Thanks for the response. The installer is very good, experienced, and will use a board over the installation, so the decking will not catch fire. I am confident that he will do terminations and seams well. My cheif concern is how a torch down (modified bitumen) roof will work in this type of installation where there could be some small puddles forming (about 1/8 inch deep)? Renovator, you are correct that PVC would perform better and last longer. However, it is more than twice the price AND most local roofers don't offer it. For the contractos that do offer it, I have no information on their work quality.

Thanks guys. Let me see if I can provide a clearer picture of what I'm working with. The house is over 100 years old--a brick row house in the center of a block. Most walls and all the ceilings on the third floor are plaster, with lots of lumps and bumps and a few small cracks, but mostly solid. There are no ceiling moldings. To call what is above this floor an attic is a an exaggeration. It is a space that ranges from about 3 foot tall at the front of the house to about half that at the back of the house (roughly 40-feet on that floor...first and second floors have a bigger footprint and do not need insulating between living space and roof.) There is a central air (newish high-velocity, narrow tube) system that snakes around the "attic". The blower is installed at the one access point there had been. This system serves ONLY the third floor and has two outlets in each of three small bedrooms and one in the tiny bathroom. The system serving the first and second floors is in a second floor closet. The insulation guys tell me that they can blow insulation in but will need to cut at least one new mansized hole in the ceiling to get in--possibly two, one toward either end. There are no recessed lights on the floor, and only three overhead lights at all. All other lights are wall brackets, wired from the floor up, rather than from the ceiling down. Of the three overheads..one was put in new by me, so isn't K&T. One the previous owner says was moved by them, so isn't K&T (But may connect in to K&T at the meeting of wall and ceiling. And one is the bathroom overhead, which can easily be checked. My electrician replaced the fixture there, so he should know what's above it. The roof is asphalt and fairly new (say 5 years old?) so, I'm not inclined to want to replace it anytime soon. I've gotten a quote for $950 to cut an access whole and blow in insulation. I'd have to pay someone else separately to fix up the access panel afterwards, probably adding another few hundred. Most neighbors don't even try to do much of anything with ventilation in their "attics", as they are all scared witless of cutting holes in their roofs. But I have found info on the Brooklyn Brownstoner blog about successful attic and whole house fan installations and one neighbor loves the whole house fan he has which sits in a sort of plastic cove on the roof. Unfortunately, he bought it with the house and has no idea who installed it. I don't intend to move in the near future, or even the more distant future. But I would like to make the third floor more habitable in the summer, especially since at some point in the next two years or so, I'd like to turn it into a separate apartment and rent it. Honestly, I seem to be finding such conflicting information and I'm so dubious about how knowledgeable folks you hire to do this stuff are about old and "out of the norm" houses that I really, really, do appreciate any and all help I can get here on this forum. Thanks,

As it turns out the problem isn't the roof but the airshaft/dumbwaiter in the middle of the house, from ground floor to roof. Major chimney effect/stack effect problem we hope to fix soon. We opened up the middle floor airshaft space (cutting through metal ducts providing passive ventilation off the ground floor bathroom) and took out the dumbwaiter space, and turns out that the duct work went from floor 1 to roof venting floors 1-2 bathrooms, with old turbines on the roof that act like an open window to the roof, above the dumbwaiter space. No venting off the third floor at all. And the airshaft is a lot of freeflowing air next to the open duct work, with a roof skylight at the top of it. So now when it's cold on floor 2 it's cold in the floor 1 bathroom - it's an open window. Our plan now is to pull out the duct through floor 3, patch the roof, take out the skylight on teh roof and use that space to vent all 3 bathrooms with 4" or 6" vents, and put a ceiling over the 2nd floor to stop the chimney effect. Hopefully this will make a big difference.

Attic insulation usually falls into two categories - (most common) leave as unconditioned space, where the attic is vented outside and insulation is installed in the room ceiling below, or create conditioned space, where the attic vents are sealed, the roof deck is insulated and the room ceiling below usually does not have insulation. In your new attic area it sounds like you have conditioned space. If you want to leave it as conditioned space, most contractors will recommend venting it to the rest of the house to maintain a moderate level of air flow through the area. This could be something as simple as an HVAC grill in each end of the area to allow air flow, or you could also install a circulating fan. I have a conditioned attic and I chose to leave it unvented. It is a relatively high volume area (full attic), and during hot weather it seems to stay within about 10 degrees of the temp set in the house. My A/C unit is also located there, so I probably get some residual cooling effect from the duct runs, even though they are insulated. Bruce