The vent cap, front and center, in the picture, is the vent cap for a bathroom exhaust fan. This picture captures perhaps 70% of the total number of such caps on this condo building roof. Since I don’t inspect from a helicopter I could not get a picture of all of them. I also was only really interested in the 6 involved with my unit of this condo building. When I climbed over the edge of this roof and into this forest of vent caps, I marveled at how cool and how wrong they looked.
I occasionally see this type of cap used as a vent cap, but to find an entire building’s vents terminated this way–in relatively new construction–threw me for a loop.
For a long time now–since at least 1991 in Washington State–it has been required that all exhaust fans terminate at the exterior of the building at a cap with a back-draft damper.
Here is what the code that was in place at the time these vents were installed said: “Outdoor air intakes and exhausts shall have automatic or gravity dampers that close when the ventilation system is not operating.” (Underlining is mine)
NONE of these caps have back-draft dampers. None of these caps have screens to keep out insects and birds. I count 33, “for-sure-and-a-couple-of-maybe,” vent pipes in the picture–how many can you see?
Every one of these vent caps is actually a little chimney. Cold air can drop into the pipes leading to condensation inside the pipes. They also have no screens to keep out vermin–so insects and birds might think they are nice places to call home.
Because they are little chimneys, they also “act” like chimneys. In other words as wind blows by the caps it will put the chimney under negative pressure. This can pull open the dampers that are built into the fan units–drawing warm air out of the building in the winter and conditioned air out in the summer.
How does this get by the jurisdictional inspectors? This was no cracker box structure either. It was a very high end Condo building that paid the big bucks for a PVC roof system and many other similar expensive upgrades throughout the building–inside and out.
By Charles Buell, Real Estate Inspections in Seattle
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