Adding insulation to a finished vault

[Tolyn Ironhand]

We have a large room above our garage that is finished. It has 6 skylights which are nice but I view them as energy wasters. I have installed some 3M plastic at the ceiling level to reduce air leakage but this room looses heat FAST! There is also windows on 3 walls. The sun will warm it up nicely in the winter but as soon as the sun drops so does the temp in the room. I am guessing that the previous owner did not insulate very well based on how the rest of the house was insulated. (which I have added to) I would also guess there maybe an R19 up in the vault.

The only options I have come up with to add some blown in itch is open the sides of the skylight shafts and blow from there. (I am thinking of removing them anyway) Or going at it from the top: Blowing through the roof vents or removing shingles/sheathing and blowing that way. Anybody have some better ideas?

[Bud9051]

Hi Tolyn, how much space is up there? Are these scissor trusses or just 2x? rafters with the drywall on the bottom?

Bud

[Tolyn Ironhand]

Not 100% sure since I haven't seen them. Based on the fact that the floor is trusses, and the angle of the vault between the roof and the ceiling, (not the same) I suspect scissor trusses. I would doubt you could move around up there but blowing through them should work.

[Bud9051]

Determining what is up there would help. Any can lights where you could get a look. If there is a double layer of r-19, then the heat loss is elsewhere. Have you run any heat loss numbers by area, like walls, ceiling, windows, each by itself. That would help target the improvement to the area of greatest loss.

Bud

[Tolyn Ironhand]

Good idea about the can lights. Trusses. And it appears to be batts for itch (which I also suspected) Here are some pictures: Great room attic pictures by TolynIronhand - Photobucket

I would doubt a double layer of R19. Looks to be a single layer. Aslo you know how porly batts can insulate if not done correctly. I have not done a heat loss calc because....well, I don't want to get that complicated. I suspect the greatest heat loss would be the skylights.

I will also say that it is a fairly modern construction. 2x6 walls, double pane windows and Tyvek on the outside.

[Bud9051]

The wood looks great so no sigh of moisture. I would assume soffit and ridge vents are in place.

As for the calculations, just do the math for that ceiling and then exterior walls.
Q= U x A x HDD x 24
Q will be your annual heat loss
U = 1/R but an r-19 ceiling would be roughly an r-12 given its condition and the thermal bridging.
A = area
HDD is obviously your heating degree days
and the 24 converts it to hours to keep the terms correct.

Do the same with the skylights using r-2 if just double pane or r-3 if low-e as well. But their area is low and this number will tell you if they are a major contributor to this cooling.

How well is that ceiling/floor over the garage insulated? If it has r-19 installed like the ceiling that could be an issue as well.

Bud

[condo-owner]

if you suspect the skylights. why not make/install some insulated plugs ? this will test your theory, before doing any major reno's .

[Tolyn Ironhand]

I do have some poly (3M shrinking plastic) sealing off the shafts which I think has helped stop air movement. Room still cold down fast. Thanks for the idea though. Might do that next year.