Roof vapor barrier

[Jeffrey]

Gentlemen,

I have recently had the flat roof over part of my kitchen replaced. I want to install insulation into the roof and I have some questions:

1) Do I need to install a vapor barrier?

2) The rafters are dimensional 2x4s (old house) so my depth is limited. Would fiberglass batts work in this application or would something else function better? Should the paper facing be up or down or do I need paper facing?

Currently there is a drop ceiling in place that is covering the old lathe and plaster ceiling. It will be replaced in the future with drywall. I'm mostly concerned with insulating the roof from the heat generated in the kitchen to avoid any freeze/thaw issues during winter. I live in Cleveland.

Thanks for your time,

Jeff

[tooltroll]

Yeah, you need a vapor barrier on the warm side of the insulation, otherwise your insulation will get soggy from condensation. You can use faced or unfaced batts, (the facing goes towards the warm side, too.)

Can you bulk out the roof any? If it were mine, I'd frame a new drop ceiling at the hieght of the old drop ceiling (knocking down all the old lath and plaster first,) insulate above that to the recommended roof R for your climate, vapor barrier and drywall.

Fiberglass is the easiest to DIY, but if you've got a few bucks to throw at it, you could see about having foam sprayed in.

[rbisys]

Greetings,
Flat roofs are huge energy wasters.

The heat energy will radiate thru the FG and the joists are directly connected to the roof surface. Foam isn't much better.

See my comments on r-38 thread.

If you want to know how to install e-m me. I'm waitng for a new printer so it would be about a wek before I could send you info.

[Big Builder]

My suggestion is to spray foam. Fast, easy, you can leave the exisiting
roof framing and genarally it is accepted as a vapour barrier too!

Even if it costs slightly more in the long run.........you won't have spent alot of your valuable spare time doing it!

[danh]

Um, yeah.

FG + Vapor barrier will only work if you detail the vapor barrier to eliminate air leakage. A standard vapor barrier installation will still leave your insulation "soggy". Even the, you will need to run the kitchen fan to control moisture.

Most people just vent the space above to prevent moisture problems. It's worked in the past, especially in old homes, but it's the reason old homes cost so much to heat.

radiant barrier will solve the radiant heat issue, but won't solve the moisture issue, or the convective heat flow issue unless detailed as an air barrier too. But honestly, you've got a high-humidity warm air mass - rbisys how do you deal with the heat conducted from the air mass? it'll have a fairly high humidity, seeing as no one recommended ventilation, and will therefore actually carry quite a bit of heat...

foam won't reflect the heat the way that the RB will - maybe you can paint it with a foil facing. Amazing; I'm a genius. Best of both worlds - moisture, convective, conductive, all solved.