Need some help with vent hood ducting and my google skills aren't cutting it.

We've done a kitchen reno and I need to install a vent hood and duct it out through the roof. There wa previously no vent hood. It's a wall mounted vent hood, the ducting will be hidden behind a false cabinet panel. I have everything sorted out as far as mounting the hood to the wall. What I'm fuzzy on is the how to route the duct through the ceiling. It will be a straight shot all the way to the roof.

I see a lot of stuff online where they use flex-pipe to connect the hood to some sort of mounting bracket in the ceiling. Do I have to do that? Can I not just run rigid duct all the way out, and if so does it have to be secured to the ceiling drywall somehow? Can the weight of the duct just rest on the hood and whatever strapping I use to secure the duct in the attic?

For now I'm thinking I'll pay someone to do the hole in the roof. I'm just wanting to get the first section of pipe through the ceiling so I can be done with the kitchen.

I had hell finding somone willing to do a project like this. They didn't want to assume liability for cutting a hole in the roof. I do have a flat roof so it's slightly more complicated. All my research showed ducting was irrelevant. Do whichever you prefer. Smooth pipe will cause less friction and should net you a higher flow rate.

Probably a dumb question, but I'm dumb - Is it an exterior wall? If so it's probably easier to vent it out the side of the house.

It's an interior wall. Besides that, 90 degree bends are performance killers. I have the room to go full 8" pipe straight out the top so I'm gonna use it.

Flex duct is against code for a vent hood, it traps grease and such and is a fire hazard over time.

As long as you don't have a ceiling joist of blocking in the way, you should be able to cut your hole for the duct, I assume a round duct, 6-8", depending on your hood adapter. You can wrap the pipe a couple wraps in the attic and screw it down with metal strapping tape (galvanized strapping with holes down the center). This will allow the pipe to be secured, carry the weight of the pipe and keep it from moving around in the attic. I'd do the same up top to secure it to a rafter.

I don't know if your cabinet guy was nice enough to leave you an access panel to access the top of the hood and the plug/ electrical. If he did, then it should be a simple job. Install the hood, then drop the duct down and tape it to the hood with foil tape, if you want the best seal, then do the additional connections in the attic. I assume you'll need more than one joint of pipe. If not, I'd consider using two pieces, just to make the connections a little simpler, vs one long joint.

As for cutting the hole in the roof, its simple, but you'll need some understanding of the flashing and tucking it under the shingles properly. It's probably worth having a roofer do it, if you can get one out for $85-100 bucks. It's basically a minimum charge for them.

I would not rest the weight of the metal duct on the vent hood. I did that once, and it worked, but the junction caused a metal-on-metal vibration noise when you turned the fan on. It would be best to frame out from the nearby ceiling joists and support the weight of it with that.

If I were you, I would probably just get the first section of pipe on there and then hire someone to cut the hole in the roof and flash out the vent. You could then pipe in the rest of the duct after they leave. That way, it's on them if there is a roof leak.

I would use rigid metal duct, not the flexible hose.