How to Install Carpet and Underlay
Learn how to fit tack strips, lay foam underlay, stretch broadloom carpet securely with a knee kicker, and trim edges cleanly into perimeter baseboard gutters.
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🧰 Required Tools & Equipment
- ✓ Knee kicker
- ✓ Carpet bolster or tucker
- ✓ Heavy-duty utility knife with hooked blades
- ✓ Heavy-duty staple gun
- ✓ Tape measure
- ✓ Claw hammer
📦 Materials & Supplies
- ✓ Wall-to-wall carpet
- ✓ Foam or rubber carpet underlay
- ✓ Carpet gripper tack strips
- ✓ Underlay joining tape
- ✓ Door threshold transition bars
⚠️ Safety Checkpoints & Warnings
- • Wear heavy cut-resistant gloves when handling tack strips; the sharp angled pins easily pierce bare skin.
- • Use knee pads with rigid caps to protect patellar joints while operating the knee kicker.
- • Always cut carpet facing away from your body and keep your free hand behind the cutting path of the utility knife.
📋 Step-by-Step Guide (6 Steps)
Install Perimeter Tack Strips
Nail gripper tack strips around the entire perimeter of the room, leaving a gap between the strip and skirting board equal to two-thirds of the carpet's thickness. Ensure the sharp pins on the strips point directly toward the wall. Do not install tack strips across doorway openings.
- • Tack strips form a continuous border around the room with angled pins slanting outward toward the walls.
- • A uniform 5mm to 8mm expansion gap is visible between the strips and the skirting board.
- • Installing tack strips backward with pins facing into the room center.
- • Butting strips flush against the baseboard, leaving no space to tuck carpet edges.
Lay and Secure the Underlay
Roll out the underlay across the subfloor with the backing layer facing upward, butting the edges tightly against the inside edges of the tack strips without overlapping them. Staple the underlay to timber subfloors every 150mm along the seams and perimeter edges. Seal all butt joints firmly using heavy-duty underlay joining tape.
- • Underlay covers the entire floor up to the inner boundary of the tack strips without covering any pins.
- • All seams lie completely flat with underlay tape sealed along every joint line.
- • Letting underlay run over the tack strips, which prevents carpet from latching onto the pins.
- • Overlapping underlay sheets, creating permanent ridges under the carpet.
Position and Rough-Cut the Carpet
Unroll the carpet across the room, centering the pile and allowing approximately 50mm to 75mm of excess material to turn up against each wall. Smooth the carpet flat from the center outward by hand to eliminate large air pockets. Make relief cuts at inside and outside corners to allow the carpet to drop flat against the floor-wall junction.
- • Carpet lays flat across the floor with uniform 50mm to 75mm margins curving up every wall.
- • Corner relief cuts allow the carpet to sit fully relaxed into baseboard corners without diagonal tension folds.
- • Rough-cutting the carpet too tight, leaving an unfixable gap before stretching.
- • Cutting corner relief lines past the top edge of the baseboard.
Stretch and Hook onto Tack Strips
Set the teeth depth on the knee kicker to grip the carpet backing without piercing into the underlay. Start in one corner, placing the kicker head 25mm from the wall, and strike the padded end firmly with your above-knee thigh muscle while pressing the carpet onto the tack strip pins with your hand or bolster. Work systematically around the room to stretch the carpet drum-tight across the length and width.
- • Carpet backing is firmly embedded on tack strip pins around the full perimeter.
- • Carpet surface is completely drum-tight and free of ripples or slack spots.
- • Striking the kicker with the patella/kneecap instead of the lower quadricep muscle.
- • Setting kicker teeth too deep, tearing through the primary backing and ripping underlay.
Trim Excess and Tuck Edges
Using a carpet knife with a fresh blade, cut the excess perimeter carpet by slicing along the crease where the baseboard meets the tack strip. Angle the blade slightly toward the wall so the cut leaves an exact 3mm to 5mm margin beyond the tack strip. Push the trimmed edge firmly down into the perimeter gap between the strip and the baseboard using the carpet bolster.
- • Cut edge is fully rolled down into the baseboard gap with zero frayed yarns visible.
- • No bare backing or tack strip pins visible along any wall perimeter.
- • Using a dull blade, which snags and frays loop-pile carpet tufts.
- • Cutting carpet above the tack strip level, leaving edges exposed.
Secure Doorway Thresholds
Trim the carpet cleanly across doorway openings so the edge terminates precisely beneath the center line of the closed door. Stretch the edge into the metal transition plate teeth, tap the top lip down with a hammer over a protective wood scrap, or screw down the transition cover plate to clamp the seam securely.
- • Transition threshold bar sits flush, level, and centered under the door line.
- • Carpet edge is fully enclosed within the bar with no raw backing exposed.
- • Trimming door carpet too short so it fails to reach inside the transition bar teeth.
- • Hammering metal thresholds directly, leaving dents and distorted tracks.
Credit: inspired by an original tutorial by Dunlop Flooring — watch the original on YouTube.
Don’t have everything?
- No Carpet bolster or tucker? Stiff-bladed 4-inch putty knife with rounded corners
- No Heavy-duty staple gun? Hammer with short clout/carpet staples or spray adhesive rated for underlay