When designing or repairing a roof, understanding the difference between open valley roofs and closed valley roofs is essential. These two types of roof valleys, where two roof planes meet, have distinct construction methods, advantages, and suitability depending on aesthetic preferences and weather conditions. This article explores the key differences between open and closed valley roofs, their structure, materials, advantages, and which to choose for various building needs.
| Feature | Open Valley Roof | Closed Valley Roof |
|---|---|---|
| Valley Type | Exposed metal valley flashing | Covered with roof shingles or materials |
| Construction | Valley flashing installed exposed on roof deck | Valley covered by overlapping shingles |
| Maintenance | Easier to inspect and clean (can debounce debris) |
Harder to detect damage without removing shingles |
| Appearance | Distinct metal line visible | Seamless look with no metal visible |
| Water Management | Highly effective in directing water flow | Effective but depends on shingle installation quality |
| Cost | Generally less expensive | Usually more labor-intensive and costly |
What Is an Open Valley Roof?
An open valley roof features a metal flashing—commonly aluminum or galvanized steel—that is fully exposed along the roof valley where two roof slopes meet. This flashing acts as a channel, directing water and debris off the roof efficiently.
The shingles on each side of the valley are cut back from the valley centerline, exposing the metal flashing beneath. This method is often preferred for its durability and ease of maintenance. The exposed metal can be periodically inspected for rust or damage and cleaned to prevent clogging.
How Is an Open Valley Roof Constructed?
Open valleys require precise cutting of shingles along the valley line. The roofing contractor installs a metal valley flashing on top of the roof deck spanning the valley, typically wide enough to account for water flow and potential debris buildup.
After the flashing is secured, shingles are placed on either side, but cut back to expose the metal flashing fully. The metal extends beyond the roof deck, creating a distinct, visible line from the ground. This setup ensures excellent runoff and reduces risk of leaks caused by shingle overlap issues.
What Is a Closed Valley Roof?
A closed valley roof merges shingles from both sides of the roof valley directly on top of one another, creating a concealed valley. In this method, no exposed metal flashing appears in the valley; instead, shingles overlap the valley line entirely.
Closed valleys use a “woven” or “lined” technique for shingle placement. The “woven” method alternates shingles from each side interlocking them in the valley, while the “lined” method places an underlayment waterproof membrane within the valley for protection under the shingles.
How Is a Closed Valley Roof Constructed?
During installation of a closed valley roof, shingles are installed over the valley after placing an underlayment. The shingles from both roof slopes extend completely over the valley, overlapping each other without any exposed flashing.
The key to a successful closed valley roof is careful layering and quality shingle installation to prevent water infiltration. The valley is generally sealed with underlayment membranes that provide waterproof protection, though the visible finish appears fully shingled and clean.
Open Valley vs Closed Valley Roof: Advantages and Disadvantages
| Aspect | Open Valley Roof | Closed Valley Roof |
|---|---|---|
| Water Drainage | Highly efficient at directing water with metal channel | Good drainage but relies on proper shingle layering |
| Maintenance | Easier to spot and access damage and clean debris | Harder to detect leaks or damage under shingles |
| Appearance | Visible metal line may detract from aesthetic | Sleek, seamless look preferred by some |
| Durability | Metal flashing is long-lasting and withstands heavy runoff | Durability depends on high-quality shingle installation |
| Installation Cost | Usually more cost-effective and simpler | Can be more labor-intensive and expensive |
When to Choose an Open Valley Roof
Open valley roofs are ideal in regions with heavy rainfall or snow where efficient water management is critical. The distinct metal flashing offers superior durability and makes it easier to maintain by allowing debris removal and leak detection.
They are also preferred when budget constraints exist because open valleys generally cost less due to simpler installation. Homeowners and contractors who favor practicality over seamless aesthetics tend to lean towards open valleys.
When to Opt for a Closed Valley Roof
Closed valley roofs are preferred in residential and commercial properties where visual appeal is paramount. The absence of exposed metal creates a cleaner, more elegant look, making the roof visually consistent.
They are suitable for areas with moderate rainfall where traditional shingles can sufficiently handle water drainage. Proper installation by skilled roofers is critical for preventing leaks, making this option best for situations where aesthetics and attention to detail outweigh maintenance ease.
Materials Used in Valley Roof Construction
Open Valley Roofing Materials
- Metal Flashing: Typically galvanized steel, aluminum, or copper known for rust resistance and longevity.
- Underlayment: Waterproof material beneath the decking providing extra protection.
- Shingles: Asphalt, wood, or metal shingles cut back from valley centerline.
Closed Valley Roofing Materials
- Waterproof Underlayment: Installed along the valley to prevent water infiltration under shingles.
- Shingles: Asphalt or other roofing material shingles woven or overlapped in the valley.
- Sealants: Sometimes used at shingle intersections in the valley for additional water resistance.
Maintenance Tips for Valley Roofs
Proper maintenance helps extend roof lifespan regardless of valley type.
- Inspect valleys regularly for debris, damage, or leaks.
- For open valleys, clear leaves and twigs from metal flashing to ensure smooth drainage.
- For closed valleys, check shingles for wear or gaps where water could penetrate.
- Schedule professional check-ups every few years, especially after storms or heavy snowfalls.
Summary Table: Open Valley vs Closed Valley Roof
| Criteria | Open Valley | Closed Valley |
|---|---|---|
| Water Management | Exposed metal flashing channels water efficiently | Covered shingles rely on proper installation |
| Visual Appeal | Metal visible, less sleek | Seamless, clean appearance |
| Repair & Maintenance | Easy to inspect and clean | Requires shingle removal for inspection |
| Durability | More durable flashing | Depends on shingle condition |
| Cost | Less costly, easier installation | More labor-intensive, higher cost |