I haven't found snow a problem with either type of cap on my house in S. NH, although differences in detail between mine and these, as well as in roof slopes, may make one or the other better in your application. For flow, attempt to determine for your duct size what the dimensions of the respective choices are. Then you can calculate the flow area. Correction for bird screening may have to be approximate. Alternatively, and better if you succeed, ask the manufacturer for the pressure drop vs. flow characteristics. kas

Thanks again, Wow, you have an enviable record with the utility bill reduction. I am not sure what your complaint about net-metering in LA is about. Could it be that if I produce more power than I use, I only get wholesale price and then only after I die? I have not looked into how it is done in other parts of the country. Maybe it is done better elsewhere. So far, I have not been pressured to buy more photovoltaic than I need. I am dealing with the big dogs in the region and a smaller NOLA-based company. The latter seems to be flexible while the former has a sales staff that seems to have "packages". The problem is that I have to decide what I need and that will not be easy. I understand that fixing the house first would be a better idea in a perfect world. There are some things that make that difficult. First, I dont know how long the generous Fed and state programs are going to last. Second. My AC is FUBAR. There are two, 2-ton, compressors, one rather old, feeding a split evaporator. One circuit in the evaporator is leaking. I have an estimate from the previous family that says it will cost $2K to replace. I guess it is a custom evaporator. We also have an unusual tax situation that makes it better to spread the costs out over a few years, though we could do a loan. One thing that I forgot to mention is that when the AC ducts were installed, the central hallway ceiling was dropped and, later, the ceiling in a closet and part of a bath were dropped all to accommodate ducts. Unfortunately, the areas appear to have been boxed off open to the attic. That is right, the attic "floor" is actually boxed "down". Part of this is under the furnace and air handler. I am having a difficult time figuring out what is going on because I can not see all of it. Sealing the supply ducts/boots to the attic floor will be a piece of cake compared to that mess. That is why I was relieved to know that sealing the attic was a great idea. Then I had to think about the flat roofs. Speaking of which, if I close off the flat roof from the gable, and leave the flat roof vented for now, I will need to add vents to let continue the air flow that enters through the soffit vents, right? Believe me, I am counting on variable speed equipment to adjust to my changes in the house in the next few years. For us, oversized, but adjustable will be a big boon. We are both gone all day so having a fast-cooling system that can throttle and control humidity will be nice whether ducted or mini-split. I have not looked at daikin. I have seen the Sanyo, Mitsubishi and LG "multi-minis" though. I will check them out. I have been to the HVAC-talk site, but not for a while. I learned a lot about AC and air quality there. I am a tech-minded guy, but I had a lot to learn about AC and humid climates since I moved here from drier places. I think I have read most of the stuff about hot-humid climates at the building science site, but I should check it again. Will you check the www.fsec.org link. I dont get a rational response. As a historical note. This home was probably one of the early adopters of central AC. There was originally a water-cooled condenser and the house still has three-phase power. There are some interesting-looking motor controls left in the attic. It is hard to say when the AC was first installed wrt the flat-roof additions. I suspect the first one was there because it is fed from the duct in the dropped-ceiling hallway. The later flat-roofed room in the back, with a lower ceiling, has AC supply that runs under the house rather than through the attic. Again, thanks from the bottom of my heart. You are very helpful.

Trebruchet, do they install or only sell? There are two companies listed in Iowa who have the material. I will email both of them. Can you make a guess as to cost for a roughly 12x24 roof? I recently got sticker shock for spray foaming my well pit, 3 walls 4x4x5 tall! Apparently, getting here was most of the cost. Most of the time living in the wilderness is fine until I need something I can't buy at Menard's and haul in my Ranger.

Try 'flat roof solutions.' EPDM joints are made with seam tape (uncured EPDM that comes in a roll and sticks by itself). You will need toluene to clean the surface before using the seam tape. Other solvents can damage the EPDM, but toluene is available in quart cans at a paint store. Be careful with the seam tape. It sticks to everything, including the tool you are goping to use to cut a piece off the roll.