Uncovering the mysteries of Crawl Spaces

Filed in Construction by on August 9, 2015

by David Pedersen | Photography by Innovative Basement Systems


In researching “what to do with a crawlspace,” found under many lake cabins instead of a basement, I learned the best crawlspace is an encapsulated one. In other words, shut the dreaded thing up.


You don’t have enough fingers to count the many problems encountered in a crawlspace involving a dirt floor, especially when vented. Designed to be less costly, crawlspaces can be a costly mistake.


In Fine Homebuilders Magazine, Bill Rose says his preference would be a product recall on the crawlspace.


“A crawlspace, closed or open, allows a high rate of exchange of soil gas with the house via barometric pumping, and soil gas may contain fungi and bacteria products, fertilizer volatiles, radon, smells, water vapor and other ground contamination,” declares Rose.


We build crawl spaces because they are cheaper than basements or because ground conditions make building a basement impractical. A crawlspace can also provide service access for plumbing, electrical and heating and cooling systems.


Symptoms of a crawlspace problem include drywall cracks in the interior, uneven floors, foul odors in the home and heightened allergies or asthma symptoms. “Your home is a system, and every part of that system plays a role that affects the rest of the structure,” said Ben Warren North Dakota Branch Manager at Innovative Basement Systems based in Fargo and Pine City. “If your crawlspace begins to rot, grow mold or experience structural problems, this will extend to every part of your home.”


Warren adds that by encapsulating or sealing a crawlspace, you keep away odors and allergenic mold spores that would otherwise rise up through the floor and into your home due to the stack effect. Studies show how a sealed off crawlspace can create a healthier living space, save money on your utility bills and provide valuable storage space in your home.


This all sounds logical enough and looks like an easy fix. Not so fast. That was not always the case in the history of crawlspaces that first appeared in the 1920’s and 30’s.


Conventional wisdom on crawlspaces over the years has ranged from always vent to always seal. As with many things, it’s not that simple. When working with a crawlspace always consider local conditions. Evaluate what has worked in your community and remember that the best crawl space design won’t make up for poor water management on the site.


The problem with a dirt crawl space is that they are prone to high humidity levels, which can lead to many related problems such as mold growth, dry rot, structural damage and poor indoor air quality.


In an attempt to control moisture in the crawlspace, local building codes across the U.S. started requiring that crawlspaces be built with vents and a vapor barrier over the floor. Closing the vents did not close the door on crawlspace issues.


“After many years and millions of dollars spent annually in crawlspace mold remediation and structural repairs, contractors and builders began to realize that there was something very wrong with a building code requirements,” notes The Crawlspace Company on its website. “Mold, dry rot and structural damages in vented, dirt crawl spaces are so prevalent in the U.S. that industry specialists call it a true housing epidemic.”


As building scientists took a closer look of how crawlspaces work, they realized that the only source of moisture being addressed was the ground moisture. They forgot to account for water seeping through concrete block walls and crawlspace vents. Not only the do the vents fail to address condensation, but they make the humidity problem much worse.


Every time the relative humidity levels rise above 65 percent in the crawl space, mold is likely to develop and grow, which over time can compromise your home’s structural integrity. The moisture can attract wood-boring insects which may also draw rodents and other pests into the crawl space.


While encapsulating crawl spaces solves many issues, tests show there can be risks in closed crawlspaces if they are not sealed properly, reports David Hales in Home Energy Magazine.


Radon levels in the closed crawls were roughly 10 times the levels measured in the vented crawls. The tracer gas testing also showed that roughly 40% of the air in the homes with vented crawl spaces originated in the crawl space.


If you decide not to encapsulate your crawlspace here are some tips provided by Hales. If the crawlspace has a dirt floor always maintain a continuous vapor barrier on the floor. If there is a high water table or periodic flooding, make sure that the crawl space is sloped to drain to a sump pump.


Make sure the outside grade slopes away from the building and that gutter downspouts take water away from the foundation. Maintain the perimeter of the crawlspace to prevent access by critters by sealing any holes, penetrations and access points. Plus, screen all vents.


Don’t vent dryers or other appliances into the crawl and make sure that any ductwork is well sealed and well supported. Insulate the floor above the crawl space to between R-30 and R-38. Arrange vents to provide cross-ventilation. Insulate the ductwork for any heating or cooling system to at least R-8. Protect plumbing pipes from freezing.


If you do want to encapsulate your crawlspace, Innovative Basement Systems is one example of a company that has a research and development department, searching for the lasting crawlspace solutions. It has 28 patented products and a guide book offers 88 pages of information on crawl space issues.


This means the issue is more technical than it appears and that it is not an easy do it yourself job. To encapsulate, IBS uses a durable 20-mil poly reinforced crawlspace liner on the walls and floors, offering a 25-year warranty against rips and tears. It is sealed with a polyurethane caulking. Installing an energy-efficient, self-draining crawl space dehumidifier will keep your space dry.


Encapsulated or not, it’s no mystery that dry, properly insulated, and critter-free is the best of all worlds inside your home’s crawl space.


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