What’s a Roof Valley (and Why Does It Matter?)
If you’ve ever looked at your roof and wondered about the dips or angles where two sections meet, you’re not alone.
These dips are called roof valleys, and they do a lot more than just make your roof look more complicated. (Or give you more headache when it’s time to wash.)
Roof valleys play a critical role in directing rainwater off your roof and into the gutters where it belongs. But, as simple as they seem, roof valleys come in different types, use different materials, and need proper maintenance to keep your home dry and safe.
Here’s everything you need to know about roof valleys and why they matter for your home.
What’s a Roof Valley?
A roof valley is either a straight line or a channel where two roof slopes meet.
Think of it as your roof’s drainage pathway. Without valleys, water would have nowhere to go but over the edges, leading to leaks, structural damage, or worse (if there is anything worse, that is!).
It’s not like every roof has to have one, though. Roof valleys are common in bigger homes with complex roof designs, like those with multiple peaks or sections. Which means, of course, that a roof can have many valleys!
They’re particularly important in areas prone to heavy rainfall, where efficient water drainage can spell an end to your anxiety at seeing the weatherman.
Types of Roof Valleys
Roof valleys come in two main types. Need we even mention that each has its pros and cons? Choosing the right one will mostly depend on your roof design, climate, and personal preferences.
1. Open Roof Valley

An open valley is the one that you can actually see.
It’s a visible channel made of metal or another durable material that sits between the two roof slopes.
The channel is left exposed on purpose because this makes it easier for water and debris to flow through. Moreover, it’s often lined with metal so that everything can just slide down easily. That’s why open valleys are excellent for drainage and make it easier to spot potential damage or blockages. (More on this lining below!)
Since it basically relies on gravity and has a smooth lining, it’s not very vulnerable to clogging and debris buildup either. So its only downside is the cost, which tends to be higher than with other types.
2. Closed Roof Valley

In a closed valley, the roofing material overlaps or weaves in to create a seamless look. The valley itself is hidden from view – almost like it isn’t there at all!
This design offers a cleaner appearance, making it a popular choice for homeowners who want their roof to look sleek and well polished.
If closed valley is your thing, you’ll get to choose between a weaved design, where the roofer doesn’t cut the shingles but weaves them in, or closed-cut design, where the shingles are being cut and neatly fit together like a puzzle.
The ups and downs of this approach?
While you don’t need to worry much about debris as it has nowhere to get stuck, a closed valley calls for precise installation to avoid water pooling beneath the overlapping materials.
What About Roof Valley Flashing?
Now, even though roof valleys divert water away, they can’t take care of it all on their own.
Enter roof valley flashing! It’s a protective layer, usually made of metal or another smooth and durable material, that lines the valley to prevent water from seeping into the roof structure.
Flashing is essential for open valleys and often used in closed valleys as well, particularly in areas where it rains often, and rains much.
The most common flashing materials include aluminium, copper, galvanised steel, and sometimes lead. Aluminium is lightweight and resistant to rust, while copper is highly durable and visually appealing, especially when turns green and gets beautiful patina. Small wonder that copper flashing is the costliest option!
Galvanised steel is cost-effective but requires regular maintenance to prevent rust. In older homes, lead flashing may still be found, though it’s less common today, and not without a reason. It’s very heavy and therefore tricky to work with. More importantly, it’s toxic!
Other than metal, you’ll sometimes see flashing made of PVC or even rubber (that is, a specific variety also known as EPDM).
Should a Roof Valley Be Sealed?
The question of whether to seal a roof valley depends on the type of valley and materials used. Open valleys are generally left unsealed to allow water and debris to flow freely, while closed valleys may use adhesives or sealants to secure overlapping roofing materials.
That said, improper sealing can lead to trapped water and leaks. So if you do opt for it, you’d better make sure to get it right.
If you can’t make up your mind whether your roof valley should be sealed, a professional will assess your situation and help you decide.
Materials for Roof Valleys

The materials used in roof valleys vary immensely in durability and maintenance needs. For open valleys, metal sheets or flashing are typically the best choice. They’re durable, weather-resistant, and allow for a smooth water flow.
In closed valleys, shingles, tiles, or other roofing materials overlap to create a seamless look while providing adequate protection.
For even more protection, you can add synthetic membranes or self-adhesive underlayment beneath these materials. This is particularly useful in climates prone to heavy rain or snow. Note, however, that most homeowners won’t need this step!
Do Roof Valleys Need Maintenance?
Let’s be honest: a roof valley doesn’t work nearly as hard as, say, gutters. It helps just by being there. Still, it doesn’t mean it won’t need at least some attention on your part.
Luckily, the only thing you need to do regularly is clear out debris like leaves and twigs is essential, especially after storms, as clogs can lead to water pooling and eventual leaks.
Other than that, take a look at the valley every once in a while for signs of rust, cracks, or loose flashing. Closed valleys may require checking the seals between overlapping materials to ensure they’re still intact.
During heavy rain, grab your coat, get outside and take a moment to observe how water flows through the valleys. If you notice any pooling or slow drainage, it’s a sign that something’s not right and may need a closer look.
Common Issues with Roof Valleys
Even the best-installed roof valleys can run into problems.
The most common issue is – you guessed it! – debris buildup. Particularly in open valleys or homes surrounded by trees.
Metal flashing, while durable, can corrode over time, especially in coastal areas exposed to salty air. Improper installation can lead to water pooling, leaks, or structural damage. And, of course, aesthetic wear can be a concern in closed valleys if the overlapping materials start to shift or crack.
Final Thoughts
Roof valleys might not be the first thing you notice about your home, but they’re essential for keeping it safe and dry. Whether you have an open or closed valley, proper materials, flashing, and maintenance make all the difference.
If you’re ever unsure about the state of your roof valleys—or wondering whether they’re sealed correctly—call a professional roofer to take a look. Catching small issues early can save you a lot of hassle (and money) down the line.
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