The space under a staircase often looks larger before anyone tries to use it. The low end, deep corners and narrow opening can turn a large volume into a small accessible area. Start with access and the existing construction rather than choosing a row of dramatic triangular drawers from a photograph.
Know what you are allowed to fit around
Identify the visible stair supports, walls, access panels and services. A stringer is the inclined member supporting the stair; it is not a convenient piece of timber to notch for a drawer runner. Posts, studs and linings can have structural or fire-protection functions even when they look like an obstacle to storage.
Have uncertain construction assessed before opening or altering it. Toronto's building-permit guidance is the starting point for checking a proposed alteration with the City. Other Ontario municipalities make their own project determinations. This article concerns storage planning; it does not establish that removing an under-stair wall or lining is exempt from approval.
What can be accessed without changing the stairs?
Reach directly
Shallow, wide access
Open shelves or removable bins can keep contents visible without deep hardware.
Bring storage out
Deep space with clear floor area
A designed pullout can bring contents forward if its full travel and load are supported.
Work around it
Obstructed by supports or services
Reduce the storage footprint and keep required access; do not cut the obstruction away.
The drawer needs room outside the opening
Measure the usable opening after allowing for trim, hinges and supports. Mark a proposed pullout's full extension on the floor and check the adjacent walking route. A deep drawer may carry a great deal but require most of the hall to open. An ordinary bin on a reachable shelf may work better for occasional storage.
Choose hardware for the complete loaded drawer and its geometry. Blum's runner resources provide installation details for specific systems; a long custom pullout cannot inherit the capacity of an unrelated kitchen drawer. Keep release fittings accessible so a jammed unit can be removed without dismantling the staircase.
Leave the important spaces empty
Do not cover electrical panels, shutoffs, cleanouts, ventilation openings or inspection access. Find out what equipment is present and keep its required working space. A removable decorative panel is not automatically adequate access if it requires unloading a cupboard and unbolting a drawer first.
Avoid fastening cabinetry through unknown stair surfaces or walls. Resolve the fixing positions in the design, including what is behind them. If a cabinet can be made and installed independently within an existing opening, future repair and removal are usually easier than with a maze of parts built tightly around everything.
Use the low end deliberately
Put frequently used items toward the tall, accessible end. Use the low end for labelled containers that can be withdrawn whole. Keep heavy contents within comfortable handling reach. The sloped-ceiling closet guide shows the same value of a measured side view, while linen-closet access explains why the opening can matter more than the space behind it.