Just in Time for Winter – 14 Inches of…

Cellulose Blow-In Insulation

For most of the country, combining the words “winter” and “14 inches” usually means one thing – a lot of snow.  However, as a rough guideline, 14 inches should be a minimum amount of insulation in your attic. More specifically, an R-value of up to 49 is recommended for most of the country.

We'll talk about R values in a minute, but the important thing to be aware of is that many houses - especially older houses (10 years and older), could GREATLY benefit from a little extra insulation.  As time progresses, many insulation types settle and compact and lose some of their efficiency.  Many older houses never had enough insulation to begin with.

As an example, a typical home in Phoenix, AZ could achieve a 12% return on investment by increasing their insulation from R20 to R35.  7% can be achieved going from R30 to R40.  And in a more extreme climate like Boston, MA, 22% and 13% can be achieved.  Move to Minneapolis, and the numbers get better still.  Good luck getting ROI's like that in any other investment!  Part II will look further into the payback and return on investment of this project.  Needless to say, this is one project worth strongly considering, even if you already have a good R30 base of insulation.

And the great news is that with the help of a friend, a little knowledge and planning, adding insulation can be a half day project in most homes, so long as a few precautions are taken.

There are a couple of key concepts that we must first understand before getting a handle on how much insulation you may have in your attic.  First, what type of insulation is it?

Insulation Types

The most common insulation types in recent construction is cellulose, fiberglass, or in some cases, fiberglass  batt.  Often you can tell by simply looking at the insulation, but before we proceed, one word of caution.  According to the EPA, houses built between 1930 and 1950 may have had asbestos insulation.  Asbestos can be dangerous in certain situations, and its best not to work in areas with asbestos.   However, there is much more to the story of asbestos - if you have a concern check out the EPA's Asbestos page.

Cellulose insulation is often made of recycled newspapers and wood that has been treated to be fire resistant and mold/fungus resistant.  This insulation is thought to be safer to handle for the general public, and my home built in 2006 was installed with Cellulose insulation.  Cellulose is generally a grayish or off-white color, and depending on the vendor, you may actually be able to discern some newsprint on it.

Fiberglass Batt

Fiberglass insulation is literally tiny strands of glass.  It is lighter than cellulose, but it can be a major irritant to eyes, nose, and throats of those performing the install or working around it.  Of course, once installed it should be out of sight and no issue, but when installing it you should wear long pants and long sleeves, as well as goggles and a mask.  In fact, that is really a 'best practice' for any insulation installation.  Fiberglass is usually yellow or pink colored.

R-Values

The R-value is the measurement of the thermal resistance of an insulating material.  Thermal resistance is simply how much the material resists heat or cold from penetrating through it.

You can get an idea for how efficient an insulating material is by its R-value at 1 inch thickness.  For example, cellulose's R-value at 1 inch depth is around 3.5.  Fiberglass can range from 2.5 to 3.5.  Polystyrene boards can achieve 4.0 to even 5.0, though rigid polystyrene does not make for a suitable attic insulation.

Thus, if you want an R-45 attic and plan to use cellulose, you'd want to fill to a depth of 45/3.5, or approximately 13 inches.  Using fiberglass, that would be about 15 inches.

Which Insulation Should I Use?
The good news is that it is OK to mix insulation types.  In other words, if your attic has fiberglass insulation, but you want to augment with cellulose, there is no adverse affect.  However, their is more to the choice of fiberglass vs cellulose.

I've summarized the pros and cons of the two types in the table below.

Type	R-Value	Pros	Cons
Cellulose	3.5-3.7	Less irritating to skin, throat, and eyes. Readily available. Good R-value per inch.  Dampens sound better than fiberglass.	Relatively heavy. Settles more than fiberglass.
Loose-fill Fiberglass	2.5	Light weight, naturally fire and mold resistant, doesn't settle as much as cellulose.	Very irritating to skin, eyes, and throat. Slightly worse R-value than cellulose.
Fiberglass batt	3.5	Light weight, naturally fire and mold resistant, doesn't settle as much as cellulose. Batting makes it less messy	Irritating to skin, eyes, and throat. Fits between joists, but may be tough to make fit where you need it due to chimneys, wiring, pipes, and other obstructions

Cellulose Insulation Package

For me, the choice was relatively easy.  I already had loose-fill (blow-in) insulation in the attic, so fiberglass batt was not really an option.  Installation of loose-fill cellulose seemed easiest as a DIY project.  Cellulose is readily available from Lowes and Home Depot, and it is safe to install so long as proper precaution is taken.  Lowes and Home Depot both offer free use of a blower machine if you purchase a minimum amount of insulation from them.

Stay tuned for Part II in the Attic Insulation series in which we'll look at how to install blow-in insulation, and analyze the payback and return on investment in much more depth.