Division of Energy
Residential Energy Efficiency - Insulation
R-Value ... What is it?
R-value tells you how a material resists heat flow. The higher the R-value, the greater the resistance. R-values per inch vary with different types of materials. Therefore, how well insulation performs is more accurately measured by its total R-value than by inches of thickness.
Where to Insulate
Insulation should be between any area that separates a heated space from an unheated space. This includes all exterior walls, attics, floors over unheated areas, heated basement walls and overhangs. Other areas that should not be overlooked include exterior walls between levels in a split-level home, rim joist area, knee walls next to unheated garages, storage rooms, utility rooms, dormer and cantilever walls and ceilings, and floors over vented crawl spaces.
In other words, the insulation should completely surround your home with the only openings being doors, windows and vents.
Places to Insulate
- Ceiling joists
- Finished attic end walls
- Attic living space
- Rafters to knee wall in finished attic
- Finished attic knee wall exposed to cold
- Short exterior walls
- Finished attic collar beams
- Wall to unheated garage
- Interior wall can be insulated for sound proofing
- All exterior walls
- Cantilever area
- Heated basement walls
- Under floor
- Open crawl space
- Under slab
- Rim joist
- Provide good lighting.
- Be careful of any protruding nails.
- Wear protective equipment.
- Provide adequate equipment.
- Keep lights and all wires off wet ground.
- Use temporary flooring to form a walkway in unfinished attics (the ceiling won't support your weight).
- Don't move wiring around. If you find brittle wiring, leave it alone and call an electrician.
A vapor barrier should be placed on the "warm-in-winter" side of the insulation. Face the vapor barrier down when insulating between ceiling rafters, on the inner (room) side of exterior walls and up when insulating floors. Do not install a vapor barrier on top of existing attic insulation.
You might note that, although a vapor barrier will protect insulation and building materials, it will also increase the humidity level in your home. The amount of moisture or the humidity level in your home will depend on a number of factors. Such factors include the amount of air leakage that occurs in your home, the amount of insulation, whether or not you use a humidifier, the number of household members, the amount of cooking, showers, washing and drying clothes and whether you have a large number of plants. Any tears or cuts in a vapor barrier should be repaired with tape to protect the effectiveness of the barrier.
Be Careful When Installing Insulation
Excessive moisture in the home filters through insulation, causes it to become damp and matted, and makes it lose much of its effectiveness.
To prevent or reduce condensation problems, the side of the insulation exposed to high vapor pressure (warm side in winter) must be covered with material that will impede the natural drive of moisture to flow through the inside surfaces of exterior walls, toward the lower vapor pressure outside. To be effective, such a material must have a high resistance to moisture flow. The material is usually called "vapor barrier" or "vapor retarder".
If moisture problems exist, you may have to increase ventilation in you home by using such items as exhaust fans or air-to-air heat exchangers. Please note that these options use energy to operate. So, in terms of conserving energy, it is wiser to try to reduce the source of humidity by following the suggestions outlined in the section on moisture considerations and control in this book.
Preparing the Attic
- There are several things you need to do to most types of attics to prepare them for insulation:
- If your roof has leaks, fix them! Look for water stains, find the leaks, and repair them.
- Inspect for adequate ventilation (see section on Attic Ventilation for requirement).
- Caulk or foam seal around all wiring and plumbing penetrations in the attic to stop conditioned air from leaving the house.
- Cover open chases or holes in the attic as necessary to prevent insulation from falling through.
- Cover dropped soffits over kitchen or bathroom cabinets, open interior wall cavities, dropped ceilings and stair wells before insulating. Gaps in insulation may tremendously reduce the overall effectiveness of the insulation.
- Chink or stuff scraps of insulation around fireplace chimney and end walls.
- Always keep insulation at least three inches away from the sides of recessed light fixtures, fluorescent light fixtures, wiring compartments and fluorescent light ballasts. Use a fire-proof baffle to keep the insulation away from the fixture when using loose fill.
- Use a baffle to prevent insulation from blocking air flow from the eave or soffit vents into the attic.
- Be sure the insulation extends far enough to cover the top plate on outside walls.
- It is not necessary to insulate above unheated areas such as a porch or patio. It may be helpful to mark and block off these areas.
There are different methods of insulating different types of attics. Take a look at the following information to determine your attic type and the type of insulation recommended.
|Attic Types||Insulation Options|
Open, unfinished, unfloored, unheated
Batts, blankets, wet-blown cellulose, or loose fill can be placed between ceiling joists. Loose fill or wet-blown can be added on top of existing insulation. A second ply of batt insulation should be unfaced and laid perpendicular to the first ply.
Loose fill can be blown under the floor between ceiling joists. If the attic will ever be heated or used as living space, insulate with batts, blanket, or wet-blown between roof rafters and on end walls.
Heated, used as living space
Use batts, blankets, or wet-blown on vertical kneewalls. Blow or pour in loose fill between ceiling joists and outer attic rafters behind kneewalls. Stuff rafter cavity above the kneewall and blow insulation down the rafter cavity.
The most common practice is to blow in loose fill or wet-blown insulation if you are insulating the ceiling where there is a cavity. If there is no cavity, rigid insulation may be applied on the interior surface and caulked.
Same as cathedral ceiling.
Insulating crawl space can be done by insulating either the perimeter (foundation) wall or by insulating beneath the floor. If you choose to insulate at the floor level, you must also insulate water pipes and seal and insulate ducts. It generally takes less material to insulate the foundation wall instead of the floor, ducts and water pipes.
Insulating at the floor level allows for ventilation and a supply of air to the furnace if it is located within the house. Areas over unheated basements, garages, porches and crawl spaces should be insulated.
Six-inch fiberglass (R-19) is recommended in Missouri. With the exception of garages, the floor joists are spaced every 16 inches or 24 inches. You can purchase standard width batts or blankets; otherwise, you will have to do some cutting and fitting.
If you are insulating the floor over an unheated dirt crawl space, lay six-mil plastic (polyethylene) on the ground to keep moisture from being drawn up during the winter. Extend the plastic sheet several inches up the walls and fasten in place with tape. Overlap and seal the seams of adjoining pieces, and anchor with bricks, rocks or sand.