For anyone living in a Victorian terrace, a Georgian townhouse or a rambling stone cottage, the staircase is usually the largest piece of unused furniture in the house. That triangular void beneath it looks useless, but it is often one and a half to two cubic metres of genuinely usable space — a serious amount in a hallway that may only be 1.2 metres wide. The trick is not simply to board it over and shove the vacuum cleaner in. With joinery designed around the rake of the stairs, an awkward cavity becomes the most hardworking storage in the home.

Measure the cavity properly before you design anything

Period staircases are almost never square, and no two are alike, which is why off-the-shelf units rarely fit well. Before choosing anything, work out the true shape of the space.

• Head height across the run. Measure vertically at 300mm intervals from the newel post to the far end. You will usually find the usable height tapers from around 1,800mm down to nothing.
• The rake of the stringer. A straight edge held against the underside of the stairs gives you the true diagonal. Drawers and shelves must follow it, not fight it.
• What is already in there. The gas meter, the stopcock, the consumer unit, radiator pipework, and in older Georgian houses, the top of a cellar stair. Anything you enclose must stay accessible.
• The construction. Lath and plaster undersides are common in pre-1930 homes and cannot take weight. Fix battens into the stair strings, the floor joists and the wall, never into plaster alone.

Take photographs with a tape measure held in shot, and sketch a simple plan. Any joiner worth their salt will re-measure, but turning up with clear dimensions saves an hour of head-scratching.

Pull-out drawers: the hardest-working option

If you do only one thing with the space, make it drawers. Cupboard doors force you to lose the back 300mm to darkness, but a full-extension drawer brings every centimetre into the light. The deepest section, closest to the newel post, can usually take a 600mm-deep drawer; the shallowest end might manage only 250mm, which is perfect for batteries, keys or dog leads.

Specify heavy-duty runners rated for 45–60kg if you plan to store shoes, boots, tinned food or tools, and always ask for full-extension rather than three-quarter. Soft-close is worth the modest extra. A run of four or five graduated drawers, faced in a simple shaker or beaded profile and scribed tightly to the architrave and skirting, will read as if it has always been there. In hallways, dedicate the bottom drawer to shoes and the top two to gloves, hats and the inevitable bag of carrier bags.

Coat cupboards and boot storage

Where the stairs sit close to the front door, the tallest portion of the cavity belongs to coats. A cupboard around 600mm wide and 1,800mm tall will comfortably hold a family's outdoor wear on a single rail set at roughly 1,700mm, with hooks on the back wall for bags and umbrellas.

• Add a low bench at 450mm to sit on while pulling boots on, with a basket underneath for muddy footwear.
• Ventilate it. Damp coats in a sealed cupboard go musty within weeks. A slatted or louvred door, or a pair of simple vents top and bottom, keeps air moving.
• Use a shoe rack at 200mm pitch rather than a single shelf, so nothing gets buried.

A small pantry when the stairs meet the kitchen

Some of the best larders in Britain are under-stairs cupboards beside a kitchen. If that is your layout, think like a cook rather than a carpenter. Adjustable shelves at 300mm pitch suit jars and packets; a bank of pull-out wire baskets makes the deepest corner reachable; and a small section of solid worktop at 900mm gives you somewhere to put a mixer or a bread bin.

Keep ventilation in mind. Under-stairs voids can be cold and slightly damp, particularly where they back onto an external wall. A vented door and a coat of moisture-resistant paint on the walls will keep dry goods in good condition. Rice, pasta and flour are also far happier in sealed glass or enamel containers than in open packets. If the space is beside a boiler, leave the manufacturer's clearance and do not block the flue or ventilation grilles — this is a safety matter, not a storage decision.

Getting the details right

Bespoke joinery is the only reliable way to fit a period cavity neatly, and a local cabinetmaker will typically charge somewhere between £1,200 and £2,500 for a full under-stairs run, depending on your region and the finish. It sounds steep until you calculate what you would otherwise spend on a wardrobe and a chest of drawers, neither of which would fit the space half as well.

• Materials. Moisture-resistant MDF for kitchens and boot areas, standard MDF for hallways, with solid tulipwood or ash for frames if you want a painted finish that lasts. Eggshell or a hard-wearing satin is far more forgiving than gloss in a hallway.
• Scribing, not hacking. Ask for the face frames to be scribed around original skirting and architrave. If skirting must come off, label it and store it — a future owner will thank you.
• Access. Meters, stopcocks and consumer units need hinged or lift-out panels. Never seal a gas meter behind fixed joinery.
• Electrics. Any new socket, light or heater should be installed by a qualified electrician, and the work should be properly certified.
• Structure. Never cut, notch or drill the stair strings or the newel post. They are carrying the staircase.

Done well, under-stairs joinery looks original, adds a genuine selling point, and quietly absorbs the clutter that otherwise colonises a period hallway. Measure carefully, favour drawers over doors, ventilate anything holding damp coats or food, and let a good joiner earn their fee.