Why Do They Put Gravel on Roofs? (Real Reasons You Should Know)

If you’ve ever looked at a flat or low-slope roof, you might have noticed it’s covered with gravel or small stones instead of shingles or tiles.
It’s something a lot of people wonder about — why do they put gravel on roofs?

It may look simple, but that gravel actually has an important job. In fact, it helps protect the roof, extend its life, and even make your home more energy efficient.

Let’s go over the real reasons gravel is used on roofs, what types of roofs need it, and what it does for your building.

First, What Kind of Roof Uses Gravel?

Gravel is mostly used on flat roofs or low-slope roofs — the kind you often see on commercial buildings, garages, or modern-style homes.

These are usually called built-up roofs (BUR). A built-up roof has several layers:

1. A base sheet (to protect the structure)
2. Layers of tar or bitumen (for waterproofing)
3. And finally — a top layer of gravel or small stones

That top layer isn’t just for looks — it’s there for a reason.

Why Do They Put Gravel on Roofs?

Here are the main reasons roofers add gravel to the top of flat roofs.

1. To Protect the Roof from Sun Damage

The sun can be tough on roofing materials.
Without protection, the tar or bitumen underneath would break down quickly from UV rays and heat.

The gravel acts like sunscreen for your roof — it shades the surface and prevents the sun from drying it out or cracking over time.

This helps your roof last much longer.

2. To Weigh Down the Roofing Material

Flat roofs can experience strong winds that might lift or move the roofing membrane.

The gravel adds weight, which helps keep everything in place — especially during storms or high winds.

It’s a simple, natural way to keep the roofing layers secure and stable.

3. To Prevent Damage from Foot Traffic

Flat roofs are often walked on — whether for maintenance, cleaning drains, or checking HVAC units.

The gravel acts as a protective layer between people’s shoes and the waterproof surface below.

Without it, walking on the roof could easily cause punctures, tears, or scratches that lead to leaks.

4. To Help with Drainage

Even though flat roofs have a slight slope, water doesn’t always drain perfectly.

Gravel helps guide water toward drains or scuppers by creating small channels.
It also slows the flow of water, preventing puddles that could damage the roof surface.

So the gravel actually plays a small but important role in helping rainwater move off your roof.

5. To Protect Against Temperature Changes

Temperature changes — especially in areas that get hot days and cool nights — can make roofing materials expand and contract.

The gravel helps regulate surface temperature by providing shade and insulation.
That keeps the roof from heating up too quickly or cooling down too fast, reducing stress on the materials.

6. To Add Fire Resistance

Here’s one many people don’t know: gravel can actually make your roof more fire-resistant.

The stone layer acts as a barrier between the roofing materials and any airborne sparks or embers — especially important for commercial buildings or homes in wildfire-prone areas.

7. To Improve Energy Efficiency

By reflecting sunlight and keeping the roof cooler, gravel helps reduce how much heat gets into your home or building.

That means your air conditioner doesn’t have to work as hard, especially in summer.
Over time, that can help save energy and lower your utility bills.

What Type of Gravel Is Used on Roofs?

Roofing gravel isn’t just any kind of stone — it’s chosen carefully.

Usually, roofers use:

• River rock or crushed stone
• Pea gravel (small, smooth stones)
• Ballast rock (for large commercial roofs)

The stones are washed and rounded, so they don’t damage the roofing layer underneath.

Does Every Flat Roof Need Gravel?

Not always.

Modern flat roofs can also use single-ply membranes like TPO or EPDM, which don’t require gravel.
These materials already have a reflective coating or protective layer built in.

However, traditional built-up roofs (BUR) still rely on gravel as an affordable, natural, and effective way to protect the roof.

So if your building has an older or tar-based flat roof, chances are the gravel is there for good reason — don’t remove it!

Should You Clean Gravel Off a Roof?

No — unless there’s too much buildup or debris, you generally shouldn’t remove the gravel.

But you should occasionally:

• Check that gravel is spread evenly
• Remove leaves or dirt that block drains
• Add more gravel if bare spots appear

If you notice pooling water or exposed black spots (bitumen), it’s a good idea to call a roofer for inspection.

Quick Summary: What the Gravel Actually Does

Final Thoughts

So, why do they put gravel on roofs?
Because it’s one of the simplest and most effective ways to protect and extend the life of a flat roof.

The gravel may look like decoration, but it’s actually doing several important jobs — from keeping the roof waterproof to making it last longer in the sun, wind, and rain.

If you have a flat roof with gravel, don’t ignore it.
Keep it clean, check it once or twice a year, and make sure the gravel is spread evenly.

A little maintenance goes a long way toward keeping your roof strong for years to come.

In short:
Gravel isn’t just there for looks — it’s your roof’s first line of defense.