spray foam is a good thing, when it is correctly installed. an unvented attic (foam @ roofline) puts ductwork in a semi conditioned space, and really adds to the air tightness of the house. read thru a few posts about upstairs being hot/cold and you will see what difficulty folks have with comfort in rooms that are built in attic space. the problem is the air leakage and heat/cold gain from attic space into these rooms. the walls, the floor and ceiling of these rooms are all surrounded by attic temp air. when you move the thermal boundry to the roofline, and make it air tight then the leaks in the walls ceilings and floors are not pulling extreme attic conditions into the house. things like recessed cans, oversized cuts at bath fans and even duct leakage become less of an issue because the air and thermal boundry is at the roofline. visit www.buildingscience.com and look for unvented attics for your climate. best of luck.

I'm guessing, but is the whole garage one open space? No floor above the walls? Just rafter ties half way to the ridge beam? No reason you can't build a platform for storage. Issues to deal with will be spanning the length(18-20 feet) without any support underneath. You can put support but then you have a pole in the middle of the garage. These are just guesses based on the info available. Ron

I went back to take a look and nope they are actually NOT in the way and yup there is room for shelves up there above the rails of the garage door, not much but enough for us so thanks for the responses- this is a pretty good site

The photos of current shop are a common rafter w/ gabled ends. I know know exactly how the trusses etc will be but I'm fairly certain they'll be less storage friendly than what I currently have. Point taken but it is what it is. I am going from 8 ft to 10 ft walls however affording me the option to build some deep/tall HD shelves down 1 or 2 sides (and if open ceiling - would have easier access to suspending supports for shelves from overhead perhaps. I currently have the silver aluminum clad sheets above and it helps with lighting. The foam would look 'splotchy' to anyone looking up - but I believe it will be a white-ish color (unless it turns yellow w/ light exposure?) yielding a simlar effect for light. I don't really care about heat even though the future split mini may offer it. I do care about cooling (Texas) and for cooling - I don't really see a downside for the open ceiling in that regard. On my current shop, when I go 'upstairs' to get something down - it's a LOT warmer up there due to heat rise. The garage doors will only rarely be open - during summer months, AC will be running pretty much all the time. I don't like the flourescent tube lights on current shop - they were cheap (years ago) but uncovered I always worry about breaking one while not paying attention. Little limited in mount options w/ only joists. But I'm sure something can be figured out for shop lighting to open rafters... I may just have the builder put the cheapest bare bones switched light fixture up there and I'll put something much nicer up at a later point. The open rafters afford a HUGE opportunity to store big things up there like bike frames and 4x8 sheets and long pipes or strips of wood... But now that I think about it - going from 8 to 10 ft makes it a little trickier to put stuff up there all other things being equal... hmmm... And I have to decide on if (and where) to put a pull down ladder or just use a step ladder. Dimensions suggest joists will run front/rear so a ladder could line up and fit between the car bays. But that's the same place I like to put pull down drop lights and power and probably lights. Sigh... it's never easy!