Insulation: Answers to your questions
The purpose of insulation is to keep warm air out and cool air in during
warm weather, and cool air out and warm air in during cold weather.
It plays an role in keeping your home energy-efficient, but it's easy to take for granted.
Below are answers to some frequently asked questions about insulation.
Please select a category from the list at the left.
Attics
Q: Do you know how many inches of blown-in insulation should be in an
attic in order to qualify for a R-30 rating? And what about the pink rolled insulation
in the walls? Walls should be R-15, right?
A: The depth of insulation required to produce a R-30 depends
on the type of insulation. Blown-in fiberglass will have about R-2.25 per inch,
blown-in cellulose has about R-3.5 per inch and fiberglass batt has about R-3 per
inch. In case you're not sure what type you have, fiberglass insulation looks like
cotton candy, while cellulose looks likes ground-up newspaper.
SRP recommends a minimum of R-30 in the attic and the thickness of the walls will
pretty much dictate what level of insulation can be installed. Two-by-four walls will
typically have R-13 fiberglass batt installed, while 2x6 walls will have R-19.
Q: I'm debating whether to add insulation to my attic. My house was built
in the early 1970s and is a concrete block home of about 1,300 sq. ft. The concrete
block walls are not insulated and do not have drywall on the inside of them. Due to the age of the house and
construction of the walls, would extra ceiling insulation be beneficial?
A: Yes, additional insulation would help reduce air conditioning costs while
increasing the comfort level inside. Homes built in the 1970s typically had R-19 or R-22 attic
insulation. Over time, these levels would be reduced due to settling of the materials.
Increasing the insulation level to R-30 can save you $50 to $60 a year on heating and
cooling costs. Moreover, it can reduce "hot spots" within your house, allowing for a more
even and comfortable temperature.
Q: I heard that homes in the Phoenix area should have attic insulation of R-49.
Do you agree? I currently have an R-38.
A: Within reason, the more insulation you have in your
attic, the better-off you'll be. However, the question is when does the cost of the
added insulation outweigh the benefits of the energy savings? Unless you are able to get a super deal on the
installation of the added insulation, the payback period for the retrofit could be lengthy.
Q: How much will I save by upgrading my ceiling insulation from R-30 to R-38?
I have a two-story, 4,400 sq. ft. home.
A: Since only about 6% to 8% of the heat that enters your house
during the summer comes in through the ceiling, any savings associated with increasing
your insulation value will be minimal. For a 4,400-square-foot home, you're probably
looking at $40 to $50 in annual savings.
Q: I am thinking about using cellulose insulation. What can you tell me
about it? Weren't there some problems with cellulose? How does it compare to
fiberglass?
A: Cellulose has been around for many years and is an excellent
insulation product. It has a high R-value per inch of material and is well suited for
blown-in attic applications and wet-blown wall installations. Blown-in cellulose has an
R-value of about R-3.5 per inch compared to R-2.25 per inch for fiberglass. This means
you can put R-30 cellulose insulation in about a nine-inch space, whereas it would take
a 13-inch space to get an R-30 rating with fiberglass.
Most early problems with cellulose have been resolved. There were concerns about the
lasting effect of the flame retardant applied to the material. Improved formulations and
field testing show that cellulose insulation is safe and does not present a fire hazard.
Another problem was that rodents used to like to nest in the material, but pesticides
have been added to the material to eliminate this problem.
The one problem that does remain with cellulose insulation is settling. Because it is
heavier than fiberglass, it does have a tendency to settle and as it does, it loses
some of its insulation effectiveness. While this is not a big problem, it points to
one other issue: If you have blown-in fiberglass insulation currently in your attic,
you do not want to install cellulose on top. The weight of the cellulose will compress
the fiberglass, reducing its effectiveness.
Q: We have a two-car garage that faces west. We're thinking of i
nsulating the attic above the garage. Would you recommend this, and can it
be done by a do-it-yourselfer?
A: Because the garage space itself is not heated or cooled,
it makes little economic sense to spend the money on insulation. However, it can
make a lot of sense in terms of comfort. Insulating a west-facing garage door can
dramatically reduce the heat buildup in the garage.
The easiest way to insulate the door is to adhere rigid board insulation to the interior
surface with construction adhesive.
If you have access to the attic space above the garage, you can roll out batt insulation.
If you're going to go to the effort of insulating the garage attic, I'd recommend you install
R-30 batt. If you decide to use a contractor they can either install batt or blown-in insulation.
Q: My 1,500 sq. ft. house was built in 1952. It has large windows, an evaporative cooler
and one turbine vent on the roof. It is always warm in summer and cold in winter. I've looked into
energy-efficient windows, vinyl siding and considered having the masonry walls insulated with foam.
How can I tell which is the best approach?
A: From the description you provided, many different things can be happening
that would make your home uncomfortable. Block homes of the 1950s typically were not highly
insulated (R-11 to R-19 in the attic and R-0 to R-8 in the walls) and either contained single-pane
aluminum or single-pane steel casement windows.
Also, because the house was built for evaporative cooling, little attention was given to making
sure that the duct system in the attic was properly sealed and insulated.
I recommend that you hire a home energy auditor to come out to the house and perform a
thorough home energy audit. It will identify the areas in your home that need efficiency
upgrades and give you an idea of what the upgrades will cost. You'll also find out what
impacts they will have on your comfort and how much energy and money they will save.
An in-home audit of this type will cost $100 to $200 depending on how detailed the audit is
and how long it takes to complete.
Q: It seems like my 30-year-old house uses more and more electricity every year.
Is it just getting hotter and hotter, or do I need to reinsulate? Does SRP who makes on-site
energy evaluations?
A: If your home still has its original insulation, it probably makes sense to
add more. Thirty years ago, not all homes were insulated with R-30 insulation and even those
that were will have insulation that has settled over the years, reducing its effectiveness.
To get an idea of how much insulation you have, stick your head up in the attic and take a
measurement. Blown-in fiberglass will have an R-value of 2.25 per inch, fiberglass batt is
about R-3 per inch and cellulose is about R-3.5 per inch. To tell what you have, fiberglass
looks like cotton candy, while cellulose looks likes ground-up newspaper. SRP recommends
a minimum of R-30.
SRP does not conduct in-home energy audits. I recommend calling the Energy Management
Council of the Electric League of Arizona for a referral.
Q: I have mobile home with R-22 in the ceiling. I had two-inch foam
insulation installed over asphalt shingles. There is still a 10-inch gap of air space between
the ceiling insulation and the bottom of the roof. Now I'm wondering if I gained anything
with the foam roof because I feel hot air coming out of the small air vents at each end of
the house. Would it make sense to blowing loose insulation into that 10-inch space to
prevent hot air from collecting there?
A: The rigid foam insulation that you had installed over your exterior
roofing is not doing much in the way of lowering the amount of heat entering your home
through the ceiling. While it's probably true that the foam is reducing the temperature in
your 10-inch attic space it, is certainly not reducing it enough to bring the temperature
down dramatically -- as you noticed by the hot air coming out of the small vent holes.
However, by filling the remaining 10-inch air space with blown-in insulation and capping
off the vents you should be able to dramatically improve the efficiency of your mobile home.
Q: My current home has R-24 insulation in the walls and R-40 in the ceiling.
I am buying a new house that has only R-17 in the walls and R-30 in the ceiling. Is
this adequate? When I asked my builder, they said they did a study and found out
that a 2x6 construction and R-19 wall insulation isn't worth the additional cost in
hot weather climates. It's more important in cold-weather environments. Is this
the truth or hogwash?
A: Your builder is not just blowing smoke. When you look at all
the areas of your home where heat enters during the summer only about 8% comes in
through the ceiling and 20% through the walls and doors. What this means is that by
spending the extra money to increase the attic insulation by 30%, you're actually only
reducing the heat gain by 2.5% (30% of 8%). The same holds true with the wall insulation.
That said, R-40 is better than R-30, and 2x6 framing with R-24 insulation is better than R-17.
The savings however are small compared to the investment - R-30 to R-40 offers $30 to $35
per year savings, compared to $35 to $40 for R-17 to R-24.
Q: My home is nearly 30 years old and has wood with siding. I am considering
adding one-inch foam and stucco for added insulation. This foam has an R-4 value.
Is there any way to calculate the energy and money savings by adding this?
A: It is tough to say for certain because there are so many variables
that enter into the picture. In a typical home, about 20% of all the heat that enters the
home in the summer comes in through the walls and doors. So even if you were to cut the
gain through the wall by half, you would only be reducing the total air conditioner load by
10% (by multiplying 50% by 20%).
Homes built in the mid-1970s typically have a total wall R-value of about R-13. By adding
R-4 insulation and stucco, you will probably bring the R-value up to R-19. Going from an
R-13 to an R-19 is an improvement of about 30%, so overall air conditioning savings can
be in the range of 6% to 7%.
If you subtract your March bill from your June electric bill, the remainder will be an estimate
of how much it costs to run your air conditioner for that month (or a heating estimate if you
subtract March from a winter month). If you multiply this number by 6% or 7%, you'll get a
savings estimate for that month. Do this for each month and you'll end up with a yearly
estimate.
Q: We are building a new home that has R-19 in the walls and R-38 in the ceiling.
It has 2x4 construction with stucco siding, sheet rock interior and a tile roof. It has a 12 SEER
heating system. We will have fans in every room. Will an upgrade to R-21 help save energy?
A: The quick and easy answer to your question is no. The estimated
savings associated with going from R-19 to R-21 is less than $25 a year. However, an
investment that will help you save energy is window shading.
About 45% of the heat entering your home in the summer comes in through the glass --
this means that almost half of the heat that your air conditioner has to remove comes in
through your windows. A few dollars spent making sure that your windows are properly
shaded can save you big dollars on air conditioning. Even if you have dual-pane glass,
make sure that you provide some form of exterior shading on all sun-struck windows.
Q: I am wondering about insulating the attic of my 40-year-old home.
I've heard about a company that installs a radiant barrier made of chips of metallic-type
material. What do you know about this material? What are the differences of blown-in
fiberglass, cellulose, foam, etc? I would like at least an R-38 rating. Right now I have
a thin layer of fiberglass up there.
A: Studies conducted by
Oak Ridge National Laboratory
have shown that radiant barriers can reduce the summer ceiling heat gain. However, the
effectiveness of the barrier decreases as the amount of attic insulation increases. This is
because the insulation laid on top of the barrier will do the lion's share of preventing heat gain.
Another factor to consider is that as a typical attic-floor radiant barrier gets dusty, its effectiveness
declines.
The Oak Ridge study shows that radiant barriers can reduce the heat gain through a
ceiling during summer in an attic insulated with R-19 by as much as 16% to 42%. However,
when you consider that ceiling heat gain accounts for only 15% to 25% of your total
cooling load, the air conditioning savings associated with the radiant barrier is somewhere
around 2% to 10%.
To estimate how much you might save by installing a radiant barrier, subtract your
March SRP bill from your June bill (what's left is roughly the cost to run your air conditioner)
and multiply it by 2% to 10%. Do this for each month of the summer and you will have an
estimate of how much you'll be saving on air conditioning for the entire summer.
The difference in insulating materials doesn't really matter; however, blown-in products
usually leave fewer gaps between the studs and wiring, providing better insulating performance.
What you're looking for is the R-value.
Q: How effective are reflective coatings? I've read about one that is a thin
layer of R-20 ceramic coating that dries to a thin layer and is supposed to have
insulation properties equal to seven inches of fiberglass batting. The manufacturer
claims it will reduce utility bills up to 40%. How effective are products like these?
A: Reflective coatings -- which range purely reflective paints to
ceramic-formulated products to radiant barriers -- have been around for some time.
While each product has its own list of benefits, their overall benefit in utility savings is
typically overstated.
Let's take for example the claim of 40% savings in utility bills. Heating and cooling typically
account for 50% to 60% of an annual utility bill. So, if you reduce the amount of heat that
enters a house by half by applying the coating to the walls (half of the 20% of the heat
that comes in through walls and doors), then you would be reducing the heating and
cooling load by 10% (.5% x 10%) which would reduce the heating and cooling cost by
about 6% (10% x 60%). This would equate to a reduction of only 4% in annual utility costs.
Q: We have a flat roof on an 1,864 sq. ft. house. Is it more economical to have a
foam roof or an asphalt built-up roof?
A: If applied correctly, a foam roof will give you higher insulating
values than a typical asphalt roof. Also the finish coating on a foam roof usually provides
greater reflectance so you get the benefits of both resistance to heat transfer with
higher R-values and better heat rejection through decreased heat absorption.