How to install a blower on a flat roof
I posted this on the home repair forum - thought I should try here as well...
I am thinking about installing a large blower unit for a cooking range ventilator on the flat roof above my kitchen. The roof looks like a torch-down modified bitumen with metallic paint over it. The blower unit is 30" by 26" and 12" high. I was thinking I could build a 2x4 frame (screwed and cemented onto the roof sheathing) encased in a plywood box and mount the blower on top of that. I am not sure how to go about weather-proofing the whole thing, and I don't have any experience with roofing, so I am looking for advice on what materials/techniques to use to seal it all up. I am really looking for a way to do it with minimal impact on the existing roof - all the holes for screws and the ducting would be inside the plywood box - but I will need to seal the box where the blower sits on top, and also where the box meets the roof. The box itself will need to be waterproof - is there some kind of paint I could use for that?
I live in Washington State, and it rains pretty heavily for 8 months of the year, so it is important that I prevent all leaks.
Thanks in advance for any advice you can give me