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Levelling a floor – a beginner’s guide

Levelling a floor – a beginner’s guide

It’s the statement found at the top of every flooring installation manual.

“Start with a level floor.”

Whether you own a period property or new build, plywood and concrete subfloors are very rarely flat – and if you wish to lay new flooring, that can be problematic! High and low spots make the installation process much trickier than it needs to be and can have a negative impact on the final results. So it’s crucial to do some preparation before you start.

Even for a DIY novice, levelling a floor is a relatively easy job. You just need a little background knowledge and the right equipment. And to help, we’ve also created this simple step-by-step guide.

So why not have a go?

Get to grips with the process and ensure your subfloor is as smooth and even as possible.


How to level a floor 

Step 1 - How to level a floor

Step 1: Identify the high and low spots

First things first, place a long straightedge or spirit level onto the subfloor – so that it’s parallel to the wall and about one 1ft away from the edge of the room. Then, look for visible gaps between the bottom of the straightedge and the floor. Most subfloors will have at least some slight variations, but you should mark any that are 3/16 inch (5mm) wide or more with a pen.

Move the straightedge in 1ft increments around the room and repeat the process – marking out any high or low spots – until the entire floor space has been covered.


Step 2: Determine any underlying problems

Step 2 - How to level a floor

Small variations in your plywood subfloor are likely due to age. They’re usually nothing to worry about and should be easy enough to correct yourself.

However, large variations (i.e. measuring more than 4 inches wide) and sagging may indicate a bigger problem. These could be caused by structural issues, such as a problem with the foundation, cracked floor joists or rotting sill plates. Therefore, it’s worth checking underneath the floorboards, and getting an engineer to fix such issues – before floor levelling begins.

Variations in a concrete subfloor are usually just due to shoddy workmanship. They’re not likely to reflect any underlying issues. In most cases, the concrete simply won’t have been levelled properly during its installation. And as such, these variations can usually be fixed without the help of a professional.


Step 3 - How to level a floor

Step 3: Repair the high spots

We recommend tackling the high spots first.

For plywood subfloors, start by screwing down any loose boards and remove stray staples and nails. Then, pop on a dust mask and use an electric sander to gradually sand down the high spots.

For a concrete subfloor, you’ll need to use an angle grinder and diamond grinding wheel instead. Be sure to wear a tight-fitting respirator (to protect against the concrete dust) and sweep back and forth over the high spots – taking care to vacuum away the dust as you work.

In both cases, it’s important to check your progress periodically with the straightedge. And once all the high spots have been removed, clean the floor with a wet-dry vacuum and sweep away debris.


Step 4 - How to level a floor

Step 4: Repair the low spots

Last but not least, it’s time to fill in the low spots or valleys in your subfloor.

This can be done by applying a cement-based floor leveller, which will settle into the low spots and set to create a level surface. But the easiest option (by far!) is to install a thick, high-quality underlay.

Sandwiched between the subfloor and your new floor covering, underlay can help to correct any imperfections in the plywood or concrete. It isn’t a miracle worker. But it can help to smooth out low spots and other minor irregularities – successfully levelling the subfloor and ensuring it’s in the best possible condition for your flooring installation.

Detailed information on the best underlays can be found in our blog, along with another helpful guide on ‘How to lay carpet underlay’. So, be sure to take a look and select the ideal ‘floor levelling’ underlay for your project.


Which underlay should I buy to level my floor?

Here at Carpet Underlay Shop, we have a huge online range of underlays for you to choose from – including products that are suitable for use with plywood and concrete subfloors. These are all high-quality, available for a very competitive price and can be delivered to your address the next working day. And the right one for you will depend on the type of floor covering you wish to install:



Carpet underlay to help level a floor

If you’d like to level a floor in preparation for a new carpet, we typically recommend Plushwalk 12mm.

This is a super-luxury carpet underlay, highly respected within the industry. In fact, it has dominated the market for a few years now – yet it’s still available for the affordable price of £6.99 per m2.

Cut from thick memory foam, it successfully adjusts to imperfections in the subfloor and will enhance the final look and feel of your carpet.





Laminate and wood

Laminate underlay to help level a floor

To level a floor for laminate or hardwood, our advice is to opt for the Royale 7mm Professional Sonic Gold Underlay.

Again, this is a leading product – one of the very best laminate underlays currently available to buy – and it’s reasonably priced at just £6.20 per m2.

Made from a unique high-density foam – called AeroFoam – it creates a smooth and flat surface, perfect for your laying your new flooring upon. And it demonstrates a range of other excellent qualities (e.g. 1.0 TOG rating, 37dB noise reduction).




Want to find out more?

Our team of in-house experts are always happy to help.

If you have any questions about our underlays, or would like further advice on how to level a floor, please don’t hesitate to get in touch. You can call us on 0203 887 0994 at any time. Or alternatively, send an email to and we’ll respond to your enquiry as soon as possible.


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  • Alex Illidge