A classic example of something done almost right . . .
Inspecting dryer vents should be as dull as doing laundry but, unfortunately, sometimes isn't. It doesn't take much effort to lift the flaps on the vent termination if it is somewhere near ground level but if it's on the roof or high on a second floor wall, the inspector won't be able to reach it for inspection. Adding to the problem is that the inspector is supposed to check the condition and length of the exhaust piping but not required to comment on the interior of the line. It's worth doing both. I ran into the height problem late last week. If you look just to the right of the dormer, you can make out the termination points for the laundry vent and the dryer exhaust. The exhaust is on the right and is gapped slightly open. Since I knew the dryer wasn't running, I grabbed binoculars and could see the lint piled high at the opening.
By now, most homeowners have seen/read/heard that a clogged dryer line can cause a fire. When the dryer is operating, the designers expected the heat to flow out the exhaust line and dissipate. If the line is partially or fully plugged, this out-flow is restricted, increasing the heat at the dryer. And the lint? It counts as a combustible material.
But there is a second problem with clogging the pipe. What happens to the water? You know, all that moisture in the damp exhaust that makes those billowing clouds of steam in winter?
If you said it gets trapped in the line, you win an award. Feel free to celebrate because that's exactly what happens. I hit the attic in the house above and found wet insulation. First instinct is to start looking up for the source of the water. Not a sign of moisture on any of the sheathing or framing materials.
I reach down and touch it. Yep, definitely wet.
Then I looked to the right, toward the exterior wall. Another wet spot and, finally, the light goes on. The water wasn't coming from above. It was getting forced into the attic space by the dryer below.
The vent piping was plugged and the excess moisture was blowing through every joint in the piping. (They had used duct tape for the joints - another bad idea as it won't hold.)
I checked the OSB sheathing. It was wet but hadn't begun to develop mold or lose integrity. Given another year, this would have transitioned from a moderate problem to a big problem.
The solution for my client was two-fold. First, get the dryer vent line cleaned. Second, make sure it meets the current best practices.
The solutions for dryer line blockage are pretty straight-forward and industry recognized. The pipe material should be rigid or semi-rigid metal ducting (NOT the white vinyl and preferably not the ribbed Mylar), have a length of no more than 25 feet (not counting turns-turns reduce the allowable length because they slow air flow), and vent to the exterior of the home. You shouldn't use screws to connect segments of pipes (lint gets captured on the screws), use an approved heat tape for joints instead of duct tape, and the point of exhaust should not have a screen. Easy. Not done correctly often but easy.
Inspecting dryer vents should be on your annual to-do list.If you have a vertical run that terminates on the roof, think about doing it more often. Clean it often, at least every year. It's better for you home and -added bonus - the improved efficiency will save you money.