Why Bother Insulating Your Home’s Roof or Attic Space?
Insulating your roof and attic space will help retain energy in your home, often leading to cooling cost savings and overall home comfort improvement.
Properly insulating in and around your roof attic space can make your home healthier and more durable. It can also help prevent costly long-term damage from moisture build up or ice damming, which often results from poorly insulated/ventilated attics that allow warm air escape through the attic and reach the apex of the roof, thus heating up and melting the snow in winter).
Additionally, roof and attic insulation serve as a way to enhance sound proofing on the uppermost envelop of your house.
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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.
Blown-in or Loose-Fill Insulation
This is one of the two most common types of insulation. Often installed into wall cavities as a way to retrofit walls lacking insulation, it can also be blown into unfinished attic spaces. Typically, fiberglass or cellulose are the most common material choices.
R-value for loose-fill insulation can range between R2 and R4, with higher R-value for fiberglass loose-fill.
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 R value between R30 and R50, and to achieve that for an area of 1,000 sq. ft., the total cost would be between $800 to $1,400, depending on the project specifics, ease of access, and property location.
Insulation blankets: Batt and Roll Insulation
This is the second of two most popular types of insulation. Fiber material is prefabricated 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, R value per inch is between R3 and R3.5.
Pros: Easiest insulation for layperson to install, fairly inexpensive, R-value doesn’t fluctuate as it does with loose-fill insulation.
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 20 to 70 cents per sq. ft. Generally, a thousand sq. ft. application costs $350-$800.
If installed by a professional, plan to pay between $1,000 and $1,500 to cover that same area.
Spray Foam Insulation: Closed and Open Cell SPF
Spray Foam is somewhat similar to the loose fill insulation, though SPF 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.
There are two material options called open and closed cell foam, where closed-cell foam is more dense (greater R-value) and much more expensive.
R-value for open cell SPF is about 3.5 per inch or board foot, while closed cell achieves R6 to R6.5 per inch/board foot.
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 $800 to cover 1,100 sq. ft., while closed cell comes in at $1,200-$1,500. For a professional installation plan to pay $2,000 or more.
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.
Radiant barriers work best on sloped roofs that are perpendicular to the direction of the sun. Also, radiant barriers are best utilized in warmer climates than in cooler 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: $25 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 $300 to $800 to adequately cover 1,000 sq. ft.
Rigid Foam Board
The previous four options are all used beneath the roof, typically in the attic space. Rigid foam board, on the other hand, is used just above the roof deck as an exterior insulation option.
Rigid foam insulation typically has 3 variations: bare foam board, one sided sheathing board or double sided which is also reference as Structural Insulated Panels. The latter is sometimes used in new construction as the interior board serves as the 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 soundproofing properties, especially for metal roofs. Rigid foam board is essentially waterproof (less than 0.1% water absorption, making rigid foam board a solid option for flat and low slope roofs with pooling water).
Cons: Waterproof (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 costs range between 50 cents and $1.50 per sq. ft. This though, being the exterior, will likely need more material to cover the entire roof (especially if the roof is sloped and cut-up), which will likely requires hiring professional installers. Plan to pay $2.00 to $2.50 per sq. ft. for this type of insulation applied professionally.
Important Points to Keep in Mind:
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 air circulation and the overall ventilation dynamics within your attic space. — This is a fairly common and very costly DIY error. 😉
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.
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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