Understanding your Options with Un-level Subfloors

  • Installing
  • Published: 6 March, 2020
  • Updated: 14 May, 2021
Levelling subfloor

Understanding your Options with Un-level Subfloors

What is Uneven or Unlevel Subfloor? 

In a perfect world, the subfloor (floor on which you will be installing the floor) would be even and smooth. However, the reality is our subfloors are often slanted, bumpy or uneven. It may not look like the case, but often you might pull away your old carpet to discover the floor is uneven and bumpy. 

So why is this a problem? You cannot install a hard floor over an uneven subfloor. Doing so could result in creaking noises and movements between the boards.

4 Ways to Level an Uneven Subfloor

Correcting uneven subfloors is a common practice in the floor installation process. Before you can even consider installing timber, laminate or other flooring, you need an even subfloor. 

The approach you ultimately take depends on how uneven and unlevel your subfloors are. Mildly uneven subfloors can easily be worked around, whereas severely uneven floors could require significant work prior to installation. There are 4 main ways to level an uneven subfloor:

1) Self-Levelling Compound

One common option is using self-levelling compounds. This compound can potentially be used on a concrete slab or a wood subfloor, and can be effective with any dips in the floor. These self-levelling compounds are similar to concrete and typically come in large bags of powder. The powder should be mixed with water to create a thick paste, and you can spread it over the floor and it will automatically level out in the effective areas.

For subfloors with large dips, we tend to use self-levelling compounds to level the floor.

2) Plywood

A second option is installing a plywood above the original subfloor to create a new smooth surface. If there are large variations in the level of the floor, you can find plywood of different thicknesses and install them accordingly, so that the different areas meet at the same level. 

To install the plywood, nail the plywood into the subfloor below for stability. If you are installing above concrete, you must use bolts that can enter the concrete surface. 

For wavy subfloors, we tend to use plywood methods to level the floor. 

3) Grinding & Sanding

A third option is to grind down any humps on the floor. You can use a floor grinder to level concrete floors and you can use a floor sander to sand the surfaces of wooden subfloors. They utilise discs which rotate to finish off rough surfaces. Grinding and sanding is most suitable if you have a large hump in the middle of a concrete slab. 

For subfloors with humps or bumps, we tend to use sanding methods to level the floor.

4) Using Thick Underlay

The final option is to use thick underlayment to patch up interior dips or waves. Underlay is a simple and efficient method when there are low variations in the floor level. At FloorVenue, we have underlay of different thicknesses and compositions that enable us to level mildly uneven subfloors. 

For mildly uneven subfloors, we tend to use thick underlay to level the floor. 

What do I do next?

If there are any floor levelling issues, it’s prudent to have them addressed before installing any floor. 

It’s also wise to have a professional on-site inspection before any flooring installation. If you’ve asked for a quote over the phone or online, most flooring companies can only provide an estimate. It’s very difficult for any installer to provide an accurate quote until they are able to see and assess the actual sub-floor situation. 

At FloorVenue, we provide free no-obligation quotations where we will send a member of our team to your house to conduct an inspection. Fill out the contact form at the bottom of the page and hear back from us within 24 hours!

Frequently Asked Questions

The first step to do is assessing the situation, finding out the key facts such as the material of the subfloor and the cause. Identify the type of unevenness will help determine the best solution.

  • Wood underfloors will most likely have to be ripped up and a new one installed to ensure consistency.
  • You can also use a flooring underlayment which can smoothen up any remaining peaks and valleys in the subfloor. 
  • Self levelling compound is ideal for fixing dips, but may not be very effective for more serious problems.

Rest assured, FloorVenue offers free on-site inspections to help identify the best subfloor solution for you.

First and foremost, we highly recommend levelling the uneven subfloor before installing any type of floor over. The best option for slightly uneven subfloors is a direct stick installation (involving nails & glue) if this is a viable option.

  • Floating flooring is not recommended for uneven floors as this increases risk of the planks moving or splitting apart.
  • Ceramic and porcelain tiles will also crack over time if the subfloor is uneven.
  • Carpet would be an ideal option as it is also cheap, flexible and attractive.

When it comes to testing the evenness of your subfloor, we recommend using a long spirit leveller of at least one metre in length. This allows you to check for bumps, dips and other uneven areas, whilst also providing how many millimetres of height difference over every metre.

Laminate flooring on an uneven floor will cause many problems. One of the major problems are loud pops and cracks that will eventually surface when you walk across due to pockets of air beneath the surface as a result of the uneven subfloor.

Other potential long term issues include buckling, loose boards, and a significant shortening of the laminate flooring’s lifespan. However, slightly uneven subfloors are simple to fix with fast and easy solutions such as sanding down the bumps or using self levelling compound prior to installation.

It is generally not recommended to install a double layer of underlay for laminate flooring. This is because the base of the flooring may become too soft, thus jeopardising the effectiveness and reliability of the locking system. Underlayment is only manufactured to be used as a single layer. If you need to use more underlay for acoustic purposes, aim for a higher AAAC rated underlay.

You can also book a free on-site inspection with us at FloorVenue so one of our professionals can help determine the best course of action for your project.

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