Summary

Carpet fitting is a skilled trade that looks deceptively simple. The difference between a professional installation and a DIY job shows within 6–12 months when the DIY carpet has rippled, the joins have opened, or the gripper rods have worked loose. Professional fitters invest in proper tools — particularly a carpet stretcher (also called a power stretcher) — and know how to plan the job so that joins fall in low-traffic areas, pile direction is consistent, and pattern repeats (on patterned carpet) are matched across joins.

In the UK, carpet fitting is primarily governed by BS 5325 (Code of practice for installation of textile floor coverings) and manufacturer installation guidelines. Most carpet manufacturers will void their warranty if the installation does not follow BS 5325, so correct installation matters for commercial and warranty reasons as well as quality.

Key Facts

  • Gripper rod spacing — 6–8mm from wall (should equal the carpet pile thickness, typically 6–8mm for residential carpet)
  • Gripper rod fixing — Concrete: hardened steel nails through the pre-punched holes using a pin hammer, or specific gripper adhesive on very hard concrete. Timber: fix through pre-punched holes with 19mm nails
  • Gripper rod type — Standard width (25mm) for most carpets. Extra-wide (38mm) for heavier Axminster or Wilton
  • Underlay types — Sponge/foam, crumb rubber, felt, combined felt/rubber (thermabond). Each has different compression ratings
  • Underlay density — Minimum 100kg/m³ for domestic. 120–140kg/m³ for heavy traffic areas. 80kg/m³ sponge is insufficient for stairs
  • Underlay depth — 8–10mm typical for domestic rooms. 12mm for luxury installations. 6–7mm for stairs
  • Knee kicker — Short-range tool for initial positioning and for stairs. Not a substitute for a carpet stretcher
  • Power stretcher (carpet stretcher) — Essential for rooms over 3m in any direction. Must be used to properly tension carpet
  • Tension sequence — Fix at one end → stretch with power stretcher from that end → fix at opposite end → repeat across width
  • Seaming — Hot melt tape with seaming iron (thermostatically controlled at 140–160°C). Never cold-seam without tape
  • Pile direction — All pieces in a room must have pile lying in the same direction (towards main window light is conventional). Check by running hand across carpet — one direction feels smooth, the other feels rough
  • Pattern matching — Full pattern repeat must be matched across joins. Measure repeat length and add to order quantity

Quick Reference Table

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Underlay Type Density Best Use Avoid
Crumb rubber 120–140 kg/m³ Heavy traffic, living rooms Stairs (compress unevenly)
Sponge/foam 100–120 kg/m³ Bedrooms, light use Commercial, heavy traffic
Felt (jute) 80–100 kg/m³ Wool carpet on wood floors Concrete (absorbs moisture)
Felt/rubber combined 110–130 kg/m³ All-purpose domestic N/A
PU foam (luxury) 120–140 kg/m³ Premium installations Budget projects
Room Size Stretching Method
Under 3m in all directions Knee kicker only acceptable
3–6m in any direction Power stretcher essential
Over 6m Power stretcher plus intermediate anchor points
Stairs Knee kicker for each tread/riser

Detailed Guidance

Preparing the Subfloor

Concrete floors: Check for moisture. Screed or concrete must be below 75% RH before laying. Pin test for hollow areas. Fill cracks and depressions with floor-levelling compound (minimum 3mm depth feathered out). Grind down any raised areas or joints. Concrete must not be contaminated with oil, bitumen, or release agents.

Timber floors: All boards must be firmly fixed — no squeaks, no movement. Re-nail or screw any loose boards. Check for protruding nail heads and punch below surface. Fill gaps over 3mm between boards with appropriate filler (the underlay bridges small gaps). Remove any existing floor coverings and adhesive residue. Check for woodworm and replace if necessary.

Floor temperature: Concrete floor must be above 10°C for installation — cold concrete with adhesive gripper or adhesive underlay will not bond.

Fitting Gripper Rods

Gripper rods are strips of thin wood or metal with angled pins pointing upward and outward at approximately 60°. The pins grip the carpet backing when it is pressed down onto them.

Position gripper 6–8mm from the wall — this gap is the 'channel' that the carpet tucks into. If the gap is too wide, the tucked edge will be visible. If too narrow, you can't tuck without the carpet pulling off the grippers.

Cut gripper to length with tin snips or a hacksaw. Mitre the ends at internal corners (45°) for a neat finish. At doorways, install threshold bars or edge strips (see below for types). Fix at every pre-punched hole — typically every 40–50mm along the rod. For curved walls, score the back of the gripper at 50mm intervals so it can bend to the curve.

Doorways: Choose the right threshold bar:

  • Gripper-to-gripper (carpet meeting carpet) — use a Z-bar or carpet-to-carpet bar
  • Carpet meeting hard floor (same level) — use a transition strip or TrimLok
  • Carpet meeting hard floor (height difference) — use a reducer strip

Laying Underlay

Underlay runs at 90° to the carpet direction to avoid joins coinciding. Tape underlay joins with 50mm gaffer tape — do not overlap underlay. Trim to the inner edge of the gripper rod — the underlay should not go over the gripper. At doorways, cut underlay flush with the threshold bar position.

Stairs: Cut underlay to cover each riser and tread separately (two pieces per step, or one piece folded around the nosing). Do not use underlay that bridges the nosing — it causes the carpet to compress unevenly and feel spongy underfoot.

Stretching and Fixing

Direction: Always plan the stretching sequence before starting. For a rectangular room, fix one short end and stretch towards the opposite short end. Then fix one long end and stretch towards the opposite long end.

  1. Cut carpet to size — add 75mm to each dimension for tucking
  2. Lay carpet in position, press onto grippers at one starting wall
  3. Use power stretcher to stretch carpet towards opposite wall — anchor head against fixed wall, extend stretcher pole across room, press with knee or body weight
  4. While carpet is stretched, press down onto grippers along second wall
  5. Repeat for the other axis
  6. Tuck edges into the channel between gripper and wall using a bolster chisel and mallet, or a carpet tucker/tucking tool
  7. Trim any excess carpet at tucking stage — do not cut before stretching

Stairs: Work from bottom to top. Each tread and riser is tensioned individually with the knee kicker. Ensure the carpet wraps tightly over the nosing. Use a carpet bolster (cold chisel) to tuck into the angle between tread and riser.

Seaming

Where joins are necessary (wide rooms, L-shaped rooms), seams must be hot-glued:

  1. Plan seam position — avoid joins in doorways and high-traffic paths. Join should fall in the least visible area
  2. Lay both pieces in position, overlapping by 50mm at the seam
  3. Cut through both layers simultaneously with a straightedge and craft knife — gives a perfect butt join
  4. Fold back both edges and lay hot-melt seaming tape along the join, sticky side up
  5. Run a seaming iron (set to 140–160°C) slowly along the tape, pressing the carpet edges down onto the molten adhesive as you go. Work in 300mm sections
  6. Weight down the seam with a board for 15 minutes while adhesive sets
  7. When cool, run a seam roller along the join. Check pile direction is consistent across the seam

Frequently Asked Questions

Do I always need a power stretcher?

For rooms over 3m in any direction, yes — without a power stretcher, you cannot apply sufficient tension, and the carpet will ripple within a few months of foot traffic. Knee kickers are for fine-tuning position and for stairs, not for stretching large areas. Professional fitters use power stretchers as standard.

How do I calculate how much carpet to order?

Measure the length and width of the room and add 100mm each direction for trimming. For joins, plan the layout and add one full pattern repeat length per join on patterned carpet. Order by the running metre — carpet comes in 4m and 5m widths. Cutting across a 4m width for a room 3.8m wide wastes only 200mm; a room 4.2m wide requires either a join or a 5m width.

Can carpet be laid on an uneven floor?

Minor undulations (under 3mm per 300mm) in the subfloor are bridged by the underlay and carpet without noticeable effect. Larger depressions or humps will telegraph through and feel uneven underfoot. Fill or grind before laying. On very uneven concrete floors, consider a self-levelling compound first.

How long does fitted carpet take to settle?

Freshly laid carpet may feel slightly lumpy or raised in places for 24–48 hours as the underlay compresses and the carpet relaxes. Minor surface ripples immediately after fitting are normal — they should disappear with a few days of foot traffic. Ripples that develop weeks or months later indicate insufficient stretching at installation.

Regulations & Standards