I had a plan for the 2nd floor duct installation, and I had my six and eight inch round ducts. But they are not your everyday ducts. They are special for a couple of reasons.
First off, they are called GreenSeam or GreenSeam Plus and they have built-in neoprene gaskets in the longitudinal seams. Once you snap and lock the pipe together along the longitudinal seam, the gasket should render it airtight.
The GreenSeam Plus, which is easily identified by the green band around the pipe end, has a gasket that is supposed to seal the travers joint, in addition to the longitudinal gasket. Furthermore, the GreenSeam ducts come in 26 gauge, compared to the thinner 30 gauge ducts you typically find in the big box home improvement stores.
In summary, I have sturdy 26 gauge ducts with gaskets for air sealing at the traverse and longitudinal joints. And the last time I checked, they were only incrementally more expensive than the big box products.
The ventilation system duct work should be airtight for a number of reasons. You want to control where the fresh air is delivered and where stale air is removed from the building. Leaky duct work would deliver or remove air where it is not needed, or where it could even be damaging.
The GreenSeam duct products with their gaskets make it a whole lot easier to air seal your ventilation system. To nip any remaining leaks in the bud, I sealed all seams on the outside with duct mastic. This is particularly important on elbows and tees, which have moving parts and joints without gaskets. And, of course, I sealed around all sheet metal screws I used to hold the duct work together.
The duct mastic also helped with air sealing the transition from a rigid to a flexible duct. The flexible duct was pushed over the rigid duct after it received a good coating of mastic on the duct end. Everything was then tightened up with a big zip tie.
Now that we had the technical aspects and quality control issues addressed, it was time to throw some ducts around!
The installation started at the ERV end for the supply and return lines. From here I could run the ducts to the various supply and return points (see also 2nd floor ventilation layout in preceding post).
We ran all the ducts in the attic above the 2nd floor ceiling joists. We had to lower a couple of ceilings toward the back end of the building (the bathroom and second bedroom) to have sufficient space for the ducts. The attic toward the front was tall enough to fit everything in.
A big thank you to our friends Vincent and Rubani for assisting me with the installation!