Derekjr. Battling with my local, and clueless, code officials,over crawl space ventilation, was one of the primary drivers for my decision to end a very successful homebuilding business. The biggest reason was that I had the chance to FIRE, and a sweet pile of cash accumulated to do so, but this whole mess instilled a deep hatred for clueless bureaucrats and the power they can wield. The code sections you cite accurately reflect what a mess the ICC residential code is, and how it fails to address technology, and mandates stupid, dangerous methods, while masquerading as the standard for life safety. Once you end up administering the thing using bureaucrats who couldn't build a dog house from a precut kit, and worship the IRC book like it's a fucking bible, all is lost. Which is where I found myself a few years ago.
For nearly a decade I built dozens of incredible, sealed conditioned crawl spaces that performed flawlessly. This was in a cold wet region, in heavy clay, where full basements were often full of water, and most crawls were a failed, moldy mess. I used poured concrete walls, exterior drainage and wall waterproofing, a poured "rat slab" thin concrete floor over a poly barrier, and insulated with R-10 closed cell sprayed urethane on the walls, covered with a fire rated intumescent coating. I varied from the 2006 & prior code for one reason. I did not use a ducted HVAC system to control the space. I did this for several reasons. First, these were typically seasonal homes, and if the HVAC wasn't run 24/7/365 the space would not stay conditioned. Second, with the extreme sealing, and insulating, the space would not go below the temperature of the building above, period. So, if you left the place in winter, and the electric baseboard was set at 50*, the crawl stayed at that temp also. Third a dedicated dehumidifier is required in the space for it to maintain a healthy environment. In that heavy, wet clay, ducted HVAC, designed to moderate the living space, will not resolve crawl space moisture issues, not to mention that HVAC, ducted to the crawl is an awesome way to circulate mold, and radon, and distribute it evenly into the living environment. Since I had local "good old boys" for inspectors at the time, this was fine. They were good builders who knew that my technique, including everything but the fire coating, was nothing new, nothing I discovered, and had a history of working well in the area, since the 1960s, when it was first tried. (That's no a typo. By the sixties a local contractor was spraying foam for agricultural/cold storage applications, and
decided that it could be useful in crawls. Fifty years ago they would put poly down. Next, they often poured a rat slab by passing bucket of concrete down to a guy who would hand trowel it, five gallons at a time. they would bang some plywood into the air vent openings, and spray a thin coating of closed cell foam. All this about 30 years before it was discovered by the industry at large)
A few years later as the corruption of the code industry spread to my little corner of the world, and local municipal inspectors are suddenly obsolete, as regional engineering firms weasel into position. They offer to take all the responsibility off the hands of the small town, and townships and give them lots of money for free. They just triple and quadruple permit fees, then give a cut to the town. Naturally, this is all administered by scum sucking apparatchiks, who have various degrees, worship the book, and can't find their own ass with two hands and a flashlight. Now the fun starts.
Shortly after the good comrades settle into their desks, my very first set of plans is rejected, with a cut and past section on unvented crawl spaces attached. What they don't know is that competent inspectors have lobbied the IRC for years on a way to allow my system, since it is superior, and there is no need to used ducted HVAC to condition the space, and lots of reason to avoid doing so. The IRC responds with 403.8, a monumentally stupid and dangerous thing to do.
I then ask the head bureaucrat why anybody would ever install the exhaust and air supply, if they had any interest in the health and life safety of future occupants, and if she was willing to accept future liability for this asinine idea. Naturally, she didn't have a clue of what I was asking. So I asked the following questions.
1. We are in a very high Radon area, yet sadly, there are no IRC requirements for testing and mitigation. Why would I install a system to potential exacerbate radon levels inside the structure?
2. There are stringent fire sealing requirements to isolate the living space from the crawl, sealing of all penetrations, prescribed thickness, and fire rating of floor materials, etc. Yet you are demanding that I cut a 4x10 open vent right through the floor, voiding that barrier, why is this a good idea?
3. In the event of a fire in occupied space, it is possible to draw flames through the floor vent, through the crawl and out the exterior vent. This could accelerate the fire, and lessen the chance that occupants could escape, are you willing to be responsible for this massively stupid error, in the event of fatalities? Do you know what a duct fire shutter is, and why is it not a requirement?
4. Here in a zone six location, where the biggest energy expenditure is heating, why would anybody want a system that created a vacuum on the exterior envelope of the home, and creates a massive loss of heated air, as tens of thousands of CFM a day are infiltrated into the structure, heated and wasted to the outside? Do you really think that the average new customer isn't calling the builder the first winter of occupancy, and asking why their first heating bill is three times what the neighbors is? Do you really think that 99% of all of these fans are not going to be disconnected within the first year? Then how do you control the crawl? Oh, yea, you seal up the hole where the fan was, and you put a dehumidifier down there.
In the end I was building the same great crawl spaces. I would add another dryer vent hood to the band joist, temporarily install a 40 CFM duct fan, and hardwire it in. Then cut a small floor register into a obscure area, like a bathroom linen closet. After the good little drones signed off on my final, I would pull everything but the floor register, and seal the space up properly. Toward the end, one of the apparatchiks discovers that they can bust some more balls, and generate another fee, by enforcing standard slab requirements on anybody who uses rat slabs. The whole purpose of the rat slab was to have a thin layer of concrete to permanently protect the vapor barrier from wear and damage. Now they want 4" of gravel under, a sealed and inspected vapor barrier, and full 4" slab, like any basement or garage floor. It is totally a waste to material and money. They could care less, it's "in the book" and they can't let you pour a floor without inspecting the vapor barrier first, so it creates another inspection step that they can bill for. So, now I'm forced to skip the concrete, and just use plastic. I simply can't take another $1500 of unrecoverable funds out of my pocket, to waste on concrete that nobody will ever see, or need, just so an inspection agency can stick another $75 in their pocket.
In the end I said screw it, enough is enough. Hopefully, I've made a more important point here. That being don't EVER use continuous, conditioned ventilation to deal with a sealed crawl space. It's stupid and dangerous for many reasons.