Roof & Attic Insulation Options, Costs, and Pros & Cons 2017

Why Bother Insulating Your Roof and/or Attic Space?

Insulating your roof and attic space will help retain energy in your home, often leading to cost savings and comfort improvement. Insulation in and around your roof attic space also prevents long term damage from moisture build up or ice damming which results from heat rapidly trying to escape through the roof, but instead heating up the snow. Additionally, insulation serves as a way to enhance sound proofing on the uppermost envelop of your house.

attic space insulation

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There are five primary types of insulation for roofs, with their own advantages and disadvantages. The key value is always the capacity of insulation to resist heat flow. This is also known as thermal resistance and is often measured in terms of R-value. The higher that value, the better the insulating power.

Loose-Fill Insulation

This is one of the two most common types of insulation. Often installed into wall cavities as a way to retro-fit walls lacking insulation, it can also be blown into unfinished attic spaces. Typically, fiberglass or cellulose are the material choices.

R-value for loose-fill per-inch is between R2 and R4, higher value with fiberglass

Pros: relatively low expense, fairly easy to install (blown-in or poured in)

Cons: as the material settles over time, the R-value is (slightly) lessened, needs vapor barrier as the material is prone to moisture absorption

Cost: Generally, homeowners seek between R30 and R50, and to achieve that for loose fill over 1,000 sq. ft. the cost amounts to $500 to $900 installed.

Batt and Roll Insulation

This is the second of two most popular types of insulation. Fiber material is pre-fabricated into a blanket roll that is pressed between two sheets of paper or foil, or just one side may be shielded as is the case with rolls. Fiberglass is easily the most popular material but mineral wool is fairly common as well. Rolls are usually used for long expanses such as length of floor for entire attic, while batts are fit between studs in attic rafters.

R-value for fiberglass or wool batts, per inch is between R3 and R3.5

Pros: Easiest insulation for layperson to install, fairly inexpensive, R-value doesn’t fluctuate as with loose-fill

Cons: The fiberglass material is known to cause skin irritation so wearing respiratory mask, goggles and long sleeves during insulation is a must, requires additional handling to fit around objects or wiring

Cost: Material runs between 10 to 50 cents per sq. ft. Generally a thousand sq. ft. application costs $350. If installed by a professional, plan to pay between $1,000 and $1,500 to cover that same area.

Spray Foam Insulation

Similar to loose fill, though this is a liquid that when applied becomes a durable layer of foam insulation. It can be fairly messy so benefits from having experienced crew do the installation. Two material options called open and closed cell, where closed cell is more dense (greater R-value) and much more expensive.

R-value for open cell is about 3.5 per inch, while closed cell achieves R6 to R6.5 per inch

Pros: For interior insulation this provides perhaps the greatest R-value and with proper installation it covers gaps better than most options

Cons: Messy, unsightly, and can be very expensive

Cost: Material costs and going with DIY, the open cell costs about $600 to cover 1,000 sq. ft., while closed cell comes in at $1,200. For professional installation plan to pay $2,000 or more.

Radiant Barrier

The final two options are more or less meant to be used in conjunction with one of the above options. Radiant barriers use large aluminum foil sheets under the roof’s interior to reflect the sun’s heat. Works best on sloped roofs that are perpendicular to direction the the sun. Also radiant barriers are best utilized in warmer climates than in cool ones.

R-values are either not applicable or negligible for radiant barriers

Pros: For warm climates experiencing hot weather, the barrier will provide a cooling effect, fairly easy to install

Cons: no actual insulation value, most homeowners will choose to spend their money on other options

Cost: 10 cents to $1.00 per sq. ft. or expect to pay closer to $2.00 per sq. ft. if going with professional installation. The DIY approach generally results in $200 to $600 to adequately cover 1,000 sq. ft.

Rigid Foam Board

The previous four options are all used beneath the roof. Rigid foam board is just above the roof deck, or an exterior insulation option. It typically has 3 variations: bare foam board, one sided sheathing board or double sided which is also reference as Structural Insulated Panels. The later is used in new construction as the interior board serves as an inner wall. Bare foam board would benefit from sheathing being used on-site when it comes to roofing applications, whereas for say siding, that isn’t necessary. What the foam is made of can vary, but is in the synthetic polymer family.

R-values are noticeably higher than interior options, ranging from R3.8 to R8.0. Spray foam comes closest, though this is even higher and a lot less messy

Pros: Excellent R-value, can increase sound-proofing especially for metal roofs, is also water-proof

Cons: Water-proof (non-breathing) barriers can trap moisture on roof deck unless properly vented, foam material when contacted with electrical wires can be dangerous, rigid foam board is fairly expensive compared to other options

Cost: Material ranges between 50 cents and $1.50 per sq. ft. This though, being the exterior, will likely need more material to cover the entire roof, which will likely require hiring professional installers. Plan to pay $2.00 to $4.00 per sq. ft. for this type of insulation applied.

Important Points to Keep in Mind:

Visual Diagram depicting the areas that need to be insulated.

When insulating your attic space, make sure that soffit vents remain open. Inadvertently covering or clogging soffit vents will disrupt the air intake and thus harm the ventilation dynamics within your attic space. — This is a fairly common and very costly DIY error.

Did you know? Hot, poorly-ventilated attic spaces can cause asphalt shingle cracking and melting and thus shorten the lifespan of your roof?

If you have any heating equipment in your attic space, it needs to be properly insulated so that no worm air can escape into the attic. The goal is to keep your attic space dry, cool, and well-vented.

sheet metal insulation in the attic

In addition to insulation some air sealing may be necessary to ensure that no air can escape from the house into the attic space.


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