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Install a Radiant Barrier

Energy Efficiency, Energy Efficiency, Insulation and Energy Conservation November 18, 2011 Sonia



By Matt Weber

 

 

Reflecting on Energy Savings.

 

 

If you’ve ever attended a potluck dinner, then you can attest to the heat-retention properties of aluminum foil. Without it, the world would be subjected to a lot of cold casseroles. Aluminum foil is widely used as a means of thermal insulation by acting as a reflective barrier. Similar in concept, a reflective barrier can also be used in homes and commercial buildings to reduce heat transfer and save on heating and cooling costs.

Here’s how it works: On a hot day, the sun heats a home’s roof, which radiates heat towards the attic floor and conventional insulation. Those materials emit radiant heat to varying degrees throughout the house. A hotter attic means a hotter house, so radiant barriers are used to block the sun’s rays from transferring heat to your attic. A product such as Enerflex Radiant Barrier can reflect up to 96-percent of the sun’s energy, reducing the attic temperature by as much as 30 degrees. This helps contribute to a more consistent and comfortable indoor temperature as less heat moves through the attic floor into the living area. As a result, there is less need to crank up the air conditioner.

The material we installed for this project was Enerflex Radiant Barrier, available in both rolls and panels (16” or 24” O.C.).

The material we installed for this project was Enerflex Radiant Barrier, available in both rolls and panels (16” or 24” O.C.).

Furthermore, this two-way reflective barrier behaves similarly in the winter. In cool weather, Enerflex helps keep radiant energy from leaving the home, reducing heat loss so you don’t have to blast the furnace as much.

A variety of radiant barrier products are on the market, but the EHT staff chose the new Enerflex brand for a recent project based on its design as an easy-to-install DIY product.

In a single afternoon, we had an attic ready and reflecting.

 

Installation Dos and Don’ts

Enerflex is available in flat panels as well as rolls to meet the installation needs of your roof. The product is made from two layers of metalized film, laminated and reinforced with a plastic scrim to reduce tears and punctures.

Start at the bottom of the rafters and work upward.

Start at the bottom of the rafters and work upward.

Utilizing three thin metal backer rods each, the Enerflexpanels friction-fit between the roof rafters, either 16 or 24 in. on-center. No tools are required to install the panels. Simply insert one edge of the panel against the roof framing, where it meets the sheathing, then give the panel a slight bow and tuck the other edge against the side of the next rafter. That’s all there is to it. The tension on the backer rods holds the panels in place. Start at the bottom of each rafter channel and work your way upward, overlapping the panels by 1 or 2 in.

The panels friction-fit between the roof rafters.

The panels friction-fit between the roof rafters.

The rolls of flexible material are for covering oddly spaced rafters or complicated framing around peaks, dormers, tight corners, etc. Simply unroll the material and pull it tight, tacking it to the underside of the roof rafters every few inches with a staple gun.

Tightly spaced framing can be covered with the flexible sheet product available in rolls.

Tightly spaced framing can be covered with the flexible sheet product available in rolls.

Both the panels and the rolls can easily be cut with a utility knife or heavy-duty snips to make angles or to cover short rafter spans.

The sheet can be stapled in place over the roof framing.

The sheet can be stapled in place over the roof framing.

 

 

 

 

 

 

 

The radiant barrier can easily be cut with heavy-duty scissors, snips or a utility knife.

The radiant barrier can easily be cut with heavy-duty scissors, snips or a utility knife.

When installing, check with your local building code official for ventilation requirements in your area. The bowed design of the Enerflex panels allows an unobstructed space for airflow from the soffit vents to the wind ventilators or ridge vent. A minimum gap of 3-1/2 inches is required between the top of the roof decking and Enerflex. Leave a minimum of 6 inches from the peak of the roof, and 6 inches in all directions from any turbine, gable or dormer vent. Never cover any vents.

Panels that don’t quite fit can be stapled, but maintain 3-1/2” airflow between the panel and the roof deck.

Panels that don’t quite fit can be stapled, but maintain 3-1/2” airflow between the panel and the roof deck.

Keep the barrier at least 6” away from any vents and the peak of the roof.

Keep the barrier at least 6” away from any vents and the peak of the roof.

Another advantage of the Enerflex system is its qualification as an Energy Star product by the EPA and Department of Energy. This means that not only can you take pride in the fact that your saving energy is beneficial to the environment, but you may also receive a tax return of 10 percent or up to $500 on its purchase through the 2010 Tax Relief Act.

As far as return on investment, the Enerflex company literature explains it this way: “The increased performance of your insulation and ductwork, and decreased workload on your air conditioner and other appliances mean Enerflex will pay for itself in utility bill savings over time.” Factors that affect the payback period include everything from home size and location to weather conditions, roof type and local utility costs. The most substantial savings will be realized during hot, sunny weather—especially in homes that have ductwork or cooling equipment in the attic.

 

Tips & Tricks for the Job

When calculating the amount of radiant barrier needed, remember to determine the area of the roof, not just the area of the home. You will need to measure the pitch of your roof to find the area. To calculate roof area square footage, first multiply the length and width of the attic to find the footprint square footage. Then, based on the pitch of your roof, multiply the footprint square footage by the appropriate factor listed in Table 1.

The resulting number is the roof area square footage. You should purchase enough material to cover this square footage amount, keeping in mind that each radiant barrier piece is to be overlapped by 1 to 2 in.

The best time to install a radiant barrier in an attic is the late fall or winter. During a hot summer, an attic can reach temperatures of 130 degrees. You can install the product in summer, but be prepared to sweat off a couple of pounds in the process.

Whether you’ve got fiberglass insulation or cellulose, working in an unfinished attic can be a very dusty and itchy job. We recommend wearing safety glasses and a dust mask, as well as gloves to prevent cuts and punctures from the metal backer rods in the panels.

A radiant barrier can reflect up to 96 percent of the sun’s energy, reducing the attic temperature by as much as 30 degrees.

A radiant barrier can reflect up to 96 percent of the sun’s energy, reducing the attic temperature by as much as 30 degrees.

Another common problem with attics is the lack of solid flooring. Most attic floors consist of framing, insulation and drywall, but no structural sheathing. This means that with one wrong move someone could fall right through the floor. If this is the case with your attic, we recommend temporarily screwing a 3/4-in. thick plywood walkway (or “crawl” way, depending on the attic’s headspace) over the floor framing. Be sure to cut the plywood panels large enough to cross a few of the framing members, but also small enough that they fit through your attic access door. Depending on the design of your home, you may even need to carry a ladder into the attic to reach the upper framing on steep roof pitches.

The job overall is very easy even for a novice DIY’er. No special tools are required, and if you can operate a staple gun and scissors, then you can install a radiant barrier in your attic and start saving on energy bills.

 

TABLE 1

Pitch     Roof Pitch Factor

2:12      1.02

3:12      1.03

4:12      1.06

5:12      1.08

6:12      1.12

7:12      1.16

8:12      1.20