LOCATION OF INSULATION
In most climates, all walls, ceilings, roofs, and
floors that separate heated spaces from unheated spaces
should be insulated. This reduces heat loss from the
structure during cold weather and minimizes air
conditioning during hot weather. The insulation should
be placed on all outside walls and in the ceiling. In
structures that have unheated crawl spaces, insulation
should be placed between the floor joists or around the
If a blanket or batt insulation is used, it should be
well supported between joists by slats and a galvanized
wire mesh, or by a rigid board. The vapor barrier should
be installed toward the subflooring. Press-fit or friction
insulations fit tightly between joists and require only a
small amount of support to hold them in place.
Reflective insulation is often used for crawl spaces,
but only dead air space should be assumed in calculating
heat loss when the crawl space is ventilated. A ground
cover of roll rooting or plastic film, such as poly-
ethylene, should be placed on the soil of crawl spaces to
decrease the moisture content of the space as well as of
the wood members.
Insulation should be placed along all walls, floors,
and ceilings that are adjacent to unheated areas. These
include stairways, dwarf (knee) walls, and dormers of 1
1/2 story structures. Provisions should be made for
ventilating the unheated areas.
Where attic space is unheated and a stairway is
included, insulation should be used around the stairway
as well as in the first-floor ceiling. The door leading to
the attic should be weather stripped to prevent heat loss.
Walls adjoining an unheated garage or porch should also
be insulated. In structures with flat or low-pitched roofs,
insulation should be used in the ceiling area with
sufficient space allowed above for cleared unobstructed
ventilation between the joists. Insulation should be used
along the perimeter of houses built on slabs. A vapor
barrier should be included under the slab.
In the summer, outside surfaces exposed to the
direct rays of the sun may attain temperatures of 50°F
or more above shade temperatures and tend to transfer
this heat into the house. Insulation in the walls and in
the attic areas retards the flow of heat and improves
summer comfort conditions.
Where air conditioning is used, insulation should be
placed in all exposed ceilings and walls in the same
manner as insulating against cold-weather heat loss.
Shading of glass against direct rays of the sun and the
use of insulated glass helps reduce the air-conditioning
Ventilation of attic and roof spaces is an important
adjunct to insulation. Without ventilation, an attic space
may become very hot and hold the heat for many hours.
Ventilation methods suggested for protection against
cold-weather condensation apply equally well to
protection against excessive hot-weather roof
The use of storm windows or insulated glass greatly
reduces heat loss. Almost twice as much heat loss occurs
through a single glass as through a window glazed with
insulated glass or protected by a storm sash. Double
glass normally prevents surface condensation and frost
forming on inner glass surfaces in winter. When
excessive condensation persists, paint failures and
decay of the sash rail can occur.
Prior to the actual installation of the
insulation, consult the manufacturers specifi-
cations and guidelines for personal-protection
items required. Installing insulation is not
particularly hazardous; however, there are
some health safeguards to be observed when
working with fiberglass.
Blanket insulation and batt insulation with a vapor
barrier should be placed between framing members so
that the tabs of the barrier lap the edge of the studs as
well as the top and bottom plates. This method is not
popular with contractors because it is more difficult to
apply the drywall or rock lath (plaster base). However,
it assures a minimum of vapor loss compared to the loss
when the tabs are stapled to the sides of the studs. To
protect the top and soleplates, as well as the headers over
openings, use narrow strips of vapor barrier material
along the top and bottom of the wall (fig. 5-28, view A).
Ordinarily, these areas are not well covered by the vapor
barrier on the blanket or batt. A hand stapler is
commonly used to fasten the insulation and the vapor
barriers in place.
For insulation without a vapor barrier (batt), a
plastic film vapor barrier, such as 4-roil polyethylene, is
commonly used to envelop the entire exposed wall and
ceilings (fig. 5-28, views B and C). It covers the
openings as well as the window and doorheaders and
edge studs. This system is one of the best from the
standpoint of resistance to vapor movement. Further-
more, it does not have the installation inconveniences
encountered when tabs of the insulation are stapled over