March, 2015
Inspection News and Views from the American Society of Home Inspectors

Don't Overlook Your Crawl Space



Every house is unique and foundation type is one

distinct difference between them. A home typically has a crawl space, basement or a concrete slab foundation. In this article author, Joe Provey explains how foundation type should be taken into consideration when upgrading a home’s energy efficiency. Joe’s article explains how a home with a crawl space foundation can increase its energy efficiency. Save energy with the bonus of controlling excess humidity and improving home air quality!

Like it or not, your crawl space and living space are joined at the hip. Holes for wiring and pipes, plumbing chases, leaky heating ducts, gaps in subflooring, ensure that your living space and your crawl space communicate freely! It is no surprise that the U.S. Department of Energy recommends you insulate your crawl space. Insulation in the floor joists is typically inadequate to offer much of a barrier. To make matters worse, the laws of physics actually cause the air in your crawl space to be pulled up into your living areas. As warm air rises in the upper levels of your home, it creates a draw on the lower areas. As much as 40 percent of the air in your crawl space eventually mixes with the air inside your home.

This creates a whole series of problems, ranging from energy loss to breathing unhealthy air. In summer, cool air is lost to the crawl space. In addition, excess humidity from the crawl space causes your air conditioner to work harder and use more electricity than it should. In winter, cold air entering through the crawl space makes your floors cold and first-level rooms drafty. Heating bills climb. Winter and summer, you’re apt to be breathing unhealthy air laden with allergens and soil gases.

There are five steps you can take to turn a crawl space into a clean, healthy, energy-efficient part of your home. Here they are, roughly in the order you should tackle them:

1. Seal and insulate rim joists

The first framing member attached to a foundation is called the sill plate. It lays flat atop the home’s foundation wall and is fastened to it with J-bolts or by some other mechanical means. Because the top of the foundation is often uneven, there may be gaps under the plate. In new construction, a gasket helps to solve this problem, but in older homes it is a major cause of air leakage. The second framing member is the rim joist. It rests on edge upon the sill plate and provides a way to secure floor joists. Subflooring is installed over the rim and floor joists. Air leakage may occur at the joints between the sill plate and rim joist, as well as between the rim joist and subfloor. In addition, the R value of the rim joist (its ability to stop conductive heat loss) is only 1.88 – about the R value of a single-pane window with a storm window in place.

To stop energy loss from the framing assembly that rests upon your foundation wall, seal all joints with a bead of closed-cell foam insulation. Then install rigid foam board insulation against the rim joists wherever possible. For example, cut the board insulation to snuggly fit between the floor joists and between the sill plate and subfloor, then press it against the rim joists. If the fit is loose, fill the gaps with spray-foam insulation.

2. Seal ducts that run through crawl space

Heating and cooling ducts often reside in the crawl space. Typically fabricated from sheet metal, they’re used to distribute warm or cool air to the rooms of your home. Unfortunately, ducts typically leak a large percent of the air they carry. This means your HVAC equipment must work overtime and that your energy bills are higher than they need to be.

To stop energy loss from ducts, seal all metal-to-metal joints and holes with mastic sealant or with metal tape. Do not use duct tape because it will eventually fail. Seal joints between the subfloor and ducts with spray-foam insulation. If you do not plan on insulating the walls of your crawl space, consider insulating the ducts with duct wrap. Duct wrap is a fiberglass product with a foil vapor barrier to the outside. Be sure to seal all seams with aluminum duct tape; Otherwise, air leaks will allow moist air to penetrate the wrap. In summer, that moisture is likely to condense on the cooler ducts and wet the fiberglass – and wet fiberglass is ineffective as an insulator.

3. Insulate walls

The above- and below-grade portions of your crawl space wall will lose heat in winter, so you will save energy and be more comfortable by installing wall insulation. Rigid foam boards can be adhered to or mechanically fastened to either block, stone or concrete walls. They are waterproof and will not support the growth of mold. The recommended R value depends on where you live. Check with D.O.E. recommendations or with local building department officials for recommendations in your area.

4. Encapsulate

A continuous vapor barrier that covers both floor and walls adds another layer of insulation by sealing out air leaks. It will also help control moisture and stop soil gases from infiltrating your home. For a vapor barrier to be effective in the long term, it must be durable. If interested in taking on this project yourself, I recommend this guide that explains how to install a vapor barrier: If your crawl space is susceptible to water infiltration, install drainage matting before installing any liner. It will allow water to drain toward either a drainage pit (no pump) or to a sump basin and sump pump for discharge. Here is a resource explaining in detail what needs to be done to fix crawl-space water leaks:

5. Dehumidify

If you’ve opted for encapsulation, install a dehumidifier in your crawl space to dry out framing and flooring that has long been exposed to excess humidity, as well as to ensure against excess
humidity on an ongoing basis. Lower humidity in your newly conditioned crawl space will translate to lower cooling costs and greater comfort in warm weather.

An investment in any or all of the above will make your home more energy efficient and improve the comfort level and health of family members. In addition, controlling moisture levels protects your home from structural damage due to rot, corrosion and termite infestation, and can give your home extra storage space.

Interested in learning more about crawl spaces? This very informative crawl space learning center can educate you on this often- overlooked part of a home:

Joe Provey is a veteran do-it-yourselfer and journalist. Joe frequently writes about DIY, energy efficiency and home building topics.