so even though the walls & ceilings are not sheetrocked the attic is decked? interesting. normally, when insulating attic floor with foam the foam is sprayed against back side of the sheetrock ceilings. since your attic floor is decked, spraying against the decking from inside the hosue would be how you'd do it. so to do that..first the perimeter of the ceiling would be sealed. you want to seal the top plates, wire, pipe penetrations. then fill the ceiling joist bay with foam. to get the full depth of the joist you'd over fill the joist bay, then trim off excess prior to installing sheetrock ceiling. this would be option three. and the one I'd chose recommend. everyone...house is North Carolina. ducts in crawlspace, so equipment is either in closet inside living space, or in crawlspace. if the roof is high, and not used for ducts then it is more cost effective to seal & insulate attic floor. OP, check into what foam is used in your area. we use open cell in hot humid climates. are you sure the ceiling joists are 2x10? if so, that gives you 9.5" for insulation with open cell..that would be about R-36 depending upon R-value per inch of product. shop foam insulators wisely. you want a full joist bay fill, not an 'average' fill. what they mean by 'average' is that if you add up low spots & high spots of foam it 'averages' out to xxx. you want full depth everywhere. excess is cut off so that sheetrock install is smooth. ask to see jobs of the foam companies in progress. ask to talk to former customers. once completed..blower door test the install to make sure it has stopped air movement between attic space above into living space below. I gotta ask....why floor the attic so early in process? and where are heating system & water heaters? tell us locations, what size & what fuel type please. how will attic above foamed floor of attic be vented? do you have recessed lights? what provision has been made for recessed lights & insulation plan? are recessed lights Insulation Contact Air Tight ICAT?? knowing the answers to these questions may change answers to previous questions. best of luck

I also have a plywood floor over most of my attic & want to add more insulation. I was told I would need to remove the plywood floor, add 2X6's to give me ~10-12" of depth for batt insulation to achieve a R-38, & replace the plywood (I need the storage). However, since I have some black mold spots on the ceiling of 3 of the 4 upstairs rms, I think there may be a problem with the vapor seal. I think I should pull up the plywood, take out the old insulation, wash down the attic floor with bleach, & make sure there's a proper vapor seal, before I put down new insulation. I also thought that if I used rigid insulation, I could achieve the desired R-38 or higher with the existing 5-6" depth. Does anyone know approximately how much more expensive would it be if I covered ~70% of my ~900 ft2 attic with rigid insulation, rather than using batt insulation? Does anyone have any experience installing rigid insulation? I couldn't find the episode of TOH which showed it, but from what I've read, it seemed as if I could do it myself. What did you do? Anyone else have any advice? Initial cost is an issue, but so is difficulty & time to recoup the cost. Although rigid insulation is more expensive, I think I could save money by installing it myself. On the other hand, since I would have to raise the existing plywood floor by ~6", in addition the cost of the 2X6's, I would need to hire someone to do the work. BTW, I have a 45 yr old colonial in CT near LI Sound. That is why I want to increase the insulation to R-38. Thanks.

Thanks for the feedback. Worthy, We'll ask the insulation company to remove the foam that could possibly be affected by the chimney heat. Even though we don't use the fireplaces we want to keep the option open. Energy rater, I should have been more specific in my posting. The foam was just used for air sealing the leaky areas and not the entire attic. Also, the foam was applied only to the perimeter of the housing of the recessed can(may be about 1/2 inch think) and not completely over the housing. The reason for foaming around the cans was because there was a possibility that the holes cut for the cans were slightly larger than the cans. I am assuming that this shouldn't cause problems with the holes in the housing. Please correct me if I am wrong. My only concern was if the housing will get hot enough to make the foam on perimeter burn. BTW, we use CFL bulbs. You are right about the flue vents, For the gas furnace and water heater. We asked the guy doing the air sealing to remove the foam around them. Should we be concerned about the dryer vent though? Other than the chimneys, flue pipes, kitchen and dryer vents we couldn't think of any other places which might get warm/hot. Should we worry about anything else?

The air flowing though it is returning unconditioned air that will be going to the coil to be conditioned. So when you AC first comes on there could be hot air sitting in the return, but then the cooler air from the condo will cool it down. There is no harm in insulating it, and you may get some efficiency advantage. If it is a not a big extra cost then have it insulated. Covering it with insulation also helps seal it which is an added benefit for the return.