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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.

Figure 3.1
Most ceilings already have at least some insulation. Your utility representative will be able to tell you the R-value of your ceiling insulation. If your ceiling is already insulated to R-19 or greater, it may not be cost-effective to add more insulation to reach the recommended R-38 level. Your utility representative can advise you.

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:
  • Protective Gear, eye goggles, gloves, knee pads, hard hat, respirator,and appropriate clothing.
  • Insulation and Materials
  • Enough loose fill or batt-type material to cover the area to be insulated
  • Wooden baffles or purchased metal cover to protect recessed lighting and vents if you're using loose fill insulation - One-inch lumber or plywood to frame attic access door
  • Adhesive-backed foam rubber weather-stripping for attic access door


Tools and Equipment
  • Portable light and extension cords
  • Wooden planks (to walk on in attic)
  • Hammer and nails, or staple gun
  • Duct tape


For Loose Fill, You'll Also Need:
  • Rake or push broom to spread insulation
  • Blowing machine. These are available on a rental basis, or you may be able to borrow one from your insulation dealer


For Batts or Blankets, You'll Also Need:
  • Sharp knife, or heavy duty shears


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.

Figure 3.2
Whether you're using blown, poured, or batt material, the following preparations are important:
  • Heat-producing fixtures should be isolated from insulation to prevent fire hazards. These include recessed lighting fixtures (those where the light is above the house ceiling line and encased in a metal box or canister), stovepipe or flue exposures. Small motors such as doorbell transformers and ventilating fans are also included.
  • Insulation must be kept at least 3 inches back from these openings. If you're using blanket or batt insulation, leave a 3-inch space on both sides of the fixtures and frame the openings with wood or metal baffles that extend at least 4 inches above the depth of the insulation (Fig. 3.3).
    Figure 3.3
  • Wrap flues and chimneys with at least 3 inches of non-combustible insulation which extends at least 4 inches above the level of the finished loose fill or batt insulation. Baffles prevent insulation from sloughing into the openings.
  • With blown or poured insulation, frame the openings with wood or metal baffles which extend at least 4 inches above the depth of the insulation (Fig. 3.4). Nail or screw the baffles to ceiling joists so that they will not move during or after insulation has been installed.
    Figure 3.4
  • If you are insulating over the top of a fixture, protect it with a metal box with closed top. Fixtures which are tested and certified by an independent laboratory (UL-rated fixtures of this type will be marked, "Recessed Fixture Type LC") as capable of dissipating heat are an exception to the procedures above. You may safely insulate over and around them.
  • Make sure all electrical wiring is in good repair. Insulation coming into contact with exposed electrical wires could start a fire.
  • Don't attempt to pull up or bend any wiring. Protect "knob and tube" wiring in one of the following ways:
    1. 1. For wiring which extends across the joint space, cut a piece of batt insulation at least 14½ inches wide and push it underneath. (Fig. 3.5) Taper blown or poured insulation back from this batt to assure that loose fill doesn't "drift" into contact with the wiring.
      Figure 3.5
    2. 2. For wiring installed along the sides of the joists, you will need to cut the batt to provide air space around the knob and tube wiring. ( Fig. 3.6.) Be sure to maintain clearance on all sides of the wire for free air circulation. We recommend using batts between the joists on both sides of the space containing the wiring so that loose fill insulation (if used) does not spill over into the knob and tube wiring. Check with your utility for details.
      Figure 3.6
    3. 3. Have the electrical system inspected by a professional to: (a) verify circuit protection with type "S" fusing or circuit breakers of no more than 15 amperes, and (b) ensure that the existing wiring and overall electrical system is in good operating order.
      Then, you may blow or pour in only fiberglass, rockwool, or cellulose insulation directly over the wiring. You may also use unfaced mineral wool batts.
  • Exhaust vents (from kitchen, bathroom, and clothes dryers) which expel their vapors to the attic must be extended to the outside (Fig. 3.7). Extension material should be moisture proof and mounted securely, and of an appropriate diameter for the vent. Kitchen range exhaust fans should be connected to an airtight steel duct and extended to the outside in a vent cap.
    Figure 3.7


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.

Figure 3.8
Insulation should be kept back from all eave vents so that 2 ½ inches of free air clearance is available at each vent (Fig. 3.9). Vents must be kept clear to ensure proper moisture control in the insulated space. Batt insulation should be at least 3 inches back from all recessed lighting fixtures, small transformers, flues, etc.

Figure 3.9
Tear off loose insulation from scrap pieces and pack into any exposed cracks or crevices.

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.

Figure 3.10
Insulating With Loose Fill Material
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).
Figure 3.11
Unlike batt-type insulation, loose fill installations require that all the eave vents be protected with batts or wooden baffles before you begin to insulate. Before spreading or blowing in insulation, stack two 6-inch batts of insulation, 24 inches long, between the joists in front of each eave vent (Fig. 3.12). The halts must permanently separate the loose fill insulation from incoming air access.

Figure 3.12
Two and one-half inches of free air clearance must be available for air coming in from all soffits or eave openings. If the roof slopes too low to leave a 21/2-inch clearance above the vent with the above method, reduce the depth of the insulation as you reach the vent by sloping it downward (Fig. 3.13). Use wood or cardboard baffles held between the joists to maintain the 2½-inch vent space, as shown.

Figure 3.13
Protect fans, small motors. and flue exposures from coming into contact with insulation. Instructions on how to do this are included in the general specifications section for ceilings.

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.

Figure 3.14
Attach measuring sticks to the ceiling joists throughout the attic to measure the correct depth of loose fill insulation to reach the recommended R-value of 38 (Fig. 3.15).

Figure 3.15
Pouring Material
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.

Figure 3.16
Blowing Material
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).

Figure 3.17
Feed the material into the blowing machine at a consistent rate to avoid intervals when nothing but air is blowing through the hose.

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).

Figure 3.18
Figure 3.19 a-d
Figure 3.19a-d, shows where to insulate for different types of attic constructions. If it is a finished room with knee walls and collar beams (Fig. 3.20), you must insulate all surfaces. Most insulation contractors accomplish this by gaining access to the unfinished space and installing up to R-38 along the collar beams (house ceiling) and at least R-11 (preferably R-19) on the knee walls. Additional instructions for insulating knee walls are included in Section VI, Insulating Unfinished Walls.

Figure 3.20
The sloped ceiling is blocked off where shown in Fig. 3.20 and insulation is blown in around the rafters and attic ceiling, leaving adequate space for ventilation. This is usually a complex job, which involves cutting holes in your ceiling and working in cramped spaces. You may want to hire a contractor to insulate a finished attic which is used for a living space.

Next: How to Insulate a Floor


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