Wood Under Door Sill Rotted And Falling Apart – What To Do?

Unassuming in appearance, the door sill is an important feature when talking about the entire door. That's because it acts as a gateway to the elements outside, preventing water and the outside air from getting into your home.

Once the wood under the door sill starts rotting, that's where the real problem starts and is what we thoroughly researched.

Over time, the wood under the door sill rot due to constant exposure to the outside elements. This can become the perfect breeding ground for fungi and mold.

These microorganisms then grow and multiply in number, spreading rot throughout the entire wooden frame and even getting inside your home.

In this section, we'll discuss the causes of door rot more in-depth and give additional details on how destructive wood rot is.

Additionally, we'll point out how to tell whether the wood is rotten and if there's any way to prevent the wood from rotting in the first place. So continue reading forward to find out more!

Door on house with extensive damage to wood framing - Wood Under Door Sill Rotted And Falling Apart - What To Do

What Causes A Door Sill To Rot?

As we mentioned, rot happens with time due to overexposure to the outside elements. Excessive dampness is one of the leading causes of wood rotting.

When there's too much moisture, fungi will start to grow. From there, the wood's fibers weaken and eventually deteriorate.

As such, always check your door frame after heavy rainfall or when it's snowing heavily outside. Ensure that any excess water from the gutters and ledges isn't splashing onto your doorframe.

Water damage to wood on door frame of house. — Photo

The Different Types Of Wood Rot

This section will introduce to you the different types of wood rot. They are loosely classified into three kinds due to their interaction with wood.

Brown Rot

If the wood you're inspecting looks dry and brown, it's best to take a closer look. That's because you're dealing with brown rot, more generally known as dry rot.

Caused by brown fungi, this species targets the cellulose of the wood. Then, a process called cubical fracture occurs, destroying the cellulose and causing the wood to shrink.

This type of fungi grows in temperatures between 65 and 90 degrees Fahrenheit.

Additionally, these fungi are hard to eliminate due to their stubbornness. That's because they can easily travel over other materials to infect wood, unlike the next two in this section.

White Rot

This kind of rot shares a couple of similarities with brown rot. They grow at the same temperatures and attack a particular element of the wood.

In this case, though, it specifically targets the wood's lignin.

This rot has earned its name by leaving behind the lighter-colored cellulose. This would give the wood a whitish, sometimes yellowish, appearance. Additionally, it provides the wood with a sponge-like quality.

Soft Rot

Usually, this type of rot exhibits itself inside the forest and among fallen trees. Compared to the other two rots in this section, it acts much more slowly.

However, this rot makes up for it in its sheer survivability. That's because the fungi responsible for this rot can survive a broader range of extreme temperatures, between 0 and 110 degrees Fahrenheit.

This type of rot breaks down the cellulose inside the wood, similar to brown rot. However, it leaves behind multiple small cavities inside the wood instead due to how slow-paced it is.

This results in a honeycomb-like structure inside the wood.

How To Tell If Wood Is Rotten

Sometimes, it's difficult to tell whether the wood is rotten. Luckily, there are some signs to look for:

Crumbling Wood

An obvious sign when it comes to rotting wood is finding pieces of wood or splinters scattered nearby. Crumbling wood indicates that part of it is deteriorating and is rotten.

Another way to check this is by gently poking the wood with a screwdriver or a pen.

With it, you can check whether or not the wood is firm. If it gives way or becomes brittle, you know that the inside of the wood is rotten.


One of the easiest ways to tell if there's rot in your wood is by checking the color. Typically, if parts of the wood are darker in color, then the presence of mold and fungi is high.

Although, in some cases, the affected area isn't darker but lighter in color. As such, these discolored areas are what you're looking for when checking for the presence of rot.

Difficulty Closing/Opening The Door

As we discussed earlier, rot can cause wood to shrink or change in size and shape. Because of that, you will have difficulty when it comes to closing and opening your door at home.

At the very least, you'll notice that it doesn't usually swing like before. And if the hinges are all attached correctly and with no other loose parts, warped wood is the cause.

This also extends to other wooden parts of your home as well. Such examples include your windows and cabinets.

How Do You Repair A Rotted Door?

Carpenter repairs — Photo

If you're dealing with a small area, you can start by removing it with the use of a knife or any other similar tool. Then, apply a wood hardener to the site to strengthen it before filling it up with polyester filler.

With a putty knife, make sure to get in as much polyester filler as possible. Don't leave any space behind, and work as quickly as possible. Most polyester filler brands dry within 10 to 15 minutes.

Next, use a chisel to chip away any excess filler. Then, use sandpaper to smoothen the area. Take as much time as you need during this process.

After that, you can paint the affected area to cover it up. For larger projects that include replacing the door frame, we suggest hiring a professional to do the work for you.

View this wood rot repair kit on Amazon.

How Can I Prevent Door Rot?

The main reason that causes door rot is due to excess moisture. To prevent that, there are vital steps that you can take.

The first is to apply a wood sealer over the wood underneath the door sill to give it a layer of protection. Then, check the gutters and make sure that there is no clogging.

Ditto for your porch overhangs. You don't want excess water overflowing out of their funnel and landing directly over your door frame.

Also, consider installing a sill pan. This helps direct water elsewhere, allowing the wood underneath to stay dry.

Still, the best way to avoid door rot is to check the wood for any signs of decay. In doing so, you can nip the issue in the bud before it can start to worsen.

Check out this wood sealer on Amazon.

How Much Does It Cost To Repair A Rotten Door?

Home inspector looking for possible problems for a potential buyer, found rotted wood frame on exterior door frame — Photo

The price to repair a rotten door can range between $200 and $650, depending on how severe the damages are. For minor repairs that you can do at home, you'll spend between $30 to $150.

We suggest hiring a professional to repair the entire door and the frame.

Their experience is second to none when it comes to handling such problems. Usually, it would cost you around $400, including labor fees, when trying to repair your entire door at home.

Do take note that this cost doesn't cover the door frame. Depending on the type of door and frame you want, it can cost you an additional $80 to $500.

See this putty knife on Amazon.

Does Wood Rot Impact Other Parts Of The Home?

If you notice that the wood underneath the door sill is rotten, check the rest of the house, especially if other parts of your home have wooden elements, like your windows and ceilings.

Additionally, wood rot can easily spread to other places in your home. There are plenty of places inside where a fungi's spores can latch onto and grow. As such, they can quickly spread to your cabinets and drawers.

Also, check places like your bathroom or under the sink. These places, where it's usually dark, cold, and wet, are perfect breeding grounds for fungi and mold.

And if not cleaned regularly, the spores from these fungi can travel around your home and latch onto the wooden areas around the house.

Door on house with extensive damage to wood framing — Photo

To Finish

In short, fungi growing on the wood caused the door sill to rot. Due to exposure to the outside elements, especially moisture, untreated wood would eventually rot. As such, it's best to treat the wood under your door sill with a wood sealer instead of waiting for it to rot.

Made it to the end? Check out these helpful related posts!

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