HRV Exhaust duct through an existing “mushroom” roof vent – GreenBuildingAdvisor

For our “Money Pit Cottage” project to rebuild a 1946 one-story cottage, we’re adding a Broan 150 cfm HRV.

We had no reasonable alternative to installing the unit in the attic. We’ll build an insulated “box” around 5 sides and connected to the thermal envelope that otherwise is across the living space ceilings.

We have all the ducting figured out as far as code and insulation, except for the exhaust vent to the outside. The “simple” location would be under the soffit on one of the walls, but that’s within 3 feet of an operable awning window.

Our local (Eugene, OR) plan reviewer says that while he agrees the “stale air” from the interior being exhausted is no worse than the air inside that operable window, there are no exceptions to the code requirement that the exhaust vent be at least 3 feet from the window.

One alterative is just to run some ducting on the outside from the opening in the wall to get 3 feet away. But the plan reviewer suggested reusing the opening in the roof through which the now decommissioned bathroom fan exhausted. (We’re using the HRV for that purpose).

So, this wouldn’t add a new roof perforation. It would require a fairly short run of duct to be insulated, which is doable. (The other option would have the duct in one of the bays between rafter ties and very well insulated by multiple layers of the attic’s rockwool batt insulation.)

Just wanted to check whether there are any significant reasons to avoid the “through-the-roof” alternative in this scenario.