediately assumed it was a roof leak. Pretty common-sense reasoning. Why else would the whole underside of his roof be wet?!

As I walked around and inspected his attic, I immediately determined the source of the built-up moisture: poor ventilation. Although a ridge vent was installed by the last roofer, it was a poor quality, low-performing design. That's very common when roofers are looking to cut expenses when bidding a lost-cost job. Additionally, the two bathroom exhaust fans were directed out the eave soffit, rather than through the roof deck above. Again, a practice common to the uninitiated.

Bathroom exhaust fans and dryer vents should always be routed to exhaust outside of the home, and not through the soffit! The purpose of a vented soffit (the eave roof overhang) is to function as an INTAKE for your roof ventilation. So it would only make sense that any bathroom exhaust routed to the soffit will only be directed right back in the attic. And what is typically exhausted through a bathroom fan? MOISTURE!

In this example, the path of moisture returning into the soffit area was clearly visible. And in conjunction with an under-performing attic exhaust (cheap ridge vent), that leads to our current moisture issue (frost) in the attic.

I suggested replacement of the current ridge vent with a free-flowing rigid vinyl vent for the peak. That would do wonders helping to evacuate any moisture that found its way into the attic in the future. I also recommended the installation of two individual bathroom roof vents for the respective bathroom exhaust fans. That would eliminate a good deal of the moisture that was being directed into that space.

Last follow-up with our customer? Happy to report no more frost or moisture issues!

So what originally was thought to be a roof leak was actually a poorly-configured ventilation system for my clients home. Taking the time to evaluate our clients home, along with our experience and industry knowledge, got the job done right the first time!

Frost in the Attic - Image 1


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