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 wall perimeter. 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 load. 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 temperatures. 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. CAUTION Prior  to  the  actual  installation  of  the insulation,  consult  the  manufacturer’s  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. INSTALLATION 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 5-22