How to Fix Dry Rot in Floor Joists

Water leaks are a nightmare for homeowners. Although wall damage is the most common, leaks also cause significant floor damage, usually in the floor joists. Either the leak is in direct contact with the floor or the leak has spread from the wall. A water damaged floor requires immediate treatment, dry rot in floor joints can weaken the structure.

Repairing damp floor joists is no easy task. And, I understand why most homeowners don’t want to deal with it. However, not everyone is used to hiring contractors, in some cases, the DIY way is more efficient. That is, if you know what you’re doing. So, today, we’ll be making a guide on how to fix dry rot in floor joists.

Fixing dry rot in floor joists consists of 4 steps. Locating and stopping the leak, removing the floor joists with dry rot, installing new floor joists, preventing recurrence.

We’ll go over these steps thoroughly, keep reading.

How dry rot spreads

It’s important to understand that dry rot is not dry at all. Dry rot is caused by spores germinating, which only happens when there is sufficient moisture in the growing medium, like your floor joists.

The life cycle of dry rot starts by an infection with spores. These spores are small, but when they’re plenty you should be able to see a dark ocher yellow / orange colouring.

After germinating, dry rot grows white threads called hyphae, eventually forming mycelium. Lastly, if you let it get this far, a fruiting body may form, threatening the spread of more spores and subsequent dry rot growth in other parts of your house.

Now let’s jump into the four steps you need to take to get rid of dry rot.

Why is my floor damp?

Naturally, floor systems are free from moisture. They are installed in a way to keep them safe from contact with water. So, there is a low chance that your floor system isn’t installed properly. Unless you built a bathroom where you shouldn’t have. Most likely, you recently had a roof leak or a shower leak.

Fixing the floor joists with dry root won’t do you any good if you haven’t eliminated the moisture. There’s still a high chance that previously unaffected joists will be affected. So, dealing with the leak should be your first priority. If you have already stopped the leak, feel free to move on.

Locating and stopping leak

As I said, leaks most often occur from the roof or the shower. Probably, the wall will be damaged first, then water will travel down to the floors. That doesn’t have to be the case, shower leaks can directly damage the floor.

Roof leaks usually occur after a rainy day. They indicate a damaged roof. If you’re lucky, you can fix the roof from the inside. Check out our guide on dealing with roof leaks.

Shower leaks occur because of a failure in the shower. The seal rings can be damaged, the shower floor can have holes, or there’s a problem with the pipes. We have a guide on dealing with shower leaks too.

Once you’ve stopped the leak, you can go to step 2.

How to remove floor joists?

Removing floor joists requires a saw and brute force. I wouldn’t say this is the easiest thing to do but you shouldn’t have any complications.

Now, what you want to do is locate which joists have dry rot. Those free from dry rot should not be touched, it will only cause you more pain. The best thing to do is mark your joists that are to be removed.

Just to be safe, we’re going to cut the joists at least 4 inches away from the rotten spots. You can go for 6 inches if you have space. This will make sure that dry rot that isn’t visible won’t sneak up on you.

Then, just cut off the marked joists. Keep the big picture in mind: cutting vertical joints requires caution. If there’s a vertical joint that has dry rot, put something else to act as support while you cut.

We are ready to install the new floor joists.

How to install floor joists?

Don’t worry if this sounds complicated to you, it’s quite an easy thing to do. All you need is the right tools.

Since floor joists should remain an even level, don’t start without making measurements. Measure the size of the joists, so you will know what replacement to buy. With a marker, mark where the replacements should start and end. Go for accuracy.

Most floor joists are made with 2×6 wooden boards. I’m guessing that’s what you will need to, do some research if you’re not sure.

Put the new boards where the ones with dry rot used to be. Lock them in place with screws. Make sure your screws are big enough, aim for twice the board’s width. To eliminate the possibility of holes in between joists, you can use wood glue (affiliate link to Amazon). Put it on both ends of the joists.

If you feel like the new joists you put in need more integrity, you can add vertical boards.

A neat trick contractors do when dealing with dry rot is add another level to the floor joists. They put chemicals in the affected board to kill the dry rot. Then, refurnish the boards and add new boards to the affected part.

To add a finishing touch, paint the new boards if they don’t match the other joists.

There you go, now you are free from floor joists from dry rot. Still one thing left to do though.

How to secure floor joists from moisture?

Now, this step actually means securing your house from moisture. Seeing as how most floor joists are damaged from related water leaks in your house.

This includes making your roof and shower immune to leaks. However, you’re not always in control of the situations, so leaks are still a possibility. That’s why you can install systems that eliminate moisture.

Ventilation systems and a dehumidifier on hand are the best way to deal with moisture. Ventilation systems require an engineer, so contact a professional if you choose that. Having a dehumidifier at your house is always useful, especially if you have a sump pump too.

There’s plenty of dehumidifiers available on Amazon that won’t cost you and arm and a leg.

If you are looking for something that you can install, a vapor barrier is the thing. Vapor barriers are a plastic sheathing added to the wall framing to eliminate moisture. This will save your floors if there is water damage in the walls. Direct contact with water will still damage your floor.

Well, that’s it. Now you know how to deal with dry rot and how to replace floor joists. Good luck fixing your floor system.

Related questions

How much do professionals charge for treating dry rot?

This all depends on how much work the professional has to do. Insulated floor joints are harder to fix because of the lack of access, so professionals will charge more. If the handyman can easily reach the joists and all he has to do is remove them, it’s cheaper. On average, it costs 300$-800$ to treat dry rot in floor joints.

Floor joints are only slightly damaged, should I ignore the damage?

I wouldn’t advise it. Even if there’s no visible damage in the floor, ignoring it is not a good idea. The thing is, dry rot spreads like crazy, more so, it attracts insects. Before you know it, your whole floor system is compromised. Call a professional or fix the joists yourself.