By Steve Shull, RHEINZINK America
Gutter systems and related architectural sheet metal trim can have a profound impact on both the functional and visual quality of the building exterior. Following the building lines, gutters and downpipes are a connected series of drainage parts that collect and move storm water away from the structure. Managing the runoff of any roof is a key strategy for keeping the building dry and façade clean. Enhancing the gutter system and trim with pre-weathered zinc can not only extend the durability and improve performance, but also provide a natural aesthetic that can’t be imitated by paint, pigmented stains or metallic coatings.
In addition to the roof drainage system, architectural metal details can have a big impact on the visual appeal and weathertightness of the building. Natural weathering metals like copper, lead and (more recently) zinc have been used for centuries as a “crafted” roofing metal to fabricate gutters, downspouts, fascia, cornice, copings and a number of other roof accessories, ornaments and trim. Selecting between a natural metal or painted material is often a complex decision based on functional, aesthetic, economic, environmental and historical requirements. The installer’s level of the experience with zinc also plays a role in how zinc competes and how well the crafted details can be properly executed on the job.
Although architectural zinc offers many advantages to a project, some contractors have failed to embrace the metal. Every day more roofers, gutter installers and sheet metal tradesmen are gaining the necessary training and experience to carry on the architectural metal craft with zinc.
Zinc — the material
Titanium-Zinc alloy consists of 99 percent high-grade zinc mixed with approximately 0.1 percent titanium and 0.1 percent copper. The alloy provides increased tensile strength and malleability while reducing creep.
Two distinct alloys (meeting ASTM B69-09, Architectural Rolled Zinc, type 1 & 2) are available in two surface color aspects: pre-weathered blue-gray and a darker pre-weathered graphite-gray (created by slightly higher copper content). Both zinc alloys form a natural zinc carbonate patina after exposure to atmosphere and water. The patina color of each is remarkably durable while providing a variegated color aesthetic that is very durable and will not stain other products. Currently priced well below copper and other zinc-tin coated substitutes, zinc has carved out a huge share of the European architectural metals market. Architectural zinc roofing, gutter, trim and façade applications have helped to create many legendary structures in Europe and in more recent years North America. Even as an ancillary roofing material, zinc can offer many benefits to contractors & building owners alike.
Zinc — the exterior color complement
Zinc is a material that supports good design by providing subtle highlights to building lines that might otherwise fade into the background. Many steep-slope roofs that use watershedding products may be good candidates for zinc trim. The variegated gray colors of pre-weathered zinc are often an elegant complement to other natural and synthetic materials. With a warm gray appeal, zinc is generally a very good color complement to other exterior product color pallets. Zinc goes especially well with the earth tone colors found in slate and clay tile. The aesthetics of other roofs made of concrete tile, synthetic shake and slate, as well as asphalt shingles are greatly improved with a touch of zinc trim.
Don’t forget to consider the siding pallet as well, solid and sometimes bold stucco facades look fantastic when you trim the roof (and façade) with zinc. Combined with other earth tone colors, zinc trim will be an instant hit.
For low-slope roofs including vegetated/ green roof designs, waterproof membranes seal the perimeter of the roof deck with the help of sheet metal profiles such as copings, gravel-stops, fascia and cornice. When the construction budget limits the use of premium roofing materials, a small accent of zinc for the edge-trim is a great way to upscale the roof lines without breaking the budget.
Both manufactured and custom shop-fabricated flashing profiles can be made from pre-weathered zinc. Prefabricated zinc fascia and coping profiles meeting ES-1 uplift requirements are available from Metal-Era, Inc. As more metal suppliers and fabricators continue to recognize zinc is not a trendy color that risks going out of style, the market for zinc in the US will continue to grow.
Zinc — material and application compatibility
From a material compatibility standpoint, there are some roofing products, processes and conditions to avoid. Topping off the avoidance list is copper runoff which is very corrosive to zinc (and other metals). Zinc also can experience premature corrosion and staining from wood products that release acidic tannins like new cedar roofs. An appropriate cedar alternative is typically Cyprus (or a faux shake product). For low-slope roofs with hot-applied BUR and modified-bitumen membranes, zinc trim should be installed with a compatible cold adhesive or non-penetrating roof-edge system. In general, zinc roofs need to breathe so sealing the down-slope edges of the zinc (also closing off a place for moisture to escape) is not advised.
Specifying zinc trim for the roof
Specifying zinc for steep-slope roof applications like valley pans, hip and ridge caps, drip edges, step flashing and roof jacks is easy when you want to use zinc. The first concept to understand with zinc is the need for ventilation and a structured underlay (ventilation mat) directly below the zinc. With a potential for trapped moisture behind the metal in some roof applications, creating a capillary break between the back of the zinc and the underlayment is a required practice. Protecting zinc’s underside from backside corrosion is best achieved with a ventilation mat and free flowing air. For details that do not allow for the inclusion of this 3/8-inch nylon mat, a backside coated zinc product is also available. Material thickness recommendations are based on application type and panel dimensions. Zinc sheets are available in 0.7 mm (24 gauge), 0.8 mm (22 gauge), and 1.0 mm thicknesses. Zinc flashing specifications may include a specific zinc manufacturer, color of pre-weathered surface aspect/alloy, and prefabricated profile/ product specific decision. Although most roofing trim is custom designed and fabricated by the roofer, some standard panel profiles may be purchased from distributors or specialty fabricators.
For weathertight conditions on the roof, soldering is the preferred seam to ensure long-term performance. Soldering of zinc alloy can be done by using the correct alloy-specific flux (ZD-Pro), 50/50 solder and a cooler iron (no torches). Roof saddles and crickets, vent stacks, roof ornaments and other critical roof details can be installed with more confidence when the metal seams are soldered rather than sealed with a pop-rivet and sealant solution. Other larger roof penetrations like chimneys, dormers and towers also provide opportunities for zinc cladding with only minor soldering required.
Two conditions that typically are not good applications for zinc are: in-laid gutters and flat-seam soldered decks (both typically do not provide adequate slope provisions for thermal movement). With the proper detailing, manufacturer technical support and a knowledgeable installer, zinc can perform well in many roofing details.
Zinc gutters as a complement to the roof
Prefabricated half-round gutters (5-inch and 6-inch) and smooth round downspouts (3.125-inch and 4-inch) are fabricated from 0.7 mm material in two preweathered alloys.
Contractors and specifiers should review and understand the differences between European-style gutter systems ( http://us.rheinzink.de/ ) and American half-round products. Outside gutter beads, fascia mount bracket supports, smooth elbows with expanded ends and funnel outlets summarize some of the unique characteristics of European gutter systems. As with most German products, the European system is engineered to provide numerous performance advantages including 30 percent added flow when gutter plug-in funnels are used for the gutter outlet. Improved structural support compared to hanging system and prefabricated miters, endcaps and downspouts that rely on friction fit connections. In all, European zinc gutter systems perform better, add a clean look with precision fit connections and often cost. Gutter systems fabricated by the zinc mill often offer the most cost competitive zinc drainage system alternative.
European gutter approach
It’s a fact the Euro half-round gutter makes more efficient use of material and gets water away from the building faster than a comparable American design. The half-round shape starts to flow sooner than any flat-bottom gutter design. Lower slope installation without compromising performance also enhances a more desirable “level” architectural aesthetic.
Gutter connections are made by soft soldering and tight fabrication tolerances. The weak link in most gutter installations is the connection between the gutter and the downspout where the water flow can get choked-off. Traditional drop-in outlets must be sized slightly smaller than the downspout diameter and create a dam from the flange and solder at the point where water is expected to flow down (but first it must fill up). The European solution to this problem is a larger hole in the gutter that sheds water to the downspout with a friction-fit funnel accessory that installs quickly and with ease. Soldered gutter joints, welded round downpipes, better performance, beautiful natural weathering zinc aesthetic and all made possible with less material (girth) to fabricate. Euro gutters make more sense.
Zinc is a crafted metal that can provide many opportunities for the progressive roofing contractor or architectural sheet metal shop. A specialty metal that has been used in Europe for almost 300 years, zinc compliments other roofing and façade materials very well. A neutral warm gray color that never fades away provides a durable metal termination and gutter solution to the best steep and low-slope roofs. The envy of every paint manufacturer, the properties of the color zinc can be imitated but never duplicated in powder or liquid form. Challenge your skills by talking to your zinc distributor about using zinc on your next roof or gutter installation.
Steve Shull, CSI, CDT, LEED AP, is the regional sales manager—Midwest, RHEINZINK America, Inc. www.rheinzink.com.