How Do I Make My Crawl Space More Energy Efficient?

Thinking about some Do-It-Yourself (DIY) home improvement projects for your Texas home, but you’re not really sure about what to do or where to start? You’ve come to the right place! Welcome to the DIY Energy Efficiency Tips series from First Choice Power. We’ll show you how to improve the energy efficiency of your home, including hints that make the jobs easier.

Caring for Your Home’s Crawl Space

How Do I Make My Crawl Space More Energy Efficient? | The Light Lab

Homes in Texas generally come in two foundation flavors, slab-on-grade and pier-and-beam. While poured slabs are more often part of new home construction, pier-and-beam construction remains a popular method and is also a feature of most older homes. While pier-and-beam construction is more expensive to build, it allows easy access to the home’s wiring and plumbing plus it’s also more forgiving when it comes to adjusting for ground surface fluctuation that occurs over time. Unfortunately, crawl spaces have long been known to to have humidity problems involving mildew, mold, warping floors, and wood rot. The primary reason is that in hot and humid climates, crawl spaces were built with ventilation under the assumption that air flowing in from the outside would keep the crawl space dry. In fact, it’s been long known that venting makes the condition much, much worse.

Outside air will only remove moisture from inside the crawl space if the outside air is less humid. As anyone in eastern Texas knows, dry summer breezes don’t happen that often. Crawl spaces tend to be dark, cool places, so humid air circulating into a crawl space is more likely to condense on the cooler wood, plumbing, and piers— depositing moisture. Running your air conditioner can actually add to this problem by helping to cool your home’s framing. A study in 1962 found “Wood decay in floor members was noted in many instances and was usually linked to wet (uncovered) soil in crawlspaces, continuous air- conditioning, or low indoor temperatures (≤70°F (21°C)).”

So, by caring for your crawl space, you’ll not only improve your home’s energy efficiency but you’ll also protect it from expensive repairs due to damage.

Eliminate Exterior Moisture Sources

How Do I Make My Crawl Space More Energy Efficient? | The Light Lab

The first step of making your crawl space more energy efficient is to keep the moisture out. That includes blocking all sources of water leaks, humid air, and water vapor. Water can get inside through holes, cracks, as well as pass through porous materials, such as wood and concrete. That’s why it’s important to be sure that rain run off is channeled away from your home. Keep an eye out for clogged rain gutters or downspouts that pool rain water next to your home. Try to grade soil around your home so that it slopes away from the foundation at a minimum of 5% for at least ten feet.

Next, knock out the air vents and seal their holes with masonry. As mentioned, the outside air brings in more moisture than it takes away. Encapsulating the crawl space solves moisture problems, improves the effectiveness of subfloor insulation, and increases your home’s heating and cooling efficiency.

How Do I Make My Crawl Space More Energy Efficient? | The Light Lab
Keep the dust off any air vents!

To insulate the walls and provide a degree of moisture barrier, install fire-rated rigid foam panels (use either blue [Dow] or pink [Owens-Corning]) around the entire crawlspace. The panels can be held in place with panel cement or fasteners. You’ll need to measure the length and height of the walls to calculate the right number ahead of time. Leave a three inch wide gap from the top to allow termite inspections. Closed cell spray foam can also be used and may be used.

Next, a significant amount of moisture enters your home just by evaporating from the soil in your crawl space. To block this, you’ll need to set up a vapor barrier. Measure your crawlspace so you can put down at least a 6 mil plastic vapor barrier over the entire bare earth floor of the crawlspace. Most 6 mil plastic comes in 100’ by 20’ rolls so expect to cut and piece sections together as you put down the barrier. Keep in mind you will need to overlap and tape all seams by 12 inches, and leave enough extra to seal the sheet 6 inches up the crawl space walls. (Note—in most instances, you’ll notice the change in the humidity of your home within 24 hours!) secure the vapor barrier with either a good elastomeric sealant or a pressure treated nailing strip attached to the concrete block.

Lower humidity means your air conditioning will use less energy removing moisture from the air.

Eliminate Interior Moisture Sources

How Do I Make My Crawl Space More Energy Efficient? | The Light Lab
See a leak? Fix it immediately!

There’s all sort of potential leaks coming down from the living area that can add to moisture levels in the crawl space.

  • Leaky plumbing— repair all cracks and bad connections. Not only do leaks add to your home’s moisture problem but they also add to your water bill.
  • Water softener discharge lines — these should empty into a drain using an appropriate 2” air gap.
  • Air conditioner condensate lines and dryer exhausts — make sure these are properly routed to vent outside.
  • Sump pump crock pits — these should be kept closed and sealed if possible.

Is it still damp? You can install some exhaust fans to push out that dap air from the crawl space and pull down some of the dryer conditioned from the living space.

Seal and Insulate

Joist bays (spaces where floor joists meet the band joist just above the foundation) are insulated by cutting pieces of rigid foam insulation to fit and then held in place with expanding foam. Most of these will be the same size so count the number of bays and note any of them that are different so you can cut the foam pieces all at once and then install them quickly.

Seal any place where plumbing and electrical lines emerge from the living space above. Also seal any place in the foundation wall where plumbing or wiring exits. Not only will this seal off outside air, it will prevent pests from entering and making it their home.

Seal and insulate all duct work that passes through the crawl space. If you have unsealed return duct work passing through crawl spaces, your HVAC system could blow mold, mildew, and fungus spores throughout your home. Not only will this ensure that only the air from the conditioned space is used but it will also help it maintain pressure and temperature efficiently.

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Vernon Trollinger is a writer with a background in home improvement, electronics, fiction writing, and archaeology. He now writes about green energy technology, home energy efficiency, the natural gas industry, and the electrical grid.