Evaluating Insulation

Tips and advice from a licensed heating and air-conditioning contractor.

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Question: I have a house heated by electricity. The ceiling of the basement has the pink insulation, but the vapor barrier is on the basement side (probably for easy stapling). I always thought the vapor barrier should be against the heated portion of the house.

The insulation appears to be quite old and compact. It also is missing in places. The basement gets very damp in the spring, summer and fall, but I use a dehumidifier. My house always feels cold. I'm sure it is time to evaluate reinsulating the basement ceiling. Can you make recommendations for me on the type of insulation I should use. I'm looking for something that the homeowner can install.

Answer: For decades, the use of a vapor barrier has been standard operating procedure when insulating a new home or an addition. However, in some climates, a vapor barrier may do more harm than good.

Moist air travels through the home, moving from warm to cool areas as well as from areas of high moisture to areas of low moisture.

For instance, the moisture in a steamy, hot bathroom will escape to the cooler, drier rooms outside the bath. In winter, the moisture from the bath helps raise the humidity levels inside the home, which makes the rooms feel warmer.

On the other hand, the bathroom fan should be used to move the moisture to the outside of the home to aid in the cooling of the home, reducing the load on the air-conditioning system.

Here's an example: When using the heating system with the thermostat set at 68 degrees and the humidity inside the home at 40 percent, the home will feel cold, so the occupants adjust the thermostat to 70 degrees or higher to get warm.

The same house with a thermostat set at 68 degrees and a humidity level of 70 percent will feel warm because moist air is warmer.

It is true that a vapor barrier should face the heated area of the home, which, in the case of an unheated basement, means the vapor barrier should be up against the floor of the rooms above the basement.

If the basement is heated, there may not be a need for insulation between the floor joists. If the basement is unconditioned and the vapor barrier is upside down, then moisture (traveling from hot to cold and from more to less) can be trapped between the underside of the floor boards and the vapor barrier. The trapped moisture soaks the insulation and the floor joists, leading to wet insulation that can fall from the joists and cause decay damage to the wood joists and floor boards.

Molds, which require moisture to survive, can grow in this type of environment.

Where to place a vapor barrier? In colder (dry air) Northern climates, use a vapor barrier on the inside stud walls to cover the insulation. In the warmer (damp air) Southern states, the vapor barrier should be on the outside of the home. But in the Midwest, with its changing seasons, a vapor barrier may not be needed. The moisture changes so often that it should be allowed to pass through the walls, ceiling and floors as the seasons change.

Heating the home forces the moisture out; cooling the home pulls moisture in.

A licensed heating, venting, air-conditioning contractor can advise you on how to control moisture in your area.

(Dwight Barnett is a certified master inspector with the American Society of Home Inspectors.)

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