20-foot vaulted ceiling & 1970s sagging insulation – need insulation retrofit advice
One of the additions to the house was a huge 20X24 living room with 20′ vaulted ceiling. I guess they were all the rage in the 70s and so was insulation that is now sagging. I was looking with IR camera and I could just see these cold spot areas behind drywall where insulation has sagged. That room also drops 2 degrees for every hour, unlike the rest of the house where temps drop 1 degree per hour.
So I am trying to educate myself on what are the options. My insulation contractor, who did the attic in the other part of the house is suggesting we make cuts in the drywall and take out all the fiberglass there and blow in densepack cellulose. I know that method is the rage in Northeast.
But since I am thinking about putting tongue and groove boards on the ceiling, another thought I had was to just polyiso over the drywall, then OSB or something more lightweight, and finally the oak planks.
Any concern about polyiso being over drywall?
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Replies
Apollo,
Q. "Any concern about polyiso being over drywall?"
A. No. But I'm concerned that your suggested insulation method won't meet minimum code requirements for ceiling insulation. The minimum requirement ranges from R-30 in the warmest part of Florida to R-49 in the northern half of the country. Where are you located?
I am in MA.
There is already insulation in the ceiling. It is just sagging, hence my thought about small retrofit over it.
Apollo,
Depending on the amount of airflow through your rafter bays, the R-value of the existing insulation might be R-0.
Going to have to cut a bay open and see what is inside. Hopefully I don't find what I found in '55 part of the house - empty walls.
Haven't cut into drywall yet, but I did take picture with my IR camera. Not looking good... Notice all those dark black areas... that is cold getting in.
So I cut a hole in the ceiling to check out what insulation we have. Looks like I have 8" deep rafters and there is only firberglass (looks yellow in color and much thicker strands than modern stuff) with paper backing towards the drywall.
There are also soffit vents, but there is no ridge vent. I went in with borescope and noticed there is also no air gap.
So that fiberglass just acting like an air filter for all the air I got cooling my drywall?
Without ripping off the roof (it got redone 5 or so years ago, before we bought the place), what can I do to insulate the cathedral ceilings then?
If there is no ridge vent, would just taping up the 1/2" wide soffit vent at least give me some R value out of fiberglass?
Apollo,
I don't recommend sealing up the soffit vent unless you are willing to install rigid foam on top of the roof sheathing.
You can try a variety of halfway measures, I suppose, but I don't recommend them. If you want to fix the problem, and you have decided to address the problem from the interior, I advise you to open up the ceiling -- in other words, remove the drywall -- and install R-49 insulation in your ceiling according to one of the methods recommended in How to Build an Insulated Cathedral Ceiling.
How can I get to R-49 with only 8" rafters? That sounds almost impossible without ripping off the roof.
Apollo,
If you take the time to read the article I linked to, you will find that I discuss several possible approaches.
I advise you especially to read the four paragraphs that follow the heading, "Are my rafters deep enough?"