Navigation Menu+
Commercial Flooring News

Guide To Wood Flooring Underlay

When considering a wood based floor covering you may require an underlay. Let’s look at the different types and explain a little about each..

The only situations that underlays are needed is when a floating floor is being installed. A floating floor means that the floor covering isn’t permanently fixed down to the ground underneath it. Underlays are generally not recommended or needed for solid wood floors.

All laminate and a lot of engineered floors are what’s known as ‘floating floors’. Some engineered wood flooring can be installed both floating and glued or nailed down to the sub-floor. In these cases, the final decision rests with yourself and installer as to the best installation method to use that suites the property i.e. If you have a sub-floor that is part solid and part wood floorboards, you may decide to opt for the floating method as this can be far easier to do. If you are installing the floor by fixing it to the sub-floor, an underlay must not be used.

If you will be floating your new floor there are several types of underlay available, all with great properties that will suite particular requirements.

Roll underlay

Wood floor underlay on a roll is often around 3 mm thick. The thin thickness is sometimes seen as a negative. However, in the world of wood flooring, less movement is better. Roll type underlays tend to compress, giving slight absorbent properties, but if they were any thicker, this would create excessive movement resulting in problems with any wood based floor covering further down the line. These underlays can have exceptional acoustic properties but do not be mistaken that they will prevent noise altogether. They do also give some insulating benefits. All of the points mentioned are very much dependent on the quality of underlay you purchase. You should compare the specification of the underlays before you buy i.e. Decibel ratings and insulation ratings.

There are four main types of roll underlay.

Silver Underlay with built in vapour barrierThe first being produced with a built in vapour barrier or DPM (glossary). A vapour barrier or damp proof membrane, which can be a slightly misleading term, will only be effective if the relative moisture content of any sub-floor does not exceed 75% (That’s relative moisture, not direct moisture!). A vapour barrier should not be considered a method of water proofing! If the moisture content of the floor exceeds the % mentioned, you can expect to have a damp musty smell before long and eventually the trapped moisture will make it’s way through the vapour barrier and start to work it’s way into your new floor, resulting in all sorts of problems.

These vapour barriers are produced to prevent moisture from a sub-floor effecting your new floor covering (within specific parameters as mentioned above) . These types of underlays are designed to be used on all ground floors. More and more flooring manufacturers are now requiring an underlay with a vapour barrier be used on suspended timber floors (floorboards, chipboard, ply board) if they are on the ground floor. You should check the installation literature of your chosen wood flooring.

The second type of underlay is produced without a vapour barrier. They will look very much like the underlay in the picture above but without the silver, gold or transparent membrane. These are ideal for first floor and upward installations. It’s worth mentioning that these thinner underlays, although marketed as helping to even out sub-floors, do not have brilliant levelling properties. As much work as possible to make any sub-floor even is recommended. It’s easy to be sold an underlay that will not perform, so heed this advice. There is very little difference in an underlays insulating properties and decibel ratings between one with a vapour barrier and one without, although this again is used as a marketing tool. Please note, there is nothing wrong with using an underlay with a built in vapour barrier on upper floors of a property. However, be aware that there is next to no gain from doing so.

White Underlay without a vapour barrier

The third type of underlay commonly referred to as white foam underlay (pictured on the left). This is generally around 2 to 3 mm thick and is essentially a very thin lightweight foam. Generally the cheapest of all the wood floor underlays. It has very little insulating properties or sound reduction properties but is suitable as a budget underlay.

Foam cantilever underlayThe forth wood underlay is essentially the same as the roll underlays described above but this is boxed and not on a roll. It is still around 3 mm thick but comes in a folded fashion. This underlay is commonly known as a ‘combi’. Due to the fact they also incorporates a built in vapour barrier. This type offers very similar insulation properties to the first example.

All of the underlays above are perfect for laminate and engineered floors. They’re easy to fit and can be cut simply with a utility knife. They can be used on top of solid floors, floorboards (caution regards cupping/crowning ~ please refer to our glossary or sub-floor prep), ply board, chipboard and pre-finished floors such as tiles or vinyl. Again, an even sub-floor is absolutely key to any flooring installation.

The insulation and sound reduction properties have not been shown here as this is a broad guide to the different types of underlays and not specific manufacturers. This should be confirmed with your supplier. All ground floor underlays should be taped at the seams to prevent moisture from getting through. Many will come with they’re own integrated tape but some don’t. Make sure your supplier has taken this into account and provided the tape with your purchase!

Block board underlay

Picture of block board fibre underlayBlock board underlay can be made with different materials like fibres, mixed wood composite i.e. cork/chipboard particles) and light weight polystyrene material . They typically range from 5 mm to 7 mm thick.

The main advantage of these types of underlays is they’re levelling properties. Do not misunderstand. Due to clever marketing language, it is easy to fall into the trap that this underlay will solve all your sub-floor problems. If your sub-floor is extremely uneven, this will not be solely resolved by purchasing block board underlay. As much sub-floor preparation work should be carried out as possible. However, if you have slight imperfections, this type of underlay is very good at absorbing these. You may find that time and usage of your room is required for this underlay to bed in. Initially, the floor may feel slightly spongy to the feel.

This is a picture displaying a separate vapour barrier Block board underlay does not come with a vapour barrier. If you are planning on using this type of underlay on a ground floor, a separate vapour barrier should be purchased and installed underneath the block board. Care should always be taken to ensure there is no sharp objects that will puncture a separate vapour barrier once installed. For example protruding nails should be sunk below the surface and grit should be thoroughly removed. A vapour barrier should always be lapped up all perimeter walls by several inches when installed.