Crawl Space Insulation

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There are several different types of insulation used in crawl spaces, some work better than others and one in particular should not be used in crawl spaces at all except on the cement foundation. There are correct and incorrect places to install the insulation depending on what environment you are working with. If it is installed improperly you will waste your money and ultimately cause damage to your home. Insulation does not make your home warmer, heat does. Insulation only helps to hold in the heat.

Typical Crawl Space Design

The open crawl space

There are three major environment situations that call for insulation in a crawl space. The first is your standard dirt floor (may have some plastic laid on the floor) crawl with open vents which is referred to as an open crawl space. This environment is similar in temperature to the outside air in the winter which causes the homes floors to be cold and rooms farthest from the furnace to be drafty. Frozen water lines are common in this situation as is an odor in the warmer months. Most often these crawl spaces will have a lot of bugs and maybe even a rodent problem. This is the most common environment for a crawl space. Here you will find R-19 insulation (usually) in the floor joist cavities. This is required by code in most areas because of the open vents and the problems they cause with energy loss. When I say open vents, I am referring to any permanent foundation vent whether it mechanically opens and closes or not. On a side note, closing a mechanical vent does very little to keep the cold air out. It would be similar to a window in your home with metal louvers instead of double pane glass. This insulation is meant to keep the warm conditioned air in your home from being absorbed by the cold winter air in the crawl space. This however causes the problem with frozen water pipes because there is no heat source to protect them. The other problem with this design is most homes have their heat ducts running through the crawl space which are cooled by the winter air before they reach their destination. This causes the furnace to run more often and in longer cycles to keep the home at the desired temperature. Some construction professionals will recommend stuffing some R-30 in the open vents for the winter to keep the winter at bay. This will work and is a very low cost solution to the threat of frozen water lines. However you may be causing a new problem by doing this. Yes, it will be warmer in the crawl space but that also means your moisture levels will raise inside the crawl space and home during the cold months. This will continue any moisture problems you may already have with the open crawl space design. You will also have to be quick to take the insulation out of the vents in the early spring to avoid a bad moisture and odor problem. In this environment anything you do to correct one problem will most likely cause a different problem to occur.

Upgraded Crawl Space

The concrete floor

In this design a concrete pad called a “mud pad” is poured on the crawl space floor. This is essentially a concrete vapor barrier meant to help control moisture in the crawl space. This is done several ways; with and with out a vapor barrier. The traditional mud pad is a poured concrete pad over a roughly graded dirt floor. There is little prep work done to flatten the area so the concrete thickness can range from 2” to 6” thick. The final grade of the concrete will appear flat. A good contractor will install a vapor barrier on the floor prior to pouring the mud pad. This is done because the concrete itself is not a good moisture barrier. Water and moisture will pass through a concrete slab that does not have a vapor barrier with little trouble. The reason this is important is because if a vapor barrier is not used then closing the vents will cause other issues. But if a barrier is used then you will have the option to close them permanently. Closing the vents is the key to fixing the cold crawl space problem. The insulation installed in this application would be R-19. Install the insulation above the foundation wall inside the rim (or band) joist cavity only. Do not install any insulation inside the floor joist cavity (the crawl space ceiling). If you do it will be waste of money and effort as it is no longer needed in this area with the vents permanently closed. Think of this design as a mini basement. Next time you are in a full size unfinished basement take a look up and you will see there is no insulation in the joist cavities. The other option is to have spray foam installed on the foundation walls. The only real benefit here is to cover the portion of the foundation that is above the outside grade. The cost of this insulation is usually by the square foot, so the more you have sprayed on the more it will cost. Do not have the rim joist sprayed with this type of insulation. You could end up with problems repairing or replacing any wood that may get damaged due to insects or water damage. It also does not allow for termite inspection and that could be a huge issue if you plan to sell your home in the future. It would be a wise move to add a few heat ducts to the crawl space to keep it warm. A few words of caution, although this design is far superior to the open crawl space it potentially has some of its own problems. Even with a vapor barrier under the mud pad you will have to find a way to control the moisture that comes in the crawl space from the unprotected foundation walls. This area has the same potential for moisture and water problems as a mud pad that does not have a vapor barrier. If you close the vents in this design you will have to install a dehumidifier to control excess moisture.

All The Problems Are Covered

A conditioned crawl space

This design is referred to as many different names; encapsulated crawl space, closed crawl space, conditioned crawl space. All of these names refer to essentially the same result but may have a different process. The vents are permanently closed. The crawl space is completely sealed off from any moisture infiltration by using a heavy duty vapor barrier like DrySpace™. The vapor barrier is draped down the foundation walls and the entire floor is covered. All the seams are lapped by at least 8” and taped with a waterproof seam tape and the supports are wrapped and sealed. The vapor barrier is sealed to the foundation wall with either a polyurethane caulk, butyl caulk or Foundation Seal Tape to keep the moisture from escaping from under the barrier. The next step is using Foundation Pins to permanently fasten the DrySpace™ to the foundation. R-19 insulation is installed in the rim joist cavity to keep the outside air outside. Once this has been completed you can successfully condition the crawl space air. Conditioning the air is controlling the temperature, humidity or both. Now that the vents are permanently closed and the perimeter is insulated, heat ducts are opened into the crawl space along with an air return. This is not about heating the crawl space, it is about introducing heat to the home one level lower than it is now. Heat naturally rises so it will come up through the floors and keep them warm. The heat is not lost as it would be if the vents were open. This process will save you between 10 – 30% on your heating cost because you have eliminated cold air from entering the homes envelope. In an open crawl space design your home is being attack from all six sides but in a closed crawl space you have eliminated the largest exposed square footage of the home and created a new clean environment that is only inches from where you live, eat and sleep. The conditioned crawl space can be created by most able bodied homeowners with the right products, guidance and information. Contrary to what some large franchise companies offer, you don’t have to mortgage the house to be able to afford this home improvement.

For more information on how the DrySpace™ vapor barrier is installed take a look at our "How To" video.