Re: Insulating a large cathedral ceiling
Vermont and Upper Michigan cold enough for you. I also think you misunderstand me, although I can see why if you are only reading my posts to this thread. I am not totally against additional insulation, but I want people to understand that throwing on more insulation does not always give the expected returns. In fact it rarely does. But "green" groups pressure local authorities to raise the requirements for insulation and that is political.
Originally Posted by bsum1
A wall insulated to R-11 is going to reduce heat loss by about 91% compared to R-1, A wall insulated to R-19 is going to reduce heat loss by about 95% compared to R-1. Not much difference is there. OK this is an unfair comparison as even an uninsulated wall has two surfaces and a cavity so it will actually have an R value of around R-4, not R-1 so going from uninsulated to R-11 saves about 63% on heat loss through that wall and going to R-19 saves about 80%.
A ceiling is a different story. It normally faces an unheated and ventilated attic. There is only one surface and no cavity to trap air. So it starts off around R-1. An R-19 saves about 95% of the heat. Going to R-30 saves about 97% and R-38 saves about 97.5%. People expect a huge savings going from R-19 to R30 or R38 and as you can see, the difference just isn't there.
As for the cost, there is a big difference between the cost of additional insulation in new construction vs. a restoration vs. adding insulation just for the sake of adding insulation to existing construction. Its much cheaper with new construction, a little higher for restoration, but to tear out walls and add insulation and support for it and then redoing all the finishing just for the insulation is usually not justified by economics.
If you want to increase the energy efficiency of a home, I strongly recommend that you have someone use a thermal imaging camera to map out the areas of high heat loss. You might find that very small amounts of strategically placed insulation will save much more money that an additional thick blanket of insulation over everything, especially if you miss the significant heat loss sources, which is often done.