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Posts Tagged ‘basement insulation’

Blanket insulation—the most common and widely available type of insulation—comes in the form of batts or rolls. It consists of flexible fibers, most commonly fiberglass. You also can find batts and rolls made from mineral (rock and slag) wool, plastic fibers, and natural fibers, such as cotton and sheep’s wool.

Batts and rolls are available in widths suited to standard spacing of wall studs, and attic or floor joists. Continuous rolls can be hand-cut and trimmed to fit. They are available with or without facings. Manufacturers often attach a facing (such as kraft paper, foil-kraft paper, or vinyl) to act as a vapor barrier and/or air barrier. Batts with a special flame-resistant facing are available in various widths for basement walls where the insulation will be left exposed. A facing also helps facilitate fastening during installation. However, it’s recommended that you use unfaced batts if you’re reinsulating over existing insulation.

Standard fiberglass blankets and batts have a thermal resistance or R-values between R-2.9 and R-3.8 per inch of thickness. High-performance (medium-density and high-density) fiberglass blankets and batts have R-values between R-3.7 and R-4.3 per inch of thickness. See the table below for an overview of these characteristics.

*This table is for comparison only. Determine actual thickness, R-value, and cost from manufacturer and/or local building supplier.

Installation

The maximum thermal performance or R-value of blanket and batt insulation depends heavily on proper installation. Therefore, it’s best to have a certified insulation installer do it. If you’d like to have it done professionally, you should do the following:

* Obtain written cost estimates from several contractors for the R-value you need. Don’t be surprised to find quoted prices for a given R-value installation to vary by more than a factor of two.
* Ask contractors about their air-sealing services and costs as well, if needed.

To evaluate batt installation, you can measure batt thickness and check for gaps between batts.

If you want to install the insulation yourself, carefully follow instructions and the necessary safety precautions. The insulation’s manufacturer may offer instructions. You should also check your local building and fire codes. Please see the Installation and Reading List resources on the right side of this page (or below if you’ve printed the page).
Cost

Blanket (batt or roll) insulation and installation usually costs less than other types of insulation.

Source: EERE, U.S. Department of Energy

To effectively insulate your basement for energy efficiency and to create a comfortable space, you need to properly control moisture in your basement.

Most basement water leakage results from either bulk moisture leaks or capillary action. Bulk moisture is the flow of water through holes, cracks, and other discontinuities into the home’s basement walls. Capillary action occurs when water wicks into the cracks and pores of porous building materials, such as masonry blocks, concrete, or wood. These tiny cracks and pores can absorb water in any direction—even upward.

The best approaches for preventing these problems will depend on your local climate, type of insulation, and style of construction. However, the following general rules apply to most basement designs for creating a water-managed foundation system (see corresponding illustration):

1.Keep all untreated wood materials away from earth contact.
2.Provide drainage, such as gutters, to conduct rainwater away from the house.
3.Slope the earth away from all sides of the house for at least 5 feet at a minimum 5% grade (3 inches in 5 feet). Establish drainage swales to direct rainwater around.
4.Add a sill gasket to provide air sealing.
5.Install a protective membrane, such as caulked metal flashing or EPDM-type membrane, to serve as a capillary break that reduces wicking of water up from the masonry foundation wall. This membrane can also serve as a termite shield on top of foam board insulation.
6.Damp-proof all below-grade portions of the foundation wall and footing to prevent the wall from absorbing ground moisture by capillary action.
7.Place a continuous drainage plane over the damp-proofing or exterior insulation to channel water to the foundation drain and relieve hydrostatic pressure. Drainage plane materials include special drainage mats, high-density fiberglass insulation products, and washed gravel. All drainage planes should be protected with a filter fabric to prevent dirt from clogging the intentional gaps in the drainage material.
8.Install a foundation drain directly below the drainage plane and beside the footing, not on top of the footing. This prevents water from flowing against the seam between the footing and the foundation wall. Surround a perforated 4-inch plastic drainpipe with gravel and wrap both with filter fabric.
9.Underneath the basement’s slab floor, install a capillary break and vapor diffusion retarder, consisting of a layer of 6- to 10-mil polyethylene over at least 4 inches of gravel.

Consult a qualified builder, basement designer, and/or insulation contractor in your area for specific basement moisture control measures concerning your climate, type of insulation, and construction style.

Source: Energy Efficient and Renewable Energy, U.S Department of Energy

Once you have determined the insulation R-value you’ll need for either adding insulation to an existing basement or new home construction, you can choose the type of insulation, including the following:

* Blanket (batt and roll) insulation
* Concrete block insulation (new construction)
* Foam board insulation
* Insulating concrete forms (new construction)
* Loose-fill insulation (good choice for finished basements)
* Sprayed foam insulation (good choice for finished basements)

The installation of insulation in your basement will depend on the type you choose and the best way to control moisture in your particular climate.

Source: U.S. Department of Energy

In most cases, a basement with insulation installed in the exterior basement walls should be considered a conditioned space. Even in a house with an unconditioned basement, the basement is more connected to other living spaces than to the outside. This connection makes basement wall insulation preferable to insulating the basement ceiling.

Compared to insulating the basement ceiling, insulating basement walls has the following advantages:

• Requires less insulation (1,350 square feet of wall insulation for a 36 x 48-foot basement with 8-foot walls, compared with 1,725 ceiling)
• More easily achieves continuous thermal and air leakage boundaries because basement ceilings typically include electrical wiring, plumbing, and ductwork.
• Requires little, if any, increase in the size of the heating and cooling equipment. The heat loss and air leakage through the basement ceiling is similar to that through the exterior walls of the basement.

These are some other advantages of insulation on exterior basement walls:

• Minimizes thermal bridging and reducing heat loss through the foundation
• Protects the damp-proof coating from damage during backfilling
• Serves as a capillary break to moisture intrusion
• Protects the foundation from the effects of the freeze-thaw cycle in extreme climates
• Reduces the potential for condensation on surfaces in the basement
• Conserves room area, relative to installing insulation on the interior.

The disadvantages of basement wall insulation include the following:

• Costs may exceed those for insulating the basement ceiling, depending on materials and approach selected
• Installation is expensive for an existing building unless a perimeter drainage system is also being installed
• Many exterior insulation materials are susceptible to insect infestation
• Some contractors are unfamiliar with proper detailing procedures that are critical to performance
• If surrounding soil contains radon gas, the house will require a mitigation system underneath the basement floor.

Adding insulation to the interior of the foundation is often more cost effective for an existing building. Interior insulation has the following advantages and disadvantages.

Advantages:

• Interior insulation is much less expensive to install than exterior insulation for existing buildings
• Almost any insulation type can be used, giving a wider selection of materials
• The threat of insect infestation is eliminated
• The space is isolated from the colder earth more effectively than when using exterior methods

Disadvantages:

• Many insulation types require a fire-rated covering since they release toxic gases when ignited
• Interior insulation reduces usable interior space by a few inches
• It doesn’t protect the damp-proof coating like the exterior insulation
• If the perimeter drainage is poor, the insulation may become saturated by moisture weeping through the foundation walls
• Superior air-sealing details and vapor diffusion retarders are important for adequate performance

Source: Energy Efficiency and Renewable Energy, U.S. Department of Energy

A properly insulated basement can help reduce your energy costs. However, basement walls are one of the most controversial areas of a house to insulate and seal. You need to carefully consider the advantages and disadvantages, not to mention moisture control.

Annual Energy Savings

The energy cost savings of basement wall insulation vary depending on the local climate, type of heating system, fuel cost, and occupant lifestyle. Typical annual cost savings by R-value in a few U.S. cities are provided in the table to the right for a 1,500 square-foot home with a conditioned basement heated by natural gas ($0.72/therm).