Heat flows naturally from a warmer to a cooler space. Insulation resists this flow of heat, and helps keep your home warmer in winter and cooler in summer, at less cost. It provides a thermal blanket around your home to reduce the amount of heat that flows out of, or into, your house.
Insulation value is commonly referred to as resistance-value or R-value. R-value is the measure of a material's ability to resist heat flow. The higher the R-value, the more effective the insulation is in reducing heat flow. Insulation should be purchased on the basis of its R-value, not thickness or weight. One brand or type of insulation may be thicker or thinner than another. But if both have the same R-value, they will insulate equally.
Common building materials, such as wood, brick and concrete used in homes, do not have high R-values. Insulation is needed to supplement these materials in order to keep your energy use and energy bills as low as possible. For example, one inch of mineral fiber has approximately the same insulating value as 30 inches of concrete.
Many homes were built when insulation was believed to be more expensive than energy. But, people now generally recognize that specifying insulation in hew homes, and reinsulating existing homes, is cost-effective.
Lincoln Electric Systems Recommends As A Minimum...
(these values are for Nebraska, for R-values for the rest of the USA and Canada click here .)
CEILINGS- R-38 insulation
This can be accomplished with 12" of fiberglass batt insulation or 12" of pouring rock wool or fiberglass.
EXTERIOR WALLS - R-16 insulation
This can be accomplished with 3 1/2" of fiberglass batts.
CANTILEVER FLOORS AND FLOORS OVER CRAWL SPACES - R-19 insulation
This can be accomplished with 6" of fiberglass batts.
BASEMENT WALLS - R-8 insulation
This can be accomplished with 3 1/2" of fiberglass batts or 2" of extruded polystyrene insulation sheathing.
You can determine the R-value of existing insulation by measuring its
thickness or depth and consulting the chart below for the appropriate
Example: You have 3+ inches of fiberglass blanket insulation in
your attic. The chart shows it has the R-value of approximately R-11. The
recommended R-value for full ceiling insulation is R-38. You need to add
insulation having an R-value of 27. This can be accomplished with 11-14
inches of loose fill fiberglass or about 9-9 1/2 inches of fiberglass
Thickness for Insulations to Obtain
R-values (Inches) (1)
Loose and Blown Fill (4)
Mineral Fiber Blanket or Batts (3)
Cellulosic Fiber (5)
3¼ - 3¾
4 - 5¼
5¾ - 6¼
7 - 8¾
9 - 9½
11 - 14
11½ - 12
14 - 17¾
15 - 15½
18 - 23
(1) Always consult the manufacturer's
recommendations for applications, because specific products may deviate
from these nominal thicknesses.
(2) Rigid cellular insulating boards
provide high R-values for a given thickness. Various thicknesses are
available; 1-inch-thick boards can have the nominal R-values.
Insulating Board Type
R-value for 1-inch
Polyisocyanurate and Polyurethane
Always consult manufacturer's
recommendations for applications, since specific R-values depend on foam
density and aging.
(3) Two blankets or batts may be needed
for R-values above 30.
(4) Failure to install both proper
thickness and density will result in reduced R-value. An increased
initial installed thickness may be required to offset any decreases in
R-values due to thickness changes after installation.
(5) These are initial thicknesses to
allow for a nominal 20 percent thickness decrease after installation.
EXAMPLES OF WHERE TO INSULATE
In unfinished attic spaces, insulate between the ceiling joists to seal off living spaces below.*
In finished attic rooms with our without dormers, insulate:
a. between the studs of "knee" walls,
b. between the studs and rafters of exterior walls, and
c. ceilings with cold spaces above.
All exterior walls, including:
a. walls between living spaces and unheated garages or storage areas,
b. foundation walls above ground level, and ,
c. foundation walls in heated basements (foundation can be insulated on inside or outside of wall).
Floors above cold spaces, such as vented crawl spaces and unheated garages, and:
a. any portion of the floor in a room that is cantilevered beyond the exterior wall below,
b. slab floors built directly on the ground,** and
c. foundation walls of crawl spaces and perimeter plates.
d. Add storm windows as recommended.
*Well-insulated attics, crawl spaces, storage areas, and other closed cavities should be adequately ventilated to prevent excessive moisture buildup.
**Slab on grade is almost always insulated, in accordance with building codes, when the house is constructed.