This post is just an observation that I hope will stimulate some conversation about the subject of closed crawl spaces. This evolved out of conversations with two builders—one a high-end custom outfit and the other an affordable builder. Both of them had been certifying their homes to EarthCraft House standards and were building with closed crawl spaces. On the same day last week I heard from both builders that they were having moisture problems in their closed crawl spaces, were reluctant to continue building them, and were considering returning to vented designs. Now, I haven’t yet visited any of their job sites, so I am working on some conjecture here, but these problems raise some interesting questions.
The affordable builder told me that all their sealed crawl spaces had HVAC systems, which were expected to maintain appropriate humidity levels. However, the builder discovered that the homeowners were often turning off the air-conditioning for much of the year as a cost-saving measure. They were willing to be uncomfortable to save money—not necessarily a bad policy—but it led to mold and mildew problems in humid months. The custom builder had problems in closed crawl spaces that did not have HVAC systems in them, and ended up having to install stand-alone dehumidification systems for moisture management.
Behavior vs. process
It appears to me that we are dealing with two separate issues: behavior and process. Assuming that the closed crawl spaces were constructed properly to keep bulk water and vapor out, the ones with HVAC systems should have functioned just fine, provided the systems were running in humid weather. The fact that the homeowners chose to turn their systems off is a behavior issue. They were not behaving as expected (does anyone?), which caused problems in the structure.
The builder could have put in a backup dehumidification system, but that would have presented a higher first cost as well as ongoing electrical costs to operate when needed. This reminds me of the quote “You can’t idiotproof things because the idiots are too smart.” This is not to demean any homeowners; in fact, I applaud them for not using their AC indiscriminately in order to save money and for being willing to live with a little less comfort. In this case, the “idiots” may, in fact, be the people who thought up closed crawl spaces in the first place, assuming that everyone would operate their homes appropriately day in and day out. No offense intended toward the smart building science folks who developed these things, but we have apparently come up against the law of unintended consequences. A well-thought-out design was taken down by someone who chose to operate the house differently than expected.
I reviewed A Quick Reference on Closed Crawl Spaces by Advanced Energy and noticed that among their recommendations they include “a mechanical drying system to reduce humidity” in the crawl space. In the case of the affordable builder, they apparently met those requirements, but were foiled by the owner’s behavior; while in the case of the custom builder, it was a process issue: They did not include a method to mechanically dry the crawl space in their projects.
So what’s the answer?
I don’t pretend to suggest that we stop sealing crawl spaces (I already had my head handed to me recently by implying that we stop insulating!), but I do think we need to take into account owner behavior and builder process when we make decisions on how to build homes.
As energy prices increase and the economy continues to stagnate, we may likely see many formerly middle-class homeowners looking for ways to save money, who are willing to live with less comfort and may use their air-conditioning less to do so. If any of them live in homes with closed crawl spaces, we will likely see more humidity-related problems in these homes. As to the other problem, it seems to me that this was a case where a very well-intentioned builder missed a key part of the puzzle in creating a closed crawl space and paid for it by bearing the cost of installing a dehumidifier.
Can we outsmart the idiots?
In both cases, these builders are leaning away from closed crawls in future projects — a decision that I don’t believe is necessarily in their best interest, but helps them to avoid liability by reverting back to older, less-efficient building techniques. Builders should carefully consider their construction techniques and get the right advice all the way through the process to make sure they don’t miss any critical pieces of the puzzle. They must also consider homeowner behavior, how it affects building performance, and how it might change over the course of home ownership.
This last one might be too challenging for anyone to adequately manage, so do we look for alternative techniques that are, in fact, truly “idiotproof”?