Eddie, just wondering, why do you feel anything more than 12 inches of insulation in a ceiling is a waste? I'm trying to determine how much insulation I need in the ceiling of my Morton building. I always thought the more the better, apparently not. Can you please explain your comment a little better? Thanks.
Thanks for asking this as it might have been misleading. Here, code is R30 for a ceiling in a residential home. R30 is reached at ten inches. R3 per inch is about how it's figured. Going two extra inches exceeds code and allows for some settling over time.
Adding more then 12 inches has a few drawbacks with minimal reward. Every inch costs money. There is a point where you don't get anything back with more. Kind of like how heavy of a jacket you need to stay warm. There is a point were you don't need to put on any more layers. You can gain a higher R factor with thicker insulation, but you start getting into that area of it not making a difference, or it's not something that you can tell in energy savings.
Most homes that I work on have parts of the 2x6's in their attic showing. Sometimes I can see the sheetrock, but usually they have some level of insulation. They are also paying allot on energy, both to cool and heat the house. Here in the south, cooling a house is done allot more then heating one. When going from 4 to 6 inches of insulation, up to 12 inches, I've heard over and over again from them that their energy bill has dropped usage has dropped by 30 percent.
It's not just the thickness of the insulation, but also the uniformity of it. I create a total blanket up there that covers all heated and cooled spaces. Each area that doesn't have insulation is like an hole in a boat.
After 12 inches, the walls, windows, doors and vents start to leak and lose more energy then the ceiling. Most double pained windows are just R3. They are the weak link in every home. You can make the ceiling insulation 2 feet thick and build with 2x6 studs on your exterior walls with solid insulation all around, but your windows will still be R3.
The next concern is the weight of the insulation. Here, ceilings are done with 5/8's sheetrock for rafters on 24 inch centers, and half inch sheetrock on 16 inch centers. Sometimes you'll come across a home where they used half inch sheetrock on 24 inch centers to save a few bucks. There is a limit to how much weight you can put on that sheetrock. I've seen the ceiling sheetrock bending and the nail heads popping out on ceilings with very little insulation. I won't add more to it in those cases and explain to the homeowner the problem. I've never heard from those people again and don't know what they did. I just wasn't going to add insulation to a ceiling where I knew the sheetrock couldn't support the load.
Eddie
