Well Susan, the short answer is it varies especially when one figures in regional issues, climates, what's available, budget, etc.
Most energy efficient roof. I am going to assume when you say most energy efficient roofyou are talking about one that allows the least amount of heat in, so I would start with one covered with PV panels followed by a well shielded / shaded one.
Material-wise a tile roof generally outperforms a metal roof, which generally will outperform a shingle roof assuming limited shading. With that you may wish to look into cool-roofing materials and choose the lightest color which fits in with your neighborhood and your home's style.
Most energy efficient product to insulate roof / attic. That is real easy - closed cell foam sprayed against the roof sheathing at least 4" thick and covering trusses / rafters. I generally prefer Demilic, but there are numerous other good manufacturers out there.
The most important thing with this and everything else mentioned is that it is properly installed which still includes air sealing the attic. Open cell will also work though you will need at least 8 inches to get the same benefit. If you do not want a hot roof system, I recommend a properly vented roof with baffles, no attic fans and no recessed lights and blown in insulation. I lean towards:
- dense packed cellulose,
- regular cellulose,
- rockwool, and
- fiberglass in that order.
These are all blown in products. If your ducts are located in the attic (especially with this system) make sure they are sealed tight and insulated.
Energy efficient paint with reflective ability to cut down on utilities.If you are talking about your roof, I recommend you check out the cool roof specs and article linked below. If you are talking about the exterior walls - a light colored paint is just fine. The "ceramic" paints are essentially snake oil.
If you wish to reduce utility costs the biggest thing is to air seal. If budget isn't an issue install R5 rigid foam on the exterior followed by a rain screed and cladding of your choice.
Tankless is not always the most efficient as most individuals buy them for the "endless" hot water. My top pick for efficiency is a Marathon super insulated water heater. A Heat Pump style one may have better "book" numbers, but reality says it depends on placement, use, etc.
Several things I would stress are to:
- place it is as close to the faucets as you can get,
- choose a proper temperature setting (120 degree is fine as most dishwashers have internal heaters now) and
- use WaterSense fixtures.
For more information:
Read these blogs posts on Sean's website: