What Is Spandrel Space Compartment Design? (Under-Stair Storage)
Spandrel-space compartment design uses the triangular volume below a stair for built-in storage. A safe design keeps stair framing and required headroom unchanged, protects the enclosed under-stair surfaces as local code requires, and preserves access to wiring, equipment, and service points. Measure first, check local rules, then frame and fit the compartment around those limits.
The space beneath a stair can look like an easy place for a cupboard, but its shape and location create limits. A new door or wall must not weaken the stair, narrow a route, cover equipment, or interrupt required fire protection. The goal is useful storage that fits the building, not extra space at the cost of safety.
What spandrel-space compartment design means
A spandrel space is the volume below a sloping stair, often shaped like a triangle in side view. A compartment uses some of this volume for storage, with an access door or opening. Its design must account for the stair structure, code clearances, fire protection, and anything already running through the space.
The available area shrinks toward the low end of the stair, so a single shelf or deep cabinet may not fit well. Start by deciding what you plan to store, then check whether the clear space and opening will suit it. Do not size a compartment from the outside shape alone.
Estimate the usable envelope
Measure the stair run, the vertical distance from the floor to the underside of the stair, the clear width between walls, and the location of stringers and supports. Also note landings, door swings, and low obstructions. A sketch with measurements is more useful than a rough estimate.
For a simple triangle, the side-view area is about one-half the horizontal run multiplied by the vertical rise. For example, an 8-foot run with a 4-foot rise gives a theoretical area of 16 square feet. That is not the usable storage area: framing, finish layers, stair supports, and the shape of the door reduce it. The volume depends on the space’s width and those same obstructions.
Planning the under-stair storage envelope
The storage envelope is the measured clear volume that remains after you account for framing, finishes, services, and required access. Mapping it first helps you choose a practical door and shelf layout without guessing. It also reveals when the space is too constrained for the storage plan you have in mind.
Before design or demolition, look for wiring, plumbing, ducts, shutoffs, cleanouts, electrical equipment, and fuel-burning appliances. Do not assume a wall or soffit is empty. If you cannot identify a service or determine whether it can be moved, ask a qualified trade professional before closing the space.
| Design choice | Useful when | Main check |
|---|---|---|
| One hinged door | The opening is wide and the floor is clear | Door swing does not block a route or hit nearby fixtures |
| Several smaller doors | The stair shape makes one large door impractical | Each opening still allows the intended items to pass through |
| Fixed shelves | Stored items are light and access is simple | Supports suit the actual load |
| Pull-out shelves | The compartment is deep | Slide rating and attachment match the shelf and contents |
| Open access | The space needs regular inspection or service | Required fire protection and access rules still apply |
Treat the table as a planning aid, not a code approval. Hardware ratings vary by product and installation. There is no universal safe load for a shelf, hinge, or slide based on its size or appearance.
Access doors, stair geometry, and required clearances
A storage opening must work without changing the stair’s required shape or blocking safe movement. Headroom, riser height, and tread depth remain key checks. The door must also avoid conflicts with landings, other doors, and required access to building equipment.
Under the 2021 International Residential Code (IRC), Section R311.7.2, stair headroom is generally at least 6 feet 8 inches. It is measured vertically from the stair nosing line and landings. Check the adopted local code and its exceptions, and make sure the new enclosure does not reduce that clearance.
The 2021 IRC, Section R311.7.5.1, generally limits riser height to 7¾ inches and requires at least 10 inches of tread depth, subject to the section’s measurement rules and exceptions. A storage project should leave the existing stair geometry alone. If the stair is being changed or appears noncompliant, get qualified advice rather than adjusting it as part of a storage installation.
Never cut, notch, drill, or remove a stringer or other structural member to gain storage volume unless an approved structural design specifically allows the work. If the proposed opening or framing would affect a stringer, landing, or support, stop and seek structural review.
Check panels and other services
An electrical panel needs clear working space. Under the 2023 National Electrical Code (NEC), Section 110.26(A)(1), the general minimum width is 30 inches or the equipment width, whichever is greater. For equipment at 0–150 volts to ground under Condition 1, the general minimum depth is 36 inches and the minimum working-space height is 6 feet 6 inches. Other conditions can change the required depth; confirm the applicable rules.
Do not use required panel working space for storage, even if the compartment door can open over it. Also keep shutoffs, cleanouts, and equipment needing service accessible. For fuel-burning appliances, do not cover combustion-air openings. Required airflow and service access depend on the appliance, its instructions, and local mechanical or fuel-gas rules. There is no single airflow figure that fits every installation.
Framing, fire protection, and finish installation
The frame should form a stable enclosure without changing the stair’s load path. The finish must also meet the fire-protection rule that applies to an enclosed, accessible under-stair space. Plan the wall, door, and gypsum layers together so the completed compartment remains both usable and compliant.
For homes governed by the 2021 IRC, Section R302.7 requires the enclosed side of the under-stair surface and supports to be protected with ½-inch gypsum board when the space is enclosed and accessible by a door or similar opening. Confirm that your local authority has adopted this edition and check for amendments. Local requirements may differ.
A practical sequence is:
- Confirm the local code edition and ask the building department whether a permit or inspection is required.
- Measure the stair and map framing, services, openings, and clearances.
- Resolve conflicts before building. Get structural review if any proposed work affects the stair or its supports.
- Frame the enclosure without cutting or notching stair structure.
- Install required gypsum protection on the enclosed side, keeping the protective layer continuous at the surfaces it covers.
- Fit the door and storage hardware according to the manufacturers’ instructions.
- Finish the surfaces, then test door operation and verify that required clearances and service access remain.
Do not treat paint, trim, or a close-fitting door as a replacement for required gypsum protection. If the layout makes continuous protection unclear, ask the building department or a qualified building professional before closing the wall.
Worked under-stair installation scenarios
These scenarios are planning examples, not reports of specific completed projects. They show how measurements and code checks can guide common layouts. Actual requirements depend on the building, the products used, and the rules adopted by the local authority.
Scenario 1: A short stair with an open end. The homeowner measures the underside, then sketches a narrow cabinet beside the lower stair area. The initial plan places the door where it would swing into a passage. Moving the opening to a clear side solves the door conflict without changing the stair. The next check is whether the enclosure can include the required gypsum protection.
Scenario 2: A deep compartment near a panel. A homeowner wants pull-out shelves beneath the stairs, but an electrical panel is nearby. The panel’s working space is measured and marked before shelf depth is set. If the proposed storage uses that space, the layout must change. The shelves also need slides selected for the actual loaded shelf weight, using the product maker’s rating and installation instructions.
Scenario 3: A stair beside a fuel-burning appliance. A proposed partition would cover an opening or make routine service harder. The homeowner pauses the project and checks the appliance instructions and local requirements with a qualified professional. Storage is not installed across the opening or access route. This avoids guessing at airflow needs or service clearances.
| Check | Record before work | Pass condition |
|---|---|---|
| Stair headroom | Vertical clearance at stairs and landings | Enclosure does not reduce required headroom |
| Stair shape | Riser and tread measurements | No change from the project |
| Structure | Stringers, supports, and framing | No unapproved cuts or notches |
| Fire protection | Applicable local code and enclosure surfaces | Required gypsum protection is installed |
| Electrical access | Panel dimensions and working space | Storage does not occupy required clearance |
| Appliance access | Openings and service needs | Manufacturer and local requirements remain met |
| Hardware | Shelf, contents, door, and hardware weights | Each part is installed within published ratings |
Final code, access, and hardware verification
A finished compartment is ready only when its door works, its contents are supported by suitable hardware, and the original safety and service conditions remain intact. A final check catches conflicts that may be easy to miss while framing is open. Keep measurements and product instructions with the project records.
Before using the storage, check that:
- The stair headroom and walking surfaces remain unchanged.
- No structural member was altered without approved design.
- Required gypsum protection is present and continuous where required.
- Doors open fully without blocking a path or required equipment access.
- Electrical panels, shutoffs, cleanouts, and appliances remain accessible.
- Shelves and slides are installed as directed and suit the intended load.
- Any required inspection has been completed.
The authority having jurisdiction (AHJ), usually the local building department, can confirm the adopted code and permit needs. When a detail is uncertain, ask before concealing it. Building the compartment around verified limits is safer than trying to correct a hidden problem later.
Frequently asked questions
These answers summarize the main planning points for under-stair storage. Local code, the building layout, and equipment instructions still control the final design. If your project changes a stair, blocks a service, or involves unclear fire protection, pause and get local guidance before proceeding.
What does “spandrel space” mean under a stair?
It is the volume beneath the sloping part of a stair, often triangular in side view. A compartment uses that volume for storage.
Can I cut a stair stringer to make more room?
Do not cut, notch, drill, or remove a stringer without an approved structural design. Get structural review before any work affecting stair supports.
How much headroom must remain over the stairs?
The 2021 IRC generally requires at least 6 feet 8 inches, measured vertically from the stair nosing line and landings. Confirm the locally adopted code and any exceptions.
Does an accessible under-stair compartment need gypsum board?
Under 2021 IRC Section R302.7, an enclosed under-stair space accessible by a door or similar opening generally needs ½-inch gypsum board on the enclosed side of the under-stair surface and supports. Check local adoption and amendments.
Can I store items in front of an electrical panel?
No. Keep the required working space clear. The 2023 NEC sets general width, depth, and height requirements, but the exact depth depends on the equipment and conditions.
Can I enclose a combustion-air opening?
No, not unless a qualified design and the applicable rules allow a compliant change. Follow appliance instructions and local mechanical or fuel-gas requirements.
Is there a standard load rating for under-stair shelves?
No. Select shelves, hinges, and slides for the actual load and use the manufacturer’s published ratings and installation instructions.
Do I need a permit for under-stair storage?
Permit rules vary by location and project scope. Ask your building department before work, especially if framing, electrical systems, or fire protection may be affected.
How do I estimate the space available?
Measure the clear run, rise, and width, then map framing and services. A triangle’s side area is one-half its run times its rise, but that is not the usable storage area.
What is the safest first step?
Measure the stair and locate services, then confirm code requirements with the local building department. Do not begin by cutting or removing framing.
(This article was written by one of our staff writers, Garrett Vance. Visit our Meet the Team page.)
