Why Do Fence Panels Rot at the Bottom?

If you've ever noticed the bottom of wooden fence panels starting to rot, you're not alone. It's a common problem with timber fencing, particularly in the UK, where wet weather can leave wood damp for long periods.

But why does rot usually start at the bottom of a fence, and is there anything you can do to prevent it?

From the way panels are installed to the type of timber used, there are several reasons why the bottom of a fence can deteriorate before the rest of it.

1. Constant exposure to moisture

One of the main causes of rot is moisture. The bottom of a fence panel is often exposed to wet grass, damp soil, splashing rainwater and puddles. While the upper sections of a fence may dry out fairly quickly, the bottom can stay damp for much longer.

When timber remains wet, conditions become favourable for fungi that cause wood decay. Over time, the wood can become soft, discoloured and brittle, eventually breaking apart.

Good quality timber and suitable preservative treatment help protect against decay, but they cannot compensate for timber being constantly exposed to damp conditions.

2. Fence panels in direct contact with the ground

Allowing fence panels to sit directly on the soil is one of the most common causes of problems. Soil holds moisture, particularly during the wetter months, and this can keep the bottom of a panel damp for long periods.

Even treated timber can eventually deteriorate if it is continually exposed to these conditions.

There is another important point to consider. Many fence panel manufacturers state that their panels must not be in direct contact with the ground. If they are, the product guarantee may no longer be valid.

The exact requirements depend on the manufacturer and the product, so always check the installation instructions and guarantee terms before fitting your fence.

Keeping panels clear of the ground allows air to circulate and helps the timber dry out after rain. A suitable gravel board can also provide a barrier between the ground and the bottom of the panels.

3. Why do wooden gravel boards rot too?

Gravel boards sit along the bottom of a fence, underneath the main panels. They help protect the panels from soil, wet grass and splashing rainwater. However, wooden gravel boards can sometimes rot even when the fence panels above them are still in good condition.

Why wouldn’t they rot? One reason is that wooden gravel boards are often made from a different species of timber to the fence panels. They may also go through a different preservative treatment process.

Different types of timber have different levels of natural durability and respond to preservative treatments in different ways. The treatment used can also vary depending on the timber and its intended application.

This means a wooden gravel board may have better resistance to decay than the panels above it. Add in its position close to the ground, where moisture tends to linger, and it is easy to see why problems can develop if it has not been treated correctly.

It's worth remembering that a wooden gravel board is not necessarily going to last as long as the fence panels it supports.

Look for fencing that has long guarantees like 25 years   

Concrete gravel boards are another option. They won't rot like timber and provide a durable barrier between the ground and the fence panels. They can be particularly useful in areas where the ground stays wet for much of the year.

Read our blog on What is a gravel board and why is it used for more information on this subject

4. Poor drainage around the fence

Even if your fence has been installed correctly, poor drainage can still cause problems.

If the ground slopes towards the fence, rainwater can collect around the bottom. The same can happen where soil has been built up against an existing fence or where flower beds sit higher than the surrounding ground.

Check the area after heavy rain. If water regularly collects along the bottom of your fence, improving drainage or adjusting the ground levels may help.

It's also worth clearing away leaves, soil and vegetation that can trap moisture against the timber.

5. The quality of the timber and its treatment

Not all fence panels are made to the same standard. The type of timber, the thickness of the boards, the construction and the quality of the preservative treatment can all affect how well a panel stands up to the weather.

Timber fencing intended for outdoor use should have suitable preservative protection, but this does not make it completely immune to rot. The quality of the treatment matters, as does how the fence is installed and maintained.

Cheaper panels can look much the same as more substantial alternatives when they're first installed. The difference may only become obvious after a few winters, when thinner boards or less suitable construction begin to show signs of wear.

It's worth looking beyond the initial price when choosing a fence. Replacing panels every few years can quickly cost more than investing in a better quality product in the first place.

6. How can you stop fence panels rotting?

You can't stop timber weathering altogether, but there are a few simple steps that can help your fence last longer.

• Keep panels off the ground. Follow the manufacturer's guidance on ground clearance.
• Fit suitable gravel boards. These help protect the bottom of the panels from soil and moisture.
• Consider concrete gravel boards. They won't rot like timber and can provide a long lasting barrier between the ground and the panels.
• Improve drainage. Avoid allowing water to collect around the base of the fence.
• Choose good quality panels. Look for sound construction, suitable timber and appropriate preservative treatment.
• Check the guarantee. Make sure the fence is installed in accordance with the manufacturer's requirements, particularly those relating to ground contact.
• Inspect the fence regularly. Look for soft timber, damaged boards and areas where moisture is collecting.

These steps won't prevent every problem, but they can help reduce the risk of rot and extend the life of your fence.

7. Should you repair or replace rotten fence panels?

If the damage is minor, a repair may be possible. However, if the bottom of a panel has become soft, brittle or structurally weak, replacing it is often the better option.

Before fitting new panels, check the condition of the posts, gravel boards and fixings. There's little point installing new panels if the supporting structure is also starting to fail.

It's also important to understand why the original panels rotted. If the cause was poor drainage or direct ground contact, replacing them without addressing the problem could leave you in the same position a few years down the line.

Choose fencing that's built to last

Fence panels usually rot at the bottom because this is where they are most exposed to moisture. Poor drainage, direct contact with the ground and unsuitable installation can all make the problem worse.

Wooden gravel boards can also deteriorate, particularly when they are made from different timber species or receive a different preservative treatment from the panels above them.

When choosing a new fence, think about more than how it looks or how much it costs. Timber quality, construction, treatment and installation all play a part in how long it will last.

Always check the manufacturer's installation instructions and guarantee conditions, especially when it comes to keeping panels clear of the ground.

A well chosen and properly installed fence should give you years of service. Taking a little extra care at the outset can help avoid unnecessary repairs and replacements later on.

Also read our blogs on the different timber species used for fencing and the different treatment processes manufacturers use