How To Do A Metal Roof Valley – Ensure Watertight & Durable Seams
To install a metal roof valley, first prepare the roof deck by cleaning it and applying a self-adhering ice and water shield. Next, carefully position and fasten the pre-formed metal valley flashing, ensuring proper overlap and drainage. Finally, trim and fit your metal roof panels to the valley, maintaining a clear drainage channel, and seal all seams and fasteners to prevent leaks.
Proper measurement, precise cuts, and meticulous sealing are crucial for a durable, leak-proof metal roof valley installation.
Every DIY homeowner or aspiring metalworker knows the roof is your home’s first line of defense. And when it comes to keeping water out, few areas are as critical—or as challenging—as the roof valley. These crucial intersections where two roof planes meet are notorious hotspots for leaks if not installed correctly. A poorly done valley can lead to costly water damage, rot, and headaches down the line.
You want a roof that stands up to the elements, a professional finish, and the satisfaction of knowing you did it right. The good news? Installing a durable, leak-proof metal roof valley is absolutely within reach for the careful DIYer. It requires precision, patience, and the right techniques, but it’s not rocket science.
In this comprehensive guide from The Jim BoSlice Workshop, we’ll walk you through every step of how to do a metal roof valley. We’ll cover everything from essential safety measures and tool selection to preparing the deck, installing the valley metal, and ensuring a watertight seal. By the end, you’ll have the confidence and knowledge to tackle this vital part of your metal roofing project like a seasoned pro.
Let’s get started and build a roof that truly protects your home!
Understanding Roof Valleys and Why They Matter
A roof valley is the internal angle formed by the intersection of two sloping roof planes. Think of it as a natural gutter, channeling rainwater and snowmelt from a large area of your roof down to the eaves. Because they collect such a significant volume of water, valleys are particularly vulnerable to leaks.
For metal roofing, valleys require specific attention to detail. Metal expands and contracts with temperature changes, and the sharp angles of a valley can put stress on materials if not installed properly. A well-executed metal roof valley is essential for the longevity and performance of your entire roofing system.
Types of Roof Valleys for Metal Roofing
While there are several valley types for shingle roofs, metal roofing primarily utilizes what’s known as an open valley. This design exposes a strip of metal flashing in the valley itself, allowing water to flow freely down a dedicated channel.
- Open Valley: This is the most common and recommended method for metal roofs. It uses a pre-formed metal flashing piece in the valley, over which the metal roof panels are trimmed. This creates a visible, open channel for water runoff, reducing the chance of debris buildup and ensuring efficient drainage.
- Closed Valley: Less common and generally discouraged for most metal roofing systems due to expansion/contraction issues and potential for water damming. In a closed valley, roof panels overlap directly in the valley, concealing the flashing underneath.
For this guide, we will focus on the open valley method, as it offers superior performance and is more forgiving for DIY installation on metal roofs.
Essential Tools and Materials for Your Metal Roof Valley Project
Before you even think about stepping onto the roof, gather all your tools and materials. Having everything on hand saves time and reduces frustration. Here’s what you’ll need:
Tools List
- Safety Gear: Fall protection harness and lanyard, safety glasses, heavy-duty work gloves, sturdy work boots.
- Measuring and Marking: Tape measure, chalk line, straightedge (e.g., 4-foot level or T-square), metal scribe or marker.
- Cutting Tools: Aviation snips (left, right, and straight cut), electric shears or nibblers (highly recommended for long, clean cuts on metal panels), utility knife.
- Fastening Tools: Cordless drill/driver, appropriate screw bits, rivet gun (if using rivets for flashing overlaps).
- Hand Tools: Hammer, caulk gun, tin snips, folding tool or hand seamer.
- Cleaning Supplies: Broom, dustpan, shop vacuum.
Materials List
- Underlayment: High-quality synthetic underlayment, and crucially, self-adhering ice and water shield for the valley.
- Valley Metal Flashing: Pre-formed metal valley flashing (usually 24-inch wide, galvanized steel, aluminum, or the same material/color as your roof panels). Ensure it has a raised rib down the center for water diversion.
- Metal Roofing Panels: Your chosen metal roofing panels.
- Fasteners: #10 or #12 hex-head screws with neoprene washers (color-matched to your roofing), rivets (if needed for flashing).
- Sealants: High-quality, exterior-grade polyurethane sealant or butyl mastic tape compatible with your metal roofing materials.
- Foam Closures (optional): For sealing panel ends at the valley, if your panel profile allows.
Always check material compatibility. Different metals can react, causing corrosion. For example, avoid direct contact between copper and galvanized steel.
Safety First: Working on a Roof
Working on a roof is inherently dangerous. Prioritize safety above all else. A slip or fall can have serious consequences. Take these precautions:
- Fall Protection: Always wear a properly fitted fall protection harness anchored to a secure point on the roof.
- Ladder Safety: Use a stable ladder, extend it at least three feet above the eave, and ensure it’s on level ground.
- Weather Watch: Never work on a wet, icy, or windy roof. Check the forecast before you start.
- Footwear: Wear non-slip, sturdy work boots with good ankle support.
- Teamwork: If possible, work with a partner. They can help with materials, spot hazards, and assist in an emergency.
- Tool Management: Keep your work area tidy. Don’t leave tools lying where they can be tripped over or slide off the roof.
Remember, no job is worth risking your life or limb. If you feel uncomfortable or the task seems too challenging, call a professional.
Preparing the Roof Deck for Your Valley Installation
A solid foundation is key to a leak-proof valley. Proper deck preparation sets the stage for a successful installation.
Clean and Inspect the Deck
- Clear Debris: Sweep the valley area thoroughly. Remove any old nails, splinters, leaves, or other debris.
- Inspect Plywood/Decking: Check for any soft spots, rot, or damaged sheathing. Repair or replace any compromised sections. The deck must be solid and smooth.
Install Ice and Water Shield
This step is non-negotiable for a durable, watertight metal roof valley. Ice and water shield is a self-adhering membrane that provides an extra layer of protection against water intrusion, especially in areas prone to ice dams or heavy rain.
- Cut Strips: Cut two strips of ice and water shield, each at least 18 inches wide and long enough to run the full length of the valley, plus an overhang at the eaves.
- First Strip: Peel back a portion of the release paper and carefully align the first strip along one side of the valley centerline. Press it firmly into place, working from the center outwards to avoid wrinkles or air bubbles.
- Second Strip: Overlap the second strip over the first by at least 6 inches, ensuring it covers the opposite side of the valley. Again, work from the center out, pressing firmly.
- Seal Edges: Ensure all edges are tightly sealed to the roof deck. Use a roller to achieve good adhesion.
The ice and water shield acts as a secondary drainage system. If any water gets under your primary metal valley, this membrane will prevent it from reaching your roof deck.
Understanding the Process: How to Do a Metal Roof Valley Right
Now for the main event: installing the metal valley flashing itself. This is where precision and careful handling of materials truly pay off.
Measuring and Cutting the Valley Metal
Your pre-formed valley metal flashing usually comes in 10-foot lengths. You’ll need to cut it to fit the length of your valley.
- Measure Length: Measure the full length of your valley from the ridge to the eave.
- Cut Sections: Cut the valley metal sections to size using electric shears or tin snips. For longer valleys, you’ll need to overlap sections.
- Prepare Overlaps: If overlapping, trim the raised rib (hem) off the top piece where it will overlap the lower piece. This allows for a smooth transition. Overlap sections by at least 6 inches, shingling them so the upper piece overlaps the lower, ensuring water flows over the seam.
Installing the Valley Metal Flashing
This is a critical step in how to do a metal roof valley to ensure a watertight system.
- Position First Section: Start at the eave. Position the first section of valley metal, allowing it to extend about 1 inch beyond the eave edge. Ensure the center rib of the valley flashing aligns perfectly with the valley centerline.
- Fasten Carefully: Secure the valley metal to the roof deck using approved fasteners. Place screws approximately 1 inch in from the outer edges of the valley flashing, and space them about 12-18 inches apart. Do not fasten through the center rib or in the main water channel, as this will create potential leak points. The goal is to hold the valley metal in place, not to puncture the drainage area.
- Overlap and Seal: For subsequent sections, slide the upper section over the lower section, overlapping by at least 6 inches. Apply a bead of compatible sealant or butyl mastic tape between the overlapping pieces before fastening them down. You can use a few rivets at the top edge of the overlap if desired for extra security, but ensure they are covered by the subsequent roof panels.
- Ridge Treatment: At the ridge, allow the valley metal to extend slightly past the ridge line. It will be trimmed flush later when the ridge cap is installed.
Ensure the valley metal lies flat and smooth. Any buckles or waves can impede water flow and create stress points.
Trimming and Fitting Metal Roof Panels to the Valley
This is where your metal roofing panels meet the valley flashing. Precision is paramount here to maintain the open drainage channel.
Marking the Cut Lines
- Align Panel: Bring a metal roof panel up to the valley, positioning it as if it were fully installed on the roof plane. Allow it to overlap the valley metal by several inches.
- Scribe the Line: Using a straightedge or a piece of scrap metal, scribe a cut line onto the panel. The goal is to trim the panel so that its edge is 2-3 inches away from the center rib of the valley flashing. This creates your open drainage channel. Do this for both sides of the valley.
- Repeat for All Panels: Mark all panels that will terminate at the valley before cutting.
Cutting the Panels
Use your electric shears or nibblers for clean, precise cuts. Tin snips can be used for shorter cuts or detail work, but they tend to leave a slightly wavy edge.
- Cut Precisely: Carefully cut along your marked lines. Accuracy here ensures a neat appearance and proper drainage.
- Fold Up Edges (Optional but Recommended): For an extra layer of protection, use a folding tool or hand seamer to create a small 1/2-inch hem or “kick-up” along the cut edge of the metal panels where they meet the valley. This small upward bend helps prevent water from creeping under the panel edge due to wind or capillary action.
Fastening Panels Near the Valley
Install the trimmed metal panels as per your roofing system’s instructions. When fastening panels near the valley:
- Maintain Distance: Do not place fasteners through the valley flashing itself. Keep fasteners at least 6 inches away from the edge of the valley metal.
- Secure Properly: Ensure panels are securely fastened to the purlins or strapping beneath.
Flashing and Sealing for a Watertight Finish
The final touches make all the difference in preventing leaks and ensuring the longevity of your metal roof valley.
Sealing Panel Edges
Even with the kick-up, it’s good practice to add extra sealant.
- Apply Sealant: Before fastening the final panel sections, apply a thin bead of compatible sealant or butyl mastic tape along the underside of the panel edge where it meets the valley flashing. This acts as a gasket.
- Use Foam Closures: If your panel profile allows, install foam closures at the end of the panels where they meet the valley to block wind-driven rain and insects.
Ridge Cap Integration
Once all panels are installed, you’ll install the ridge cap. The valley metal that extends past the ridge line should be trimmed flush with the top of the roof deck or slightly folded down before the ridge cap is installed. The ridge cap will then cover the intersection of the valley metal and the ridge, providing a clean, sealed finish.
Final Inspection and Cleanup
- Check All Fasteners: Ensure all fasteners are tight and properly sealed with their neoprene washers.
- Seal Any Gaps: Inspect the entire valley for any small gaps or potential leak points and apply sealant as needed.
- Remove Debris: Clear away all metal shavings, screws, and other debris from the roof. Metal shavings can rust and stain your new roof.
Take pride in your work. A well-installed metal roof valley not only looks good but will protect your home for decades.
Common Mistakes to Avoid When Installing a Metal Roof Valley
Even experienced DIYers can make mistakes. Being aware of common pitfalls can help you avoid them.
- Improper Underlayment: Skipping the ice and water shield or not properly adhering it is a recipe for future leaks.
- Fastening Through the Valley Channel: Never put screws or nails directly through the main drainage area of the valley metal. This creates holes where water can penetrate.
- Insufficient Overlap: Not overlapping valley metal sections enough, or overlapping them in the wrong direction (bottom piece over top), will lead to leaks.
- Cutting Panels Too Close: Trimming metal panels too close to the valley centerline restricts water flow and increases the chance of debris buildup. Maintain that 2-3 inch gap.
- Using Incompatible Materials: Mixing different types of metal (e.g., copper with galvanized steel) can cause galvanic corrosion, leading to premature failure.
- Ignoring Safety: Rushing or neglecting safety gear is never worth it.
- Poor Sealing: Not using compatible sealants, or not applying them thoroughly, will compromise the watertight integrity.
By taking your time and following these steps, you can confidently complete a durable and leak-proof metal roof valley.
Frequently Asked Questions About Metal Roof Valleys
Can I use standard asphalt shingle valley flashing for a metal roof?
No, you should not. Metal roofs require specific metal valley flashing designed to accommodate the expansion and contraction of metal panels and to provide a durable, open drainage channel. Shingle flashing is not robust enough and typically not compatible with metal roofing systems.
What is the purpose of the raised rib in the center of the valley metal?
The raised rib, or “hem,” in the center of the valley metal serves as a water diverter. It prevents water flowing down one roof plane from crossing over to the other side of the valley and potentially being driven under the adjacent metal panel by wind. It ensures water stays within its designated channel.
How far should metal roof panels be trimmed from the valley centerline?
Generally, you should trim your metal roof panels so their edges are 2 to 3 inches away from the center rib of the valley flashing. This creates an adequate open channel for water flow, prevents debris buildup, and reduces the chance of water being driven under the panels.
Do I need to use sealant in the valley?
Yes, sealant is crucial. Apply a compatible, high-quality exterior-grade sealant or butyl mastic tape between overlapping sections of valley metal flashing. You should also consider applying a bead of sealant or tape along the underside of the metal panel edges where they meet the valley flashing for an extra layer of protection against wind-driven rain.
Is it possible to install a metal roof valley by myself?
While possible, it’s highly recommended to have at least one helper, especially for handling long sections of valley metal and roof panels. Working on a roof alone is more dangerous, and a second pair of hands can make the job safer and more efficient, particularly for tasks like positioning materials and ensuring proper alignment.
Your Watertight Metal Roof Valley Awaits!
Installing a metal roof valley is one of those DIY tasks that truly tests your attention to detail and craftsmanship. But as you’ve seen, by breaking it down into manageable steps, prioritizing safety, and using the right tools and materials, you can achieve a professional-grade, leak-proof result.
You’ve learned the critical role of underlayment, the precision needed for cutting and fitting valley metal, and the importance of proper sealing. Now, armed with this knowledge, you’re ready to tackle this essential part of your metal roofing project with confidence.
Remember, patience and precision are your best friends here. Don’t rush the process, double-check your measurements, and always put safety first. Your efforts will be rewarded with a durable, beautiful, and most importantly, watertight roof that protects your home for years to come.
Keep honing your craft, stay safe, and happy building!
