The Architectural Roof

Typical Architectural Profiles Figure 2

A second major grouping of panel profiles are referred to as architectural panels. Like shingled or slate roofs, architectural roofs carry rainwater off the roof. They are said to be hydrokinetic. Such roofs generally have a pitch of at least 3:12, although some architectural panels have been designed for pitches as low as 2:12. Architectural profiles are suitable for projects in which the roof requires weather resistance and performs as a visible, decorative element in the overall aesthetics of the building. Dramatic visual effects can be created with architectural roofs that are not possible with structural roofs.

Architectural roofs are generally designed to be installed over a solid substrate, the most common of which include plywood, metal decking or OSB, an engineered wood product, laminated to rigid insulation. Z-purlins, which are stronger than standard purlins, can also be used in combination with rigid insulation. The appropriate span for Z-purlin installations is dependent upon the type of panel and material, and the thickness of the material. Appropriate purlin spacing information is available from manufacturers.

Roof panels are fastened to the deck. Virtually all architectural panel profiles feature the use of concealed fasteners and clips.

Design Variants.The most common variants of architectural panels are shown in Figure 2. The "snap-seam profile" is one of the strongest and most popular. It affords superior strength due to its male/female panel interlock, which has a one-piece design that requires no tools to install, enabling labor cost savings during construction. The integral panel profile is suitable for mansard and canopy applications. The snap-on profile is used where applications involve a slope transition. The pan and cap can be easily altered in the field to accommodate the change in slope. These panels should be installed over a waterproof solid substrate.

The Basics of Underlayments

A key consideration in any roof design is keeping the building's contents dry. Since the roof is the primary barrier to water penetration, specifying the proper underlayment is critical in protecting the building from precipitation.

A properly installed underlayment can control water entering a roofing system. In structural roofs, if metal panels are installed over intermittent supports, an underlayment typically is not used. If there is a solid substrate, the National Roofing Contractors Association recommends using an underlayment. To minimize leaks, an underlayment of 30# felt or an ice/water guard membrane underlayment can be installed on top of insulation and along roof edges, valleys, ridges and hips, which are particularly prone to leaking. While such a waterproof membrane won't assure a totally leak-free roof, it will help prevent water from leaking directly into the building envelope.

As an alternative and an upgrade to traditional roofing felt, a peel-and-stick membrane can be applied as an underlayment. A fast-growing roofing trend, peel-and-stick products reduce the amount of time, labor and materials needed to install roof membranes and accessories because the adhesive is factory applied.

In architectural roofs, panels are usually installed over a moisture barrier such as roofing felt that acts as a secondary water barrier. The moisture barrier serves to direct off the roof any water that gets past the panels, flashing or trim.

Peel-and-stick membranes are the best solutions in architectural roofs, and are often recommended for use at all valley, ridge, hip and eave areas. It is also considered good practice to install barrel vault-type applications over a peel-and-stick membrane. One reason that this is prudent is the fact that a barrel vault application has zero slope at the top of the radius. All underlayment should be laid horizontally from eave to ridge. Peel & stick membrane is recommended for use at all valley, ridge, hip and eave areas.