Do It Yourself Energy Efficiency Projects: Your Home’s Thermal Envelope (Part 1)

By Vernon Trollinger, January 15, 2010, Energy Efficiency, Home Improvement

That first week in January was bitterly cold, wasn't it?  And lots of people all across the state had their heating systems cranked to full throttle just trying to keep their homes warm and their pipes from freezing.

Of course, your Texas Electricity bill will be higher than normal.  And there's still a whole lot of winter left to go.

But don't worry.  There are a few things you can do around your home to save money during the remaining winter months.  These will also save you money during the hot summer. Basically, you need to air seal your home's "thermal envelope". Because of the price and use of energy, architects and builders now design a home to be a "thermal envelope". This is the sum total of the home's insulation systems including walls, ceilings, foundation, floors, windows, and doors. These work more effectively with good, tight fits that seal-out the weather, moisture, and air. By having a tight seal on your home's thermal envelope, the less energy you waste or lose by exchanging it too often with the air outside. 

Over the next few weeks, I'm going to take you from ground level and work our way up to seal your house. You might think it is beyond but these are easy tasks for any average person.  Plus, you might be able to take advantage of the Federal Energy Efficiency Tax Credit and save on your taxes, too.

One word of warning:  you will get a little dusty and dirty.  

So, let's get to the bottom of it all: your foundation.

Moisture Barrier

 A moisture barrier covers the earth beneath a structure to prevent moisture from infiltrating the structure from the ground. Wooden structures last years longer if they are kept dry and out of contact with the ground. For a house, not only does it help prevent rot but it also helps keep the living space drier. Because moisture in the air holds heat, even during the most humid months, a moisture barrier will make your Texas home feel drier and cooler. 

Most Texas homes are built on either a slab or have crawl spaces under them. Newer houses with slab foundations typically have concrete poured on top of a plastic moisture barrier. This limits the infiltration of moisture into the thermal envelope of the house. Homes with crawl spaces, meanwhile, feature a moisture barrier in their crawl spaces. Some older homes do not have a moisture barrier and these can be installed by the home owner very easily. 

A moisture barrier is plastic sheeting, usually about 6-8 mils thick and is available at any hardware store, typically in sizes ranging from 25 x 25 feet to 100 x 100 feet. It also need not be one single piece of plastic. As long as the sheets overlap each other by about 6 inches or so, the barrier will be effective in reducing moisture infiltration. 

To install, you will need to know the dimensions of your crawl space and buy enough plastic sheeting to cover the ground in that space. Simply cut the plastic sheeting to cover the earth from wall to wall, laying it flat. You can use either black or clear plastic, but I would use clear because black plastic would make your crawl space feel like a cramped version of Batman's lair. 

You should feel the difference in your home within 24 hours. If your house feels too dry, simply fold back some of the plastic sheeting to expose the earth underneath. Continue adjusting until your home feels the most comfortable to you. 

As mentioned, moisture barriers limit the infiltration of moisture into the thermal envelope of the house. The house feels drier: It will be easier to cool in the summer and less likely to develop mold or contribute to wood rot in the winter.

Visit the Bounce Energy Education Center for more tips on saving energy.

Stay tuned for next time:  Mudsill and Rim Joists!
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