The International Residential Code "IRC" requires access to the crawlspace which is sometimes referred to as under-floor.
"Access shall be provided to all under-floor spaces. Access openings through the floor shall be a minimum of 18 inches by 24 inches. Openings through a perimeter wall shall be not less than 16 inches by 24 inches. Where any portion of the through-wall access is below grade, an area-way not less than 16 inches by 24 inches shall be provided. The bottom of the area-way shall be below the threshold of the access opening. Through wall access openings shall not be located under a door to the residence."
Crawl pace Door Systems, Inc. specializes in crawlspace preservation. Please give us a call if you have any questions.