I am the 2nd owner of a house that was built in 1932. We bought the house in 1982 and turned the attic into a bedroom by insulating between the 2x6 rafters with unfaced fiberglass and then covering that with plastic and sheetrock. It is a 12/12 pitch roof, and we did put in some venting from the soffit up to the roof vents. Now, 40 years later, you can see the drastic heat loss through the roof, melting the snow and creating rather dramatic icycles. We are in the process of remodeling the attic/2nd floor and I was hoping that I wouldn't have to "start over" by demo-ing the whole thing, tearing off sheetrock, re-insulating, etc. etc. Is there a product out there that can cover the sheetrock, insulate, and is "nailable"? I know that putting 2' foam on the walls would insulate the hell out of the room, but I need to paint/wall paper, etc. I also know that there will be issues around windows, doors, skylites, etc. with regard to trim, but I have a professional finish carpenter for a brother.

You might want to cut a square out of the sheetrock and look to see the actual condition of the fiberglass. If it is dry and fluffy, your options might be different than if it is wet and compacted.

-Rosalinda

Whatever you can do on the interior won't be as good as either removing the sheetrock & insulating the roof from the framing, or do an energy retrofit to the roof - tear off the shingles, install some sheet insulation, strapping, plywood and new shingles. There are detailed methods discussed in these forums for doing each type of upgrade. If you were to open the rafter cavity, you'd want to make the cavity deeper to increase the insulation value - and there are numberous ways to add insulation. Thermally, the exteior method is better.
On a slightly different note- when the 3rd owner eventually moves in he probably won't be remodeling the area you are doing now, so the work you do now may very well be unchanged for 50+ years.

What Rosalinda said- make sure that you aren't already rotting out the roof deck before going ahead with anything. If the roof deck looks good and the fiberglass isn't wet, put it back and carefully air seal any splits you made in the plastic vapor barrier to do the inspection. It's probably better to drill a few half-inch inspection holes for inserting a fiber-optic camera (a cheapie like this one is fine but there are better pro-versions if you thing you'd use it a lot: http://www.harborfreight.com/digital-inspection-camera-67979.html ). You can then seal the hole with squirt of can-foam once you're satisfied.

If you used full-depth R19s between the rafters you may very well find some moisture issues, unless you also installed chutes to guarantee a ventilation gap. But if you used unfaced R13s which would nominally have a 2" ventilation gap, it's most likely going to be just fine.

One issue with leaving it in place is that you can't use foil-faced iso on the interior side, which would give you a high R/inch, but create a moisture trap at the existing gypsum, which would almost certainly create a mold issue on the paper facers of the gypsum at some point in the future. A couple inches of XPS would still be able to dry toward the interior, and would not be so much R as to have a dew-point issue at the existing gypsum layer even if you have only R13 between the rafters. At 2" it would roughly double the R value, cutting the heat loss in half. Over 2" becomes a bit of a moisture trap, and pushes you closer to having a dew-point issue.

I KNEW it couldn't be as easy and "just nail something up" ! But, I was expecting to have to gut the room anyway in order to make it right. I think the idea of creating a deeper cavity for insulation is the right way to go.

thank you.

I KNEW it couldn't be as easy and "just nail something up" ! But, I was expecting to have to gut the room anyway in order to make it right. I think the idea of creating a deeper cavity for insulation is the right way to go.

thank you.

If you need a new roof, doing an energy efficient retrofit would be the way to do this upgrade and mitigate thermal bridging through the roof framing, which is a good thing.

-Rosalinda

If you gut the ceiling 2" of closed cell foam on the underside of the roof deck with R15 rock wool or high-density "cathedral ceiling" batts is sufficiently vapor-tight to protect the roof deck without interior vapor retarders, then adding an inch of XPS or UNFACED EPS between the gypsum and rafter edges brings you to a reasonable R21-R22 for whole-assembly R with the thermal bridging of the rafters factored in, assuming a 15% framing fraction (typical for roofs with 24" o.c. rafters.)

That's the thermal-equivalent of R30 cathedral ceiling batts in 2x10 framing, which isn't terrible, even though it's quite a bit shy of R49 (IRC code min for zone 6), and about 2x the whole-assembly R of your current stackup.

If you can find a local installer, it's far cleaner-greener to use water-blown 2lb foam (Icynene MD-R-200, which is ~R5.2/inch or Aloha Energy's 1.8lb foam which is R6/inch) rather than foam that is blown with HFCs (Don't confuse MD-R-200 with their higher-R MD-C-200, which is blown with HFC245fa, with more than 1000x the greenhouse gas potential of CO2 or water.) High-R goods between rafters is usually a waste, since the thermal bridging undercuts it's performance dramatically- it's there for moisture control more, and the difference between R5/inch and R6/inch foam in whole-assembly performance is negligible- you would buy far more performance with just R1 rigid foam thermally breaking the rafters than any difference you'd see between a R10 vs R12 layer on at the roof deck between rafters.

XPS is also blown with the high-greenhouse potential HFC134a, whereas EPS is blown with pentane, at ~1/200 (0.05%) the greenhouse gas hit of XPS, but you're giving up about R1 (~5% of the total R.) While the R1 difference between XPS & EPS may "pay off" in lifecycle greenhouse potential over the life of the building from the 5% carbon emissions reduction in heating & cooling energy use, it may not, depending on the actual energy sources used over the next 25-50 years.

When it's time to re-roof you can fatten out the R and lower the thermal bridging with exterior rigid foam. A 3" layer of polyiso (also blown with low GHG-impact pentane) above the roof deck, with the previously recommended interior-side stackup would meet or exceed current code-min performance.