The depth of the insulation is not the problem that first comes to mind for me. The issue with fiberglass insulation is that it allows air to move through it. Your house in Rio Vista, CA, is quite new and modern yet I everything I read says that it still leaks air through the fiberglass when the wind blows. This is called "wind washing", and it is why you would probably lower your heating and cooling costs with air sealing work and covering the insulation with a layer of cellulose insulation, which does stop air from moving through it.

Is this a two story house? If so, the problem could be exacerbated by the "stack effect".

What I think would benefit you now is to take advantage of the Energy Upgrade California program. It can get you up to $4,000 for a 40 percent reduction in energy use down to $1,500 for a 15 percent reduction.

You'd start off with an energy assessment consisting of a blower door test and a duct pressure test to measure the leakiness of the house's shell and ducts. The test would also check combustion gasses from the water heater and furnace to make sure they do no get into the air your family breathes. I'd also do an infrared thermal scan on top of that to find any spots in the house that are improperly done or uninsulated.

Finally the assessment would consist of inputting your house's specs into a program that could identify the percentage drop in energy use achievable with existing upgrades.

At 11 years old, some of the systems in the house may be ready for retrofits, some may not have been the best quality to begin with as I have found in production houses.

An energy assessment by a contractor participating in the Energy Upgrade California program could answer all your questions.

George Matthews
Home Energy Retrofit