How to Fit Carpet Underlay Like a Pro: A Step-by-Step DIY Guide When planning a new carpet installation, it’s easy to focus all your attention on the colour, style, and pile of the carpet itself. However, the secret to a truly luxurious, long lasting, and comfortable carpet lies beneath the surface. The unsung hero of any great flooring project is the carpet underlay. Choosing a quality underlay and fitting it correctly is arguably just as important as the carpet you lay on top of it. Learning how to fit carpet underlay like a professional is a fantastic skill for any DIY enthusiast. It not only saves you money on installation costs but also ensures you get the maximum performance from your investment in terms of comfort, sound insulation, and durability. This step by step guide for 2025 will walk you through the entire process, from choosing the right type for your home to achieving a flawless, expert finish. Jump to Section: Why is Carpet Underlay So Important? Choosing the Right Carpet Underlay for Your Home Your Toolkit: Essential Tools & Materials for the Job Preparation: The Foundation of a Professional Finish How to Fit Carpet Underlay: A Step by Step Guide Common Mistakes to Avoid When Fitting Underlay The Perfect Foundation for Your New Carpet Why is Carpet Underlay So Important? Carpet underlay is much more than just a layer of foam. It’s a high performance product that provides several crucial benefits: Superior Comfort: This is the most noticeable benefit. A quality underlay provides a cushioned, springy feel underfoot, making your carpet feel significantly more luxurious and comfortable to walk on. Excellent Insulation: It acts as a vital thermal barrier, helping to keep your room warmer and potentially reducing your energy bills. This is a significant advantage in the often chilly UK climate. Sound Reduction: Underlay is brilliant at absorbing sound. It dampens the noise of footsteps within a room and significantly reduces sound transfer to rooms below, creating a quieter, more peaceful home. Protects Your Carpet: It acts like a shock absorber, protecting the carpet backing from wear and tear against the hard subfloor. This helps prevent the carpet pile from flattening and can dramatically extend the life of your carpet. Choosing the Right Carpet Underlay for Your Home Before you start fitting, you need to select the right product. Here’s what to consider: Types of Underlay: PU Foam: The most popular choice in the UK. Made from recycled polyurethane foam, it offers excellent comfort and sound insulation for a great price. It’s lightweight and easy to handle. Sponge Rubber: A traditional option that offers fantastic durability and sound reduction. It comes in flat or waffle patterns. Crumb Rubber: Made from recycled car tyres, this is an extremely durable and dense option, perfect for high traffic areas like stairs. Felt: A traditional, dense underlay that provides superb thermal insulation. Underlay Specification: Thickness: A common misconception is that thicker is always better. For most rooms, an underlay between 8mm and 11mm provides a perfect balance of comfort and stability. Using an underlay that is too thick can cause issues with carpet fitting and door clearance. Tog Rating (Thermal Insulation): The higher the Tog rating, the better the thermal insulation. For a cold room, look for a high Tog rating (e.g., 2.5 or above). If you have underfloor heating, you must choose a specialist low Tog underlay (typically below 1.0). Sound Reduction (dB Rating): If reducing noise is a priority (for example in an apartment or upstairs bedroom), look for an underlay with a high decibel (dB) rating (e.g., 40dB or more). Subfloor Type: For concrete subfloors, you may need an underlay with a built in Damp Proof Membrane (DPM) or to lay a separate DPM sheet first to block moisture. Your Toolkit: Essential Tools & Materials for the Job Having the right gear ready will make the process much smoother. Tools: Tape Measure & Pencil Sharp Utility Knife or Stanley Knife (with plenty of spare blades) Knee Pads & Gloves Staple Gun (Hammer Tacker) or Spray Adhesive Duct Tape or Specialist Underlay Tape Materials: Carpet Gripper Rods Your chosen Carpet Underlay Preparation: The Foundation of a Professional Finish A professional finish starts with perfect preparation. Clear the Room: Remove all furniture. If you’re replacing an old carpet, use your utility knife to cut it into manageable strips and roll it up. Pull up the old underlay. Clean the Subfloor: Sweep and then vacuum the entire subfloor thoroughly. Remove any old staples or nails. The subfloor must be completely clean, dry, and free of debris. Fit Carpet Gripper Rods: Gripper rods are wooden strips with angled pins that hold the carpet in place. Nail or glue them around the entire perimeter of the room. The crucial part is leaving a gap between the gripper rod and the skirting board that is slightly less than the thickness of your carpet (typically around 7 to 10mm). The angled pins must be pointing towards the wall. How to Fit Carpet Underlay: A Step by Step Guide With your room prepped, you’re ready to lay the underlay. Step 1: Roll Out the First Section Start in a corner and roll out your carpet underlay along the longest wall. Different underlays have different instructions for which side faces up. A general rule for PU foam is to lay it with the branded film side up. For rubber underlay, it’s usually the rubber side down against the subfloor. Always check the specific instructions for your product. Step 2: Cut the Underlay to Fit Roll the underlay out until it reaches the far wall. The most important rule here is to cut the underlay so it fits inside the gripper rods. It should butt up snugly against the inner edge of the gripper but never overlap it. Use your sharp utility knife for a clean cut. For cutting around obstacles like radiator pipes, make small, precise cuts. Roll the underlay out until it reaches the far wall. The most important rule here is to cut the underlay so it fits inside the gripper rods. It should butt up snugly against the inner edge of the gripper but never overlap it. Use your sharp utility knife for a clean cut. For cutting around obstacles like radiator pipes, make small, precise cuts. Step 3: Secure the Underlay (Optional but Recommended) To prevent the underlay from moving while you work or when the carpet is fitted, it’s a good idea to secure it. On a wooden subfloor, you can use a staple gun or hammer tacker to place staples around the perimeter, about 10cm in from the gripper rods, and then every 20cm or so. On a concrete subfloor, you can use a light spray of contact adhesive around the perimeter. Step 4: Lay Subsequent Sections Roll out your next piece of carpet underlay alongside the first. The most important thing is to make sure the edges of the two pieces butt up against each other perfectly. They should be touching snugly, with no gaps, but they must not overlap. An overlap will create a hard ridge under your carpet. Step 5: Tape the Seams Once two pieces are butted together, run a line of strong duct tape or specialist underlay tape along the entire length of the seam. This is a crucial step that many amateurs miss. Taping the seams stops the pieces from moving apart, prevents grit from getting between the joins over time, and creates a more stable, continuous layer for your carpet to sit on. Continue this process until the entire floor is covered. Common Mistakes to Avoid When Fitting Underlay Overlapping Seams: This creates hard ridges that you will feel under the carpet and will cause premature wear. Covering the Gripper Rods: The underlay must sit inside the grippers. If it covers them, the carpet fitter won’t be able to hook the carpet on correctly. Leaving Gaps: Any gaps between the pieces of underlay will create soft spots and reduce insulation. Using the Wrong Underlay: Using a high Tog underlay with underfloor heating, or a non DPM underlay on damp concrete, will cause problems. A Dirty Subfloor: Any debris left under the underlay will be felt through the carpet and can cause damage over time. The Perfect Foundation for Your New Carpet Congratulations! By following these steps, you have now correctly fitted your carpet underlay and created the perfect foundation for your new carpet. This professional level preparation will make your carpet feel more luxurious, last longer, and contribute to a warmer, quieter home. Taking the time to get the underlay right is a DIY job that pays dividends in comfort and quality for years to come, ensuring your final floor looks and feels absolutely fantastic. Get Your Project Started A professional finish starts with the right materials. For securing your underlay and ensuring a stable, long lasting installation on concrete subfloors, a quality adhesive is key. Our Multi-Tak General Purpose Spray Adhesive is perfect for tacking down the perimeter of your carpet underlay before fitting. Shop Multi-Tak Spray Adhesive
