Homeowner wants a little storage closet under the basement stairs with a door on it.

Yes, drywall matters to the inspector for a basement stair closet. Here's what applies:

Code Requirements (IRC):

• Ceiling/Walls: The underside of stairs and any enclosed closet space must be drywalled with ½-inch gypsum board (IRC R313.1, R302.1). This includes the closet's walls and ceiling if it's enclosed.
• Fire Separation: If the basement is a separate dwelling unit or the stairs serve multiple units, 5/8-inch Type X drywall may be required on the stair side (IRC R302.3, R301.1).
• Door: The closet door must be solid wood (≥1¾ inches thick) or solid core (IRC R302.1). Hollow-core doors are not permitted for fire-rated assemblies.

Inspector Focus:

• They’ll check drywall thickness, joint treatment, and coverage of all surfaces (no exposed framing).
• Penetrations (electrical boxes, vents) must be properly sealed.
• Door fit and material will be verified.

Practical Tips:

• Use fire-rated drywall if required by local amendments.
• Ensure tight joints with taped seams.
• Install a self-closing door if the closet is large (>10 sq ft) or local code requires it.

If the space is small (<10 sq ft) and not a separate unit, ½-inch drywall and a solid-core door should suffice. Always check local codes, as some jurisdictions adopt stricter standards. When in doubt, consult a licensed inspector or contractor.

Yes, it matters significantly.

Under IRC R302.11, the walls and ceiling enclosing the usable space under stairs must be protected with ½-inch gypsum board (or equivalent) on the enclosed side (the closet side). This is a fire-blocking requirement to protect the stair stringers and framing from a fire originating in the storage area.

Practical details:

• Material: Standard ½" Type X or regular ½" gypsum board is acceptable (IRC Table R302.11).
• Coverage: All walls and the sloped ceiling/soffit inside the closet. The underside of the stairs (the "ceiling" of the closet) must be covered.
• Finish: Taping and mudding are not required by code for fire protection, but inspectors often expect seams taped and fastener heads covered to prevent flame passage through gaps. One coat of mud on seams/screws is standard practice.
• Door: The door does not need to be fire-rated (solid core or 20-min), but it must be self-closing or kept closed (IRC R302.11 Exception). A spring hinge or door closer satisfies this.

Common fail points:

1. Leaving the sloped ceiling (underside of treads/stringers) open.
2. Using ¼" paneling, plywood, or OSB instead of ½" drywall.
3. Gaps around pipes/ducts penetrating the enclosure (fire-block with mineral wool/caulk per R302.11.1).

Bottom line: Hang ½" drywall on the closet side of the framing, tape the seams, install a self-closing door. If the space is inaccessible (no door, <30" high), R302.11 doesn't apply—but you have a door, so it does.