Retrofitting Undermount Drawer Runners: Soft-Close Systems as Alternatives to Grass Runners

February 11, 2026

An undermount runner is a concealed runner system mounted beneath the drawer base, while the integrated soft-close damping gently decelerates the drawer over the final centimetres and shuts it silently.

# Retrofitting Undermount Drawer Runners: Soft-Close Systems as Alternatives to Grass Runners

Replacing or installing drawer runners requires precision. When old runners stick, wear out, or need upgrading to modern damping, many fitters and joiners look for functional alternatives to established systems like Grass. An undermount runner offers the advantage of keeping the mechanism entirely hidden beneath the drawer box, preserving the side aesthetics of the wooden drawer.

This guide is aimed at trade professionals and skilled DIYers. It covers the technical requirements, correct measurements, and step-by-step installation of undermount runners with soft-close technology. The estimated working time per drawer is around 30 to 45 minutes.

System Comparison and Technical Principles

Before beginning installation, the characteristics of the new system must be clearly defined. A modern runner differs substantially from older runner types.

Extension type: A full extension allows the drawer to be pulled out 100% from the cabinet. This provides complete access right to the back corners. In contrast, a single extension only extends to around 75%.
Damping: Mechanical drawer runners with soft close absorb the momentum of the closing drawer. A cylinder (often pneumatic or oil-filled) decelerates the movement, and a spring gently pulls the drawer shut over the final millimetres.
Distinction: Soft-close must not be confused with push-to-open. While soft-close cushions the closing action, push-to-open is an ejection mechanism for handleless fronts that responds to pressure. The two systems work on opposite mechanical principles.

Changing a runner system is like replacing a chassis – the geometry must match the frame precisely. Anyone installing classic undermount drawer runners as an alternative to existing branded products will usually need to drill new hole patterns in the cabinet carcass.

Required Tools and Materials

To carry out professional removal and new installation, have the following tools and fixings ready:

Cordless screwdriver with torque control
Pozi screwdriver bit (PZ 2)
Chipboard screws (countersunk, Ø 3.5 mm or 4 mm, typically 16 mm length for the cabinet)
Tape measure or folding ruler
Engineer's square
Bradawl or wood drill bit (Ø 3 mm or 5 mm, depending on the runner system)
New undermount runner system (consisting of right and left runners plus front locking catches)

Preparation: Checking Measurements and Ensuring Compatibility

Accurate fit is the most crucial criterion when retrofitting. The following parameters must be verified prior to purchase and installation:

Nominal length (NL): This is the length of the runner that extends into the cabinet. Common lengths range from 250 mm - 800 mm. The nominal length of the runner must match the depth of the drawer.
Internal cabinet width: The internal distance between the two cabinet side walls. Undermount runners require strict tolerances. The drawer box must generally be narrower than the internal width by a specific deduction (often a 21 mm to 22 mm deduction, depending on the manufacturer).
Base thickness and side panel thickness: The side panels of the wooden drawer must not exceed 16 mm in thickness for most undermount systems. If the wood is thicker, the drawer will rub against the runner.
Load capacity: For standard kitchen drawers, runners with a 30 kg load capacity are sufficient. For deep pan drawers, heavy-duty runners with a 40 kg to 50 kg load capacity should be chosen.

Step-by-Step Guide: Fitting Undermount Runners

The following instructions describe how to fit a typical undermount system with front locking catches.

Step 1: Dismantle the Old Fittings

Remove the old drawer from the cabinet. Completely unscrew the old runners (e.g. an outdated roller runner). Also remove any existing clips or pins from the underside of the drawer. Check the timber for tear-out; old screw holes can be filled with wood filler or wooden dowels if necessary to provide stability for new fixings.

Step 2: Position and Screw the Cabinet Profile

The position of the new drawer runners determines the subsequent front height and reveal.

Use the System 32 if your cabinet features a corresponding line of holes (5 mm drilling hole diameter). The frontmost hole is positioned standardly 37 mm from the front internal edge of the carcass.
Place the runner in position. Ensure the correct setback (distance from the front edge of the runner to the front edge of the carcass), calculated according to the front thickness.
Secure the profile using the chipboard screws. Use at least three screws per side (front, centre, rear), and more for wider runners. Ensure the runners are set completely level and parallel to one another.

Step 3: Prepare the Drawer (Mounting the Catches)

Undermount runners are usually secured at the back of the drawer box via a metal pin (hook) on the runner. At the front, the drawer is held in place by catches or clips.

Drill holes in the rear panel of the drawer for the runner retaining pins (typically Ø 6 mm, exact position according to the manufacturer dimension sheet).
Screw the locking catches to the front underside of the drawer base, flush against the inside of the drawer side panel.

Step 4: Insert and Adjust the Drawer

Place the drawer onto the extended runners. Push the drawer horizontally backwards until the pins at the rear engage with the drill holes and the front catches audibly click into place.

Modern undermount systems, especially high-quality full extension drawer runners, offer versatile adjustment options directly on the front catch:

Height adjustment: Turning a thumbwheel raises the front by approx. +2 mm to +3 mm to align the gap pattern.
Side adjustment: Allows a correction of ±1.5 mm to the left or right.
Tilt adjustment: Often located at the back of the runner to help if the top of the front leans away from the cabinet.

Avoiding Common Installation Mistakes

Even professionals occasionally encounter errors during a system change that impair the soft-close function:

Incorrect screw heads: Using round-head screws instead of countersunk screws for the cabinet profiles can cause the screw head to catch on the running carriage. This blocks movement or causes long-term damage to the ball bearings.
Ignoring tolerances: If the internal cabinet width is not adhered to precisely, the runner will be under tension. The drawer will then be stiff to pull out, and the soft-close mechanism will not be able to overcome the resistance, preventing the drawer from closing completely.
Debris in the mechanism: If drilling dust or wood shavings remain in the greased running tracks after drilling into the cabinet, it will cause rough running.

Further Detail: Matching Soft-Close Hinges

When retrofitting drawers with modern damping, you should also consider cabinet doors to ensure a uniform closing feel throughout the furniture. A smooth-closing drawer loses its tactile impact if the door above it slams shut without braking.

This is where concealed cabinet hinges with damping (Soft Close) come into play. A cup hinge is a concealed hinge whose cup (usually with a diameter of 35 mm) is drilled into the door. For standard doors, an opening angle of 110° is generally selected. When fitting these, ensure you choose the correct mounting type: a full overlay is used when the door fully covers the cabinet side edge. Matching 110-degree concealed cabinet hinges can be fastened with a cruciform mounting plate using the same 32 mm system as the drawer runners.

FAQ: Frequently Asked Questions on Retrofitting

Can I swap Grass runners 1:1 with another undermount system? No, rarely. The drilling patterns in the carcass as well as the position of the locating pins on the drawer back panel vary from manufacturer to manufacturer. Old holes must usually be disregarded and new drill points marked.

Why is the soft-close drawer not closing fully? This is usually due to an installation error. Either the cabinet is out of square (not level), the runners were not fitted parallel, or the drawer is slightly too wide and binds between the profiles.

Is an undermount runner always better than a roller runner? Technically speaking, yes. A roller drawer runner runs on basic plastic wheels, has more lateral play, and is usually only available as a single extension without damping. Undermount runners use precision ball bearings or rollers, offer superior lateral stability, and integrate complex damping mechanisms.