18 inches is no longer mandatory and hasn't been since the revised Appendix D was issued.
• Check the distance from the bottom of floor joists to ground. Space should be adequate for maintenance and repair. A minimum distance of 18 inches from the ground to the bottom of the joists is highly recommended but not mandated.
This is straight from the 4000.1:
m. Crawl Space Observation Requirements
The Appraiser must visually observe all areas of the crawl space and notify the Mortgagee of the deficiency of MPR and MPS when the crawl space does not satisfy any of the following criteria:
• The floor joists must be sufficiently above ground level to provide access for maintaining and repairing ductwork and plumbing.
• If the crawl space contains any system components, the minimum required vertical clearance is 18 inches between grade and the bottom of the floor joists.
• The crawl space must be properly vented unless the area is mechanically conditioned.
• The crawl space must be free of trash, debris, and vermin.
• The crawl space must not be excessively damp and must not have any water pooling. If moisture problems are evident, a vapor barrier and/or prevention of water infiltration must be required.
The Appraiser must report any evidence that may indicate issues with structural support, dampness, damage, or vermin that may affect the safety, soundness and security of the Property.
In cases where access through a scuttle is limited, and the Appraiser cannot fully enter the crawl space, the insertion of at least the head and shoulders of the Appraiser will suffice. If there is no access to the crawl space but there is evidence of a deficient condition (such as water-stained subflooring or smell of mold), the Appraiser must report this condition and the Mortgagee must have a qualified third party perform an inspection.
If there is no access, the Appraiser must report the lack of accessibility to the area in the appraisal report. There is no requirement to cut open walls, ceilings or floors.
Not all houses (especially historic houses) with a vacant area beneath the flooring are considered to have a crawl space; it may be an intentional void, with no mechanical systems and no intention or reason for access.
