Author Topic: Construction-- Insulation question.. (Read 378 times)

rabbidrabbit · « **on:** October 27, 2004, 04:08:33 PM »

OK,

Doing a remodel and going with a cathedral style ceiling in the great room. My question is what kind of insulation would be best? There is a total drop in the center of the roof of 4 ft and I'm supposed to have R39 in the ceiling. I think there is attic batting to get up to R39 but is that my best option? Isn't it really expensive? How do the different types of insulation compare.. batting vs. styrofoam vs the blown in stuff... Any thoughts?

Lizking · « **Reply #1 on:** October 27, 2004, 04:15:38 PM »

Styro is the best and easiest, but also the most expensive. If it is a cathedral ceiling, how much space do you have between rafters and actual ceiling?

rabbidrabbit · « **Reply #2 on:** October 27, 2004, 04:23:02 PM »

well.. at the peak of the roof I have 4 ft between the bottom of the ceiling and the top of the roof. The frame is 2x4 trustle. Can you get blown in styrofoam anymore? I guess I'm trying to figure out price vs performance and making sure I'm not forgeting any options. Got to be somone here who can give me some straight numbers on what my options are and a rough price per square ft . I'm figuring a total roof area of 900 square Feet. Any pointers would be appreciated!

Lizking · « **Reply #3 on:** October 27, 2004, 04:27:30 PM »

Sheet styrofoam placed between the rafters is optimal, but blown in will most likely be cellulose. Bat is the cheapest, and if you have 4' is probably the best option.

bigsky · « **Reply #4 on:** October 27, 2004, 05:26:33 PM »

yup, 18 inch fiberglass is best for that.

Lizking · « **Reply #5 on:** October 27, 2004, 05:30:58 PM »

Are you going to use sheitrock for the ceiling?

rpm · « **Reply #6 on:** October 27, 2004, 05:47:08 PM »

The best insulation is sprayed foam. It turns your house into an icechest and acts as it's own vapor barrier, but it is a bit pricey and it's permanent.

Murdr · « **Reply #7 on:** October 27, 2004, 05:48:52 PM »

R30 bats cost about .52/sf. I do remodeling. Ive never used or been asked to install batts higher that R30 in residential construction.

Rigid foam board would be more expensive to reach the same R value.

Make sure you have proper venting at the eves. Styrofoam makes a thin molded channel that keeps insulation from closing up airflow where the wall and trusses meet. Its really important in a vaulted ceiling. Lack of venting under the roof sheeting shortens shingle life, and can even cause moisture problems in the ceiling.

bigsky · « **Reply #8 on:** October 27, 2004, 05:54:44 PM »

yes but i thought he had 4 feet beteen his roof and his ceiling. if thats tha case r38 bat will do.

Murdr · « **Reply #9 on:** October 27, 2004, 05:58:41 PM »

I suspect they are sissor trusses, and at the bearing point he has about 7-1/2" between the top and bottom. Less than that if you measure perpendicular with the ceiling.

Lizking · « **Reply #10 on:** October 27, 2004, 06:26:34 PM »

The only problem with foamed in is the moisture problem. I'm also guessing that the actual clearance will be too small to lay bats.

rabbidrabbit · « **Reply #11 on:** October 27, 2004, 06:47:26 PM »

How thick do R39 bats run? I have plenty of room at the peak (4FT) but it gradually thins down to about 10-12 inches by time it hits the outer wall. As far as bats go, whats the best brand to use or does it matter? Is the cheapest the best? Any real difference?

bigsky · « **Reply #12 on:** October 27, 2004, 06:50:58 PM »

18 inches

Murdr · « **Reply #13 on:** October 27, 2004, 07:06:13 PM »

Huh? R30 is 10" R38 is like 12" standard, but iioc owens makes a dense line that is a little thinner than standard.

Murdr · « **Reply #14 on:** October 27, 2004, 07:18:27 PM »

For residential batt products its pretty much certianteed and owens corning. Cant say Ive noticed a diffrence to prefer 1 over the other for like products.
Assuming you are using kraft faced batts, and a drywall ceiling, I'll add another pointer. Dont staple the tabs on the bottom of the truss. Staple them just around the corner on the sides of the bottom truss cord. Otherwise the paper tabs are apt to cause 'nail pops' in the wallboard over time. Plus if you plan on glueing it (as recommended on a ceiling) the glue is worthless if its on the paper.