Metal roofing is built to shed water fast, but the roof only stays leak resistant when the flashing system is planned correctly. Most metal roof leaks do not come from the field material. They come from valleys, roof to wall transitions, chimneys, and pipe penetrations where water is forced sideways by wind, ice, debris, or volume.
Top Tier Metals is supply only. If you want a second set of expert eyes to confirm you have the correct flashing plan and a complete bill of materials before ordering, start here:
Schedule a free metal roof flashing and materials review before you order
This guide explains how flashing works in the highest risk leak zones and what you should include in your order to prevent delays and failures.
What flashing does on a metal roof
Flashing is the engineered transition that keeps water on the outside of the roof system when the roof surface changes direction or ends. Flashing also protects seams and fasteners from water pressure and capillary action.
Think of leak prevention as a layered system:
- Primary water shedding layer: the metal roof surface
- Transition protection: flashing at edges, valleys, walls, and penetrations
- Secondary protection: underlayment and self-adhered membrane in critical zones
- Sealing and closure: butyl tape, closures, and compatible sealants where required
If you are not sure which underlayment stack fits your roof slope and environment, use this guide:
Metal roof underlayment options and when each one matters for leak prevention
Valley flashing: the highest volume water path on the roof
Valleys are where two roof planes dump water into a narrow channel. Add debris, ice, or wind and the valley becomes the highest stress test on the roof.
Two common valley approaches
- Open valley: a dedicated valley metal channel remains visible and carries water
- Closed valley: roof material covers the valley area and channels water underneath
Which approach is best depends on the roof system, slope, and how the specific manufacturer details valley components. In many climates, an open valley with correct underlayment and correct fastening practices is a reliable approach because it keeps water moving and keeps debris from forcing water under the roof surface.
Common metal roof valley leak causes
- Fasteners placed too close to the valley center where water flows
- Valley metal not wide enough for the roof pitch and water volume
- Missing ice and water shield under the valley in freeze zones
- Panels or shingles cut and terminated without correct sealant and closure plan
- Debris buildup that redirects water sideways under the roof surface
Valley ordering checklist
- Valley flashing in the correct width and finish for the system
- Self-adhered membrane for valley liner where required by environment
- Butyl tape for lap edges and termination edges where specified
- Compatible sealant for detailing where the system requires it
- Closures or foam where needed to block wind driven water under profiles
If you want to make sure your accessory set matches your roof system, use:
Metal roof accessories and trim options that improve performance and finish quality
Sidewalls and headwalls: roof to wall transitions that leak when the details are wrong
Roof to wall transitions are where water gets pushed sideways. These are common on dormers, second story walls, sheds, porches, and any roof plane that runs into siding or masonry.
Key transition types
- Sidewall: the roof runs alongside a wall
- Headwall: the roof terminates into a vertical wall
- Kickout diverter: a small but critical piece that forces water into the gutter instead of behind siding
Common roof to wall leak causes
- Missing kickout diverter at the base of a sidewall
- Flashing that is too short behind the wall cladding
- Underlayment not integrated correctly at the transition
- Sealant used as the primary water barrier instead of as a supplement
- Incorrect termination that allows water to run behind the wall surface
Ordering the correct wall flashing depends on the roof system. The safest move is to confirm your wall runs and headwall runs during takeoff so these line items do not get missed.
If you need measurement guidance before building your takeoff, use:
How to measure a roof for metal roofing including walls, rakes, ridges, and valleys
Chimney flashing: where water load and geometry collide
Chimneys combine vertical surfaces, backwater areas, and multiple direction changes. Many chimney leaks are caused by missing cricket design where water volume demands it, or by improper integration between roof surface and counter flashing.
Chimney flashing components to plan
- Apron flashing on the downslope face
- Step flashing along the sides where the roof runs up the chimney
- Backpan flashing or saddle on the upslope face
- Cricket or diverter where chimney width and water volume require it
- Counter flashing approach based on chimney material and existing joints
Chimneys frequently overlap with other penetration planning. Use this leak prevention guide for penetrations and vertical transitions:
How to detail skylights, vents, and chimneys on a metal roof without leaks
Pipe boots and vents: small openings that cause big leaks
Pipe penetrations look simple, but they fail when the boot material does not match heat exposure, when the boot is sized incorrectly, or when the boot is installed in a location that forces water uphill around the penetration.
Pipe boot planning checklist
- Confirm each pipe diameter and choose the correct boot size range
- Choose boot material appropriate for roof temperatures and exposure
- Plan placement to avoid valleys and high water flow lines
- Confirm compatibility with the roof profile and rib geometry
- Include butyl tape and compatible sealant if required by the system
- Include correct fasteners for the boot flange and profile
Most common pipe boot leak causes
- Boot cut too large, leaving no compression seal
- Boot installed on a high rib without correct support or seal plan
- Sealant used as the only barrier instead of correct boot compression and tape
- Fasteners missing, overdriven, or placed where water pools
- Boot placed too close to a ridge or valley where water behavior is unpredictable
If you want your penetration list reviewed as part of your order, use:
Sealants, tapes, closures, and fasteners: what actually keeps water out
Most leak investigations come back to four root causes: missing closures, incorrect tape placement, incompatible sealant, or fasteners placed in the wrong location.
Leak prevention rules that apply to most systems
- Do not place fasteners in high flow water paths like valley centers unless the system explicitly requires it
- Use butyl tape where specified for laps and transitions, because it maintains compression sealing
- Use closures where the profile geometry creates a wind driven water entry path
- Use sealant as a supplement, not as the entire water control strategy
- Keep accessory families consistent so finishes and compatibility match
Warranty language often ties directly to correct detailing and approved components. Review this before installation:
Metal roofing warranties and the installation mistakes that void coverage
What to include in your metal roof flashing order
Use this as a bill of materials cross check so you do not discover missing flashing after tear off.
Flashing and accessory checklist
- Valley flashing sized for roof pitch and water volume
- Drip edge for eaves and edge metal for rakes
- Ridge cap and hip cap components, plus required closures
- Sidewall flashing and headwall flashing for roof to wall transitions
- Kickout diverters where sidewalls end into gutters
- Chimney apron, step flashing plan, backpan, and cricket approach as needed
- Pipe boots for every penetration, correctly sized and matched to exposure
- Butyl tape, closures, and compatible sealants as required by the system
- Fasteners, clips, and attachment hardware approved for the profile
- Underlayment and membrane for valleys, eaves, and critical zones
To make sure your accessories and trim match your selected system and finish, review:
Metal roof trim and accessory options for complete system ordering
Delivery and staging: prevent damage before installation
Flashing pieces are easy to bend and easy to lose. Plan storage and staging so critical parts stay straight, dry, and organized.
- Stage flashing on a flat surface, off the ground, and protected from standing water
- Keep small accessory parts in labeled bins by roof area
- Inspect for damage before sign off and document with photos
Review shipping expectations here:
Top Tier Metals shipping policy for delivery timelines and freight requirements
Quick inspection checklist to catch flashing issues early
You can prevent many problems by inspecting the highest risk zones during and after installation.
- Valleys are clear, properly lapped, and free of fasteners in high flow zones where not required
- Sidewalls include correct step transitions and kickout diverters where needed
- Headwalls have correct termination and water control into the roof surface
- Chimney flashing is layered correctly with backpan and counter approach
- Pipe boots are compressed correctly, sealed correctly, and not located in water traps
- Sealant is used where required, but not as a replacement for flashing geometry
If you need fast answers on ordering and planning, use:
Top Tier Metals FAQs for ordering, timelines, and project planning
