Wet Floor Joists – Drying Water Damaged Floor Joists

Wondering What happens If Floor joists Become Wet? Is there any way to dry them out?

In this guide you will learn:

  • Signs of Wet Floor Joists & the common Causes of Water damaged Floor Joists,
  • What happens If Your Floor Joists become wet & How serious is this,
  • How to Dry out your Floor joists & How to tell if they have started to rot.

Are your floors squeaky, bouncy, or warped? Did your home spring a leak recently?

If so,you might need to dry out your floor joists.

Floor joists can absolutely get wet. Floor joists are the beams that the rest of your home sits on. Unfortunately, wet floor joists can easily become water-damaged, warped, or rotten.

These issues can become severe, and can lead to wet/dry rot infestations, toxic mold issues, and dangerous/costly structural damage.

As such, it’s best to learn how to recognize and deal with this issue before it becomes a major problem.

Signs of Wet Floor Joists

Common signs of wet floor joists include:

  • Uneven or Sloping Floors – Water damaged floor joists often sag before failing completely. If your floors are starting to look uneven, you might want to check for water damaged floor joists.
  • Squeaky floors – Water damaged floors also squeak sometimes, due to uneven gaps in flooring materials. Watch out for: squeaky floors that were otherwise previously silent.
  • Musty Odors – Wet floor joists attract mold and can quickly become rotten. This can lead to large mold infestations and strong musty odors throughout the house.
  • Rocking Toilet –Wet floor joists under bathrooms are often discovered when the toilet is no longer stable. If a previously stable toilet begins to move around: check for wet floor joists.
  • Loose or cracked floor tiles – Tile floors crack and break when the flooring underneath them starts to warp. Cracked tiles in your kitchen or bathroom? Check your floor joists for damage.
  • Warped Hardwood floors – Moisture damage is the main reason hardwood floors warp. This happens because of moisture from above (interior) or in the joists underneath the subfloor.
  • Bubbling linoleum – This is usually caused by moisture buildup in subfloors.
  • Window/Door Issues – A house functions as a unit. Cracked windows or nonfunctional doors is often a sign that there is structural damage in the form of wet and/or sagging joists.
  • Discoloration – Discoloration due to water and/or moisture buildup on floors/ceilings means that it’s time to check for wet floor joists and subfloors.
  • Pest Problems – Moisture buildup in floor joists attracts ants and termites. These critters can’t/won’t live in properly dry wood, so keep an eye out for unexplained pest invasions.

Common Causes of Wet Floor Joists

Floor joists can get wet for a number of reasons, including:

1.Leaking and/or Flooding

Plumbing leaks and floods are two of the worst things that can happen to your floor joists. Even a small flood can cause serious damage to floor joists in a small time period.

2.Condensation (often due to lack of proper ventilation)

This is one of the most common causes of wet and/or water-damaged floor joists.

Simply put: all floor joists must be in well-ventilated areas, or they will eventually succumb to water damage.

In fact, blocked-off basement/crawlspace vents (leading to poor ventilation) are one of the most common causes of wet joists and subfloors.

3.Sideways Penetration

This term describes what happens when water leaks from wet concrete/brick/mortar into the ends of the floor joists that the concrete is supporting.

Concrete is not inherently waterproof. Thus, if a foundation wall is absorbing more moisture than it should, it means that this moisture will eventually be absorbed into the ends of the floor joists.

4.Rising Damp

Rising damp is what happens when water (and salt) flow upwards through a masonry foundation wall. his happens because of ‘capillary action’ – the water is drawn up through the pores of the brick/mortar work itself.

Though this is not as common as condensation issues, it is still a possible culprit for wet floor joists.

Rising damp is more common in older homes constructed with traditional brick and/or stone foundations.

Suspecting Wet Floor Joists?

Call 844-488-0570 for a Risk Free estimate from a Licensed Water Damage Restoration Specialist in your area.

We Can Help Dry out your Floor Joists & Repair any Water Damage

What happens if joists get wet?

Severe structural damage, danger to inhabitants, and high repair costs are all inevitable outcomes associated with wet floor joists as water can cause immense damage to your floor joists.

In addition, wet floor joists can cause a whole host of specific issues. More specifically, it usually does so in the following ways:

  • Rot – Wood rot can be divided into wet/dry types. It is very important to understand the difference when trying to diagnose the type of rot during an initial damage assessment. For more specific information, please see the below section on this topic.
  • Termites – Termites and other wood-boring pests do not usually attack properly dry wood, especially in subfloors. They will, however, attack at moisture levels over 20%.
  • Warping (Structural Damage) – The wetter wood becomes, the more it loses its inherent stiffness and load-bearing strength. Wet floor joists do not necessarily need to be attacked by fungus or pests in order to become structurally unsound or to bend and/or warp.


How To Dry Out Wet Floor Joists

1.Fix The Source

First: find, diagnose, and fix the source of the problem. Until this is done, there is little point in trying to manually dry out floor joists.

In addition, wet floor joists might actually dry out by themselves if the source of the problem is fixed.

This doesn’t apply to severely warped or rotten joists, as those will need to be replaced. For less serious damage though (one-time leaks, etc), fixing the cause of the issue might solve the problem entirely.

2. Safely Expose The Affected Area

For enclosed floor joists: make sure to expose as much of the area as possible. In an open basement or crawlspace this step might not be necessary.

Specific measures to take:

  • Remove flooring and/or peel back carpeting if necessary
  • Cut through and/or pull up plywood subflooring
  • Open up as large an area as possible to ensure that damage is not more extensive
  • Clear debris and wet or damaged insulation from around joists (dispose of it and replace with new)
  • If possible, make a 4” inch hole in the opposite side of the floor (top/bottom). This will allow the moist airflow to vent to either the basement or the rest of the home (direct airflow outside the home).

3.Vacuum and/or Wipe Excess Moisture

Use a wet/dry shop vacuum, sump pump, or rags to clean up standing water or excess moisture from the floor and from the surface of the wood.

This will drastically speed up the drying process. This must be done before attempting to dry out the wood.

4.Apply Airflow and Heat

Drying out wet floor joists requires a large amount of air movement. Wood can absorb large amounts of water, and it takes time to draw all of it out.


  • Get as much airflow as possible directed at the affected area. Large fans work well for this purpose.
  • If possible, direct the airflow away from the subfloor and the interior of the home.
  • This can be accomplished by opening windows or by venting into an open crawlspace, basement, or attic.
  • This is extremely important. Toxic mold spores and rodent debris/droppings can be extremely dangerous to human health.
  • It is critical that homeowners do not blow large amounts of air from unclean crawlspaces and/or unfinished basements into the rest of the home, especially in older homes.
  • Give the process time to work. Wood can take up to several days to dry out, depending on the circumstances and airflow levels involved.

5. Reassess/Reinspect

Use a moisture meter to check how dry the floor joists are.

These are small devices that are easy to use, affordable, and found at most home improvement stores.

A consistent moisture content of less than 20% is ideal.

6.Apply Sealant/Mildewcide

Once your floor joists are completely dry, it is time to decide if you want to apply protective coatings to them or not.

This step is not usually necessary, and all products of this type are inherently limited. However, these products can be useful in certain situations.

  • Mildewcides: these anti-rot wood coatings can be found at most large hardware stores. These will kill mold and might help prevent floor joists from rotting in the future.
  • Water-Resistant Sealant: these sealants can help keep moisture from penetrating wood. If you use these, please make sure they are appropriately breathable and designed for joist/subfloor usage.

Wet Floor Joists in Basement

It’s usually a fairly straightforward process to dry out wet floor joists in a basement.

This is especially true for unfinished basements with no ceilings. In addition to following the general steps above to dry out wet floor joists, you’ll want to also do the following:

  • Make sure and remove insulation prior to starting the inspection/drying process.
  • Look out for wiring and plumbing, and take steps not to damage such.
  • Check wet joists for sideways penetration where they touch the basement walls.
  • In unfinished basements, take additional safety measures. Use face masks/ventilators, direct airflow outside, open windows for ventilation, and use gloves and protective clothing.
  • During winter months, ensure the space remains warm enough so that pipes/drains don’t freeze.

Wet Floor Joists in Crawl Space

Crawlspaces are no fun to work in. In addition to following all the additional steps above for drying  out wet floor joists in unfinished basements, you’ll also want to do the following:

  • Make sure the crawlspace is properly ventilated prior to starting work (mold is dangerous).
  • Consider wearing full-body protection (insects and debris are dangerous)
  • Spend time clearing debris, setting up lighting, and planning the job before starting repairs.
  • Take time to inspect the rest of the joists, beams and sill plates under the house with a moisture meter while making repairs. This will alert you to any additional issues (leaks, mold, etc.)

Wet Floor Joists in Bathroom

Floor joists underneath bathrooms almost always get wet and/or water damaged at some point.

There is no reason to worry more about these joists than any others, but as a homeowner, it’s helpful to understand the reality of the situation.

It doesn’t hurt to check bathroom floor joists once a year for water damage.

Additional items to check for in bathrooms include:

  • Cracked/damaged caulk around the edges of bathtubs
  • Improperly installed shower curtains
  • Gaps in tile or linoleum along the edges of walls
  • Leaking toilets or sinks

When attempting to dry out bathroom floor joists, please consider:

  • Bathtubs (and tile floors) are very heavy. Before removing subflooring or crawling underneath a bathroom floor: inspect for serious damage/rot. In case of serious damage (or if in doubt): please call a professional for a structural inspection before proceeding with DIY drying or repairs.
  • When drying out bathroom floor joists, ensure all water sources are turned off prior to starting.
  • After drying, reinspect after a few days to ensure there isn’t a chronic water or moisture issue. This might require leaving a subfloor open for a few days or crawling back underneath a house.

Wet Floor Joists?

Call 844-488-0570 for a Risk Free estimate from a Licensed Water Damage Restoration Specialist in your area.

We Can Help Dry out & Repair your Floor Joists!

Water Damaged Subflooring

The reality is simple: if you’re dealing with wet floor joists: you’re probably also dealing with wet and/or water-damaged subflooring.

For regular OSB or plywood subflooring, this usually not a major issue, and can be dealt with in a very similar manner to wet floor joists.

Some things to keep in mind though:

  • Plywood/OSB warps very easily. It’s better to dry these panels out slowly and with normal air.
  • When in doubt: replace instead of repairing. For rot and/or mold infestations, it is better to replace subfloor panels or boards rather than attempting to repair and/or treat them. Floor joists are tied into the frame of a house, but panels are much easier and more affordable to replace.
  • When replacing subflooring, remember to leave a 1/8th inch gap between panels for movement.

How can you tell if a floor joist is rotten?

Rotten Floor Joists are extremely dangerous to the safety and functionality of a home. The term “rot” in this case refers to one of several different types of known and common fungal infestations.

As a homeowner, it helps to know what to look for in this regard.

There are only two main types of wood rot commonly found in homes: wet rot and ‘dry’ rot.

Wet Rot – Wet rot is a type of fungus that will start destroying your joists when wood reaches 50% or greater moisture content.

This type of rot in your joists usually occurs when there is a serious plumbing leak or if a flood has occurred. Although this type of fungus can cause serious damage, it is usually confined to wood that has been immersed in water or heavy moisture.

It is also harder to spot because most of the fungus grows inside the wood.

Wet rot is characterized by:

  • A dark brown color
  • Large discolorations or “wet” spots on your joists.
  • The occasional black fungus on the joists.
  • Soft crumbly wood (Joists)

Note: Floor joists with severe wet rot are “soft” and “crumbly” enough to push a screwdriver through them by hand. In other words: they are extremely structurally unsound.

Dry Rot – ‘Dry’ rot in floor joists occurs at moisture levels of 20% or greater.

This type of fungus usually grows over time due to condensation, moisture build-up, and poor ventilation. Dry rot is a serious threat to floor joists and to the structural integrity of a house.

Because this type of fungus usually grows in unseen areas it can go unnoticed for very long periods of time. Dry rot also spreads rapidly to other wood, and can cause an increase in internal humidity and condensation levels by itself.

Dry rot is characterized by:

  • Musty odors
  • Whitish strands of fuzzy mold on the surface of your floor Joists.
  • Extremely brittle wood (Joists)
  • Condensation on interior windows
  • Mold issues and/or musty odors

Will a dehumidifier dry out my floor joists?

Dehumidifier can indeed help dry out your Floor Joists,however, they are best used along with fans and if the joists are exposed.

  • Place fans around the edge of the room/crawlspace, pointing at the dehumidifier.
  • Ensure any rot/mold infestation has been dealt with and cleaned up. Dry mold is just as dangerous as wet mold, and dry mold releases many more airborne spores.

Will my wood stove dry out my floor joists?

The short answer here is: no, not by itself. To put it simply: airflow is much more important for drying out wood than heat.

In fact, heat can be downright dangerous. Wood warps very easily when drying out. Thus, it is critical to make sure there is much more airflow than heat when drying out wooden floor joists or subfloors.

Safety note: the above section covers the basics of drying out wet floor joists. Such advice is not meant to include situations where serious structural damage has occurred or where wet/dry rot is present.

Please see our Guide here for How to Deal with Rotten Floor Joists

When to Call a Professional

Occasionally, drying out wet floor joists can be an easy fix. For example, after a one-time small leak, especially if it’s dealt with in a timely manner.

However, we strongly recommend calling a professional in any of the following scenarios:

  • Any serious wet/dry rot or termite infestation
  • When help is needed diagnosing an unknown source of condensation or moisture build-up
  • For dangerous and/or complex crawlspace operations
  • For help safely removing subflooring or plumbing fixtures
  • During winter months when frozen plumbing is a potential issue
  • If the homeowner has any doubt as to their own personal safety or to the structural integrity of their floor joists and/or framing system.

We have Water Damage Restoration Technicians that can help Identify, Dry out & Repair Water Damaged Floor Joists.

For Disasters of all Sizes,available in 95% of the USA

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