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Insulation is brought about by tiny air pockets in an insulating material that resist the transfer of heat. This keeps the heat inside your home during cold weather and outside when the weather is warm. Heat flow resistance is measured in resistance values or R-values. When the R-value of a material is high the greater the insulating power of the material. Armed with this knowledge you should always buy insulation material according to its R value and not choosing according to thickness. The R-value of all insulation should be printed directly on the material or on the package covering the materials.
There are several different types of insulation. Batts are precut in four foot or eight foot lengths. Blankets are continuous rolls. Insulation can be made out of fiberglass or rock wool. These are both sold with or without a vapor barrier facing. Loose fill insulation made of rock wool, glass fiber, vermiculite or perlite must always be poured in place by hand. Loose fill made of poly urea foam must be blown into enclosed walls with special equipment. Most rigid insulations are used for interior or exterior sheathing and around a foundation perimeter.
A vapor barrier will help to prevent moisture damage with the proper ventilation. This is because during the winter warm, moist household air moves toward the colder drier air outside. When insulation has been installed without a proper vapor barrier, water vapor will migrate into the walls and condense against the cold inner surfaces of wall or roof sheathing, as well as, inside the insulation. As a result wet, inefficient insulation promotes the growth of mold, exterior paint peeling and structural rot. A vapor barrier is usually a layer of impermeable aluminum foil, craft paper or polyethylene that faces the warm in winter side of the wall, floor or ceiling that is being insulated. Even when you install loose fill insulation, unfaced batts or blankets, you should also install a separate vapor barrier of 6-millimeter thick polyethylene sheets. Although insulation with a vapor barrier already attached is more convenient, it is less efficient. Always consider adding polyethylene sheeting to face your insulation for the best results. The vapor barriers flanges should always be stapled to the studs so that the flanges overlap. When you cover insulation with polyethylene sheeting, join the sheets at a stud and overlap before you staple the edges. Be very careful not to puncture or tear the vapor barrier. If you do, patch it with duct tape when using polyethylene. To create a vapor barrier in an unpaved crawl space or basement floor use polyethylene. For a finished wall you can use a vapor barrier paint, vinyl wallpaper ore two coats of oil base paint.
All surfaces should be insulated that separate your living area from unheated spaces or the outdoors. The amount of insulation you will need depends on the local climate, area to insulated and fuel bills. Local utility companies and insulation contractors should be able to tell you the R-value needed for your area. To insulate an unfinished attic determine the square footage by multiplying the length by the width. Vapor barrier faced glass or rock wool batts that are wide enough to fit through the joist work best in these areas. This is the most cost effective space you will insulate so do not scrimp on this area. Always be sure when you are installing insulation to wear safety glasses, a breathing mask and gloves to keep the material from causing damage to your health.
Start by laying a temporary plywood floor and hanging up work lights in the attic. Lay the batts with the vapor barrier side down at the outer edges of the attic and work toward the center. Butt the batts tightly against each other and when you need to cut one set it on a board then compress it with a 2 X 4. Use a serrated knife when cutting. B e sure you compress insulation so it will fit under any wiring. Where there is any recessed lighting leave a 3-inch space around it. To prevent condensation make sure you do no block the eave vents. If you do not have eave vents you might consider installing vents or power ventilators. When you want to add more insulation place batts or blankets without vapor barriers on top the old insulation or pour in looser fill. To install a vapor barrier when using loose fill, lay strips of 6-mils thick polyethylene in the spaces between the joists and pour the loose fill insulation to the desired thickness. If your attic has a finished floor fit batts between the rafters facing you and staple the outer edges of the vapor barriers to the rafters every 6 inches.
When insulating finished walls, keep in mind that blowing loose fill or foam into walls or even the installation of rigid insulation is best left to a professional. Be sure to get estimates for at least three contractors and ask for references before signing papers. An unheated basement or crawl space will need to fitted with batts or blankets with the vapor barrier side up between the overhead joists. You will need to staple a wire mesh to the joist to secure the insulation. Air conditioning and heating ducts should have insulation wrapped around any exposed ducts with the vapor barriers facing you. To seal the edges, secure them with duct tape. A heated crawl space will need to have the entire covered with a 6-millimeter sheet of polyethylene. Place the strips of insulation against the headers and use furring strips to nail lengths of unfaced insulation to the sill. Insulation should extend two feet along the ground over the polyethylene. You may need to use bricks to anchor the insulation. A heated basement will need a framework of furring strips or studs on the walls. When you fit the insulation be sure the vapor barrier is facing you and is between the studs or furrings. Secure the insulation with staples and cut pieces to fit the headers.