The Use of Vapor Barriers Under Houses

Slab Foundations

• Concrete is porous, and any water underneath it will wick right through into your house. Moisture causes wood framing to rot prematurely and damages flooring and carpeting. Avoid this when building a home on a slab foundation by installing a 10-mil polyethylene vapor barrier over a minimum of 4 inches of gravel before applying the concrete foundation. Add French drains along exterior foundation footings to aid in drawing water and moisture away from the house.

Crawl Spaces

• When the house is built on a foundation consisting of concrete or block foundation walls raised above the ground by a few feet, install a 6-mil polyethylene vapor barrier attached to the bottom floor joists. Unroll the plastic vapor diffusion barrier and staple it along the exposed edges of the floor joists. Don’t stretch it taut but ensure it is smooth. Overlap the polyethylene by 12 inches and tape all seams. Apply caulk to any areas that leak air.

Retarding Moisture Movement

• Moisture enters a home by three ways, air currents, heat transfer and by diffusion through wood, insulation and sheetrock. According to the Energy’s Saver website, 98 percent of the moisture movement into the home occurs with air movement. Air moves naturally from high-pressure areas to lower ones by the easiest path open. Seal all cracks or holes with caulk underneath floors and all other areas as well.

Mold, Mildew and Fungi

• Vapor barriers are used to help prevent mold, mildew and fungi from occurring. Most people are unaware how quickly moisture can spread – close to several hundred cubic feet of air per minute – so using vapor barriers in conjunction with insulation helps to promote a protective energy envelope around the home and keep occupants healthy and warm.

Ventilation

• While having an energy-efficient home keeps energy costs down, it is also important to consider ventilation for the home. An airtight home also keeps indoor air pollutants locked in place, so installing a whole house fan and ensuring an exchange of clean, fresh air, goes a long way to promoting your family’s health.