How to Fit Carpet (or Prep for a Fitter)

Carpet is the most forgiving floor covering for a DIYer to fit in a simple rectangular room, but it quickly becomes technical in rooms with bay windows, alcoves, and stairs. Getting it wrong means wasted carpet, visible seams, and rippling within months. This guide walks through the full process and also covers how to prepare a room so a professional fitter can get the job done quickly and without extra charges.

Tools and Materials

Essential:

• Gripper rods (perimeter of the room minus door openings, in linear metres)
• Underlay (same area as room, allow 10% extra)
• Carpet (the room’s length and width, each plus at least 100 mm for trimming; many fitters allow more)¹
• Staple gun or adhesive (for underlay)
• Knee kicker
• Bolster chisel and hammer (for tucking edges)
• Carpet knife or hook blade
• Steel straight edge
• Tape measure

Useful but not essential for simple rooms:

• Power stretcher (available from tool hire shops; worth hiring for large rooms, where a knee kicker alone cannot get the carpet tight)
• Seam iron and heat-bonding tape (for joins)

The knee kicker is the one specialist tool you can’t substitute for. Most tool hire shops hire them out by the day, and they are also cheap enough to buy if you have several rooms to do.

Step 1: Subfloor Preparation

Like all floor coverings, carpet telegraphs what’s underneath it. Raised nail heads and floorboard edges create ridges through both underlay and carpet within weeks.

For timber floorboards:

• Punch all nail heads 3 mm below the surface.
• Screw down any squeaky or lifting boards.
• If boards are very gappy (over 5 mm), fill with a flexible filler or overlay with hardboard or thin plywood (3–4 mm) pinned every 150 mm.
• Sand any very uneven joints flat.

For concrete:

• Fill cracks and hollows with a self-levelling compound.
• Allow it to dry fully before laying underlay, following the product’s stated drying time (often 24 hours or more).
• A damp concrete floor can ruin carpet and underlay. A polythene sheet taped down for 24–48 hours gives a rough check (condensation under it means moisture is coming through), but a hygrometer test is the reliable one; flooring installers generally look for a reading below 75% relative humidity.

Step 2: Fitting Gripper Rods

Gripper rods are thin strips of wood with angled pins that hold the carpet edge taut. They run around the perimeter of the room with a gap left between the gripper and the skirting, usually a little less than the thickness of the carpet, so the trimmed edge can be tucked into it.²

• Cut rods to length with a hacksaw.
• Fix every 300 mm with the provided nails (timber floor) or concrete nails / construction adhesive (solid floor).
• The angled pins should face the wall, angling slightly toward it.
• Leave a gap at doorways, a threshold strip or door bar covers the transition instead.
• Fit gripper in archways and alcoves too.

Step 3: Laying Underlay

Underlay affects the feel, insulation, and lifespan of carpet more than most people realise.³ A cheap carpet on good underlay will feel and wear better than an expensive carpet on poor underlay.

Underlay types:

Density varies widely between types: crumb rubber is much denser than foam, and Interfloor’s Durafit 650 crumb rubber underlay, for example, has a nominal density of 415 kg/m³.⁵ For stairs, choose a dense rubber or PU underlay sold as suitable for stairs rather than the thickest, softest option. For UFH (underfloor heating), the Carpet Foundation treats 2.5 tog as a realistic maximum for carpet and underlay combined and recommends an underlay below 1.3 tog; check the heating manufacturer’s specification as well.⁶

Lay underlay flat, butt the edges, and staple or tape-join edges together. Do not overlap. Trim the underlay to butt up to the inside edge of the gripper: it must not lie on top of the gripper or run between the gripper and the wall. Staple to timber floors every 300 mm; use double-sided tape on concrete.

Step 4: Cutting and Laying the Carpet

Roll the carpet out in the room (face up), leaving 100–150 mm up each wall. If the room is larger than the carpet width, plan where the seam will fall, ideally out of the main traffic routes, running in the direction people walk rather than across it, and towards the main window rather than across the light, which shows up seams.

For a standard rectangular room:

1. Roughly position the carpet so excess is even on all sides.
2. Trim to leave approximately 75 mm turndown at each wall.
3. Hook one edge over the gripper pins on the longest straight wall by pressing the carpet down onto the pins with the bolster or a carpet knee kicker.
4. Use the knee kicker to stretch the carpet from the fixed edge toward the opposite wall, kicking with your knee into the padded end while hooking the head into the carpet surface, about 75 mm from the edge. Work across the wall in a fan pattern.
5. Hook the stretched carpet edge over the opposite gripper.
6. Repeat for the remaining two walls, always stretching from fixed edges.
7. Trim the excess at the walls with a carpet knife, then tuck the edge into the gap between gripper and wall using the bolster.

For cuts around door architraves, use a scribe or cut from beneath by pressing the carpet against the profile and cutting freehand, this takes practice.

Step 5: Thresholds and Doorways

At doorways, fold the carpet edge under itself and secure with a threshold bar (also called a carpet bar or door bar). These are available in gripper type (pins, like a mini gripper rod), Z-bar type, or cover strip type for carpet-to-hard-floor transitions. Fix through the carpet into the floor.

Fitting Carpet on Stairs

Stairs are the most challenging carpeting job. The two usual layout options are:

• Waterfall: the carpet runs over the nosing and drops straight down to the gripper at the back of the tread below, without following the riser. Quicker to fit.
• Hollywood (also called upholstered): the carpet is wrapped tightly around each nosing and fitted close to the riser. A neater, tailored finish, but slower to fit and uses slightly more carpet.

Cut a piece of dense underlay for each tread, running from the gripper at the back over the nosing; the risers usually need none. Gripper goes at the back of each tread and the base of each riser. Knee kicker plus a wider stair tool head is the right approach. Work out the quantity step by step rather than from the plan area: a tread of about 250 mm, a riser of about 200 mm and the wrap over the nosing come to roughly 0.5 m of carpet per step, so a straight flight of 13 risers takes about 6.5 m of carpet at the stair width, plus extra for any winders or landing.

If You’re Prepping for a Fitter

A professional fitter charges less and finishes faster if the room is ready. To prepare:

• Remove all furniture from the room.
• Remove old carpet, gripper, and underlay yourself if you can (fitters usually charge extra to lift and dispose of old flooring).
• Punch nail heads and fix loose boards.
• Have the carpet delivered and in the room 24 hours before fitting (acclimatisation).
• Be available to discuss door thresholds and seam positions before the fitter starts.

A good fitter working in a prepared room will typically fit an average bedroom (12–15 m²) in a couple of hours. Fitting is commonly quoted at £3–£6 per m², but at that rate a 12–15 m² bedroom comes to only £36–£90, and most fitters set a minimum charge, so £100–£200 per room is a more realistic budget once stairs, seams, door bars or awkward shapes are involved.

Common Mistakes

• Not stretching enough: carpet that isn’t properly stretched will ripple within months of heavy use.
• Gripper too far from the wall: leaves the tucked edge visible or causes it to pop back.
• Underlay on the gripper: prevents the carpet hooking onto the pins correctly.
• Seaming across the traffic flow: a seam that people walk across takes more wear and shows sooner, so run seams in the direction of traffic and keep them out of doorways where possible.
• Skimping on underlay thickness on stairs: thin underlay on stairs compresses fast and makes each step uncomfortable.