Common Defects Found in Subfloors (and how to fix them)

subfloor void

Is there a soft spot under your carpet? Are your floorboards squeaking a little louder than usual? If you answer is yes, then your subfloor is probably damaged which can be a problem. In some cases, damaged subfloors can be downright dangerous.

In this article we’ll talk about the subfloor area of the house, its common defects, as well how you can check if your subfloor is damaged… even before an inspection takes place.

What is a subfloor?

A subfloor is a structure attached to the floor joists, supporting the finish flooring. Subflooring spreads the load imposed by persons or furniture, cabinetry, or other weighty items on the floor above several joists, producing less deflection or spring. It also provides a level surface, making the flooring installation more simple, whether you hire a professional to do it or you decide to do it yourself. In addition, subfloors protect the surface floor against moisture damage and mould in a damp environment.

What is a subfloor void?

Subfloor void is the area beneath a ground floor, suspended timber floor. This area’s actual size can vary significantly from virtually nothing, where floor joists are in contact with the substrate beneath, to something you could crawl under. The standard for this sort of space is often found to be around 300-400mm deep. That’s from the undersides of the floorboards to the substrate beneath.

Building inspection in Brisbane

Why do inspectors need to access this area?

There are several reasons for building inspectors to perform a routine inspection even though the subfloor is often hidden from the day-to-day field of vision. The subfloor can tell a lot about the property and its condition. That’s why it is recommended to be inspected quarterly, or once per year at a minimum.

It is essential to understand what may be happening under the raised floor that can cause damage. Things like drainage, ventilation, condition of the construction materials, and pest infestation signs are crucial aspects of any property maintenance program.

Are Annual Inspections Important?

How to help the inspector

During the inspection, you must ensure the inspector can get reasonable access to enter your sub-floor void if one exists. If you can’t be on the property during the inspection, make sure you have a representative who knows where the entrance to the void is and can open the hatch. It will also help if you remove any stored items to clear the space.

Ensure that the entrance point is not blocked by any items as the inspector cannot move anything around as part of his inspection. And to help close any information gaps that may arise from the inspection, you have to keep receipts for any repairs or improvements in this space.

List of common defects and how to fix/prevent/identify them

It is normal to see some signs of wear as your property ages. Most of them are relatively easy to fix. With regular maintenance, these should not cause too many troubles. Here are the common defects that our inspectors usually see in the subfloor area of your home.


There are more than 300 species of termites in Australia, but only a dozen are a problem for timber in buildings. The possibility of damage depends on the type of construction and other conditions present at the property.

Causes: The subfloor is the closest part of a building to the ground and can be susceptible to dampness, creating perfect pests conditions. The subterranean species cause the most damage to building timbers. They can contain up to several million members, so when they find a good food source, they cause a lot of destruction.

Identify: Termites build mud-covered shelter tubes over the foundations sometimes and up piers or walls to get to the subfloor timbers. There are several signs of termite damage to subfloors, such as squeaking floors, sagging floors, top floor layer that is disengaged from the subfloor, and loose floor tiles.

Fix: It’s essential to inspect for termites regularly. If you find live termites in your property, the best thing to do is cover up the runway and then contact our pest inspectors. It would help if you disturbed them as little as possible so that the pest controller can work with the active runway to access the nest, which may be some distance away.

Find out more:  Is Your Home Conducive to Termites?

Termite inspector in residential crawl space inspects a pier for termites.

Squeaky floors

It is quite common for an old property to have a squeaky floorboards and any homeowners ignore the sounds, which can be a huge mistake. Squeaky floors can mean that the subfloor was not secured to the joists correctly.

Causes: Squeaks are caused by adjacent parts of the floor rubbing against each other when they’re walked on. Other causes include loose-fitting or broken tongues and groove, nails that have missed the joist underneath.

Fix: Squeaky floor can be fixed by going under the floor and filling the gap between the joist and flooring. In general, all boards or sheets must be re-nailed wherever there is movement. For structural problems, you need to call in a carpenter to install extra joists.

Sinking floors

Cause: The main reason for the sinking floor is an original subfloor that was not installed correctly. Another cause is the excessive moisture, causing certain areas of the floor to sag.

Fix: The best solution is to call in a professional to have a good look at your floor. It is essential to have a property inspection before purchase to inspect a subfloor.

View our gallery from previous inspections to see some of our findings.


Causes: Downpipes that are not connected are often the cause of leaks. Water pooling around concrete footings can cause major structural problems.

Fix: Look for any damaged pipes and get these repaired or replaced immediately. Check also where the water flows at your property during periods of rainfall. Even in summer months, make sure to know where the water is being directed. It is a relatively straightforward process connecting the downpipes to the stormwater systems.

Subloor - leak

Gaps between boards

Causes: Older properties with tongue and groove strip flooring will often have gaps between boards. This is because it was once common practice to use green boards. As they continued to dry over the years, the boards would shrink, and small gaps would appear.

How to Fix: If the gaps are wide enough to show through the floor covering, the easiest solution is to fill them with a suitable compound or cover the floor with hardboard or MDF underlay.

Insufficient Ventilation

Causes: Inadequate subfloor ventilation is a common problem for many homeowners. There are several reasons for limited ventilation, including obstructed or blocked vents, old vents and lack of natural ventilation.

Identify: If your subfloor is damp, mouldy or smelly or you have fungi growing, you have insufficient ventilation.

Fix: Obstructions or stored items under your house can block vents and limit natural airflow. Removing these obstructions can remedy this problem. If you have older vents made of terracotta or cast iron, you need to change them because they do not allow as much ventilation as open metal vents do. You might also consider adding vents or ventilation fans.

Inspect your property

For property inspections in QLD, NSW, or WA, Inspect My Home can provide you with a professional  professional building inspection service to help you assess the quality of your property and it’s subfloor.

We have a team of licensed and experienced inspectors that can give you a detailed building report, whether you’re selling a residential or commercial property. Call us on 1300 337 447 or book online to schedule a building inspection for your property today.

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