Jennifer Davis, author of this blog, has over 25 years experience in the residential design and construction industry. With nearly 800 projects completed in her career so far, Jennifer provides expert tips, advice and commentary about the residential construction trades.
Please visit her website at: www.jddesigns.net
How much do I need and how do I
know if I have enough?
The most important
factor in effective insulation is to create an “envelope” which includes floor,
walls and ceiling areas. In order of importance; #1 the ceiling, #2the floor
and last #3 are the walls. If
one of these areas is under insulated or not insulated, the effectiveness of
the envelope system is breached.
Most people overlook the floor as a critical
space to insulate properly. Cold air is dense and warm air is lighter, therefore
cold air comes up through the floor and pushes out the warmer air through the ceiling
and out of the building.
is measured in an “R-value”. The R refers to the amount of thermal
resistance in the material. The bigger the number, the more (or higher)
insulative properties it has. Bigger is better here.
of insulation (R-Value) depends on the climate zone of where you live. Click here
to view the recommended Energy Star map of which you can then determine your
climate zone. These R-values are a minimum and can always be increased as you
so desire and as space allows.
of insulation are available?
generally 4 types of insulation:
(fluffy blanket type)
BATTS are the most common. These are
usually fiberglass batts that are rolled out like a blanket, are flexible and
can be installed in all 3 building surfaces (walls, floor, and ceiling). This
is also the most cost effective.
RIGID FOAM boards are dense and typically used
in cases where you need a higher R-value and very little space to do it in. For
example; on a vaulted ceiling you may need an R-38 and have a 2x10 rafter to
work with. A fiberglass batt of R-38 will be approximately 12” thick and a 2x10
is actually 9” deep. You are now 3” short of your goal. TIP: You should never
compress a fiberglass batt into a smaller space as you will reduce the R-value
that it is designed for. Rigid foam is more expensive than batts and requires
more labor to install. If installing between framing members, every piece must
be cut individually.
BLOWN-IN insulation is on the lower end of the
cost spectrum, similar to batts, and can be cost effective if installed in an
open attic area in terms of labor. However, because of the nature of the
application, the material can shift or compress over time and become uneven in
open spaces (attics) and slide down wall cavities resulting in a reduced
R-value. It is also really annoying if you have to dig through gobs of the
stuff to service something in your attic and breathe the resulting dust fibers
as well as being terribly itchy. For obvious reasons, it cannot be installed in
raised wood floor applications.
EXPANDING FOAM is a product that must be
installed/applied by a professional. It is NOT a DIY kind of project. This is a
newer type of material that starts out being a liquid and when it hits the air,
it expands and hardens in place. It typically has a much higher R-value per
inch than most other types of insulation because of its density. It is similar
to the cans of spray foam that you use to seal cracks, but applied on a much
larger scale. It is the most expensive material on the market by far. However,
it has advantages such as sealing the entire space (wall/ceiling/floor cavity) and
no drafts or critters. Some products are approved for use in non-ventilated
areas such as vaulted ceilings (or cantilevered floors) and therefor you are
not required to provide a 1” air gap between insulation and roof sheathing, giving
you a higher R-value in the end. Products that are “closed-cell” are minimal
expanding and won’t damage your framing if over applied.
some disadvantages of expanding foam insulation. It is flammable and will
release deadly, toxic fumes when it burns. If you read the manufacturer’s fine
print, it cannot be left exposed and it must be covered with a fire rated
material such as ½” cement or fire rated gypsum board. Some forms of this
insulation even contain hazardous chemicals that can cause you to suffer from
lung cancer or skin-related problems. Check with the vendor of the product for
compliance with LEEDS and low VOC content.