Not sure which foam attic insulation to choose… open- or closed-cell? One builder is using both and saving money in the process. To understand the reasoning behind his decision, let’s begin with the benefits of a sealed, foam-insulated attic and move onto the open / closed-cell argument. There are several benefits to a sealed, foam-insulated attic:

* Energy Efficiency: Estimates as high as a 50% energy savings have been noted by incorporating a sealed, foam-insulated attic into a tightly built residential structure. The normal vented attic, with traditional blow-in or batt insulation on the floor, can easily reach temperatures of 140 degrees in the summer and freezing temperatures in the winter.

One inch layer of closed-cell foam

Now imagine the energy loss that occurs when ductwork runs through this unconditioned space. Think about how much of the conditioned air temperature is lost as it travels through the ductwork to its destination. In addition to the cooled or heated air losing its conditioned temperature, the hot air that’s formed in the ductwork is blown into the room first each time the air conditioner comes on in the summer, and vise-a-versa during the winter.

Because a foam-insulated, sealed attic maintains a temperature of only about 10 degrees difference from the conditioned living space, the entire home maintains a more even temperature. In addition, HVAC equipment and duct systems can be housed in semi-conditioned attic space – a much more energy-efficient scenario. A better insulated house and an HVAC system operating more efficiently are big contributors to energy savings. Further savings are achieved through the use of a smaller sized (tonnage) air handler. Because an efficient HVAC system doesn’t have to work as hard, the size of the air handler MUST be reduced accordingly.

Three inch layer of open-cell foam covering 1 inch of closed-cell

* Added strength: According to testing performed by the University of Florida, a 3 inch layer of closed-cell foam provides nearly a 300% increase in roof uplift resistance compared to traditional framing methods. See Green Builder Magazine, page 47, for more information on the testing methods and results,

* Home Insurance Discount: Your insurance company may offer a discount for the use of closed-cell foam in the attic, particularly if you are located in a hurricane-prone area of the country. According to one of the foam companies in my area (central Florida), it is best to contact the insurance company headquarters, as opposed to your local representative, to inquire about the discount.

* Reduction in Critter Intrusion: Because ridge or off-ridge vents and vented soffits are eliminated in a sealed attic, the opportunity for invasion by unwanted furry guests is significantly reduced. If you live in any of the states that deal with drywood termites, a sealed attic also impedes infestation by these flying pests. See my article entitled, Is Your Brand New Roof an Invitation to Furry Guests, Detailed Solutions Ezine Archives.

The Closed-Cell / Open-Cell Argument: When discussing foam insulation, you will hear the terms “open-cell” or “closed-cell.” Here’s a brief description of the differences:

Closed-Cell Foam: Because closed-cell foam insulation is rigid and dense (1.7–2.0 pounds per cubic foot), it acts like glue, which adds strength to the structure. Because it is watertight, it provides a vapor barrier in addition to a thermal and air barrier. Some builders prefer this product because a roof leak is encapsulated in the foam. The concept here is that the roof decking will be damaged but the leak won’t find its way into the home. Closed-cell foam is generally more expensive than open-cell.

Open-Cell Foam: The fans of open-cell insulation prefer this product because the source of a leak can be more easily determined. Because open-cell is not a vapor barrier, water runs through it. Open-cell is softer, less dense (1/2 pound per cubic foot), and more permeable. It also has a greater ability to contract and expand with the decking. You’ll hear arguments for both types. The bottom line is that each has desirable properties and each is used successfully in a variety of applications across the country.

Combining the Best of Both Worlds: One of the homes I’m green certifying is actually incorporating both open- and closed-cell foams into the attic. The builder has achieved the best of both worlds and saved money in the process. First, the attic was sprayed with 1 inch of closed-cell (providing a vapor barrier and added strength to the roof) and then topped with a 3 1/2 inch layer of open-cell foam. This combo was less expensive by about 50 cents per square foot than using a 3 1/2 inch layer of closed-cell alone. This savings is not always the case. Check with your supplier on pricing.

Should open-cell foam have been used by itself, a 5 1/2 inch layer would have been needed to achieve the required air barrier.  Exclusive use of closed-cell foam would have required a thickness of 3 1/2 inches. Icynene was the foam used in this house.The thickness needed to form an air barrier varies between foam insulation products.

As always, The Difference is in The Details.

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Here are a couple areas of your home that can easily become energy-wasting “holes” simply because of construction timing. Here’s where and why:

Why is it common for the exterior wall behind the tub to never see insulation or drywall? Because bathtubs are installed before these two products are needed in the rest of the house. As you can see from the picture on the left, there is no way to install insulation and drywall once the tub is in place. The thermal image taken in the winter on the left shows the result of this common practice. The purple color indicates cold air. The homeowners are going to wonder why their bathroom is so chilly in the winter.

Courtesy of Energy Star

The exterior wall behind a fireplace can also be left out of the insulation picture. The photo on the left  below shows how an air barrier (drywall) has been installed over insulation behind this corner fireplace. The rest of the house is not ready for insulation or drywall but this builder’s schedule included a separate timetable for the installation of of these two products behind tubs and fireplaces.

The thermal image on the right, taken in the winter, shows the result of an uninsulated exterior wall behind the fireplace.  The purple indicates a temperature in the 50′s compared to the warm insulated walls on either side of the fireplace. Can you see why missing insulation is like having a hole in your home? I wouldn’t want to pay the energy bills for this house.

Courtesy of Building Science Corp and Energy Star

Fortunately you can avoid insulation “holes” in your new home by including an insulation inspection during the construction process. The building code in your state may require an insulation inspection but remember the inspectors are only empowered to enforce the code requirements. Building code is the lowest level of construction acceptable in your area.

Thorough and proper installation of insulation is a requirement of an Energy Star-certified home via their Thermal Enclosure Inspection. Green-certified homes can also include an insulation assessment. These programs are designed to exceed building code requirements.

Not building a green- or Energy Star-certified home. No worries, a Thermal Enclosure Inspection is available to anyone building or remodeling. This process is performed by a HERS (Home Energy Rating System) Rater. You can find a list of HERS Raters in your state through the Energy Star Site.

Let your builder know that you’d like to include a Thermal Enclosure Inspection so that he/she can add it to their cost and the construction schedule. Because the examples of overlooked insulation discussed in this blog are just two of many insulation and sealing requirements included in the Thermal Enclosure Inspection, your builder will want to review both the checklist and the pictorial guidebook explaining the details. Both can be accessed on the Energy Star Site.

 

 

 

 

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