After cutting away some of the plywood ceiling in my garage (what were they thinking???) to trace a loose drainpipe (uncemented, my cutting it at the other end shook it loose) I am in some ways pleased to see the garage ceiling is not that well-insulated, pleased because I can do something about it - the master bedroom above has carpet I want to replace with hardwood but the floor is already pretty cold underfoot.

Where the pipes appear, the ceiling is dropped and the insulation (a single layer) sits right on top of the ceiling so there is a huge air gap up to the underside of the floor. No moisture/air barrier there either, the garage walls have one (originally a carport I think) but since the garage isn't officially heated, I assume that's wrong, not to mention the plywood (1/4") ceiling too....

So I am leaning towards the spray-on foam insulation, since I understand that will provide an air/moisture barrier (BC Canada) and will sit nicely up where it needs to, and, I suppose I can still put the old fibreglass insulation underneath if I want. Only downside I can see is the garage may end up a little colder (last winter, conveniently, it stayed above freezing pretty much the whole time, thanks to heat leakage, the car parked in there, and the radiated warmth from the dryer vent pipe running through) since there won't be the heat leakage, but I will put an electric heater in there to keep it above freezing, since I now have exposed pipes...

My question is, how do I insulate for this area with the pipes? I know the pipes (mostly drains) need to be kept on the warm side of the insulation, at the point where they are, that will mean there will be very little insulation underneath, because they lie right over the framework for the dropped ceiling - can I insulate/wrap the pipes themselves, should I box them in on the sides so I can have decent insulation in the other areas? I was figuring sheet foam insulation, the high efficiency stuff, laid underneath would be good. The other point is, I intend to make some sort of inspection hatch underneath so I have access to the pipes and what's above (there's a cutaway which goes right up behind the upstairs bath, you can see right up to the back of the showerhead) - I don't trust the work they did that much (already have a leak to fix) and it seems convenient to have access- I suppose if the garage will always be heated the point is moot but I don't want to rely on it. Garage door is insulated, double skinned so as far as that goes, it's not too bad.

My canadian building code book is not very clear on the requirements, I know I should go with relining the ceiling with drywall at the least, I was told with the grandfathering laws, 1/2" would be ok but I figured I'd go 5/8"