Insulating an Attic

Determine your type of attic

If you are building a new home, skip this step

Unvented or Vented Attics?

Your attic ventilation type is quite easily determined. If there are openings in your roof assembly, such as a ridge vent at the peak of your roof, or eave or soffit vents near the lower edge of the roof, then your house has a vented attic. Often, there is older insulation such as fiberglass between the joists on the attic floor. Rather than fiberglass, there may be cellulose, which is dusty, shredded paper.

If there are no openings (other than imperfections) in the roof assembly, then you have an unvented attic.

Unvented attics are quite uncommon.

Understanding vented vs. unvented attics >

Understanding vented vs. unvented attics

Vented Attics

The very common vented attics are often aired by natural ventilation. Typically, this is accomplished by constructing vent openings near the ridge of the roof and in the overhang of the roof at the joist level. In this case, air is heated by the sun shining on the roof, which causes the air to rise. This creates a vacuum in the lower part of the attic space, which is refilled by cooler air flowing in through the eave vents. If the ceiling over the living space is not perfectly air tight, then of course also conditioned air from the living space is sucked into this vacuum, causing drastic increases in your energy bills. Natural ventilation is often enhanced by electrical fans. Many builders like this design because it is easily built at very low cost. The disadvantage: the ventilation is not sufficient for any meaningful relief. Attics across almost all climate zones are hot in the summer, an obvious indicator of a flawed design. In hot climates, the air conditioning systems are required to be oversized, causing excessive energy bills. In colder climates, this system also extracts vast amounts of energy. The conditioned air of the home is constantly exhausted into the atmosphere with little resistance.

Unvented Attics

In this method, the underside of the actual roof is insulated. There are no direct openings between the roof and the outside. This system is very energy efficient provided the roof assembly is airtight. The actual R-value of the insulation is not as important as the air-tightness of the structure. Of course, the attic space cannot just be dead space, and therefore the attic space becomes part of the conditioned space of the house. This approach saves enormous energy due to the fact that there is no continuous, uncontrolled airflow through the actual roof structure. In retrofit situations, it may be difficult to include the attic ventilation in the house ventilation.

Deciding on insulating between rafters or joists >

Deciding on insulating between rafters or joists

Remodelers: Please read about both options

New construction: we recommend you skip to option 2, unvented design

Option One

The attic is vented, and it is not feasible to include the attic ventilation in the conditioned space of the home

This option offers nearly the same energy and comfort benefits as the unvented attic. In this scenario, it is absolutely critical that the deck between the joists is completely airtight. We already know that only spray-in-place foam insulation can accomplish perfect air-tightness. In this design, the space between the joists is sprayed with a continuous layer of foam. If the joists are not deep enough, it may be necessary to “bury” them in the foam. In this scenario, it is recommended that you install wood planks or similar options to provide a walkway, in case mechanical equipment or other items require service. The disadvantage of this option is that the attic space is not conditioned and is not convertible to living space. Due to the extraordinary heat accumulation in the attic, conventional insulation such as fiberglass or cellulose is not an option, as these provide no air seal, and also greatly increase the mold risk. In case of existing homes, we strongly recommend the complete removal of installed fiberglass or cellulose before installing foam. Implications for ducts run through the attic are discussed next.

Option Two

The attic is vented, and it is feasible to include the attic ventilation in the conditioned space of the home

In this case, you are ready to enjoy extraordinary comfort combined with excellent energy efficiency. The entire roofline, including all openings, is foamed with E:zero insulation foam for a complete air seal. To avoid condensation problems, it is very important that there is no air between roof assembly and insulation material. Only spray foam insulation can achieve this, as it forms a fully adhered, completely bonded and continuous layer of material on the underside of the actual roofline. On the side facing outside, the foam layer will be of the same temperature as the roof assembly. On the inside, the temperature is the same as that of the living space. Not only is the temperature very gradual between the inside and outside of the foam block, there is no air or airborne moisture between the inside and outside. Accordingly, there is virtually no condensation and no related mold risk. As a bonus, in this scenario the attic space can be converted into living space without spending any additional money on heating or cooling the newly gained living space. The impact of ducts installed in the attic is described in a separate section below.

Continue to Implications for Duct Works in the Attic >

Implications for Duct Works in the Attic

Option One: Unvented Attic

In this situation, the ducts need no insulation from a thermal perspective, since they run exclusively inside conditioned space. Nonetheless, ducts are very often not as airtight as desired, and thus it may make perfect sense to spray a thin layer of spray foam on the ducts and especially duct joints, to ensure delivery of all the air the entire way to the destination. Ducts are said to lose about 30% to 50% of the transported air before reaching the destination. With a complete cover of foam, that loss is eliminated.

Option Two: Vented Attic

In this scenario, ducts need to be foamed for multiple reasons:

• For thermal performance. Typical fiberglass duct insulation is only R-4.2, which is definitely not enough, especially since the ducts are not air tight.
• For air flow considerations. Ducts lose more than 30% of all air before reaching the destination; however, if they’re sealed with foam, that loss is cut to nothing.
• For mold prevention reasons. Ducts insulated with fiberglass are notorious for condensation and related mold issues. It is critical that you remove fiberglass from the ducts and replace it with foam.
• For health reasons. Our breathing air runs through the ducts insulated with fiberglass. Since they are leaky, air will not only go out, but fibers will also go into the ducts. These will then be blown into our living space, posing serious health risks. The installers wear masks, but not the occupants of the house.

Continue to Selecting your preferred E:zero spray foam >

Select your preferred E:zero spray foam

Vapor barrier required?

Vapor barriers are required in many communities, especially when there is continuous vapor drive in one direction. This may be a result of extreme climatic conditions, where the home is almost always heated or air conditioned. -> Recommendation E:2000 vapor barrier spray foam

High R-Value required? Budget concerns?

In these cases, low-density E:500 soft foam may be the best option. E:500 is considered a vapor retarder, and it fulfills the main goal of spray foam insulation, namely providing a perfect air seal. Most water transfer through the building envelope is by means of moisture-laden air, which will be effectively stopped by the foam. E:500 is very cost effective in high R-value applications that may be dictated by building codes in your community-> Recommendation: E:2000 vapor barrier spray foam

Additional Structural Strength Desired?

If you live in an area where your home may be exposed to hurricanes, you may benefit from a structure which has been strengthened by the very hard E:2000 spray foam. Not only is a foamed structure far more rigid, it makes it much less likely for the wind to penetrate the house initially, leading to weakening and further destruction. -> Recommendation: E:2000 insulation spray foam

Mild Climate

The key requirement for any energy savings is air-tightness. In mild climates, E:500 soft foam will provide the full benefits of a foamed home. -> Recommendation E:500 soft insulation foam

Excessive interior moisture, basements, wine cellars?

In case of indoor pools, hot tubs, wine cellars and the like, we strongly recommend our higher density E:2000 foam, which prevents vapor drive due to its extraordinary perm rating of 0.98 perms at 2” thickness. Properly spray-applied, the E:2000 spray foam forms a monolithic layer, including a high performance vapor barrier, in a single application.

Continue to the attic insulation summary >

Summary

E:zero offers different foams for different applications leading to optimal results. In the scenario of interior attic insulation, we offer two different formulas, each with its own advantages. Please contact E:zero to learn about foams suitable for exterior roofing or other applications.

You have arrived at E:500 soft foam insulation.

E:500 soft foam offers high R-value at low cost with an integrated, complete air seal. This product offers the following benefits:

• R-value is 3.9 per inch
• Open-cell structure which allows it to breathe, but slowly, so that it is still an excellent air barrier
• Significant renewable contents, including the use of water as a blowing agent and polyols derived from sugar cane
• Safe to use in all normal construction above ground

You have arrived at E:2000 high-density foam insulation.

E:2000 offers several benefits in a single application:

• Ultra-high R-value of 6.5 per inch
• A vapor barrier at an application thickness of only two inches or thicker
• 100% effective air barrier
• Ability to strengthen the structure
• Ultra-low ACH (rate of undesired air changes per hour) for all sprayed areas
• Safe to use in all types of buildings. Application even in basement, indoor pool rooms and other excessively moist areas is approved.

Fill a specific request for an attic insulation job >