Posted by: SherlockHomesSY | 12 Oct 2010

Solution Basics: Insulation

INSULATIONPlaces to Insulate

Installed right, insulation will slow, not stop, heat transfer across the shell (walls, ceilings, and floors).  The keys are as follows:
. Provide at least what’s required by your building
– Ensure it’s against an air barrier
– Don’t let air flow through it
– Leave no gaps

Provide Required Insulation

Installers really ought to provide more than is required.  Remember, the building code is a minimum standard.  Believe it or not, the way better insulated floors are installed, the effective insulation value is R-5 though it says R-19 on the batt.  In a perfect world, the best that could be done is a little less than R-16. Perhaps it’s better use the Department of Energy’s (DOE’s) recommendations than it is the building codes.

Ensure Insulation is Against an Air Barrier

Insulation works best when air can’t flow between the insulation and the surface it’s trying to protect.  Usually, this is your ceiling, interior wall covering on exterior walls, and floor.  It could be the exterior wall sheathing, roof deck, and floor.  Whatever surface is chosen to be air sealed should be the air barrier.

Don’t Let Air Flow Through Insulation

Insulation works because it traps air.  When air flows through insulation, trapped air is blown away.  The best way to do this is to enclose the insulation.  Living space walls enclose insulation on six sides.  So should attic kneewalls.  Total enclosure isn’t necessary when most types of foam insulation are used.

Leave No Gaps

Most types of insulation need to fully fill the cavity it’s installed in, without compression or gaps.  Batt insulation takes time and patience to install correctly.

For example, a 2×6 wood wall with R-19 fiberglass batt insulation in it.  The best we can do is with perfectly installed insulation is R-15.  Most reputable batt insulation companies can install it to R-11, until someone shows them how to do it right.   Most of the time, this wall is R-4 with only 5% gaps.  Bottom line: insulation gaps and compression is expensive!  Take your time to get it right!

One insulation company told me installing batt insulation correctly could cost as much as using a blown-in product, such as foam, cellulose, or fiberglass.  Blown is better for a lot of reasons.

Foam Insulation

Foam insulation is great, but it must be used with care.  Foam cannot be left uncovered inside the living areas.  It’s got everything to do with fire: smoke spread index and flame spread index.  Most of the time, gypsum board (e.g., Sheetrock) is used.

When there are combustion appliances, such as furnaces or water heaters, in uninhabited areas, foam must be covered in those areas too, unless the product is rated for fire.  One such product is Thermax: foil covered polyisocyanurate rigid foam board.

Insulation Installation

Though these are the basics of installing insulation, air sealing and vapor management must be considered too!  This not only applies to the building shell, but also to ductwork.

After air sealing and duct sealing, the most important energy-efficient thing to do is insulate properly.  From experience, I know that reworking the insulation installation around my skylights and sealing the holes in my ceiling made the difference for my air conditioner to cool my office in the summer time.


Diagnosing and correcting insulation issues are discussed on my home performance website, and are the principles of insulation.

The North American Insulation Manufacturers Association (NAIMA) has batt insulation instructions.  It also is a wealth of information about all kinds of insulation concerns.

As always, if you have any questions or comments, share them with the rest of us by leaving your comments.  Otherwise, email me at

Next time, another Solutions Basics subject: Ventilation!

Don’t forget to heed our warning . . .

WARNING! Do not implement any of these solutions without considering the impact on IAQ, moisture control, & heat transfer. A combination of solutions are usually needed to improve health, building durability, comfort, and energy efficiency. Ignoring this warning may lead to disease, deterioration, high energy bills or worse!


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