Here's a bit more info to give you a better idea. Zone 5B, Cold winters, hot summers (rarely humid but like this year...humid and hot summer!) My walls will be 2x6 with either dense fiberglass or mineral wool insulation (products readily available locally). My current debate among my thoughts is trying to decide about the WRB (MY HOUSEWRAP) and at what tier/level/plane to install it (Or even two). Windows are not permanent, and in a forever home (God willing), windows will need to be replaced in the same lifetime I live. Therefor, I don't want to choose some method that would hinder future upgrades/replacement. (Such as installing foam over a flange so it must be cut out, or installing a type of flashing that requires more of the foam wall or window box to be torn out to replace the next time around. I am debating between a quality house wrap to prevent moisture and also act as an *air* barrier not a *vapor* barrier. Basically, on a cool winter day with 50 MPH Wind, I don't want that wind (air) easily permeating through the house because I will a.) not be sealing the joints of foam b.) possibly not even taping the foam joints c.)not going to use any internal poly as a air or vapor barrier. I am not sealing the foam joints because foam shrinks and expands and those joints will not stay tight forever. If I have the luxury, I will install (2) layers of 1" thick versus (1) layer of 2" thick to provide staggered joints and prevent air from moving inwards that much more. There is a wealth of information on greenbuildingadvisor, but it seems to boil down to personal preference on two things. One being that I can opt for innie (windows set towards the OSB wall sheathing layer) or outie (windows that are at the most exterior plane as possible). And we all know that flashing a window opening is important for multiple reasons, and that the standard way includes integrating your house wrap (WRB) into the rough opening with multiple methods. I would like to use a flexible peel & stick flashing that will seal to/against the house wrap. My concerns for those who have rigid foam on the exterior are a.)where did you locate a house wrap (Or WRB)? and b.)in what fashion did you set your windows? It varies by foam thickness, but generally 1.5"+ of foam requires framing out a window frame/buck for window support whereas under 1.5" doesn't seem to need the additional support. And of course the other option is the fasten the window like standard construction, on the sheathing level right against the sheathing (osb in my situation) and into the studs. This would then mean I would either use the WRB at the same time to detail the window opening, or perhaps not. But also means I would have to design a custom flashing to cover the exposed foam around the window, since the window is set inside from the foam and siding. I am surprised house wrap (a WRB) seems to not be the norm. It is here...and it is something I do not want to overlook. My understanding is that in new construction with rigid on the outside, builders extend the window opening (like you said Mushcreek) to the same thickness as the foam, therefore that foam will not have an exposed edge. I read on GBA that instead people build plywood boxes for the windows the thickness of the foam + 3/4" and then use a 1x3 or 1x4 flat around the window opening fastened thru the foam into the window opening studs. Then the window flange is fastened to this flat 1x3 or 1x4 frame, and it also brings the window out the extra 3/4" so that 3/4" firing strips can be used to install siding. I do not think house wrap *over* the extended window frame would be as effective as if I just installed the windows flush with the foam level, allowing my flexible sticky flashing tape to easily fold over the opening and adhere to the foam. ---starting to think I should just not be so concerned about this detail. Turning my hair grey.

I'm not getting into the vented vs sealed crawlspace pro & cons. but to answer OP's question, 3.5 to 4' is sufficient working room for spray foam install. closed cell has a stronger smell than open cell IMO. but the smell fades after a couple of days with either. if you are anyone in the family are sensitive then install should be done when ample time is allowed for any smells to dissipate. I'd start by investigating the recommended install (joists covered or exposed). I'd think that 4" would be ample at R-28, but I don't know your requirements in your area. just remember that you have to meet the code minimums. R-value of foam into inches of foam. not "performs like R-xx" or "average fill" same depth or MORE...not less everywhere. No Q or K values, R-values only. it is the installer that is the key figure in the install, not the salesman. make sure you are on page with the installer & be willing to go into the crawlspace & measure low spots before they leave for the day. it is worth your time. and yes dehumidifier in vented crawl is trying to dehumidify a portion of the great outdoors. best of luck.

3650 PSF is equal to 25 PSI..... Their dricore products are just massively overpriced, at least in the US they are. I think it is better to put down a foundation wrap (DMX), then 1" XPS foam (25-30 PSI). Assuming that the floor is flat, you could probably get away with putting flooring (with a membrane) directly on top of it. If your floor isn't flat, you probably will need a dedicated subfloor. I'd also be sure to use some kind of flooring that is somewhat rigid and install it perpendicular to the foam boards, so that if the foam boards do try to lift or sink, the flooring will add some rigidity to prevent it from mattering.

Thanks for the help. I definitely planned on sealing to prevent convection air movement and maintain internal AC pressure. I knew R value wasnt as important as up-north but I thought R13 was the goal. I'm no expert though. As for radiant heat I am not sure I have many options at the moment but overhangs and awnings. On a hot day I can feel the heat coming through the cement blocks holding my hand an inch from the surface of the cement. I don't feel I can use a radiant barrier in the wall though as that would require about a 2" gap and being an existing house I'd have to extend walls/jams/etc. Yes, foam would be better on exterior and interior but the exterior is intact and I don't want to get into that yet. I may in the future. For now, I need to solve the interior wall mold and wetness problem. Some people here use the foil faced rigid insulation and put the shiny part against the cement. I guess as a radiant barrier, but without an air gap what good does that do? It just becomes a heat conductor. It also acts as a vapour barrier too so will just cause condensation yet again that would have trouble drying. It seems to go against what I am learning but when I asked someone about this they didnt seem to know why they do it.