Is there a way to insulate a ceiling that is already finished and has no access point? More details below:

Recently purchased a home in Eastern Massachusetts; one of the features was a room off the back that appeared to have been built as a screened in porch and eventually finished as a new family room. There's a gas radiator (though that doesn't work currently), so there isn't heat to the room, so I expected it to be cooler, but manageable. Unfortunately, I've come to find out it appears there isn't insulation in the ceiling.

The walls are almost entirely glass (there are 6 60" square sliding windows which I just replaced because the seals on the old windows were shot), so there is nominal wall insulation, but it is there. When changing the bulbs in the recessed light fixtures, I realized it was frigid up above. There doesn't appear to be an access port from the outside on either side of the room, and there's no entry point from inside the rest of the house.

I'm guessing that this won't ultimately be a DIY project, but is there even a technique to add insulation to a ceiling like this? I assume it's going to be blown in or foam of some kind, but I can't figure out what product would work well; it's a long room (20' end to end) and I don't know how to approach it. Any insights would be appreciated.

  • This could be a DIY project, but we'll need more details. Is it a cathedral ceiling or a flat ceiling above a sloped roof? Is the ceiling finished with drywall, T&G wood, or something else? Is there any evidence of water leaks through the ceiling or water damage on the ceiling material? Is it roofed with shingles or something else? What's the condition of the roofing materials?
    – iLikeDirt
    Commented Jan 21, 2015 at 15:07
  • What's the U-value of your new windows?
    – Ecnerwal
    Commented Jan 21, 2015 at 16:10
  • Is the ceiling high enough to drop it 6-8" or so? If so, you can create a dropped ceiling with insulation between the new ceiling joists.
    – bib
    Commented Jan 21, 2015 at 16:32
  • It is a flat ceiling, with a sloped roof over it. It is finished with drywall, and there are no leaks (thankfully). It is roofed with shingles, and they're in pretty good shape (roof was redone in 2009). I can't drop the ceiling (and honestly don't want to pull it down if I don't have to; I don't like drywalling if I can help it, especially overhead as I need to do it on my own). I'll need to double check the U value; they're Harvey replacements, double pane with argon gas and the Low E glazing; they're good, but not bullet-proof.
    – JT81
    Commented Jan 22, 2015 at 15:53

1 Answer 1


In most cases it's more effective (insulation-wise) and cost effective to either insulate on top (Add sheets of rigid foam, plywood over, new roof surface on top of that) or to tear out the interior ceiling, insulate, and put up a new ceiling.

Depending on the structure, some sort of blown-in (cellulose, or fibreglass if you like insulation that gets less effective in the cold) is the only reasonable option without opening the ceiling up - you still have a bunch of holes you'll need to patch. Foam is problematic in closed-off spaces due to over-expansion. That is probably best hired - it's easy to DIY in an attic where you can see what you are doing, while blind insulating is helped by experience.

Or (rather less expensively) face the fact that the "room" is still really a screened porch (now with windows) and don't try to heat it in the winter - use the gas heater to extend fall and spring use a little, but close the door and leave it be in winter...Even with perfect roof insulation, a room with walls that are mostly windows is going to cost a LOT to heat in Massachusetts in the winter. Floor insulation, if any, is probably not great either, based on the porch conversions I've seen...

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