Ok… ok. I get it. They are less expensive to build. Compared to basements, crawl spaces mean you dig smaller holes, haul away less dirt, and use less concrete. They have a reduced exposure to ground water problems. They allow you to build more usable space above ground at the same or lower cost. And compared to building on a concrete pad, they allow for access to utilities.
But let me tell you what I find as a home inspector. I get to see a space almost nobody goes into. I see a space that more often than not houses more critters than you probably care to know about. I see insulation that has been torn down, if not by the weight of rodents, then by the weight of their waste products. I find carpenter ants, moisture ants, Anabiid beetles and dampwood termites. I find insulated flexible ductwork that probably looked great when it was installed but now has its insulation torn up and holes chewed through it. I find insulated flexible ductwork that has been wrenched from the main trunk line, and when I find that I know the homeowner’s heating bill is probably three times what it ought to be, and they don’t want to know what has taken up residence in those soft heated tubes.
Crawl spaces that are out of sight in far too many instances means work done after the home’s original construction is sloppy and incomplete. I find gas, water and drain lines inadequately supported. I find coaxial cable lying all around, and occasionally find live electrical wires lying around as well. And it’s a good thing for the original contractor that they were not there when I discovered a bunch of wood construction debris, loaded with nails, lying on the ground underneath the plastic ground cover. Ignoring the fact that they didn’t care that someone (me) at some point in the future would be innocently crawling through the space on their elbows and knees… but what they prepared was a termite and ant buffet. Might as well have posted the address on the termite facebook page!
Sometimes the lack of thought or just plain laziness creates a real safety hazard. I didn’t get close enough to the abandoned electrical cable sizable enough to carry a 50 amp load to find out whether it was live or not. An inspector colleague in Connecticut talks about feeling a soft spot in the plastic groundcover in a crawl space, and being curious, pulled back the plastic. What he discovered was that he had been about to crawl over the thin plastic sheet covering an unsecured opening to a well!
If we can’t keep the insulation in the ceiling above… the home’s floor… tight to the plywood/OSB, we do not really have effective insulation. If it gets pulled down by rodents, how effective could it possibly be? If the ground cover is moved and bunched up by past workmen or your vents are blocked, how effectively can you keep moisture levels low? And high moisture levels in our area means the possibility of Anabiid beetles. They will live in your home’s structural timbers for about 6 years, just munching away. In Western Washington, they are a bigger threat than termites, and they love crawl spaces with wood whose moisture levels are between 13% and 20%. I always test several timbers with a moisture meter, and I see a lot that fall into this range.
After crawling through a lot of crawl spaces, I would have to say it is a real minority that still function as designed.
So what can you do if your house has a crawl space? My first recommendation is that you become familiar with it. I know it’s dark and full of spiders. Dress appropriately, strap on some knee pads and bring a flashlight (I bring three flashlights!) Know how it’s designed, what’s in it, and what needs to be done to make and keep it right. Then do it. Get the woody debris left behind by others out. Make certain the plastic ground cover effectively covers the ground. Keep the ventilation vents open and functional. Re-secure any insulation that is not tight to the ceiling above. Know where your plumbing lines are, find out if you have any drain line leaks and get them fixed, and keep your pressure lines insulated.
My second recommendation, particularly if you have an outside access hatch, is to make that hatch impenetrable. I can count on one hand the access hatches that have made me step back and be impressed, but if you want to keep rodents out, you cannot skip this step. Mice can slip through openings as small as ¼”, and rats don’t need holes much bigger than that. If the basic rodent creepy factor isn’t sufficient motivation, try and remember that as much as 20-30% of the air entering your home’s first floor comes from the crawl space through cracks, plumbing openings, leaks in duct work, etc., and rodents don’t bring portable outhouses with them when they enter.
In our climate, crawl spaces have become the default method of construction. I still don’t think they make any sense, but if you have one, don’t ignore it. The more attention you give it while you own the house, the less likely you will be surprised by my report when your future buyer hires me to find out what problems it hides. Because I will find them.