That is a great question with a couple of different answers, primarily dependent upon budget and if other projects are scheduled.
The principles of building science tell us to address insulating a home in a specific order.
- First, you must create an effective air barrier (more on this later), because insulation does not function well unless it is directly in contact with an air barrier.
- Then, you want to upgrade the attic first, crawl space second, and only address walls/windows/doors if needed.
- I live in a mild climate (Santa Barbara), where windows/walls can usually be left alone, but I believe it gets much hotter in your neighborhood. Given that is true, wall insulation and windows would generally be good investments for you.
- However, if over-heating is a problem, it would certainly be worth looking into shading strategies (like overhangs, trees, trellis, etc.) first.
Insulating your walls
If you are insulating walls, keep in mind you will need to patch and paint afterwards (which often costs more than the insulation).
- Thus, if you want to paint anyway, adding insulation to the process is a great investment.
- For insulation, I'd recommend using Greenfiber blown cellulose to R-19 or higher.
If you are doing windows, now is a good time to make sure best practice waterproofing is used. There are a huge variety of window options, but make sure to consider:
- solar heat gain (SHGC),
- R-value (insulation level),
- low-e, and
- other performance factors.
For your attic, I'd recommend starting by air sealing all penetrations (can lights, bath fans, interior walls, hatches, etc.). A Building Performance InstituteAccredited Contractor should be able to do this for you. Find one near you with GreenHomeGuide's nationwide Find a Pro directory.
Then I usually install Greenfiber Blown Cellulose insulation to about 12-15" deep in the entire attic space.
- Insulation should bury all water pipes, framing, and as much of the ductwork as possible.
- This also brings up the fact that you should test, and most likely replace, your existing ductwork.
For your crawl space, you again need to start by air sealing all penetrations.
- This is very important for moisture management and indoor air quality (IAQ).
- The best practice would be to custom cut 4-6" of rigid foam board for insulation; however, this is expensive.
- The typical strategy is to install un-faced Eco-Batts to R19" with metal rod stabilization.
Since a home is a system, you always need to consider side effects of other improvements.
- Now that you have air sealed your home, you need to make sure there is still sufficient air exchange. A BPI Accredited Contractor will be able to tell you that.
- In addition, you should consider other projects like using a more efficient furnace and/or A/C system or improving the safety of your water heater.
The bottom line is there are many details, but a BPI Accredited Contractor (find onehere) should be able to figure out a good path for you.
For more information:
Read "What's the best insulation for my uninsulated 1930s era wood frame clapboard house?" a Q&A answered by Danny Kelly.