What is the best type of insulation to use for a completely uninsulated house in Coastal Southern California, built in 1974?


What is the best type of insulation to use for a completely uninsulated house in Coastal Southern California, built in 1974?

Asked by Senait

House is in Coastal Southern California. It is two story high with an attic space and high ceiling in the living room area.

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Lucas Johnson's picture

Actually, I am not surprised about this at all...very similar to Santa Barbara, where the lax building code and mild climate allowed for pretty poor construction.

The good news is that having no insulation will make it very easy (and relatively inexpensive) for you to dramatically increase the comfort, health, and efficiency of your home! The caveat is that you need to use building science to follow the whole-house approach if you want to get it right!

Begin with an energy audit

The first step is most likely investing in an energy audit. I believe the Energy Upgrade CA rebate program exists in your region, and if not, your local utility should be able to help you find an auditor.

They will perform a series of tests to help determine the most cost-effective solutions and to make sure you are not creating combustion safety, indoor air quality, or moisture damage risks.

Air seal your home

The next point to make clear is that insulation will not work well unless it is combined with comprehensive air sealing.

The analogy I most commonly use is that insulation is like a fleece jacket and air sealing is like a hard-shell rain jacket. Imagine going skiing in just a fleece...you would freeze since the cold air would move right through the fleece. Once you add the hard-shell, which is an air barrier, then you stay nice and warm. The reason is that insulation is supposed to create a "dead air space" to retain your body heat and it cannot do this while air is moving through it.

Also, since you have a two story home, it is important to note that you will most likely experience something called the "stack effect". As air leaks up into your attic space it will pull "make-up air" into your home, which could contain toxins at worst, or at minimum, the air will not be conditioned, thus leading to decreased comfort and increased heating/cooling bills.

Start with the attic

This is a good point to mention that you should always address air sealing and insulation projects in this order:

  1. Attic space - do not use batt insulation in your attic, other than maybe on knee walls
    • The least cost option is usually to air seal the attic floor and then use blown cellulose insulation to a depth of 12-18"
    • Another option, which is best if you want to use the attic for conditioned storage, is to use a spray foam insulation project in the attic rafters to create a "closed conditioned" attic
  2. Crawl space or basement (not much you can do if it is a slab foundation) - Unfortunately, batt insulation is usually the only option that is realistic given cost and access constrains. Make sure to air seal first, insulate to R-30, and use netting or rods to keep the insulation in place
  3. Vertical Envelope - this is your walls, windows, and doors (make sure to upgrade wall insulation before investing in windows!!!)


Lastly, please make sure that you consider in-home ventilation as you air seal and insulate your home.

  • You should always have a quiet and efficient bath fan in every bathroom as well as a kitchen hood.
  • In addition, if you are making your house really tight, then you may need an additional "whole-house" ventilation system like an Energy Recovery Ventilator (ERV).

It is also most likely worth it to have a "test-out" audit to make sure everything is done correctly!"

For more information:

The Find A Pro directory on GreenHomeGuide listsapproximately2,500energy auditorsand ratersacross the U.S.Click hereto find one near you.