How big does a crawl space access opening have to be?
Floor access must be at least 18 inches by 24 inches, while wall openings are a minimum of 16 inches by 24 inches (IRC R408.4, 2012 edition).
Access openings through the floor must be at least 18 inches by 24 inches. Openings through a perimeter wall must be at least 16 inches by 24 inches.
If any part of the through-wall access is below grade, an areaway of at least 16 inches by 24 inches must be provided with its bottom below the threshold. Wall access openings shall not be located under a door to the residence.
This answer is based on Section R408.4 of the 2012 IRC. Section numbers and details can change in later editions and through state or local amendments, so confirm the edition your jurisdiction enforces with your building department before you build.
Related answers
- How wide and thick does a footing need to be? — IRC §R403.1
- How deep do exterior footings have to be below the ground? — IRC §R403.1.4
- How deep below the frost line do footings need to go? — IRC §R403.1.4.1
- How thick does a foundation wall need to be? — IRC §R404.1
- What is the anchor bolt spacing for a sill plate on a foundation? — IRC §R403.1.6
- Is a vapor barrier required under a concrete slab? — IRC §R506.2.3
- How much bearing do floor joists and girders need at the ends? — IRC §R502.6
- How much can you notch or bore a floor joist? — IRC §R502.8.1
Need this scoped to your jurisdiction?
Adopted edition and local amendments vary by city and county. Ask Donnie checks your jurisdiction and cites the exact adopted section.
Ask Donnie →General information based on the International Residential Code (a model code). This is AI assistance to verify — not legal advice. Confirm the adopted edition and any local amendments with your local building department (AHJ) and a licensed professional before you build.