In your home, the subfloor is the layer between the structural ribs of your floor, and the finished flooring you can see. Subflooring protects the structural integrity of your floor, so it’s very important that you get it replaced if it’s showing signs of damage.
Here are some signs that you may need to have your subfloor replaced, and the sooner the better.

A picture of a house being remodeled.

1. Cracked Tile Flooring

Many bathrooms are lined with tiles rather than wood to prevent water damage. You can tell that your old bathroom subfloor needs renovating if the tiles have started to crack.
Cracked tiles can indicate that the subfloor is not rigid enough to hold them up, which is a sign of damage or old age. For this reason, wood does not make a good subfloor material in the bathroom, at least without a concrete support layer on top of the planks.

2. Loose Toilet

In the bathroom, if your toilet is not securely fixed to the floor, your subfloor may have become too rotten to hold it in place. The toilet area is at an increased risk for this due to the attached water pipes.
A leak in any of these pipes will cause damage over time, so a loose toilet should be addressed as soon as you notice it. This can prevent even worse water damage in the rest of your home.

3. Sunken Floorboards

When you walk on your floorboards, do you notice that some spots seem softer or uneven? This happens when the subfloor underneath is rotting. The sooner you find this problem, the better, since replacing a single weakened spot is much cheaper than ripping up the floor of your entire home.
Other indicators of a decayed subfloor are when the floorboards have a “spongy” feel, or when they shift underweight. These definitely need to be replaced and are more likely to break under heavy furniture.

4. Musty Smell

If your home smells musty for no apparent reason, check the flooring. The smell being strongest near the floor is a very likely indicator of water damage, which means you’ll have to replace your subfloor.
If your home was subjected to a flood, mold and mildew underneath the floorboards are guaranteed, so you will need to replace everything regardless if the smell is not yet noticeable.

5. Leaky Ceilings

If your ceiling is leaking, it could mean anything from a burst pipe to a particularly heavy rainstorm. However, the fact that it is leaking may mean that the water has already soaked into the rest of the structure, and you may have to replace your subflooring.
At the very least, you should get an evaluation of it to see if a full replacement is necessary.

6. Squeaky Floorboards

Squeaking usually happens in the subfloor when you walk, coming from the action of the nails underneath being pushed and pulled out of place. Excessive squeaking can mean that the subfloor is warped or damaged and needs to be replaced.

The Bottom Line

Typically, subflooring should only need to be replaced more than once if it experiences a lot of moisture. The average homeowner will never have to worry about it, but you should still keep an eye out for signs of damage, since leaving the problem alone can cause more structural damage down the line.
Don’t forget to find the root of the problem, too. Knowing what went wrong and being able to fix it can go a long way in protecting your home for as long as you live there.