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|BPA Home EE Home Energy Tips Do-It-Yourself Home Weatherization Guide How to Insulate a Ceiling|
How to Insulate a Ceiling
Insulating the ceiling will prove cost-effective and simple to do in most cases. The ceiling is the most important place to insulate because up to 45 percent of the heat loss from an uninsulated house is lost through the ceiling (Fig. 3.1). In the summer, an uninsulated ceiling will provide little protection from the heat. Your house will be much more comfortable and energy efficient year-round with a small time and money investment in installing insulation.
Loose Fill or Batt Insulation
Ceilings can be insulated with blown, poured, or batt-type materials with or without attached vapor barriers. Fiberglass or plastic foam board may be used for interior open-beam ceilings and other special constructions.
Loose fill is poured or blown into place. Vapor barriers can only be installed in attics where no insulation is in place already, and they must be installed separately. Loose fill is easy to install once you have gone through your attic and protected all vents, recessed lighting, and fans with baffles or insulation batts. It is often easier to use loose fill insulation in attics with cross bracing or with many obstructions between the joists. Make sure your attic has good cross ventilation, as described in Section IX, if you are going to install loose fill. This will help reduce moisture build-up if you cannot install a vapor barrier.
Batt-type insulation can be purchased with a vapor barrier attached, so less ventilation is required. (If you are adding batt-type insulation to increase the R-value of existing ceiling insulation, however, purchase the type without vapor barrier.) It is usually possible to install batts around recessed fixtures without having to use baffles, as you must with loose fill.
Before you start, check to be sure your ceiling can support the weight of insulation required. Look for separation of finish material (gypsum board, lath) from joists or studs; cracks or openings in the joists between boards; or deflection of finish material between joists. These signs may mean that the construction is too weak to support the required load. (Obviously, none of these signs should appear after insulation is installed, for the same reasons.) Inform your utility so the problem can be evaluated and resolved.
Before getting started, read the section on Protective Gear and on Vapor Barriers and Ventilation.
Some General Specifications for All Ceiling Insulation Jobs
To Insulate Your Ceiling, You'll Need:
Tools and Equipment
For Loose Fill, You'll Also Need:
For Batts or Blankets, You'll Also Need:
Preparing the Attic for Insulation (Fig. 3.2)
1. Lay walking planks across ceiling joists (don't step on the ceiling between the joists; it won't support you)
2. Hang portable lamp
3. Have someone hand all the bags or packages to you through the attic access door (except with blown-in insulation). Distribute the unopened bags or packages in the approximate areas they'll be used, laying them carefully across the ceiling joists. If the attic access is too small for packages of batt insulation, measure and cut them before entering the attic.
Insulating with Batts or Blankets
Start in the least accessible areas of the attic and work toward the entrance. Press insulation firmly into place between the ceiling joists, with the vapor barrier facing away from you as you work (toward the floor). Fit each batt securely against the next.
Take care not to damage the vapor barrier facing as you cut the bans, repairing any tears with duct tape. If joists in your attic are fitted with cross-bracing (Fig. 3.8) cut and fit the balls around the braces.
You may need to install a second layer of insulation to reach the recommended R-38 level. Lay the second ball or blanket perpendicular to the joists, as shown in Fig 3.10. The second haft must be unfaced (without a vapor barrier, to prevent condensation between the insulating layers.
To start . . . Using pouring or blowing materials is an easy way to insulate your attic. If you decide to install a vapor barrier, use sheets of 6-mil opaque polyethylene between each joist space. Staple onto the joists every 6 to 8 inches ( Fig. 3.11).
Frame the attic ceiling access door with lumber or plywood at least 1 inch thick to prevent insulation from sloughing through the opening (Fig. 3.14). Or, you can lay bans of insulation at least 14½ inches wide into the joists surrounding the access door, beginning to install loose fill where the batts end. Make sure the bans have the same R-value as the rest of the ceiling insulation.
Beginning in the most difficult areas, pour the insulation into the spaces between the joists (Fig. 3.16). Spread it evenly between ceiling joists with a rake or push broom, withdrawing the walking planks as you work toward the attic entrance. Cover the level indicated on the measuring sticks slightly to allow for settling of the insulation.
Insulating attics with blowing material is probably the easiest way to weatherize. After the vents, small motors, and recessed fixtures are protected with baffles or bans as described on page 8, the entire job takes an hour or two to complete.
Blowing machines are available on a rental or loan basis. The process requires at least two people: one to feed the machine and the other to spread the insulation in the attic (Fig. 3.17).
Begin by blowing material into the outer spaces of the attic and work towards the attic entrance. Install to a depth slightly deeper than the desired level indicated on the measuring sticks, to allow for settling.
Finish up with the steps described in the following section.
To Finish Up: (bats-type or loose fill insulation)
Install R-30 insulation on the attic access door (R-11 for vertical access doors), with the vapor barrier against the door. Begin by cutting an R-19 batt to size. Peel back 1 inch at the top and bottom of the insulation facing. This forms a stapling flange. Staple the insulation in place with the vapor barrier against the door. Stack an R-17 batt on top of this to reach the required R-value. Or, you may use mastic to glue three or four pieces of insulating foam board to the back of the door. Be sure to use enough to reach the required R-30.
To prevent cold air from escaping through the cracks around the attic access door into the heated house, apply adhesive-backed foam rubber weather-stripping around the access door. See Section VII for more information about weather-stripping.
Seal and insulate any operating ductwork in the attic with R-11 batt material. Information on insulating ducts is included in Section V.
Insulating Finished Attics
To insulate a finished attic with floor, finished walls, and ceiling you must pry open access holes through which insulation can be stuffed or blown.
If the attic is simply floored over and is not heated or used as a living space, you may staple batts directly onto the floor. However, make sure that there are no soffit or eave vents under the attic floor which will be blocked with this type of application.
If you use your attic for storage or other purposes, you can pry up enough floor boards to blow in insulation between the floor joists. Most floored-over attics have blocking nailed between floor joists in one or two places along their span, so you'll need to pry up floorboards on both sides of the blocking (Fig. 3.18).
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