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Crawl Spaces – Vented and Unvented…

Crawl Space Facts & Remediation

  • FACT #1 – 40% of the air you breathe in your home comes directly from the crawlspace.
  • FACT # 2 – A crawlspace of 700 square feet can produce 10 gallons of moisture, rising into the floor system EVERY DAY.
  • FACT #3 – Number one cause of hardwood floors buckling is high humidity levels in crawlspace.

There are generally two accepted designs for crawlspaces. The most common and traditional system is a “VENTED” or opened-air space.

A “VENTED CRAWL SPACE” is one that has foundation vents or is an open air space under the home.   A vented crawlspace has temperature and humidity similar to the outside environment contained underneath the homes flooring system.  This means that a home that has a vented crawlspace should then also have in addition to proper amounts of ventilation,  a proper vapor barrier covering the earth as well as  a good, complete insulation barrier up under the subfloor system.

The problem with this system are many. First, rarely is the ground properly covered.  This allows excessive moisture vapor / humidity in the area.  Secondly, the floor systems we have seen are usually fiberglass which is very porous, rarely insulated properly if at all. 

This is a terrible combination when both of these deficiencies are present. All of that ambient temperature and moisture is right up against your floor system. Thus allowing the hot or cold air and all of that humidity to come up through the fiberglass or your uninsulated floor and directly through your homes floors. A budget friendly approach to a vented space is to properly cover the ground with plastic and seal but with the side vents all around hot / cold moist air still gets into the crawlspace “between” the plastic and your floor and then rises up.

The next to the Best Option …

The next best option is to focus on sealing the sub-floor. Sealing up your entire sub-floor system with the installation of closed cell spray foam under the floor system. Thus, making your floor impervious to hot / cold and moisture migration upwards.

The use of closed cell foam makes the need for plastic less necessary. It is like having a home suspended up on stilts above a lake or the ocean. If the bottom of the home is completely sealed with closed cell foam it doesn’t matter how much water is under the home, the foam is it’s own vapor barrier. But the plastic does have a function, and that is to still aid in moisture prevention, decrease the amount of moisture tremendously and to also help eliminate mold growth, rot and odors in the crawlspace area. So, the plastic does aid in a more complete, controlled space.

Unvented Crawl Space …

The second type of crawlspace design that has gained much popularity in recent years due to advances in our knowledge ofbuilding science and the systems-approach, is a un-vented or ‘sealed crawlspace‘.

A properly sealed crawlspace is defined as one that has no foundation vents or if it does, they are sealed up during the foam process, and has properly sealed ground covering, insulated foundation walls and maintains acceptable temperature and humidity levels.

These crawlspaces are the optimum in promoting good health and safety for home occupants by enhancing indoor air quality (IAQ).   Another benefit is that these homes floors are more comfortable, air quality is greatly improved and much more efficient.

Either of these systems if strategically used and properly installed can have a profound influence on the performance of the home.  We have seen these applications literally make a home ‘livable’ again. Clients who for years suffered the consequences of an unhealthy crawlspace, were very appreciative of these approaches to solving their problems.

A Remediation Solution for a Crawl Space …

We recommend an application of closed cell spray foam insulation to the underside of the sub floor.  Even if floor is already insulated with fiberglass, we recommend removing this material, which has been proven to be completely ineffective and unsafe, and discarded, and in exchange apply a layer of closed cell foam. 

Fiberglass is only 34% efficient as compared to Foam which is 94% to 96% efficient. There is just no comparison. This is a truly effective material which we have recommended and installed for many years with nothing less than remarkable results.

Only closed cell foam combines  the low Perm Rating [it is its own moisture barrier] you need in an insulation material with the very high effective  R-Value.

The benefits of our application of closed cell foam on subfloors are:

  • Dramatically improved comfort
  • Improves indoor air quality (IAQ) by acting as perfect barrier from the crawlspace environment.
  • Seals out pest and rodents.
  • Seals all penetrations is floor.
  • Quiets floors and promotes greater strength.
  • Protects floors from problems associated with moisture.

In short, an application of closed cell foam does everything that fiberglass does not do….IT ACTUALLY WORKS!!!