I Need a What in my Crawlspace?
RickGreg has decided on an insulated crawlspace for an addition he’s building to his house Connecticut. The crawlspace, or “more accurately a short basement,” will not be connected to the existing basement under the rest of the house, and the only mechanical equipment housed there will be an air handler for the air conditioning system.
“Apparently, our local building department still thinks crawlspaces need venting,” RickGreg writes in a post at Fine Homebuilding’s Breaktime forum. “I have been feeding my contractor articles from the Building Sciences site and posts from Breaktime on the logic behind unvented crawlspaces.
“He has gotten the inspector to agree to no venting,” RickGreg continues, “but only on the condition that we include a fan in the crawlspace to ‘move the air around.’ Does this make ANY sense?”
Take the course of appeasement
RickGreg could install the fan and just not use it, a course recommended by Andy Engel. And while this may be the simplest way out, it’s not very appealing.
“It just annoys me that if there is no good reason to do this,” he says. “I need to pay an electrician to run a line, buy and install a fan, etc. As with any project, I am bumping into budget limits, so this is an annoyance. I’d rather ‘educate’ the [building inspector] and help myself and those who follow after me.”
To Junkhound, there’s logic in Englel’s approach.
“IRC says stairs have to not pass a 4-in. ball,” he says. “OK, inspector shows up with a 4-in. all, one spot allows it to pass, you stick a piece of scrap wood onto that spot with double back tape, viola! YOU PASS! Tear it off later.
“Like Andy says, appeasement — you can hold up your permit in the air, wave it around, and cry, ‘Peace in our time,’ eh?”
If the local building code really does require a vented crawlspace, the inspector may actually be doing RickGreg a big favor by requiring something as simple as fan, Sapwood suggests,
“You may get away with a simple breeze box fan plugged into the outlet near the AC unit,” Sapwood writes. “Once inspection is done, either return the unused fan to Home Depot or use it to cool your jets during the summer. If code is on your side, and you like a good fight, you can tell the inspector to go pound sand.”
IdahoDon casts his vote with the appeasers.
“Spending time to educate and change the mind of someone who appears on the surface to not be all [that] sharp sounds like a lot of wasted effort,” IdahoDon writes. “Fans are cheap. Tapping into a crawlspace wire for power is cheap. Time spent butting heads with an inspector is time taken away from other more worthwhile activities.”
Wait, there’s more to it
Whatever RickGreg may have been told about the purpose for a fan, Rdesigns says, it wouldn’t be there just to “move some air around.”
“Sound to me like you didn’t get the full story, or maybe the inspector doesn’t understand how a fan would be used to meet the requirements of IRC section 408.3 that addresses unvented crawlspaces,” Rdesigns says.
That part of the code permits an unvented crawlspace if certain other conditions are met. One option, Rdesigns says, is the installation of a continuously operating fan that exhausts air to the outdoors at a rate of 1 cubic foot of air for every 50 sq. ft. of crawlspace area.
“The other option is to have a small opening for conditioned air to flow into the crawl a the same rate, along with return air transfer pathway to the common area above,” Rdesigns adds. “In both cases the walls must be insulated and the exposed earth of the crawl must be covered with a Class I vapor retarder, like 6mil poly with any joints sealed and overlapped by 6 in., and extends up the stem wall 6 in. and is attached and sealed to the stem wall.”
Just skip the crawlspace idea altogether
To Perry525, the solution is simple: replace the crawlspace with a slab.
“A crawlspace is perhaps useful for running cables — anything else?” Perry writes. “Constucting a crawlspace involves time and money — what do you get back for it?
“About two hundred times a year warm wet air arrives and we get frost or dew on the ground. This air is pulled into our homes by the passing wind and the stack effect. We then spend a lot of money heating this air. If our joists and other wood items are below the dew point we get condensation — this can lead to mold and wood rot,” Perry says.
“Tell me, why do people have crawl spaces? A nice solid concrete pad, is draft proof and if insulated correctly, is warmer.”