Flooring underlayment is a thin layer of soft material that is installed between a room’s subfloor (usually concrete or floorboards) and the finished carpet or hard floor. Made from rubber, fibre, felt or foam, it helps to even out any bumps or dents, provide heat and sound insulation and make the flooring more comfortable underfoot. 

However, depending on your finished floor choice and the condition of your subfloor, it’s not always necessary to install underlayment. To make sure you don’t spend extra time or money where it’s not needed, we’ve put together some advice on when underlay is needed and which type is best for your needs.

Introduction to Flooring Underlayment

Whether you’re installing your own new floor or are having it done by a professional, then you might already be factoring in the cost of underlay for the project. However, it’s important to check whether underlayment is actually needed for your particular installation or not. You might need underlay to:

  • Even out a subfloor that’s irregular due to dents, holes or bumps
  • Protect your finished floor from mould, mildew and moisture coming through the subfloor
  • Stop heat from being lost through your flooring, helping you save on energy bills
  • Add cushioning between a finished floor and the subfloor, adding comfort and durability
  • Soundproof the floor so the noises of any footsteps or movements are reduced

It’s often recommended that you install an underlay with hard floors to offer extra protection and ensure a quality, comfortable fit next to the subfloor. You’ll also need to match the type of underlayment to your specific requirements. For example, a thermal underlayment will offer heat insulation. 

Types of Flooring and Underlayment Requirements

The underlayment you choose will vary depending on your flooring type and the room you’re installing the floor in. For example, some hard floors may already have integrated underlay, meaning you don’t have to install an extra layer. Others may be thicker (up to 12mm), meaning they’re already comfortable underfoot and well-insulated. 

If you’re installing your floor in an upstairs room or loft conversion, then underlayment with acoustic insulation can stop noises from disrupting people on lower floors. For converted garages or spare rooms, using thermal insulation may help retain warmth alongside any wall or ceiling lining. 

For areas where you’ve got underfloor heating, your underlayment also needs to be compatible with these systems. Choosing an underlay that’s not suitable could become a hazard or cause damage to your system. 

Does a Wood Floor Need Underlay?

It isn’t essential to install a real wood floor with an underlay. Instead, a ‘floating floor’ method can be used, where the wooden planks are laid unfixed on top of the underlayment. However, professionals may recommend that you fix your wooden floor directly to the subfloor in some cases. This is possible with engineered wood, which is more resistant to temperature and moisture changes than real wood. 

However, using an underlay can provide extra protection, particularly for natural wood floors. It’ll stop any moisture, cold or heat spreading from the subfloor and causing damage. Similarly, it can offer extra cushioning underfoot and insulate any sound from the movement of the hard wooden planks on the subfloor. In short, using underlayment with wood floors can help them last longer. 

Do You Need Underlay for Laminate Flooring?

Unless you’re using a product with integrated underlay, then you should install an underlayment below your laminate flooring. Laying laminate directly on a subfloor can leave your floor feeling very hard and uncomfortable underfoot. Moisture can also enter through the subfloor, causing damage such as discolouration and warpage. 

Choosing an underlayment that’s thick or has a moisture barrier will help protect from these problems. It’ll also stop the laminate hitting the underfloor and cause creaking or clacking sounds, preventing noises from spreading through the whole house. This helps the flooring last longer, even with heavy usage. 

Is Underlay Always Needed for Vinyl Floors?

Vinyl is the only hard flooring type where underlayment isn’t required. Cushioned vinyl or products with integrated underlay are already comfortable underfoot and are moisture and heat resistant. This means they can be laid directly over a smooth, prepared subfloor. 

If you’re installing a sheet vinyl or LVT using a floating floor method or the product is particularly thin, then you should add in the extra protection of an underlayment. This won’t just provide extra softness underfoot, but stop any moisture or unevenness in the subfloor from causing damage. 

Key Considerations for Choosing Underlayment

When you’re choosing underlayment, it’s important that it fits your particular requirements. Whether you want protection from moisture, heat or noise will affect the type of underlayment and material you choose. 

Material Composition

There are several different types of materials that floor underlayment can be made from. They include: 

  • Foam can be laid under laminate, engineered wood or vinyl and offers cushioning as well as some moisture protection 
  • Fibre board is a good underlay for wood and laminate, forming a stable base that insulates sound and heat and can be fixed onto directly if needed
  • Rubber will offer thermal and sound insulation under wood and laminate flooring, it also usually has a vapour barrier to provide damp proofing
  • Polythene is useful for damp proofing and can help increase the lifespan of various floor types
  • Cork is good for sound absorption and resists moisture while being porous and allowing for airflow
  • Felt is suitable for wood floors as it is a stable, level base that can be fixed to or used for floating installation

Moisture Barrier

Wooden and concrete subfloors will all have moisture content in them. If this comes into contact with flooring tiles or planks, it can cause it to shift or warp. As well as using a moisture metre to determine the level in a subfloor, you should install an underlayment with a moisture barrier to prevent any damage to your new floor. Choose a product with a vapour or moisture barrier and fix it with vapour tape to prevent water from entering your floor. 

Heat and Sound Insulation

Installing underlayment is essential for providing heat and sound insulation. This will help keep your energy costs low and stop noise disturbance between rooms. Using these types of underlay is particularly important if you’re using floating floor insulation, as sound and air can spread through them more easily. 

When you’re looking for an underlay that provides heat insulation, you should look at the tog ratings of your different products. Typically they run up to a tog of 3. In contrast, underlayment made specifically for sound reduction can reduce noise by up to 26db. If sound reduction is a priority, you should look at a product’s decibel absorption levels when making your final selection.

Compatible with Underfloor Heating

If you have an underfloor heating system, then any underlayment you use needs to be able to withstand high temperatures. Choosing a specially-designed thermal underlay will cushion and insulate your floor against heat and sound without becoming a hazard. It’ll also help your flooring last and provide underfoot comfort for longer. 

Home Installation Tips

If you’re installing your own flooring, then preparing your subfloor and laying your underlayment correctly is the important first step. 

Preparing the Subfloor

By taking time and care to prepare the subfloor correctly, you give your new flooring the most level, clean surface possible to be laid on. Here are the steps you should take:

  • When you pull up your old floor, take a good look at your subfloor to check for unevenness and damage. Walk over it to see if any areas creak or move
  • If you can, you should level it off. This can usually be done by fixing and firmly screwing in any wooden floorboards or laying in extra concrete. You should also glue any big gaps between floor boards with a wood adhesive
  • Once you’ve levelled off your floor, you need to leave it to dry completely. Use a moisture metre to make sure it has a water content of only two or three percent before laying a floor
  • Then, dust and vacuum the subfloor so it’s free from dirt and debris
  • You should also undercut any trims or door jambs before beginning your installation

Attaching Underlayment

Here are step-by-step instructions on how to properly attach underlayment to the subfloor:

  • Measure out the underlayment to the correct size of the room and cut out the pieces using a pen knife or scissors
  • Tape up the gaps between seams using vapour tape, this will stop any moisture from escaping through your underlay
  • Once you’re ready to attach the underlayment to the subfloor, remove the sticky backing, apply glue or use tacks to lay it down so it's flush to the edge of the room. It should be smooth and have no lumps or rucking
  • If you’re using tile or board underlayment, you should apply silicone sealant using a caulking gun to fill the gaps between the material and the walls

Common Mistakes to Avoid

Choosing the right underlayment product for your needs is the first step towards effective floor installation. Then, when you’re installing the underlayment, make sure you don’t:

  • Lay it on an unclean or uneven subfloor, as this can cause 
  • Lay it on a damp subfloor, as this could lead to a build up of mould and cause damage
  • Lay it in the same direction as any floorboards, you should run it the opposite way to them
  • Don’t overlap different sections of the underlayment, as this will cause unevenness 
  • Lay it the incorrect way up, one face should be in contact with the subfloor (e.g. a foil or coloured side), which will be indicated on the product package
  • Leave any wrinkles or gaps, as this could lead to an uneven or unprotected finished floor

Evaluating Underlayment Products

When you’re choosing an underlayment for your floor, you don’t just need an option that suits the specific needs of your floor and room. To get the best value for money, make sure you check the specific product reviews and get recommendations from other users. This will help you narrow down the different options and figure out the best performing underlayment for your needs. 

It’s also important to weigh up the cost of any product you consider against its quality. Although you might be tempted to choose a budget option to keep your DIY project pricing low, it could lead to problems with your finished floor down the line. Choosing the best option you can afford for your flooring type will ensure you get a level, warm and comfortable result. 

Lay Comfortable, Quality Flooring

Getting the right underlayment is essential to ensuring a quality finish on your hard floor. However, with so many options available, it can be difficult to narrow down the ideal underlayment for your needs. To get advice and find the best quality underlayment for your flooring project, contact our expert team.