How to Install a Vapor Barrier in Basement: Do it Yourself

Do it yourself project – how to install a vapor barrier in your basement and is it really needed? There are different opinions and facts from construction experts on whether vapor barriers improve the homes environment or do vapor barriers promote mold, mildew and property damage to a house. Throughout my 38 years experience in residential/commercial remodeling and construction, I have observed many methods & techniques of installing moisture vapor barriers and have witnessed the results, good and bad. In this do it yourself tips guide I will explain the pros & cons of installing vapor barriers in residential applications to help you understand and decide what works best in your home. The regional climate in your residential area is a major factor that causes dampness and moisture in house crawl spaces, attics and basements. The following information will help to you to determine how to approach to control the moisture content in your home.

The reason for installing a moisture – vapor barrier is to control and contain the natural cause of condensation and to redirect where that temperature difference & vapor will occur. The fact is that when an object is exposed to changing temperatures and relative humidity it is naturally going to sweat (condensate) until the object reaches the same temperature as its environment. An example of this is like a cold bottle of water in a refrigerator, it doesn’t sweat (condensate) until it is taken out of the refrigerator and placed on a table at room temperature. Once the water is exposed to a warmer environment the bottle immediately begins to sweat (condensate). The sweating will continue until the water in the bottle has reached room temperature. Let’s analyze what just happened. The (sweat) condensation dripped off the bottle and collected on the table top and when the bottle of water reached room temperature the bottle surface was dry, but what else happened? The change of temperature condensation collected and was now laying on your table around the bottle leaving a puddle on the table top, so here is the question – What do you do to stop that moisture from collecting on the table? Do you lay down a piece of plastic wrap under the bottle to protect the table? Possibly, but that doesn’t stop the problem because now the moisture is collected on the piece of plastic wrap. So what if you used a napkin instead of plastic wrap – the napkin would absorb the water and would eventually dry out if it was exposed to moving air. The big question is where do you want to redirect all of the moisture in your basement? Will it dissipate in the air, will it need to be absorbed in the building materials in your house.

To understand how to control moisture in your basement inspect and identify the following conditions:

1. Do you have an existing water or moisture problem in your basement.

2. Can you identify where the water or moisture is coming from.

3. Does you basement have an existing perimeter drain trough or French drain leading to a sump pump?

4. Do you currently use a humidifier or dehumidifier in the basement?

5. Do the appliances or furnace in the basement have excessive rust areas?

6. Are there windows or vents that open on the exterior in the basement?

7. Are there traces of mold on the exposed wood members of the house framing?

8. Are there signs of water or damp spots on masonry foundation walls?

9. If the walls are painted are there signs of excessive pealing or chalking of paint finish?

10. Does the basement have a musty or mildew odor?

If you live in the Northeast U.S. or in a climate that has a cold and warm season, I suggest considering the following guidelines for installing a vapor barrier in your basement.

The items above are signs of excessive dampness and moisture in your basement and need to be corrected to eliminate mold and mildew which is the reason for understanding the purpose of a vapor barrier. My suggestion is not to install a vapor barrier in a basement as I believe a barrier only compounds the problems of dampness and moisture. If your are considering finishing your basement I recommend insulating the inside of the masonry walls with a rigid foam board insulation that is applied directly to the masonry. Now build your stud walls 2″ beyond the face of the insulation board and do no more. I don’t believe in insulating the framed walls with fiberglass insulation as this will only be another place for condensation and moisture to build up on. Keeping the 2″ space between insulation board and framed wall will be a void for air to pass thru to dissipate any moisture. When you panel the walls do not seal to the floor joists above as this also an airflow space needed to vent the vapors. I recommend using a de humidifier to remove humidity for the basement and to help circulate the air. Consider adding fans to keep air circulating to prevent mold, and if your furnace is in the basement add a register diffuser to let a small amount of warm dry air from the furnace enter the basement. Paint the exterior masonry walls with a waterproofing paint/sealer before applying insulation on walls. My theory is to dissipate and control moisture by circulating air to have an exchange of fresh air to prevent and control moisture in the basement.