Good insulation cuts heating costs and adds to comfort by making the temperature in the house more uniform. Humidification increases comfort and saves fuel by reducing the temperature level required for comfort. While both insulation and humidification are desirable, their addition to older homes without vapor barriers in walls and ceilings may create moisture condensation problems. Where large differences exist between indoor and outdoor temperatures, pressure forces water vapor out through the walls.

In the uninsulated house this vapor usually moves on to the outside without any problem. Where insulation is added, the dewpoint often occurs within the insulation, so water vapor condenses into free water with consequent wall insulation and siding.

In some instances, where indoor relative humidity is low and the outside covering material allows moisture in the walls to escape readily, no moisture problems may result. However, mechanical humidification, in addition to normal moisture from cooking, bathing, and respiration, amplifies moisture problems; the water vapor pressure drive is increased and consequently the rate of moisture movement into the walls.

Vapor barriers in walls and ceilings reduce the rate of moisture movement into these areas and thus help to control the moisture problems otherwise created by adding insulation or humidification.

The ceiling represents the greatest source of heat loss on cool days, as well as the greatest source of heat gain on warm days. At least 4- 6 inches of insulation should be provided for those homes located in cold climates and in warm climates where summer cooling is essential. Insulation is also needed under floors of crawl space houses in cold climates.


Vapor barriers should be provided on the warm side of all insulation. Most houses built before the mid-1930's do not have vapor barriers. If the ceiling insulation is in blanket form with a covering around it, the covering material may resist the passage of moisture. However, if the ceiling is loose fill, look under it fore separate vapor barrier of coated or laminated paper, aluminum foil, or plastic film. The same thing is true of insulated walls, where the vapor barrier should be on the inside of the walls.

Check in crawl spaces for a moisture barrier laid on top of the soil. If there is none and the crawl space seems quite damp, a moisture barrier could be added.

There is no convenient way to determine if there are moisture barriers under floor slabs. If the floor seems damp most of the time, there probably is no moisture barrier. A barrier would then have to be added on top of the slab, with a new finish floor applied over it, to have a dry finish floor.


The two major areas where good ventilation is required are the attic or roof joist spaces( in the case of a cathedral ceiling or flatroofed house) and the crawl space. The general adequacy of existing ventilation can be observed just from the degree of dampness.

Moisture passes into the attic from the house and condenses as the air cools down or where the moist air contacts the cold roof members. Both inlet and outlet vents must be located properly for good circulation of air through all the attic area. These vents not only help keep the attic dry in winter, but keep hot air moving from the attic during summer and help to cool the house.

Observe the size and location of crawl space vents. There should be least four vents located ear building corners for optimum cross ventilation and minimum dead air space.

Home || Our Company || Home Manual || Services || Contact Us

, Habitat Home & Building Inspection Services, Inc.
Another Poughkeepsie Journal Website