Can You Spray Foam
Insulation Over Old Fiberglass Insulation?
Plenty of homeowners have decided to treat their home with
spray foam insulation, even though they already use
fiberglass. So a typical question is whether or not you
would need to remove the fiberglass insulation from your home,
or if you can simply have foam insulation sprayed over it.
The short answer is that
you can spray foam over fiberglass, but there are several
reasons why you should seriously avoid doing it.
How your insulation
deals with moisture in the home
The first thing to understand about insulation and moisture in
your home is what a "dew point" is. When you walk
outside early in the morning, there's often fresh dew on the
grass. It forms because there is water vapor in the air,
and when the temperature changes, the vapor turns into the
liquid water that gets on the grass. We call the
temperature that the change happens at the "dew point."
If you were to spray only a
thin layer of spray foam insulation over the fiberglass that
is already in your home, you wouldn't be able to keep the top
of your foam above the dew point.
Okay, so what exactly does
that mean for your home? It means that warm and moist
air that passes through the fiberglass will turn into dew on
your spray foam insulation. Then you've got moisture
trapped inside of your walls or attic, and that can lead to
mold and other problems.
When you remove fiberglass
and treat your home exclusively with spray foam insulation, it
keeps the warm and moist air from getting to the surface and
turning into dew.
Spray foam insulation
doesn't stick to fiberglass well
When you spray foam into walls or your attic, it expands and
forms an airtight seal. This keeps heat out of your
house, and keeps moisture from forming. But if you try
to spray foam over fiberglass, over time the foam will not
stick to the fiberglass. And again, you have to deal
with outside air and inside hair from your home mixing, which
leads to moisture (and mold).
So why keep is keeping
moisture out important?
When cold air from outside
of your home mixes with the warm air inside, you get moisture.
Moisture can eventually turn into mold, in both your attic and
your walls. The New York times states that mold in your
home can lead to plenty of health problems including:
If you get too much mold in
your home, removing it can cost you thousands of dollars.
So if you want to keep your home sturdy and your family
healthy, do what it takes to keep moisture from forming in
your walls and attic.
Using only spray foam
means keeping your home cooler
If you remove your
fiberglass insulation, and only use spray foam, you will keep
heat out thanks to a better R-Value. What's an R-Value?
It's just a term that is used to tell how well an insulation
keeps heat out. The higher the R-Value of an insulation,
the better it will keep heat out of your home.
The U.S. Department of Energy
website tells us that fiberglass insulation is between R-2.9 and
R-3.8 per inch, which is a bit low. But spray foam
insulation is as high as R-6.6 per inch. As you can
obviously see, spray foam works literally twice as hard to
keep heat out of your home.
As everyone knows, if you
run your air conditioner less, you're going to pay less in
electric bills every month. So if spray foam insulation
used by itself keeps your home cooler than fiberglass, or
fiberglass and only a bit of spray foam, you won't need to run
the A/C as much. Some home owners that had fiberglass
removed, and spray foam added, saved as much as 50% on their
monthly electric bills.
Spray foam insulation by
itself can be a safer choice
There's another good reason
to not spray foam over fiberglass, and it has to do with
fumes. Here's something that many people don't realize:
fiberglass is often held together by something called a resin.
That resin can release formaldehyde fumes into your home.
The problem with
formaldehyde is that if someone breathes too much of it, they
can experience problems such as asthma. The EPA even
states that the fumes may be a possible cause of cancer.
There's no need to panic,
of course. Having fiberglass in your home doesn't mean
that there's necessarily an immediate threat to your health.
But the fact remains that most fiberglass resin releases
formaldehyde fumes over time. Spray foam insulation
doesn't, though. So when some people decide to make a
choice between some fumes and no fumes, it's not surprising
that they choose to only use spray foam as an insulation.
So should you spray foam
over fiberglass or not?
Obviously, you can spray
foam insulation over fiberglass. But based on everything
that you've just read, you should understand the benefits of
using only spray foam, rather than trying to use both
We're Advanced Foam
Insulation of Louisiana. We specialize in treating homes
with spray foam. If you live in
Louisiana and would like to get a free estimate, please call us
today or click here to
reach us by email.