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Increase Attic Insulation To Lower A/C Costs

Should I Add Attic Insulation To Lower Air Conditioning Costs?

Which Is Better?  Adding Insulation To The Attic Floor — Or To The Attic Ceiling.

thermo-image of attic temperature

This Thermo-Image shows the attic temperature at 170 degrees.

In DFW, we are aware attics get very hot in summer.  The thermo-image above shows the house’s attic to be 170 degrees.   A post (from a home inspector) said Dallas attic temperatures of 160+ degrees during summer are uncommon.  With temperatures that high, attic heat is forcing itself into your home through the ceilings.  Adequate attic insulation is your first (and best) line of defense for lowering cooling bills during DFW summers.

map showing zones within U.S. for insulation values

insulation recommendations for each U.S. zone

DFW is in Climate-Zone #3.  Insulation recommendations are R-30 — R-60, that’s quite a spread.

Adding Attic Insulation

If you have an existing 4 inch batt of attic insulation, it’s R-Value = R-13.  For R-38, you need an additional 10 inches of blown fiberglass insulation (on top of the batt insulation).   R-60 requires +19 inches of blown fiberglass attic insulation (each 1 inch of blown fiberglass insulation has an average value of R-2.5).

attic batt fiberglass insulation

blown fiberglass insulation being installed over batt insulation









Batt Insulation In Attic                                        Adding Blown-In Insulation Over Batt Insulation


How Much Attic Insulation Is Enough?

graph showing diminishing returns of adding more insulation

This blue graph line (above) shows how much less heat is lost (on the left) as you add additional insulation (at the bottom).   As you add additional attic insulation, the amount of attic energy-loss reduces notably up to R-28.   At higher than R-28, additional attic insulation provides only a little additional insulating-performance.   Based on this, R-38 is enough for a DFW attic.

  • TX Building Code requires R-38 starting in Nov of 2016.
  • Energy Star recommendations are R-30–R-60.

With notable evidence that R-38 (current TX Building Code) is enough, does it make sense to add additional insulation?  The best way to determine this is to get 2 bids from your insulation contractor: R-38 and R-60.   Why?   The cost of more insulation material (during the installation) will likely be less than you think.

Lets look at the retail cost of 1 brand of attic insulation:

owens corning blown in insulation retail package

This retail package of blown insulation will cover:

  • 110 square feet of attic floor with an R-19 thickness — which requires +7.5 inches of (this particular) blown-in insulation
  • 68 square feet with an R-30 — which requires +12 inches
  • 39 square feet with an R-49 — which requires +19 inches

At the time this article was written, the retailer charged $33.00 for each package of insulation.  (And, if you buy 30 or more at one time, the price drops to $23.00 each).  So, the cost of the insulation material to increase to R-38 (remember, the existing 4″ batt provide R-13, so +10″ of blown insulation is needed for R-38.

  • To add +R-25 (+ 10 inches) of blown-insulation for a 2,000 sq. ft. (one story) home = 25 packages, or $825.00.
  • For a 2-story home, the attic is 1,000 sq. ft. — the cost for material drops to $410.00.

Once you have the insulation contractor’s bids, you can decide if you want to upgrade from R-38 (minimum TX Building Code) or add more insulation for a higher R-Value.  If you are doing the work yourself, it makes a lot of sense to add to the highest value recommended (Energy Star value) R-60.

Why would you choose to insulate above R-38?

Another Benefit Of Additional Attic Insulation — Your Home Will Be Quieter

Adding attic insulation helps to reduce the amount of noise coming into the living space through the ceilings.   It’s important to note that fiberglass insulation is not a noise blocker, it’s a noise absorber.  This means the noise you will hear will be reduced, not eliminated. **


Several Studies have been performed on “common walls” — the walls between apartments.   For one study (results below) — all walls have 2 x 4″ metal studs +  1 layer of 5/8 inch Gypsum Board (drywall) on each side.

The following STC (Sound Transmission Class) Ratings are:

Insulation:               STC Rating *    (The Higher The STC Rating, the less noise passes through).

  • No insulation           38
  • Fiberglass                 49  — the STC rating improves +9 with 4 inches of fiberglass batt insulation added
  • Mineral fiber            47
  • Cellulose (spray)     45


While the STC of blown-in insulation may vary (because it’s not as tightly packed as batt insulation), this study demonstrates that fiberglass insulation reduces the amount of noise passing through a wall, or ceiling.   For R-38 attic insulation, typically a 4″ batt of insulation + 10″ of blown insulation are used.

Insulating The Attic Ceiling For Lower Attic Temperature

There are many schools of thought regarding insulating the attic ceiling.  There is no argument the attic will be notably cooler, but there are concerns about moisture or water becoming trapped within the insulation material — causing the roof deck to rot (roof deck is what the shingles are nailed to).   Additionally, Spray-Foam Insulation creates a tremendous Fire-Hazard if not property covered with an Ignition (fire) Barrier.

home under construction during the framing phase

home under construction before shingles are installed

home under construction with shingles installed








Homes Under Construction:  Before Roof Deck           (wood) Roof Deck Installed, no shingles yet                                      Shingles Installed

Insulating The Attic Ceiling (underneath side of roof deck) –The Good News:

Insulating the underneath side of your roof deck can help reduce attic temperature.  Since most DFW homes have the furnace, air conditioner’s cooling coil, and ductwork in the attic, this allows the a/c and furnace to perform more efficiently because the attic temperature is notably lower.  

Insulating The Attic Ceiling (underneath side of roof deck) — The (possible) Bad News:

Moisture coming in from a leaking roof AND / OR  moisture in the air (leaking into the attic from inside the home) can possibly get trapped and cause water or moisture damage to your roof deck (what the shingles are nailed to).

There are many opinions about using Open-Cell or Closed-Cell Spray Foam on the Underneath of your roof deck.  If you insulate your attic ceiling, the overwhelming advice is to use Closed-Cell Spray Foam.  We explain why below the photo.

spray foam open cell and closed cell

  Note: Open-Cell Foam on the left.  Closed-Cell Foam on the right.

Open-Cell Versus Closed-Cell Foam:   What’s the Difference?

  • With Open-cell foam, the air-bubbles are broken.  The prevailing opinion is that open cells can hold moisture or water.
  • With Closed-cell foam, the air-bubbles are unbroken.  These closed cells cannot hold water.
  • Open-cell foam is not a vapor barrier.  When subjected to a standardized test, Open-Cell foam absorbed up 34% of its volume in water after 96 hours of submersion.
  • Closed-cell foam can be an effective vapor barrier.  *

* Source:


 During A Fire, Exposed Spray-Foam Insulation Accelerates Existing Flames.

When exposed to a fire, Spray-Foam Insulation Creates Huge Amounts Of  Combustible Smoke.

  Spray-Foam Insulation requires a Thermal-Barrier or Ignition-Barrier to cover it (depending on where the foam insulation is located).

According to the:

  • International Building Code (IBC 2603.4)
  • International Residential Code (IRC R316.4)

“All foam insulation must be separated from the interior of the building by an approved 15-minute THERMAL-Barrier”.

  • A thermal barrier separates occupied (living) space from the foam insulation, to delay or prevent the foam’s involvement in a fire
  • A 15-Minute Thermal Barrier means the barrier must withstand a fire for a minimum of 15 minutes.
  • Ceilings and walls constructed with 1/2″ drywall typically provide the required THERMAL Barrier.


If a home has spray foam insulation in an attic or crawl space, Building Code requires an IGNITION-Barrier in these locations.  Ignition Barriers are constructed using materials that offer some fire-resistance (though not as much as is required for a THERMAL Barrier).

These 6 materials are approved as Ignition-Barriers by the International Building Code & International Residential Code (local Building Code dictates what you can use):

  • 3/8″ drywall   (1/2″ drywall is required for a Thermal-Barrier)
  • 1.5″ mineral fiber insulation  (mineral fiber is high-density, non-combustible insulation made of inorganic fibers).  
  • 1/4″ wood
  • 3/8″ particleboard
  • 1/4″ hardboard
  • 0.016″ corrosion-resistant steel



What Happens When The Ignition-Barrier Is Missing Or Breached?

In May of 2012, Spray-Foam Insulation accelerated a fire in this residential high-rise building in France, leaving 94 homes uninhabitable plus causing 10 injuries and 1 death.

france fire in building with foam insulation and no ignition barrier



This YouTube Video shows how quickly spray-foam insulation accelerates a fire:Spray Foam Insulation Accelerating A Fire.

The video shows the rate the fire spreads, and (at what point in time) “flashover” ** occurs (fire engulfs the area).  This test-data below clearly demonstrates that exposed spray-foam creates a deadly fire-hazard.  This is why most Building Codes require spray-foam must be covered.

This test in the video was 3 parts:

  • no insulation in wall                             Flashover ** occured at  7 minutes & 18 seconds
  • sprayed cellulose insulation *             Flashover ** never occurred
  • exposed sprayed foam insulation       Flashover ** occured at 44 seconds!

* Cellulose is composed of 75-85% recycled paper fiber. The other 15% is a fire retardant.

** Flashover is the near-simultaneous ignition of nearly all exposed combustible-materials within an enclosed area.

Alternatives to using Spray-Foam Insulation In Your Attic

This article describes 2 potential risks when using Spray-Foam Insulation on your attic ceiling.  The most accepted solution (for each risk) is also presented:

  • Moisture:  Use Closed-Cell Spray Foam
  • Fire Hazard:  Cover all exposed Spray Foam Insulation with a fire-retarding product.  In most cases, Building Codes will dictate the fire-retarding product(s) that can be used.


Before installing Spray-Foam Insulation, you must ensure you will be in compliance with all Building Codes.    If you are not comfortable with the risks of adding Spray-Foam Insulation to your attic, there are other options.  The options shown below will be less effective (the spray foam) in lowering attic temperature.

Attic-Temperature Lowering Solutions Other Than Spray-Foam Insulation

1. Choose Energy Star Rated Roof Shingles

energy star rated roof shingles

This Marketing Verbiage is found on a website of a major shingle manufacturer for their Cool Series Shingles (a Google search will help you find it): **

Traditionally, only shingles with white granules have been considered “cool” by energy-saving standards.  Not any more.  Thanks to our cool shingle using special cool granules, our shingles are highly reflective.

These special granules reflect light to lower the roof temperature, which lowers attic temperature.  According to the Cool Roof Rating Council, Cool Roofs can save an average of 7-15% on cooling costs using a cool (Energy Star) rated shingle.

NOTE: Al’s Plumbing, Heating and A/C does not sell or install roof shingles.  Al’s does not endorse any specific roof shingle.

2. Choose the lightest shingle color which works with your home’s colors.

Compare wearing a black shirt (in the sun) to an ivory shirt.  The lighter colored shirt will feel much cooler.  This same color-principle works with shingle color and attic temperature.  When you replace your roof, choose the lightest shingle color that compliments the home.

A study by the  U. S. Department of Agriculture (USDA) found roof deck wood under black shingles was 10-15 degrees warmer than the same panels under white shingles on a sunny day.

3. Add a Foil Radiant-Heat Barrier (stapled to the roofing beams in your attic).


a foil radiant heat barrier during installation

You may have noticed foil-surfaced sun-shades at the windshields of cars.  In the attic, Radiant-Heat Barriers work similarly to a car’s sun-shade (reflecting the sun’s heat outward).  Like car sun-shades, radiant barriers are effective at cooling attic temperatures & reducing cooling costs.  Radiant barriers are installed in homes to reduce summer heat gain and winter heat loss, helping to lower heating and cooling costs. The barriers consist of a highly reflective material that reflects radiant heat rather than absorbing it.

The sun’s radiant-energy makes the roof hot, and most of this heat travels into attic.  A radiant barrier reduces the radiant heat transfer into the attic.  A foil radiant-barrier will lower attic temp by -24 degrees from the temperature of the roof outside.   Your attic insulation will reduce the heat by another -25 degrees at the ceiling.  The (no a/c) temperature of the room will be 85 degrees.  The DOE says radiant barriers can reduce cooling costs by 5% – 10% in a warm, sunny climates (like DFW). *

A foil radiant heat-barrier is installed with an open area at the top and bottom.  This allows the heated air to move upward, while cooler air enters at the attic floor.  Then, the attic’s ventilation system removes the heat, rather than having the heat radiate deeply into the attic.  The radiant-heat barrier + attic-ventilation work together to keep much of the sun’s (radiant) heat from entering deeply into the attic, and reaching the attic floor (the ceilings to the rooms inside the home).   Coupling this system, at the attic ceiling, with adequate to ample insulation at the attic floor, and you have a highly energy-efficient solution.

All foil radiant-barriers have an emittance rate (heat passing through the foil) of 1% or less.  In contrast, radiant-paint emits (allows) 25% of the heat into the attic, so paint is not as effective as foil.   Radiant-barrier paint products are not true radiant barriers according to the US Department of Energy (DOE).

* Source:

NOTE: Al’s Plumbing, Heating and A/C does not sell or install Radiant-Heat Barriers.

benefit of radiant heat barrier

A Foil Radiant-Barrier will reduce attic temp by as much as 24 degrees lower than the roof shingles.

Foil radiant heat barrier performance photo

This shows the effect of a Foil Radiant-Heat Barrier laid on top of insulation.  NOTE:  This is not a correct or acceptable way to install the barrier in the attic (see photo above).


SUMMARY:  The attic is the largest area of your home for gaining heat into the living spaces.   This article gave many details about adding insulation to your attic’s floor or ceiling.

Additionally, this article describes potential risks caused by insulating the attic’s ceiling with Spray-Foam Insulation.   Other than Closed-Cell Foam Insulation, there are no other types of insulation that can be used on the attic ceiling, due to the possibility of water or moisture collecting within the insulation material.

The article goes on to describe other ways to reduce the amount of (solar) radiant-heat entering the attic.   3 options were discussed: Energy Star Rated Shingles, lighter shingle colors, and Foil Radiant-Heat Barrier — which blocks the radiant-heat from entering deeply into the attic.  Instead it moves the heat upward to where the attic’s ventilation system can remove it.

As stated at the beginning of this article, attic (floor) insulation provides the best line of defense against summer heat coming into your home and winter heat escaping your home.  Additionally, there are several options for further reducing the attic temperature (and the amount of heat forcing itself into your home through the ceilings.

thermal image of missing attic insulation

The photo above shows the amount of heat at the ceiling (due to missing insulation).  The bright yellow is hot drywall above the cooler (purple) surfaces within the room.  Also the yellow (hot) ceiling on the right side of the photo (insulation missing) compared to the purple (cool) ceiling on the left side of the photo.

This example can also demonstrate the effects of different thicknesses of insulation.   Up to R-28, each inch of additional insulation has notable effect on heat loss or gain.  Above R-28, the amount of additional heat lost /gain drops off with more insulation.  TX Building Code requires R-38 insulation at the ceilings.   This article describes the benefits of adding insulation above the R-38 level (reduced noise and some additional insulating-performance).

The article went into great detail about one major aspect of cooling costs.   We also have an article describing 55 Ways To Reduce Cooling Costs Without Replacing Your A/C.  You can access that article from our Blog Section, or click on this link: 55 Ways To Lower Cooling Costs WITHOUT Buying new A/C.   We also have an article discussing the Nest Smart Thermostat, and the savings you can realize from having one in your home.  See that article in our Blog Section, or click on this link: Nest Smart Thermostat

5% Of Your Attic Not Covered By Insulation Drops The Overall R-Value Of Attic Insulation By 1/2!

It’s common for people working in the attic to kick insulation out of their way as they walk.   Do any required work in the attic before insulating.  After insulating, keep workers out of the attic unless it’s absolutely necessary, and check to see if they moved insulation out of their way.

ceiling temperature where no insulation is present

This room’s ceiling has reached 111 degrees where no insulation is present in the attic.


Al’s Plumbing, Heating, & A/C maintains and repairs ALL brands of HVAC Systems.  Additionally, we replace HVAC, offering Systems from American Standard, Ameristar (made by the same company as American Standard) and Coleman HVAC (made by the same company as York HVAC).   Al’s also provides Full-Service Plumbing maintenance, repairs and replacements.

Since 1989,  Al’s has served southern Denton & Collin counties, northern Dallas County & northeast Tarrant County with up to a 12 Truck Service Fleet to serve you promptly. We are locally owned & operated.  Contact Al’s today to discuss any problems or concerns you have with your HVAC System or Plumbing — we’re here to help resolve any issues you have.





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