When it comes to roofing, one important decision is whether to use a closed valley or open valley design. Both have their pros and cons, so let’s take a detailed look at the key differences between closed valley and open valley roofs.
What is a Closed Valley Roof?
A closed valley roof refers to a roof design where two adjoining sloping roof planes are joined by a sealed seam. The valley flashing is tightly folded and closed off, which prevents water from entering the seam.
With a closed valley roof:
- The two roof planes are joined together by valley flashing that is tightly folded and sealed with sealant.
- Shingles from one roof plane overlap on top of the valley flashing.
- Shingles do not penetrate the valley itself – it is completely sealed off.
- Water is directed around and over the valley, but cannot enter inside.
- The valley flashing is often made of galvanized steel or copper.
The key benefit of a closed valley design is that it prevents water infiltration. The tightly sealed valley helps force water up and over the roof ridge rather than allowing it to pool in the valley seam. This can help prevent leaks and moisture damage.
What is an Open Valley Roof?
An open valley roof takes an alternative approach to joining two adjoining sloping roof planes. With an open valley:
- The two roof planes converge to form a V-shaped open seam rather than a sealed joint.
- Valley flashing is installed over the open seam but is not tightly folded or closed off.
- Shingles from both roof planes overlap and penetrate the valley center.
- Water running down the roof can enter and flow through the open valley.
- The valley flashing is typically galvanized steel or aluminum.
The main advantage of an open valley design is that it allows for better drainage. By leaving the valley flashing open, water can flow freely through the valley and down roof gutters. However, this free drainage comes with an increased risk of leaks.
Closed Valley vs. Open Valley: Key Differences
So what are the main differences between closed and open valley roofs? Here’s a quick overview:
| Closed Valley | Open Valley |
|-|-|
| Tightly folded sealed metal flashing | Overlapping open metal flashing |
| No shingle penetration | Shingles overlap into valley |
| Valley is sealed off | Valley left open for drainage |
| Prevents water entry | Allows water flow through |
| Lower leak risk | Higher leak risk |
| Potential for debris buildup | Debris washes away |
Below we’ll explore these differences in more detail.
Flashing Style
The biggest difference lies in the valley flashing. With a closed valley, the flashing is tightly folded and sealed with waterproofing sealant to prevent penetration. Open valley flashing overlaps but remains open to allow drainage.
Closed valley flashing takes more precision to install correctly. The flashing must be measured, cut, and sealed meticulously to prevent gaps where leaks could occur. An open valley is easier to install, but also more prone to shingle damage and uplift.
Shingle Installation
How shingles are installed also varies significantly. For a closed valley, shingles from one roof plane overlap on top of the sealed valley flashing. The key is that no shingle can penetrate the folded valley flashing.
With an open valley, shingles from both roof planes will overlap and penetrate the open valley. The bottom edges of the shingles will often be trimmed so they sit flush within the valley seam. Flashing is installed over top of the penetrating shingles.
Water Flow
The water flow differences are quite apparent. A closed valley forces water up, over, and around the roof. But water cannot penetrate inside the sealed valley seam, which prevents leaks.
Open valleys allow free drainage as water can flow straight through the open valley and down gutters. But having an open penetration point does leave open valleys more prone to potential leakage.
Leak Risks
Leak risks come down to the open versus closed flashing. The tightly folded, sealed flashing of a closed valley leaves little opportunity for water intrusion and leaks. An open valley’s free drainage does allow more potential entry points for leaks.
However, a properly installed open valley can still be quite water tight. It takes precision workmanship to cut shingles flush and maintain proper overlaps. Leaks most commonly occur from uplift or shingle damage over time.
Debris Buildup
Leaves, sticks, and other debris washing down a roof can accumulate in valleys. With a closed valley, debris can potentially build up since there is no flow path through the valley.
Open valleys allow debris to freely wash through the valley and down gutters. So open valleys are less prone to debris accumulation and potential clogging.
When are Closed Valleys Preferred?
Given the pros and cons, here are some of the situations where closed valleys tend to be the preferred design:
- Roofs with a steep slope – Closed valleys work better on steeply angled roofs where water flows quickly. The valley flashing can better prevent leakage.
- Cold climates – In areas with snow and ice, closed valleys hold up better than open. They prevent buildup of debris, ice, and snow that could potentially cause leaks.
- Tight valley angles – For roof lines that join together at tight, acute angles, closed valleys allow for better water runoff control.
- Areas prone to debris – Closed valleys prevent leaves, pine needles, and other debris from clogging the valley. This can be a concern on roofs near trees.
- Low-sloped shingles – For roofing materials with a more flat profile, like tile or low-sloped shingles, closed valleys work better than open.
- High water table homes – In areas with a high groundwater table, preventing any water entry into the valley is critical to prevent leaks. Closed valleys provide added protection.
- Leak repair – If a roof is already experiencing valley leaks, switching to a tightly sealed closed valley design can often improve water protection.
When are Open Valleys Preferred?
There are also situations where an open valley design would be the recommended best practice:
- Low-angled roofs – On gently sloping roofs, open valleys allow for better drainage as water won’t pool.
- Warmer climates – In hot regions without snow and ice risks, open valleys provide adequate water runoff control.
- Wide valley angles – Where roof planes join at a wide angle, an open valley works well for drainage.
- Budget option – Open valleys cost slightly less to install than closed valleys.
- Simple roof design – For straightforward gable roof shapes rather than complex multi-plane designs, open valleys suffice.
- Roofs with large debris – In regions with regular leaf droppings from trees, open valleys allow debris to wash away rather than accumulate.
- New construction – On new roofs where leaks are not a concern, open valleys provide an affordable option.
- Roof retrofits – Switching to an open valley design can make reroofing over an existing open valley simpler.
Closed Valley vs. Open Valley: Pros and Cons
To recap, let’s summarize the major pros and cons of each valley roof design:
Closed Valley Pros:
- Prevents water entry into the valley
- Reduces risk of leaks and moisture damage
- Holds up better on steep roofs
- Handles cold weather and snow/ice conditions
- Does not allow debris and buildup
Closed Valley Cons:
- More complex to install properly
- Flashing is prone to buckling and cracking over time
- Not preferred for low-angled roofs
- More expensive than open valleys
Open Valley Pros:
- Provides efficient water drainage
- Less potential for debris buildup
- Easier retrofit option for reroofing
- Works well on gently sloping roofs
- Less expensive option
Open Valley Cons:
- Increased risk of leaks from water penetration
- More prone to damage from weather elements
- Not ideal for steep roof pitches
- Can allow debris and shingle buildup
Frequently Asked Questions
What is better for regions with heavy snow – open or closed valleys?
Closed valleys are usually the preferred design for areas that receive heavy snowfall. The sealed valley prevents snow and ice buildup which could potentially lead to leaks or even ice damming. Open valleys allow more opportunity for packed snow accumulation.
Do open valley roofs leak more than closed valleys?
Open valleys do carry a higher risk of leaking since water can penetrate the open seam. Closed valleys completely seal off that water entry point. However, a properly constructed open valley using the right flashing and shingle overlaps should still perform reliably.
Can you convert an open valley to a closed valley?
It is possible to convert an existing open valley to a closed design, but doing so involves replacing all of the valley flashing and shingles. The roof planes would need to be disassembled down to the decking to allow old shingles to be removed and new sealed flashing installed.
Should you use a closed valley design when reroofing?
When reroofing a home, it’s a good idea to evaluate whether a closed valley would improve roof performance, especially if the existing open valley has had leakage issues. Converting to a closed design provides extra leak protection. But it also complicates the installation process.
Which flashing material works best for closed valleys?
The optimal flashing material for closed valleys is copper. Copper is completely waterproof, very malleable, and withstands movement well without cracking. Galvanized steel can also be used effectively, though it is more prone to buckling over time.
Do closed valleys require more maintenance?
Closed valleys are not inherently much more maintenance-intensive than open valleys. However, the sealed flashing should be periodically inspected for any cracks or gaps that could compromise water protection. Any damaged flashing should be repaired quickly.
Closed Valley vs. Open Valley: Which is Right for Your Roof?
Deciding between an open or closed valley design requires carefully weighing the pros and cons and evaluating the specifics of your roof shape, climate, and maintenance capabilities.
Closed valleys provide enhanced leak protection, but involve a more complex installation. Open valleys optimize drainage, but allow more opportunity for water intrusion.
Generally, closed valleys work best for steep roofs in cold climates. Open valleys are often preferred for gently sloping warm weather roofs with limited snow risk.
Whichever design you choose, make sure to hire qualified roofers who follow best practices for proper valley flashing installation and shingle integration. This will maximize performance and longevity for your roof.
With the right design and quality workmanship, both open and closed valleys can effectively direct water runoff and minimize leakage risks. Analyze the factors outlined here to choose the ideal valley configuration for your home.