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Encapsulating a crawl space is a common way to deal with moisture or flooding. It is also an easy way to quickly get control of the air quality in the home and lockout rodents and insects. When you’re thinking about “green-ovating” your home, or simply getting control of the moisture or humidity, when you have a crawl space, you must encapsulate.

Encapsulation does a great deal for the crawlspace and for the home above.

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What the process is and what it does

The practice of encapsulating or “sealing off” a crawlspace is done to lock out moisture and cut off the connection between moisture, water and the joists of a home. By running a vapor barrier down the walls of a crawl space to completely cover the floor, you essential separate the outside from the inside of the home.

This vapor barrier will be the flexible membrane between the walls and floor and the rest of the home. A properly designed vapor barrier will limit the transfer of moisture through it while regulating the speed at which air will naturally pass through. This helps to limit and control the amount of moisture that will find its way into the air space and completely segregate liquid water and direct it to a sump location.

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5 helpful tips when having a Vapor Barrier installed in your crawlspace:

1.) Not all vapor barriers are made for this task – careful. There are many products out in the world that claim to be able to fully encapsulate a crawl space. Make sure that your vapor barrier has a low “perm” rate and that it is at least 14mil thick. If you’re planning to use the space for storage make sure that a flexible sub-flooring product is also placed on top of the vapor barrier to protect it.

2.) Cover the walls too – all too often contractors forget to also encapsulate the walls of the crawl space when installing a vapor barrier. This can still allow water and moisture into the basement and therefore render the whole project useless. Take care to make sure it’s installed properly.

3.) Don’t use sprays. – Sealants and sprays aren’t designed to be applied on the interior of the basement. They are good in many circumstances as the “first line of defense” but as the last, they can’t hold the pressure and moisture trapped in a wall.

4.) Install a sump and a dehumidifier – to totally control the moisture level in the crawl space it’s imperative that you have a sump pump and a dehumidifier installed. Moisture will still exist, although not to dangerous levels, but a sump will remove any liquid water your encapsulation traps, and the dehumidifier will deal with any residual moisture that naturally collects in the space.

A Closed, Sealed Crawlspace - What a Really Bad Idea

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Many homeowners try to cut costs and increase their home's comfort level by installing a crawl space vapor barrier. This will instantly make your home healthier for you and your family, and prevent moisture damage, mold, mildew, foul smells and odors.

Most homeowners tend to look at their crawl space as separate space from their home, but in reality, the two are one. Water vapors that surface from the ground are continuously entering, creating undesirable conditions for you, your family, and your home.

Purpose

The purpose of a crawl space vapor barrier is to stop moisture and wetness from entering and affecting the floor and walls of your basement. Moisture tends to flow from warmer to colder spaces.

Many homeowners don't realize the importance of the proper installation, in order to keep moisture and water vapors from getting in the walls and floor of your basement-- condensation can lead to expensive structural damage. Also, if you can help control the moisture and dampness, you can greatly reduce the amount of energy required to cool and heat your home.

Preparation

When considering the installation of a vapor barrier, take into consideration two spaces in your home; the crawl space and the attic. Humidity tends to build in the walls of both these areas causing mold, mildew and dry rot. This can cause severe health issues for adults and children, especially for those with asthma, breathing difficulties, and allergies. In addition, it can cause severe structural damage to your home.

Some homeowners think that because they insulate the floor joists there is no need to do any additional work, but these items do not serve the same purpose!

Tips for Installation

One of the most popular do-it-yourself vapor barrier products is polyethylene, or plastic sheeting. This plastic sheeting comes in various thicknesses; 4mm, 6mm and 10mm.

With today's technology, this product is made from a high quality material, resistant to rips and punctures. Always check the soil so there aren't any objects or materials that may damage the lining. The slightest puncture, rip or tear could compromise the entire system.

Always, make sure the space is dry before you begin any repairs. To remove the moisture, you may need a dehumidifier.

Overlap the barrier a minimum of 12 inches on the side walls. Be sure it is tight. Use furring strips and masonry nails to firmly secure the lining then caulk along the joints.

Seal all the seams with a heavy duty tape. However, it is recommended not to use tapes that are not specially designed for sealing vapor barriers. When working in the basement you will be forced to contend with pipes, make the proper cuts and seal securely with tape.

The completion of your crawl space vapor barrier will be the best investment you can make in your home.

Crawlspace Vapor Barrier Mythbusters

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Outlined below are the most common 4 methods I have seen used in installing a vapor barrier. If you talk to different builders, you usually will end up with many different methods of installing a vapor barrier in a crawlspace. Here are the most common:

1. Pea Gravel on top of plastic vapor barrier - This has to be the all time dumbest thing I have ever seen, and yet it is probably one of the most common. I have had builders tell me that the plastic on the ground KEEPS ground water and moisture from coming up from the ground. Now if there is no moisture or water in the soil, this might be possible; but if that was the case there would be no need for the barrier in the first place. So here is the basic idea - ground floor (bottom) - plastic (middle) - 4" pea gravel fill (top). Once the crawl foundation is built, builders install a 4 - 6 mil plastic on the ground and dump about 4" - 6" of pea gravel on top of the plastic. Eventually, what always happens is that water comes in from the walls and the ground floor and ends up on top of the plastic. So what you end up with is a swimming pool liner that holds water in the gravel for prolonged periods of time. Nearly all the water and moisture in the gravel back fill has to evaporate into the structure. Another example of building practices and science turning a blind eye to crawlspaces for decades.

2. Vapor barrier on top of ground floor - By far the most common practice for installing a vapor barrier. A 6 mil polyethylene vapor barrier is placed over any ground floor. Here is the idea - ground floor (bottom) - plastic (top). The ground floor could be river rock, pea gravel, dirt floor, sand, etc. The seams are typically overlapped 6" - 12" and almost never taped. While this will temporarily stop some moisture evaporation, it does not seal out moisture from the internal perimeter wall where most water penetration occurs. Also moisture can come up from the seams, and the plastic is not durable enough to crawl on. It nearly always ends up with many punctures and holes in it.

3. Vapor barrier on bottom of floor joists - This is rarely seen, and usually only home owners attempt this. This is probably the method that accounts for more wood rot than any other method. If you are even thinking of doing this, quit thinking and call a professional to fix your crawlspace. Most crawlspaces are vented and the cooler surfaces such as duct work, pipes, and the floor will condensate in the summer. The plastic will trap the condensation up against the floor structure and mold and wood rot will occur. Good intentions do not always produce good results.

4. Vapor barrier fastened to sill plate - There is a new industry in crawlspace repair that encapsulates crawl spaces. The process of encapsulation is to install a heavy think plastic liner on the floor and up the foundation walls. The plastic liner is fastened and sealed to the foundation wall and all the overlapped seams are taped. Every potential gap or seam in the liner is meticulously sealed to prevent any moisture from evaporating. Then the vents are sealed in the encapsulation system to prevent hot humid air from entering in the summer. There is another system being sold and installed out there being represented as an encapsulation system, but is far from it.

This "other" system is a 6 mil plastic that is ran up the foundation walls and stapled to the sill plate. None of the overlapped seams are taped. It is basically a glorified vapor barrier on top of the ground floor being ran up the walls and stapled to the wood. They seal the vents without properly sealing the moisture from the ground floor or foundation walls. The problem with fastening plastic to the sill plate is that moisture will "wick" up the foundation wall, and moisture will absorb into the sill plate and floor joists. They are giving free access to all the moisture under the liner to rot the sill plates and floor joists. Not to mention that all the moisture will evaporate up through all of the seams that aren't taped and the plastic liner is only 6 mil and eventually will puncture and tear. Be very careful in the contractor you choose to properly encapsulate your crawlspace.