Attic Insulation

When designing and building any new home, especially a green home, the attic space is one of the most important places to insulate in order to maximize energy efficiency and reduce energy bills. The attic is often one of the easiest places in a home to insulate, whether you're building a new home or adding insulation to an existing house.

Types of Insulation for Vented Attic Spaces

In a traditional vented attic, insulation is placed in the floor of the attic to insulate the ceiling from the seasonal heat or cold, and keep conditioned or heated air in the living space below. The rest of the attic space is left uninsulated and vented through vents in the roof. There are several types of insulation product available for insulating an attic floor.

Batt-Type Attic Insulation

Batt-type insulation is the familiar roll of blanket insulation that is trimmed and placed between the floor joists of the attic floor. Batt-type insulation is most commonly made from fiberglass, a product which contains recycled glass product. Batt insulation can also be made from other green materials, including cotton insulation from recycled textiles and rockwool mineral insulation made from recycled steel and natural stone materials. All have similar R-values, typically between 3.0 and 4.0 per inch.

Batt insulation installation is a good choice for a do-it-yourselfer, but care should be taken to protect yourself from irritation by wearing protective gloves, eyewear and breathing masks. Batt insulation can also be installed by a contractor.

One drawback to batt insulation in an attic installation is that it is easy to leave gaps between the rolls of insulation and the floor joists, which will reduce the efficiency of the insulation and allow for the transfer of hot or cold air through the attic floor.

To find out more on this Insulation, go to our article on Batt Insulation.

Loose-Fill Insulation

Another option for insulating an attic floor in a vented attic space is loose-fill insulation. This type of insulation is blown into the attic floor space, usually by a professional, and once in place the insulation will cover the attic floor, providing a complete insulating layer. This ability to cover the attic floor thoroughly and eliminating any gaps gives loose-fill insulation an advantage over batt-type insulation, and make it a good choice for retrofitting an existing attic space where batt insulation may be too difficult to install.

Loose-fill insulation, like batt insulation, can be manufactured from fiberglass, cotton fibers, or rockwool mineral materials. Loose fill insulation is also often made from cellulose fibers, which come from recycled newspapers.

Loose-fill insulation such as cellulose has r-values per inch comparable to batt type blanket insulation, but has the advantage of being able to be installed at deeper depths to increase its insulating performance.

Loose-fill insulation can settle over time, especially if blown-in dry, which will gradually reduce its efficiency. While loose-fill insulation is better at filling attic floor cavities than batt insulation, it is important that it be installed at an adequate and uniform depth to be most effective.

As a rough guideline, the installed cost of insulating an attic floor to an R-value of 19, per square foot installed, from least expensive to most expensive, is as follows: blown cellulose, fiberglass batt, cotton batt, rockwool mineral batt, with spray foam insulation being the most expensive.

For a lot more information on the Cellulose Insulation, be sure to visit our informative article Blown Cellulose Insulation.

Spray Foam Insulation

Using spray foam to insulate the attic floor can provide a higher level of insulating performance than the other types of insulation.

Sprayed into place on the attic floor by a professional contractor, foam insulation can provide r-values per inch approaching 7.0.

Spray foam insulation does a superior job at blocking air leakage, and outperforms other forms of insulation by covering and filling all areas of an attic floor completely and permanently. Unlike loose-fill insulation, spray foam hardens in place and will not settle or contract over time.

While initial costs may be higher for spray foam insulation than other types, its long-term performance and outstanding insulating performance make it a serious choice for attic floor insulation. Environmental drawbacks to spray foam insulation stemming from its petroleum-based origin make seeking out alternatives made from sustainable materials such as soy a priority.

To get more information on this insulation, be sure to read our article on Spray Foam Insulation.

Spray Foam Insulation in Non-Ventilated Attic Space

While the vast majority of attic spaces are ventilated and insulated in the attic floors, there are a growing number of builders building homes with non-ventilated attic spaces, and placing spray foam insulation directly to the underside of the attic roof itself. This is a growing trend in areas that experience very high summer temperatures.

In a traditional ventilated attic with attic floor insulation, the space itself is not insulated, and the air temperature inside the structure can heat to 130 degrees or more in the hot summer even with ventilation. Due to the ductwork for the house moving through this hot space, it can increase the air-conditioning cost even in an otherwise well-insulated home.

By applying the spray foam insulation to the attic roof rather than the floor, it insulates the entire attic space from the extreme heat that once radiated through the roof. The attic then becomes a conditioned part of the house, eliminated energy loss from ducts located in the attic. The attic space of the home is now much tighter , which results in less air infiltration, so moisture isn't pulled into the attic.

Which type of attic you have in your green home, vented or unvented, as well as what type of insulation you use will depend on good communication between yourself and your home designer. An experienced green home builder will work with you to match the right kind and type of insulation and attic for your home based on location, budget constraints, and your environmental preferences in materials.

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