Under-Stairs Storage: Creating Deep Drawers with Heavy-Duty Runners

A heavy-duty runner is a ball-bearing telescopic slide that accommodates dynamic load capacities from 45 kg to over 130 kg depending on the model. Due to its construction, it is ideal for extremely deep and heavy drawers beneath sloping ceilings or staircases.

The space under a staircase offers enormous potential for storage, yet it requires precise technical planning. Standard carcases fail here due to the given depth, which often ranges between 800 mm and 1200 mm. To make this space usable, bespoke pull-out systems are required. Installation into the inclined plane under the stairs is much like aligning a shaft on a test rig: without exact preparatory work down to the millimetre and accurate calculation of tolerances, the system will run unevenly or jam later on.

This guide leads you through the most important technical specifications to dimension and flawlessly install the correct fittings for deep under-stairs storage units.

Key Purchasing Criteria for Under-Stairs Drawers

Anyone planning drawers with a depth of more than 500 mm must select fittings according to strict physical criteria. The leverage exerted when the drawer is fully extended requires solid steel and precisely calculated fixing points.

1. Extension Type: Full Extension is Essential

A full extension runner extends to 100%, whereas a partial extension runner opens to only around 75%. For an 800 mm deep drawer, a partial extension would mean that 200 mm of the rear storage area remains hidden in the dark of the cabinet. For under-stairs solutions, drawer runners with full extension are the only technically viable choice to ensure full access to stored items.

2. Load Capacity (kg)

The load capacity is stated per pair of runners and refers to dynamic load (in motion). When calculating, the unladen weight of the drawer (often built from 16 mm or 19 mm thick boards) must be added to the intended payload.

• Light use (hats, scarves): approx. 30 kg to 45 kg.
• Medium use (shoes, lever-arch files): approx. 45 kg to 80 kg.
• Heavy use (tools, crates of drinks, firewood): 90 kg to 130 kg.

Heavy-duty drawer runners must be used in these instances.

3. Nominal Length (mm)

The nominal length of the runner must correspond to the depth of the drawer. Special lengths are frequently required for under-stairs structures. Standard sizes for the medium section of the stairs are drawer runners in 600 mm or drawer runners in 700 mm. For the deepest points of the stairs, lengths from 800 mm to 1200 mm are used.

Overview of Runner Types and Mechanisms

The choice of runner determines the running action, the space requirements within the carcase, and the maximum possible load.

Ball-Bearing Runner (Telescopic Slide)

This is the standard for heavy loads. The runners are screwed to the sides of the drawer box and the inner carcase wall. A metal ball cage ensures smooth travel. They require exact installation clearance (usually 12.7 mm or 19 mm per side, depending on the weight class). They are robust, maintenance-free, and available in lengths exceeding one metre.

Undermount Runner

With an undermount runner, the mechanism sits concealed beneath the drawer base. This provides a very clean appearance, as no metal side runners are visible when the drawer is open. However, undermount drawer runners reach their limits with extreme depths and weights. They are typically specified up to a maximum of 40 kg to 50 kg and lengths up to approx. 600 mm.

Roller Runner

A roller runner operates on nylon rollers. It is economical and forgives minor tolerances during installation. For deep under-stairs cabinets, however, it is unsuitable due to its low load capacity and lack of lateral stability. It can only be used for very small, shallow pull-outs at the uppermost, pointed section of the stairs, where a drawer runner of 250 mm might be fitted, for example.

Convenience Features: Soft-Close vs. Push-to-Open

When planning frontals, you must decide in advance how the drawers will be opened and closed. The two most common systems are generally mutually exclusive mechanically.

Soft-Close (Damping) An integrated hydraulic damper catches the drawer over the final few centimetres and pulls it shut gently and silently. Drawer runners with soft-close require a handle on the front to pull the drawer open against the initial resistance of the damper. A similar but simpler principle is offered by drawer runners with self-closing action, which pull the drawer shut via spring force, but without soft damping.

Push-to-Open (Tip-On) If the under-stairs wall is intended to look like a flush, handleless surface, an automatic ejection mechanism is required. Pressing lightly on the front pops the drawer open by a few centimetres so it can be gripped. Drawer runners with push-to-open work using a spring mechanism that is tensioned upon closing. Soft-close and push-to-open are opposing mechanisms (damping vs. pushing away) and cannot be combined in standard fittings.

Decision Guide: Which Fitting for Which Application?

• If the drawer is used for storing heavy drinks or tools and has a depth of 800 mm, then select a ball-bearing heavy-duty runner with at least 90 kg load capacity as a full extension.
• If the under-stairs unit is situated in a hallway and needs to blend seamlessly into the wall (without handles), then select a telescopic runner with an integrated push-to-open mechanism.
• If you are planning small drawers for keys or shoe polish kits in the lower, shallower section of the stairs, then standard ball-bearing runners are sufficient, such as drawer runners in 450 mm.
• If you are building timber drawers with visible dovetail joints and want to hide the hardware, then use undermount runners—ensuring that the depth does not exceed 600 mm and the total weight remains under 40 kg.

Installation Guidelines

Installing heavy-duty runners requires precision. A deviation of just 2 mm out of square can cause the ball cages to jam on deep pull-outs.

1. Calculate installation clearance: Measure the internal width of the carcase. Subtract the exact thickness of both runners (e.g. 2 x 19.1 mm = 38.2 mm). The remaining dimension is the mandatory external width of the drawer box.
2. Fixings: Use all designated fixing points on the runner. Use suitable wood screws (chipboard screws) with a diameter of 4 mm to 5 mm. A PZ or TX drive prevents the bit from slipping when assembling in tight carcase spaces.
3. System 32: If using carcase panels pre-drilled with System 32 hole patterns (32 mm hole spacing, 5 mm hole diameter), you can use Euro screws. This greatly increases pull-out resistance under extreme loads.
4. Alignment: Always fit runners using a spirit level. Beneath staircases, floors are often not completely level. Level the carcase beforehand using height-adjustable cabinet feet.

Frequently Asked Questions (FAQ)

How do I correctly calculate the weight for a heavy-duty runner? Add the unladen weight of the drawer to the maximum planned payload. An 800 mm deep drawer constructed from 19 mm thick boards already weighs around 12 kg to 15 kg empty. Always include a safety margin of 20%.

Can I retrofit soft-close onto a handleless front? No. A handleless front requires push-to-open to eject the drawer. Soft-close pulls the drawer shut and dampens the movement. The two systems obstruct one another. For handleless fronts, soft-close must be omitted.

What runner length do I need for my drawer? The specified nominal length of the runner matches the depth of the drawer box. If you build a drawer with an external depth of 750 mm, you will need drawer runners in 750 mm. The carcase depth must provide at least 3 mm to 5 mm more internal space than the runner length.

Why does my full extension runner jam halfway? This usually occurs if the installation clearance has not been maintained accurately (the drawer is slightly too wide or too narrow) or if the runners have not been fitted parallel and at a 90° angle to the front. With heavy-duty runners, the ball cage will not tolerate dimensional discrepancies.