Is It Metal?

May 15, 2002

Over the past several years, architects and designers have
often used steep sloped roofing as a prominent architectural
building feature. Prefabricated metal has been the most widely
used roofing application for these roof areas. Although the
metal panels themselves are attractive and watertight, as a system
there are some issues that still need to be addressed by the metal
roofing industry.
Leakage Problems with Metal Roofing
There are a variety of seaming techniques used with varying
degrees of success. Although many manufacturers provide flashing
details, leaks through metal roofs often originate at details.
At ridges and hips, metal or foam closures are typically sealed to
roof panels and seams, but eventual sealant failure can result in
leaks. Penetrations are flashed with some type of flexible membrane
and then sealed in compression to the metal panels, resulting
in a gasket approach.
The transverse seams between panels are another source of
leaks. Metal panels are overlapped with the flow of water. A single
bead of sealant is applied within the panel overlap. The most
common sources of leakage are at intersections of different detail
conditions, where three-dimensional detailing is required.
Examples of these conditions include ridge and hip intersections
or valley and ridge intersections at dormers.
Unlike traditional metal roofing made from copper or
other solderable materials, pre-painted metal roofs rely on
sealant at flashing areas for primary waterproofing protection.
Sealant is prone to deterioration from weathering
and/or movement.
Snow accumulation and ice dams also lead to leakage
problems because they can cause water to pond on low
sloped areas. Submerging a metal roof system in water
and water back-up are major concerns because a metal
roof is not intended to be waterproof and must rely on
slope in order to shed water.
May 2002 Interface • 31
By Brian Whelan
Welding rib in place.
Post and rib installation.
A Single-Ply Alternative to Metal Roofing
The appearance of metal roofing can be created on both
new and re-roofing projects by using a thermoplastic PVC
single-ply membrane and various decorative rib configuration
systems that are permanently installed without affecting the
watertight integrity.
Architects, designers, and building owners throughout
Europe have been using single-ply membrane and decorative
profiles to create the appearance of metal for years. Now, the
same cost-effective and innovative technology is available in
North America.
Two Systems Available
There are two systems available. In both, a colored
thermoplastic PVC roof membrane is adhered to an
acceptable substrate. A felt-backed membrane can be used
to hide insulation joints and insulation plates.
In the first system, a proprietary rib made of the same
membrane formulation is welded to the thermoplastic
roof membrane using an automatic hot air welder with a
patent-pending welding kit. The kit permanently welds
the rib to the thermoplastic membrane in a straight line.
The second option utilizes a post and rib system. A
uniquely designed post with a pre-welded, colored PVC
membrane base plate supports a rail and a cover piece of
PVC-clad metal. The PVC metal is the same color as the
roof membrane.
The post and rib system gives the designer and building
owner more flexibility with the size and shape of the
profile system. The profile can even be laid out on a portion
of the roof for the building owner and roof designer
to examine and determine final spacing and location of
ribs for desired aesthetics before welding into place.
A complete set of details is available to replicate metal roofing
and ensure a watertight condition. There is also the ability,
using AutoCAD, to show an architect and owner what the profile
roof will look like on a specific building. The isometric of
the roof can show color options and can vary spacing of the ribs
– a “virtual roof” presentation.
In many applications, there are both sloped roof areas and
low sloped (0 – 1/2″/foot) areas. Owners and architects like the
idea of getting one warranty for the entire roof area. Others
have selected the decorative profiles as a very cost-effective
alternative to architectural metal. n
Brian Whelan is Vice
President of Sales and
Marketing for Sarnafil Inc.,
manufacturer of the Décor
Profile. Whelan has two
patents pending on hot air
welding of thermoplastic
membranes and profiles.
He is a former Project
Manager of Simpson,
Gumpertz & Heger and has
a degree in Architectural
Technology. He is a member of SPRI, RICOWI,
RCI, and CSI. Brian has participated in many ASTM
committees on roofing and waterproofing.
Table 1
32 • Interface May 2002
Roger Williams Zoo, Providence, RI.