Wet crawl spaces make for wet houses - a follow up.
My previous post about wet crawl spaces and wet houses spurred me to do additional research.
When I have HVAC or ventilation questions, I contact Dr. Max Sherman. His team at the Lawrence Berkeley Labs is integrally involved with ASHRAE and RESNET/HERS energy standards. Familiar with him for decades, I have an engineering book in my library he wrote years ago! Dr. Sherman has always been exceptionally generous with his time and has always answered my questions.
I wrote him about the confusing info out there about ventilation - summer vs. winter, hot weather vs. cold weather, forced air movement vs. passive air movement, etc. And I discussed the very wet crawl space yesterday, sending some photos.
The terrifically wet crawl space in question was intended to be ventilated. But the vents had been closed, perhaps for some time. There are "vent less" crawl spaces created now, but those have particular criteria as regards materials and techniques. So my questions concerned ventilated crawl spaces in general.
One specific in my email was this: "My philosophy is that dead air is not good air."
The first line of his response: "Either a vented or sealed crawlspace can work. One must look at heat, air and moisture transport and make sure the design is sufficient whatever the choice."
The 2009 International Residency Code states this as regards crawl space ventilation: "R408.1 Ventilation. The under-floor space between the bottom of the floor joists and the earth under any building (except space occupied by a basement) shall have ventilation openings through foundation walls or exterior walls. The minimum net area of ventilation openings shall not be less than 1 square foot (0.0929 m2) for each 150 square feet (14 m2) of under-floor space area, unless the ground surface is covered by a Class 1 vapor retarder material. When a Class 1 vapor retarder material is used, the minimum net area of ventilation openings shall not be less than 1 square foot (0.0929 m2) for each 1,500 square feet (140 m2) of under-floor space area. One such ventilating opening shall be within 3 feet (914 mm) of each corner of the building."
The National Association of Insulation Manufacturers (NAIMA) defines a Class 1 Vapor Retarder as: Class I - Very low permeability vapor retarders - rated at 0.1 perms or less. Sheet polyethylene (visqueen) or unperforated aluminum foil (FSK) are Class I vapor retarders.
To be effective, this vapor retarder, a thick sheet of plastic, must cover the entirety of the soil, be sealed together and go all the way to the edge of the foundation wall.
Dr. Sherman further: "If the crawlspace is isolated from the main space (i.e. by good thermal, moisture and air barriers) then the question is only about keeping the crawlspace from having moisture problems. (A crawlspace that has leaky ducts going through it can never be isolated from the main space.)"
This crawl space did not have good moisture barriers, and as the vents were closed off there was no way to carry off moisture.
In 2000, Clemson University studied ventilation in what they call "Clear Vent Areas (CVA)," meaning attics and crawl spaces, and concluded with what became the IRC standard for crawl space ventilation which came later - one square foot of venting is needed for every 1500 square feet of soil area. And, further, the obvious - that the soil needs vapor retardation. Another reason the Clemson study says venting is needed is to carry off gases from termite treatments, pressure-treated wood and radon.
The house, of course, needs to be separated with vapor retardation from this moisture also. Dr. Sherman addresses that above in that the "crawlspace is isolated from the main space ... by good moisture and air barriers." And he concludes to me: "If there is proper venting, and moisture control, then a vented crawlspace can work fine."
So, as he stated - heat and moisture need to be transported, moisture has to be retarded and controlled, and the house has to be isolated from the moist crawl space.
The mistakes in this house included not having proper soil vapor retarded and then closing off the vents to prevent air movement. And the results are hideous.
My recommendation: information on the Internet can be confusing! Name your topic - medicine, history, sports, ventilation, or whatever - and you can probably find competing philosophies. But common sense should be good sense. Moving air transports moisture and gases. And moving air is beneficial when a space is not intended to be sealed. And this crawl space was NOT intended to be sealed!