The choice between an open valley roof and a closed valley roof can significantly affect a building’s aesthetics, durability, and weather resistance. Both valley types serve to direct rainwater and snow off the roof, but their design and installation vary considerably. This article explores the differences between open and closed valley roofs, their advantages, and installation considerations relevant to modern American homes and commercial buildings.
| Feature | Open Valley Roof | Closed Valley Roof |
|---|---|---|
| Appearance | Visible metal flashing with clean valley lines | Shingles extend over valley, hiding flashing |
| Water Drainage | Valley flashing directly channels water | Shingles overlap, less direct drainage |
| Installation Complexity | Requires precise metal flashing placement | Requires careful shingle alignment |
| Durability | High, due to exposed metal flashing | Depends on shingle integrity over valley |
| Maintenance | Easier inspection of flashing | May require more frequent shingle repair |
What Is an Open Valley Roof?
An open valley roof features a visible metal flashing strip running along the valley, where two roof slopes meet. This metal flashing is often made of galvanized steel, aluminum, or copper. The shingles on each side are trimmed back to expose this flashing, creating a clean, defined channel for rainwater to flow off. The exposed metal offers a traditional and neat appearance favored in many architectural styles.
Open valley roofing is prized for its excellent water drainage and ease of inspection. The metal flashing can be visually assessed during routine maintenance, making it simpler to spot corrosion or damage that could lead to leaks. This design is typically used in regions with moderate to heavy rainfall, where effective water channeling is critical.
What Is a Closed Valley Roof?
A closed valley roof, also known as a woven or covered valley, hides the metal flashing underneath overlapping shingles. Both sides of the roof have shingles that extend into the valley, overlapping each other to form a solid, continuous surface over the valley. The metal flashing underneath is not visible, providing a seamless and uniform roof appearance.
Closed valleys offer a sleek look and can blend well with modern shingle patterns. However, because the metal flashing is concealed, water drainage depends heavily on proper shingle installation and maintenance. These types of valleys are commonly installed in residential homes with asphalt shingles, providing a softer roofline without the metallic highlight of an open valley.
Comparing Water Drainage and Weather Resistance
The primary function of any valley roof design is to channel water away from the roof efficiently to prevent leakage and damage. Here’s how both compare:
- Open Valley: With exposed metal flashing directly handling runoff, open valleys excel in quickly moving heavy water loads. The metal acts as a durable waterway resistant to deterioration and blockages.
- Closed Valley: Water runs over shingles in addition to the metal flashing underneath. If shingles are improperly installed or damaged, water can seep through vulnerable spots. Proper overlap and quality materials are crucial for closed valleys to prevent leaks.
In snowy climates, open valleys allow snow to slide off more readily, reducing buildup and ice dams. Closed valleys can sometimes trap snow and ice, increasing the risk of damming and water infiltration.
Installation Process and Material Requirements
Installing an Open Valley Roof
Open valley installation involves carefully fitting metal flashing along the valley, securing it tightly to the roof deck. Shingles are cut neatly on each side to expose the flashing by approximately 6 to 8 inches. The metal must be corrosion-resistant and sealed at overlaps and edges to prevent leaks.
Metal types used include galvanized steel for affordability, aluminum for rust resistance, and copper for longevity and aesthetics. Precision is key: gaps or loose flashing can lead to water penetration.
Installing a Closed Valley Roof
For closed valleys, the installation involves weaving shingles from each side of the valley over the underlying metal flashing. Each row of shingles overlaps the previous row on the opposite roof plane, creating a woven pattern or capped valley look.
Accuracy in shingle alignment and overlap is essential to maintain waterproofing and a clean appearance. The metal flashing protects the roof deck but remains hidden, so shingle quality and installation technique are paramount.
Advantages and Disadvantages of Open and Closed Valleys
| Aspect | Open Valley | Closed Valley |
|---|---|---|
| Durability | Very high due to exposed metal; less shingle wear | Dependent on shingle condition; potential for wear |
| Appearance | Traditional, defined metal look | Smooth, continuous shingle surface |
| Waterproofing | Superior drainage; less risk of water pooling | Depends on shingle installation quality |
| Maintenance | Easier to inspect flashing; metal may need replacement | Inspection complicated; shingle repairs more frequent |
| Cost | Potentially higher due to metal materials and labor | Generally lower; uses more shingles, less metal |
Choosing the Right Valley Roof for Your Home
Selecting between an open or closed valley roof depends on several factors including climate, architectural style, budget, and maintenance preferences. Open valleys are ideal for homes in areas with heavy rain or snow due to their superior drainage performance and durability. Their visible metal flashing adds a distinct aesthetic suitable for traditional or Craftsman-style homes.
Closed valleys fit well with asphalt shingle roofs and provide a cleaner look preferred in modern or suburban homes. They may be less expensive upfront but require careful installation and maintenance to prevent leaks, especially in regions with heavy precipitation.
Maintenance Tips for Valley Roofs
- Open Valley Roofs: Regularly inspect metal flashing for rust, dents, or loose fasteners. Keep valleys clear of debris to maintain drainage.
- Closed Valley Roofs: Check shingles in the valley for cracking or curling. Promptly replace damaged shingles to maintain water resistance.
- Regardless of valley type, annual roof inspections and gutter cleaning help prevent water-related damage and extend roof life.