What is a valley on a roof?

A roof valley is formed where two sloping faces of a roof meet at the internal angles of a building. It is a V-shaped feature which channels rainwater into a central liner, down to the gutters and away from the roof. Removing water efficiently is vital to the long-term performance of any roof system, making the valley one of the most important features of a roof.

The valley is usually made watertight with either lead, fibreglass or another material which can withstand rainwater and snow effectively, such as our GRP dry valley system.

What are the types of roof valley?

There are three main types of roof valley that can be designed and specified as part of an overall roof system:

Open valley roofs

An open roof valley is where the roofing material does not meet over the valley. There is a space between the roof tiles on either side which creates an open channel for rainwater or snow to drain down into the gutters.

The main advantages of an open roof valley are:

• Efficient water drainage – An open valley provides a highly effective route for directing water off from the roof. The gap between the roof coverings either side of the valley can help to reduce the risk of water either pooling or infiltrating the roof. Open valleys formed in lead or other suitable materials can also be made wider which makes this type of valley a potentially better choice if you are specifying a roof in a higher rainfall or snowfall area.
• Simplified maintenance – An open valley can be easier to maintain. Debris is less likely to accumulate in an open valley, and you can see when it does more easily. That allows for more efficient preventative maintenance.
  
  

Closed valley roofs

A closed roof valley is where the double-lapped roof tiles, extend across the valley and meet in the middle, covering and ‘closing’ the valley.

The possible advantages of a closed roof valley are:

• Types – Typical closed valleys include mitred, where tiles are cut neatly together at the valley junction and weathered with lead soakers, or purpose made valleys which use special fitting tiles to finish the detail. There are also more traditional details such as laced valleys and swept valleys, nowadays often more associated with conservation or heritage work.
• Aesthetics – Some people will prefer an unbroken roof as it can look cleaner and make the roof system as a whole seem more cohesive.
• No valley lining – In a closed valley, a valley lining is not required which can save on costs and future maintenance. covered by the roof tiles. This can create a more continuous appearance across the roof while still providing an effective route for rainwater when the valley is correctly designed, specified and installed.

See our range of clay roof valley tiles and get technical assistance when specifying your closed valley roof system

Dry Valleys

Modern dry valleys use pre-formed GRP liners to replace traditional open valleys with the main difference between them being that instead of an open channel, the tiles either side are cut neatly to an upstand in the centre of the liner.

The possible advantaged of a dry valley are:

• Weatherproofing – Dry valleys can often deal with a greater capacity of water than some other types of valleys
• Installation – Dry valleys are designed to be easy to install when compared to other types of valleys
• Maintenance – Dry valleys are also designed to be low maintenance and are less prone to storm damage than some other types of valleys, especially when the cut tiles are properly secured to manufacturers instructions.
  
  

How do roof valleys work as part of the wider roof system?

The job of the roof is to protect the home from the elements and help to insulate the internal space. The valley helps protect the roof system by directing water off the roof and safely into the guttering, allowing the roof to continue performing as intended.

However, the valley is also a vulnerable part of the system and needs to be maintained accordingly. Regular inspections should be undertaken to detect:

• Leaks – A damaged roof valley can leak water into the roof, potentially damaging the roof system and the home as a whole.
• Debris build-up – If debris such as dried leaves builds up in the valley, it can stop water draining effectively, potentially even allowing it to pool in the valley or infiltrate the roof.
• Wear and tear – The valley will see a lot of water flowing down it. If it is an open valley, it can also be affected by high winds and other weather. Wear and tear is a real issue, and like debris build-up, it can lead to water infiltration which damages the roof and the home.
  
  

When specifying a roof system, it is important to consider the above factors when designing your valleys. The local conditions can inform your choice of an open, closed, or dry valley as part of the wider roof system.

See our roof valley products and get technical assistance when specifying roof valleys on your next project. 

Disclaimer - The information shared in this blog is correct at the time of publication. Guidance, standards, and best practices may change over time, so if you’d like further clarification or the latest updates, please get in touch with the Marley Technical Advisory Team, who will be happy to help.