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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.
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.
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).
- 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.
- 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. 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.
- 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.
- 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.
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.
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.
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.
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).
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.
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.
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.
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).
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.
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).
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 3.19a-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.
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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