Last time I wrote about the importance of controlling air movement through your home for energy efficiency in the air conditioning season. If you live in a house with a ventilated crawl space as historically most have been throughout North Carolina, the most effective step you can take to avoid the unwanted infiltration of humid air is encapsulation. It can also protect your respiratory health.
How does this work? Encapsulation is the process of applying a comprehensive moisture and air barrier to the floor and foundation walls together with thermal insulation to the walls so that the crawl space air is protected from outside humidity and temperature cycles. Your crawl space is now effectively clean, conditioned space, virtually on a par with the air inside your home. Not only does this procedure block the updraft of air leaks through the home, saving you money, it also ensures a clean and protected space for the air handler and ductwork of your HVAC system. A ventilated crawl space is a mold factory: after encapsulation, minor leaks in the mechanical system are no longer capable of introducing mold spores into the ductwork and distributing them through your home. Win/win!
More information here:
A typical vented crawl space. Note the moisture on the foundation walls and fiber insulation hanging in tatters from between the floor joists.
After encapsulation. Heavy polyethylene sheeting with carefully taped joints covers the floor and extends up the exterior walls and piers. Foil-faced board insulation is applied to the interior of the foundation walls leaving a narrow strip at the top to allow periodic termite inspection. Insulation is no longer needed between the floor joists leaving plumbing, electrical and ductwork completely open for inspection, renovation and repair. Mechanical equipment and ductwork is completely protected from humidity and mold.
... and the humidity. Here in central North Carolina the mercury hit the high eighties last week moving us from an often chilly spring into a warm early summer: time to fire up the A/C! What can we do to reduce the energy load from all that grateful cooling to save money and help the planet?
Turns out that in the humid summers of the southeastern US much of that energy is used not to cool the air but to wring the moisture out of it, and if our home continuously allows humid air to enter from the outside it’s like bailing a very leaky boat. Back in the energy crisis of the seventies air sealing meant caulking windows and air stripping doors. Now we know that our biggest air leaks in summer happen not through doors and windows but through our ceilings and floors because of the stack effect, where hot air rises, exits the building and and is replaced from below. Stack effect cooling can be a good thing if the replacement air from outside is cool and dry, but what if that replacement air entering the home is already hot and humid? That’s what's happening in the summer if you have an older home with a traditional ventilated crawl space, even when the windows and doors are tight shut. A multitude of small holes in the floor below and the ceilings above from electrical and plumbing penetrations allow an astonishing amount of unfiltered outside air to flow through your home, and your air conditioner is working overtime to cool and dehumidify that constantly changing air.
The good news is that there is something we can do about this which can pay for itself in short order with much-reduced summer energy costs, with a side benefit of better indoor air quality and mold control. It's called crawl space encapsulation, and I'll tell you all about it next time.
We've been designing custom homes for a quarter of a century but writing blogs is a new venture, so bear with me and wish me luck. I'll be writing about the ways that thoughtful design can help your home live its very best life. I hope you'll be chiming in with your comments and questions as we go.