Step 1. Crawlspace Foundation Encapsulation
Determine if the crawl space can be encapsulated in its current form. If not, either make any changes needed to prepare it for sealing, or do not encapsulate. Encapsulating a crawl space can create new problems if it’s not done correctly, so in some cases, a crawl space should not be encapsulated. Two big issues that must be looked at carefully are bulk water problems and the possibility of backdrafting combustion appliances in the crawl space. Pest control also places some restrictions on the details of encapsulation.
You can still seal a crawl space that has bulk water problems or atmospheric combustion appliances – but only after eliminating the water problem and replacing the atmospheric combustion appliances with sealed combustion or non-combustion (i.e., electric) models. With water problems, most of the time the source is bad drainage outside, so that must be addressed. Sometimes you need to install a perimeter drain and sump pump in the crawl space.
Problems Caused by Moisture
Moisture is one of the main foes of a home’s structure—potentially causing both structural problems and health issues. Uncontrolled moisture can cause rot and decay in wood framing and other materials, and it fosters mold and mildew that can cause allergies and asthma. The amount of moisture that is present determines if you can finish a basement, for example. Moisture also determines what type of below-grade flooring you are able to install. It affects the kitchen and bathroom walls, floors, and especially ceilings. At its most extreme, moisture can even determine if the construction of a home or room addition is possible at all. Where moisture is a known problem, vapor barriers are integrated into wall, ceiling, and floor construction to combat the effects.
But nowhere is moisture more damaging than in a crawl space, even though it is not seen. Because the crawl space has direct contact with the ground, it should be no surprise that moisture will develop here. It is difficult to overstate the problems that can occur because of crawl space moisture.
Mold and Mildew
One of the most serious problems caused by moisture is mold, mildew, and other fungi. According to the CDC, mold can cause nasal stuffiness, throat irritation, coughing or wheezing, eye irritation, and skin irritation to people with sensitivities. And people with mold allergies can have much more severe reactions, including lung infections. Eliminating mold is difficult, and fully remediating mold-related problems is expensive. Mold’s effects go well beyond just harming people. As a direct byproduct of crawl space moisture, mold can blacken floor cavity insulation and structural elements. Because there is often no light and only minimal ventilation in a crawl space, the problem never improves unless preventive or remediation methods are enacted.
Structural elements of your house, such as joists, sills, posts, and beams, are made of wood. Being an organic material, wood will begin to rot when it comes into contact with water for prolonged periods.
Rodents and Other Vermin
Animals of many types are drawn to water and can infest your home. These pests include carpenter ants, termites, rats, mice, snakes—even skunks and armadillos.
Even where moisture has not yet created obvious problems, its presence may turn away home buyers and erode the resale value of your home. When you try to sell your house, the property inspector will explore the crawl space and note the presence of water on the report. Prospective buyers will almost certainly want the problem fixed or demand a lower sale price because of it.
How Vapor Barriers Work
One method of controlling crawl space moisture is with a very simple and inexpensive project: laying out rolls of ordinary sheet plastic. Traditionally, this plastic has been called a vapor barrier, but this strategy has been retitled by the U.S. Department of Energy, which now defines it as a vapor diffusion barrier. This is a more accurate term, since plastic sheeting, even with seams sealed, cannot seal off 100 percent of the moisture migration. Rather, the plastic slows down the process.
Sheet plastic barriers tend to help with the migration of gaseous water vapor up through the soil into the crawl space. They do not offer a remedy when water pools up in the crawl space. Pooling water comes from one of two sources:
A high water table or rainwater runoff may be causing water to pool in the crawl space. In this case, you will need to hire a water remediation company. In most cases, they will dig a trench around the perimeter, add drain pipe, cover the pipe with drain gravel, and add a sump pump. In other cases, adding roof gutters and downspouts, and reconfiguring the earth grading may be enough to eliminate pooling water.
Leaking plumbing pipes, either water supply pipes or drain pipes, may be allowing water to pool up in the crawlspace. Water leaking from damaged pipes above must be fixed before you put down a vapor barrier, or water will simply pool up on top of the plastic sheeting.
Basic features of an encapsulated crawlspace:
- 100% coverage of the ground with a vapor barrier
Seams and junctions of vapor barrier sealed
- Sealed crawl space vents
- Insulated foundation walls and band joist (usually)
- Conditioning of air with one of three methods: (i) dehumidifier, (ii) small amount of supply air from HVAC system, or (iii) small exhaust fan
- The benefits of this treatment are significant. As shown in the first article of this series, the relative humidity will stay below 60%, even when the outdoor humidity is much higher. With dehumidification, it’s not difficult to reduce the humidity to less than 50%.
Some other benefits are:
- Breathe easier. Vented crawl spaces have a huge negative impact on indoor air quality.
Reduce the chances of costly floor repairs. Moisture rots wood and causes hardwood floors to buckle.
Enhance comfort. Floors won’t be cold in winter. House won’t be muggy in summer.
Lower energy bills. Crawl space encapsulation can reduce energy bills by up to 20%, according to Advanced Energy’s research.
Make your heating & cooling equipment and ducts last longer. An air handler and ducts in a vented crawl space will not last as long as equipment in a conditioned crawl space.
Qualify for rebates and tax incentives. Some utilities offer rebates. The federal government has tax incentives for home performance improvements. Some state and local governments offer incentives as well.
An encapsulated crawl space is an attractive selling feature. Potential buyers comparing two similar houses will find the one with an encapsulated crawl space more appealing.
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