Rotten Floor Joists – Repairing & Replacing Rotting Joists

Are your joists rotten? In need of fixing? Unsure where to start or what to look for?

In this guide you will learn: 

  • Common signs & Causes of Rotten floor joists,
  • How to Repair or Replace Rotten Floor joists in your home,
  • How to repair joists underneath bathtubs and in crawlspaces as well as Prevent them from rotting in the Future.

How To Tell If Your Floor Joists Are Rotten

A simple visual inspection should tell you if your joists are rotten.

However, floor joists are often covered up by floors and ceilings and hidden away in crawlspaces. This means that you might want to look for other common signs of failing water damaged joists before tearing your floors up!

Common signs and symptoms of rotten/failing joists include:

  • Floors that are uneven or beginning to sag
  • Dysfunctional or cracked doors and windows
  • Visible presence of mold, allergens, or odors
  • Large blotchy stains on floors or ceilings
  • Unusually high levels of condensation inside the home
  • Termite and/or pest issues

If your home is experiencing these symptoms: it’s time for a visual and physical inspection of your joists.

Wet Rot

“Wet” rot is a type of fungus that grows when wood becomes saturated with water over a period of time.Wet rot in joists will usually occur when there is a serious plumbing leak or in a flood situation.

Wet Rot most of the times will be much harder to notice due to the fungus mostly growing inside the floor joists.

Signs of Wet Rot:

  • A dark brown color of your floor joists
  • Large joist discolorations or “wet” spots
  • Possible black fungus on the Joists
  • Joists will be soft and Crumbly

Dry Rot

“Dry” rot is another very dangerous and destructive fungus. Unlike it’s namesake though, dry rot only occurs when wood is exposed to high moisture levels. Appropriately dry wood will not experience “dry” rot.

This type of fungus usually takes over the joists over a longer period of time primarily due to condensation, moisture build-up in the floor structure, and poor ventilation of joists.

Dry rot also spreads rapidly to other wood, crosses brick and mortar surfaces, and causes an increase in interior condensation levels by itself. Dry rot can be a very serious threat to the structural integrity of not only your joists but also your whole house.

Signs of Dry Rot:

Note: Dry rot infestations can spread rapidly and should be taken as a very serious threat to the safety of a home.

Common Causes Of Rotten Floor Joists

Floor joists usually become rotten for one or more of the following (but preventable) reasons:

1.Exposure To Water Leaks

Damage to leaky pipes (and/or flooding) is a primary cause for rotten joists. Fortunately, most wood dries out quickly.

The real issue many homeowners overlook: slowly leaking pipes and/or fixtures.

These small leaks can go unnoticed for long periods of time and cause serious rot infestations in the meantime. Whole house water meters and/or leak detectors are a great way to check for and prevent this simple issue.

2.Moisture Build-Up

All houses are built to withstand a certain amount of natural condensation moisture throughput.

Unfortunately, some houses suffer from this issue more than others. If an area of a home doesn’t have proper ventilation, rotting timber is an inevitable result.

Basements and crawlspaces are especially vulnerable in this regard. As a homeowner, it is imperative to ensure that ventilation paths to these areas are properly installed, unblocked, and functioning properly.

3.Sideways Penetration

Occasionally, concrete foundations wind up absorbing excess water. This water then finds it ways into the floor joists that rest directly on the foundation walls/runners.

This is called “sideways penetration,” and it is the reason why floor joists often rot at the ends before rotting in the middle. To prevent this issue – check into properly grading and/or waterproofing your foundation.

And don’t forget to check the ends of your joists for rot!

4.Rising Damp

This is an issue that is far more common in older homes with stone or brick/mortar foundations. Strangely enough, water can actually flow upwards through brick and/or mortar, and find it’s way into floor joists and walls.

This issue is less common in modern homes, but it’s still worth checking for if your home is constructed in this manner. 

Water Damaged & Rotten Floor Joists?

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

We Can Help Assess the Situation & Repair/Replace your Rotten Floor Joists.

Can You Replace Rotten Floor Joists?

Yes, you can replace rotten floor joists in your home.

In fact, this is usually a much better option in the long run than repairing/sistering. Doing so, however, is usually a complex and time-consuming process.

Please see below for more details on how to do this.

Here’s when to Repair Or Replace your Rotten Floor Joists

Most professionals use a simple rule of thumb when making this decision. If the rotten area of your joist(s) is larger than six inches across: you need to either replace the joist completely or “sister” it from end-to-end (or with significant overlap).

For large rot infestations, and for sections of floor where multiple joists have been affected, it will be necessary to completely replace the joists.

It is usually best to call a professional for this, for many reasons.

However, there are times when it is acceptable to replace a rotten floor joist on your own. DIY repairs are possible:

  • If the joist does not support a load-bearing internal wall.
  • If the rot infestation is contained to a specific location or specific joist.
  • If it is possible to access both ends of the joist without compromising structural integrity.
  • If the homeowner has the proper tools, knowledge, hardware, and lumber to complete the job as well as the confidence to accomplish the joist replacement safely.

“Sistering” is the process of bolting another joist to the original in a side-by-side configuration. The joists then function as a single unit with the strength of the second joist added to the original.

For the purposes of this article, we use the term “repair” in place of “sistering.” In other words, when we talk about “repairing” a joist: we really mean that we’re “sistering” it.

Safety Note: “Sistering” is a complex process. The person doing it needs to understand basic structural engineering concepts:

  • Which fixtures to use (carriage bolts, lag screws, epoxy, etc)
  • How many of such to use and where to place them (this differs greatly for various joist types)
  • The amount of weight sitting on the particular joist(s)
  • How to properly jack up the floor while performing the repair
  • Whether or not the rot has been dealt with properly
  • How much of an overlap is needed

… and so on and so forth.

As such… we do not cover how to ‘properly’ sister specific joist types in this article. Instead, we’re listing the steps for the process as a whole, along with general tips and advice.

How To Repair Rotten Floor Joists

1.Fix the Moisture Source

The first step is to fix the source of moisture and/or water damage that is causing the rot infestation.

Tthis will probably take some time. However, there is no point in trying to repair anything until this is done. The rot will simply come back!

2.Access The Joist

Generally: you’re going to want to replace floor joists from underneath if they are in the basement or crawlspace. Doing so means you don’t have to compromise subfloor integrity or remove expensive flooring, and it also means that you’re not walking around on a possibly compromised joist while performing repair work.

However, for joists in second floors or ceilings: you’re going to have to remove flooring and cut away the subfloor (from above) or remove the ceiling (from below) to access the joist.

Exposed joists in basements and crawlspaces are often easier to access from below. Please see our section below for more info on dealing with rotten floor joists in crawlspaces.

3.Jack Up The Floor

Be aware: this can be a critical and complex process.

For a section of floor with one or more rotten joists: you’re going to need to use two or more floor jacks and a temporary beam to support the floor while you’re performing repair work.

In addition, the floor will need to be level before attempting to sister the joist. Rotten floors often sag over time, and even a small fraction of an inch difference can cause major issues.

To install the temporary beam:

  • Place two jacks capable of supporting the floor weight underneath the surrounding joists.
  • Make sure the jacks are properly anchored (if necessary), that they run perpendicular to the joists, and that the temporary beam will be supporting solid (rather than rotten) wood across most of its length.
  • Affix a beam capable of supporting your floor to the top jack plates in the appropriate manner.
  • Turn the jacks until the beam makes contact with (and is obviously supporting) the floor joists.
  • If necessary, nail the beam to the underside of the floor joists for safety and stability.

At this point, either continue to slowly raise the floor over the next few weeks/months -or- proceed with repairs (in the case of a level floor).

4.Sister The Joist

First, obtain lumber of similar type and dimensions as your current joists. Then, cut it to a length that will ensure sufficient overlap with the non-rotten parts of the current joist.

In this regard: longer is better. If possible: cut it to match the entire joist from end-to-end or as long as constraints allow (beam-to-beam).

Then: bolt the “sister” joist to the original one in a side-by-side configuration. (But don’t forget the bead of subfloor adhesive on top before you do!)

For this purpose, heavy structural steel carriage bolts work best. Lag bolts/screws are also acceptable in some situations. Using epoxy resin to bond the beams (in addition to bolts) or creating a “fletch” beam are also viable options. For more info: please consult a professional or your local hardware store.

How many bolts to use? This depends on many things, but a good rule of thumb for generic dimensional lumber is to put at least one every six inches, in an alternating “V” pattern.

Note: for engineered lumber, LVL’s, I-Beams, or open web floor joists: please consult a professional or the relevant catalogue for specific instructions on how to affix and/or “sister” these types of joists.

5.Remove/Replace The Rotten Section

This step is not always necessary. For joists where the rot infestation has been thoroughly dealt with: it is acceptable to leave the joist as it is.

For severely rotten joists though, you’re going to want to remove the rotten section.

To do so:

  • Make two vertical cuts through the joist a safe distance away from each end of the rotten section.
  • Use a ply bar (or a Sawzall with a nail blade) to separate the rotten section from the subfloor.
  • Remove nails and debris from the subfloor if necessary.
  • Cut lumber of similar dimensions and type to match the section that was removed.
  • Use structural steel plates (floor joist plates) to bolt the new section into place. You’ll want to do this on the bottom of the joist or on the opposite side of the one that is “sistered.”

And… that’s it. When you’re done with this step, you should be able to remove your temporary beam, replace flooring and ceilings as necessary, and move on.

When To Replace Your Subfloor As Well

If your subfloor has sustained water damage or become rotten it is time to replace it. Replacing subflooring is usually a much faster process than replacing joists.

If in doubt: replace it now rather than waiting for future issues.

Fixing Rotten Floor Joist Under Bathtub

Bathtubs are enormously heavy. Unfortunately: the floors underneath them just love to rot.

Don’t worry: repairing rotten floor joists under bathtubs is really no different than in other locations. That having been said, there a few things to take into consideration:

  • First, make sure all the water is shut off. Turning off primary water mains is a good idea. In case plumbing in the bathroom floor gets damaged or needs to be moved: the water is already off.
  • Second, you’ll want to use a sturdy beam and jacks to temporarily compensate for the weight of the tub. This should be in addition to jacking up the floor in other locations.
  • Third: plan on finishing the job in a limited timeframe. Bathrooms are hard to go without in most households, and you don’t want to have shut your water off for long periods of time.

Rotten Floor Joists In Crawl Space

Floor joists in crawlspaces are the same as joists elsewhere. They’re usually harder to deal with though, due to space constraints. When dealing with rotten floor joists in crawlspaces:

  • Consider replacing the joists from above, rather than below if space is an issue. This will necessitate removing flooring and subfloors, but it could lead to a safer and cleaner experience.
  • Make sure to wear all PPE (gloves, goggles, etc) and use appropriate lighting.
  • Have someone available to help with maneuvering lumber and tools in tight spaces.
  • Take your time. It’s easy to rush crawlspace jobs. Instead, be patient and do the job right.

Rotten Floor Joists?

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

We Can Help Repair or Replace your Floor Joists.

Repairing Rotted Sill Plate

Replacing a rotten sill plate, or even a sizeable section of one, is an endeavor best left to the pros.

Sill plates are very often victims of rot. However, replacing one involves compensating for the entire weight of the house that’s resting on it.

In addition, attempting to do this type of repair without understanding load paths and how to properly compensate for them can lead to catastrophic damage.

If a small section of your sill plate is damaged, this is what to do:

  1. Remove the interior wall material above the section of rotted sill plate.
  2. Jack up the top plate (next to the section of rotted sill) at least an inch. Always use two jacks to do this, and always raise them no more ¼ inch at a time, in an alternating fashion.
  3. Using a Sawzall, remove the wall stud on top of the rotted section (cut through the nails).
  4. Remove the rotted section of sill. To do this, cut vertically through it on either side of the rot, then either pry it up or use a Sawzall to cut underneath it. Watch out for steel rebar or foundation bolts. 
  5. Once the sill plate has been removed, remove any protruding metal or debris on the top of the foundation wall.
  6. Cut to size and place the new section of sill plate in. Use composite shims to keep it level.
  7. Drill through the sill plate and into the foundation wall with a masonry bit to make holes for your foundation bolts. Place them in the holes, but don’t tighten them yet.
  8. Nail the stud (or the replacement stud) to the top plate using angle brackets.
  9. Lower the section of wall, ¼ inch at a time, checking to ensure the stud and wall are level.
  10. Once the wall has been lowered, nail the bottom of the stud in to the sill plate using angle brackets, and set/tighten the foundation bolts.
  11. Replace the interior wall, if necessary.

Joist Repair Plates – Should They Be Used For Rotten Joists?

Joist repair plates are great. The options available to DIY’ers and homeowners these days are reliable and affordable.

However: joist plates are not usually enough to fix a rotten joist all by themselves. In fact, we don’t recommend using them by themselves for anything other than very small issues.

In our opinion: joist plates are meant to be used in conjunction with larger-scale or professional repairs.

How To Prevent Joists From Rotting

The best way to prevent joists from rotting is to stop excess water and moisture from entering your home and to ensure that all areas of your home are well-ventilated.

However, this is often easier said than done! The good news: there a few other products that can help prevent rot infestations.

Borate-based products and sealants are usually the go to in this regard. Borate and borax-based rot prevention products are widely available, and are known to kill wood rot and prevent termites.

Of course, the longevity of these products is limited, and their effectiveness depends on both the quality of the product and the external circumstances.

Hydrogen peroxide and bleach are two other chemicals commonly used for treating wood rot, although these two chemicals cannot prevent future rot infestations through simple application.

How Much Does It Cost To Replace Rotten Floor Joists?

Professional floor joist replacement often runs from $100-300 per joist. Replacing a whole room can cost anywhere from $4000 to $10,000.

On the other hand, a simple DIY repair can cost as little as the price of the necessary materials.

The main deciding factors are the size and complexity of the repair. Rooms with plumbing and wiring will cost more than those without, and severe rot infestations will always cost more.

Are Rotten Floor Joists Covered By Insurance?

Unfortunately, homeowner’s insurance usually doesn’t cover rot damage that occurs over time.

However, if the rot was caused by a specific (and accidental) water-damage issue: you might be covered.

For example: your insurance might cover damage from a flood or burst water pipe. Of course, it’s best to let your insurance company know as soon as possible in these situations.

When To Call A Professional

Repairing/replacing floor joists is the type of work that’s best left to a professional.

Floor joists carry immense weight, they’re tied into the structure of a home, they often contain plumbing and wiring, and the process to repair/replace them is dangerous at the worst and complex at the best. T

hrow some wood rot into the mix, and the process gets even more risky and complicated.

Our rule of thumb – if you don’t feel completely confident performing repairwork yourself: call a pro.

We have Water Damage Restoration Technicians that can help Repair or Replace your Rotten Floor Joists.

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

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