Check with your local planning department. With 10" ducting, you definitely need a roof jack that doesn't constrict air flow. The standard Vent-A-Hood recommended roof jack is fairly low profile. It seems unlikely that it wouldn't comply with your local wind resistance standards. Are you sure it's not just your roofer's resistance to using something different from what he usually installs? It's a pretty sure bet that yours isn't the only house in Miami-Dade County with a 900 cfm Vent-A-Hood.

It looks like I received a question above that I didn't notice. Sorry. A point that may provide some clarity is that actual MUA flow rate is always balanced with output air flow rate. Seal up a house and turn on your hood, and the air that flows out will be whatever leaks into the house at the negative pressure that the hood fan can manage. It might only be 100 cfm at 0.1 inches of water. Deliberate MUA makes up for this sealing with a big hole to the outside. Depending on what is in the path of this hole (such as filtering) the output air will increase until it is balanced with the MUA at some new combination of pressure and flow. The goal is to have enough MUA to allow the hood fan to reach its flow capability at 0.03 or less house pressure. Note that the pressure loss in the hood and ducting is still in play for the hood, so if rated for 400 cfm it may still only move 300 cfm, even with perfect MUA (no MUA pressure loss). A blower door test is probably the best way of finding out what air flow a given house is capable of leaking as a function of pressure. This can be used to specify the amount of MUA needed. Or, with some MUA system installed, what the overall house + MUA system is capable of doing. A blower test can be dispensed with if you build a pressurized MUA system capable of moving the total cfm required for all exhaust fans while overcoming calculated pressure losses in the MUA ducting/filtering. Ultimately though, the final test is determining what house pressure results with MUA when the hood is on high. One hopes that the AHJ would accept a pressure test that shows that the pressure drop is low enough that combustion appliances won't backdraft. kas

No suggestion other than keep your bend from vertical to horizontal gentle. That is, two 45* bends are better than 1 90* bend.

Wow, I'm very grateful to all of you who took the time to reply! Great to see your pictures, too. Some responses (if you're interested), now that I've finally been able to go through: Sammy and The Kitchen Place are correct that we could put it in the upper above the dishwasher — that's the only upper that is the right size that wouldn't block other cabinets. (Thanks for the pictures, The Kitchen Place!) I was intrigued by nidnay's idea of bumping into the bedroom closet, but that closet is filled with custom cabinetry so it would be a huge project to put the microwave there.If Icould put a Miele microwave (/speed oven) in an upper cabinet, I'd try for that, but of course our uppers are only 13" deep and the Miele opens down, so not workable. My better half is against mounting a "normal" microwave in an upper cabinet (he thinks in that case we might as well go OTR, and that it will pull away from the pretty stove/hood that's the whole reason for this conundrum). (ci_lantro questions the whole premise of opening the kitchen. Others in our building have done it and it makes a significant difference in the feeling of the whole unit—we're confident it's the right move, long term.) Helen, HU-41121833, Buehl, Interior Concept, RTHawk and others: Thanks for saying good things about the Sharp microwave drawer. nidnay, thanks for your criticisms of it, too! The slimline microwaves are attractive too! Unfortunately induction sounds great, but not in the cards for us. I do believe everybody who says we need something more powerful than a microwave fan — the Vent-A-Hood system does look quite good. kaseki, thanks for your hood comments. pittsburrito, I hear what you're saying about external ventilation. There is a small vent in the kitchen and windows in the living room, so we try to be careful. Thank you all! Still not sure what we'll do, but I'm grateful for all the advice on the Houzz forums.