Snap-Lock vs Standing Seam Roofing: Lessons from a Failed Dormer Roof Installation
- Jun 8
- 4 min read
Snap Lock vs Standing Seam Roofing is one of the most common comparisons homeowners, architects and builders make when researching metal roofing systems.
Both systems can provide an attractive and durable finish when correctly specified and installed. However, the long-term success of any metal roof depends on proper design, detailing and workmanship.
Recently, Alu Zinc Metal Roof Solutions was asked to inspect and replace a dormer roof that had been constructed using a combination of roof tiles and a snap lock metal roofing system. Unfortunately, the installation had been poorly detailed and was already suffering from significant water ingress issues.
This project highlights the importance of selecting the correct roofing system for low-pitch applications and demonstrates how poor detailing can lead to costly remedial works.
Snap Lock vs Standing Seam Roofing: What's the Difference?
Before examining the issues discovered on this dormer roof, it is important to understand the key differences between snap lock and traditional standing seam roofing systems.
While both systems share a similar appearance, their installation methods, movement accommodation and suitability for low-pitch roofs can vary significantly.
The Real Problem: A Low-Pitch Roof Covered with Tiles
One of the most significant issues we discovered was that the flat section of the dormer roof had been finished using roof tiles despite the roof pitch being far too low for a tiled roofing system.
Most roof tiles require a minimum pitch of approximately 17.5°–20° (depending on the manufacturer and specification) to shed water effectively.
This dormer roof was considerably flatter than that.
As a result, rainwater could not drain correctly from the surface. During periods of wind-driven rain, water was able to track beneath the tiles and onto the underlying felt and roof structure.
Over time, this led to:
Water ingress
Ceiling leaks
Saturated roof timbers
Timber decay and rot
Damage to the dormer structure
This is one of the reasons why architectural metal roofing systems are frequently specified for dormers and low-pitch roofs.
Traditional standing seam roofing systems can be installed on pitches as low as 3°, making them particularly suitable for low-pitch applications where tiled roofing systems may not be appropriate.
Problems with the Existing Snap-Lock Installation
As the roof was stripped, further issues became apparent.
The existing snap-lock system relied heavily on silicone sealants rather than correctly detailed flashings and metal roofing principles.
We discovered:
Excessive use of silicone throughout the installation
Exposed fixings driven through the face of the metal panels
Poor flashing details
Inadequate allowance for thermal expansion and contraction
Detailing that did not follow recognised architectural metal roofing practices
In several areas, silicone had been used where properly formed flashings should have been installed. Fixings had also been driven through visible areas of the metal rather than being concealed within the roofing system.
It is important to note that these issues were not necessarily a reflection of the snap-lock roofing system itself, but rather the way the roof had been designed and installed.
Like any roofing system, snap-lock roofing requires correct detailing, suitable applications, and proper installation methods to perform successfully.
Why Excessive Silicone Is a Concern
Architectural metal roofing should not rely on silicone sealants as its primary waterproofing method.
Over time, sealants can:
Deteriorate under UV exposure
Lose adhesion
Become brittle
Crack as the metal expands and contracts
When this occurs, water can penetrate behind panels and into the structure below.
A correctly detailed metal roof should manage water through its seams, flashings, folds, and drainage design rather than relying on exposed sealants.
Snap-Lock vs Standing Seam Roofing
One of the most common questions homeowners ask is whether snap-lock roofing is as good as standing seam roofing.
The answer depends on the project, roof design, detailing, and installation quality.
Snap-lock systems can be an excellent solution when correctly manufactured, specified, and installed.
Traditional standing seam systems, however, remain the preferred choice for many architectural projects because they offer:
Superior movement accommodation
Fully folded seams
Hidden fixing systems
Exceptional weather resistance
Proven long-term performance
Suitability for low-pitch roof applications
This is particularly important on dormers where roof pitches are often lower and detailing is more complex.
The Solution
Due to the extent of the issues discovered, the existing dormer roof was completely stripped.
Damaged timber sections were replaced, the roof was redesigned to suit the application, and a correctly detailed standing seam roofing system was installed.
The new installation incorporated:
Hidden fixings
Correct flashing details
Proper allowance for thermal movement
Traditional standing seam construction methods
A roofing system suitable for the low roof pitch
The result is a durable, weather-resistant dormer roof designed to provide decades of performance while maintaining a clean architectural appearance.
Final Thoughts
This project serves as an important reminder that the success of any roofing system depends not only on the material chosen, but also on the quality of the design and installation.
Low-pitch roofs require careful consideration, appropriate materials, and correct detailing.
Whether using snap-lock roofing, standing seam roofing, zinc, aluminium, or copper, choosing an experienced architectural metal roofing contractor can make the difference between a roof that lasts decades and one that requires costly remedial work only a few years later.
If you are planning a dormer, low-pitch roof, or architectural metal roofing project, contact Alu Zinc Metal Roof Solutions for expert advice and specification guidance.
See the Full Dormer Roof Replacement Project
This article is based on a real dormer roof replacement completed by Alu Zinc Metal Roof Solutions. View the full project gallery to see the original installation issues, remedial works, standing seam installation and completed roof.
