Low
Slope Metal Roofs Provide Years of Low Cost, Low Maintenance Performance
Low slope metal roofs have been a preferred roof covering for commercial,
institutional and industrial buildings for years because of their ability
to protect against the elements, to allow water to drain away from the
roof surface, and to keep building contents and occupants dry and
comfortable.
Recently, building owners and architects have come to recognize and
appreciate still other attributes of low slope metal roofs – their long
service life, low life cycle cost, sustainability, recyclability, low
maintenance requirements, light weight and resistance to wind.
Low slope structural roofing, generally used on roof pitches ranging from
¼:12 to 3:12, consists of interlocking panels, commonly called standing
seam roofing, that run vertically along the roof surface. These panels
generally come with a painted mill finish or a clear acrylic finish. Some
metal roofing used on low slope applications requires machine seaming
during installation to ensure a watertight seal. A seaming apparatus is
simply rolled along the panels to crimp the panel seams together.
A standing seam design assures adequate draining from rain and snow,
effectively eliminating ponding, leaks and related problems typically
associated with built-up roofs. In retrofit projects, a sub-framing system
is attached to the existing flat roof surface to provide a minimum ¼:12
roof pitch.
Moreover, low slope metal roofs are not prone to the degradation
experienced by organic materials, enabling these roofs to better resist
the elements. This, in turn, results in a longer life span and a very low
annual operating cost.
Study Substantiates Low Life Cycle Cost
As a result of the durability and reliability of these systems, low slope
metal roof manufacturers offer 20- to 40-year warranties on their
products. Their long life and low maintenance requirements also put metal
roofs on a very attractive life cycle cost track.
This was confirmed in a 2004 study of low slope roofing conducted by
Ducker International. Respondents to the study said they expected the life
cycle cost of a metal roof, including outlays for maintenance, to be about
30 cents a square foot per year, far less than their expectations for
built-up and single-ply roofs, at 37 cents and 57 cents, respectively.
Metal roofs also have a significantly longer expected service life than
either built-up roofing or single-ply roofs. Study participants said they
expect metal roofs to last 40 years – 17 years longer than built-up and 20
years longer than single-ply systems.
Not only can low slope metal roofing contribute to the bottom line, it can
also contribute to LEED credits, which are awarded to buildings that use
high recycled content and other “green” construction materials. A typical
low slope metal roof has
at least 25% recycled content, and at the end of its long useful life is
100% recyclable.
In addition, “cool metal roofing” can significantly reduce a building’s
long term energy use. With heat deflecting metal coatings, energy costs
can be reduced up to 40% or more, according to a study conducted by Oak
Ridge National Laboratory.
Metal Roofs Place Fewer Demands on Structure
Typically, low slope metal roof systems vary in weight from 40 to 135
pounds per 100 square feet, making them among the lightest roofing
products and the easiest to install. A lightweight roofing system also
places fewer demands on a building’s structural support system, an
important consideration in earthquake-prone areas.
Unlike non-metal systems which require an underlying substrate or deck,
low slope metal roofs can be applied directly over bar joists or purlins.
And, because of their interlocking or active fastening systems, metal roof
panels are designed to meet the requirements of ASTM E1592, UL 580, UL1897
and other severe wind and uplift tests.
Metal roofing products come in a variety of materials as well as many
colors, textures and profiles. To ensure longer life, almost all low slope
roof materials are protected from the elements by high performance, highly
durable metallic coatings.
While the idea of protecting a building with metal originated centuries
ago, the concept is still valid today. Whether the goal is many years of
low-cost, low maintenance, problem-free performance, or an environmentally
responsible approach to roofing, low slope metal roofs make sense.
Steep
Slope Metal Roofs Offer Long-Term Performance as Well as Long-Term Beauty
When building owners and architects require an attractive and affordable
steep slope roof covering for a commercial project, chances are that more
and more of them will choose a metal roof.
Steep slope metal roofs, often defined as roofs with pitches of 3:12 or
greater, have long been favored by environmentally sensitive building
owners and architects who appreciate the roof’s aesthetic appeal, long
service life, low maintenance requirements, light weight and resistance to
wind.
Steep slope metal roofs, for example, can enhance the appearance of
virtually any building thanks, in large measure, to their receptivity to
various coatings and their ability to be formed into a wide variety of
shapes.
Because steep slope metal roofs accelerate the rate of water run-off, they
also reduce the likelihood of a build-up of debris, mold and mildew. At
the same time, they are less likely to experience staining from acid rain
or UV degradation than non-metal steep slope systems. The durability and
reliability of steep slope systems have led metal roof manufacturers to
typically warranty their products for 20 to 40 years.
Metal Roofs Contain at Least 25% Recycled
Content
The environmental aspects of metal roofs have also prompted building
owners and architects to take notice. For example, the use of steep slope
metal roofs can contribute to LEED credits, which are awarded to buildings
that use high recycled content and other “green” construction materials. A
typical steep slope metal roof contains at least 25% recycled content, and
at the end of its long, useful life is 100% recyclable.
In addition, “cool metal roofing” can significantly reduce a building’s
long-term energy use. Through the application of heat deflecting metal
coatings, energy costs can be reduced up to 40% of more, according to a
study conducted by Oak Ridge National Laboratory.
Steep slope metal roof systems typically weigh from 40 to 135 pounds per
100 square feet, making them among the lightest roofing products. A
lightweight system places fewer demands on a building’s structural support
system, an important consideration, especially when choosing a roof
material for buildings located in earthquake-prone areas.
Metal roof systems, with their interlocking or active fastening systems,
are also excellent options for steep roof applications in areas subject to
high winds. Metal systems are designed to meet the requirements of ASTM
E1592, UL 580, UL 1897 and other severe wind and uplift tests.
Steep slope metal roofing products come in a variety of materials,
including steel, aluminum, copper and zinc, as well as many colors,
textures and profiles. To ensure longer life, almost all metal roof
products are protected from the elements by high-performance, highly
durable coatings. Natural metal roof panels such as those made from zinc
and copper are often left unfinished because of the protective patina that
naturally occurs.
Two Categories of Steep Slope Metal Roofs
Steep slope roofs fall into two general categories – structural and
architectural. Steep slope structural roofs are generally applied over
open framing, but they can be installed just as well over a solid deck.
Structural systems come in various styles, including vertical standing
seam systems that are fastened to underlying purlins with hidden clips or
fastening flanges. Also available are corrugated or tile facsimile metal
roofs that are attached with exposed fasteners directly through the metal
roofing panels. These products overlap or interlock on their side and end
laps for a watertight fit.
Architectural steep slope roofs, unlike structural systems, always require
a solid substrate beneath them – typically plywood, oriented strand board,
concrete or a metal roof deck. Architectural roof panels also come in a
variety of styles, including standing seam, corrugated and tile profiles,
as well as a variety of horizontal panels. Most architectural metal roofs
are coated with a paint finish for added aesthetics.
Whether building owners or architects choose a structural or architectural
steep slope metal system, they can be assured that they will obtain an
environmentally sustainable product that will deliver exceptional
performance and curb appeal along with an attractive return on investment.
AESTHETICS
Today’s residential metal roofing comes in a wide variety of styles and
designs. When choosing a roof for your home, make sure that the product’s
design is appropriate for your home’s construction. Most metal roofs will
require solid decking (or, frequently, an existing shingle roof) and some
can be installed over lathe boards or over wood shingles on lathe. Some of
the more textured designs can even be installed over slate and asbestos
roofs. Next, choose a product with an appropriate appearance for your home
and neighborhood. You can find quality metal roofing with about any
appearance, whether it is standing seam or a facsimile of shake, slate,
tile, or standard shingles.
BASE METAL
Metal roofing is made from a wide variety of metals including galvanized
steel (which is zinc coating on carbon steel); galvalume steel (aluminum
and zinc coating on carbon steel); exotic steels such as terne and
stainless; aluminum; copper; and rolled zinc. Each metal has its own
properties and the type of metal used is sometimes dictated by the design
of the roofing panel. When making a wise investment in metal roofing,
consider all the available options. Many consumers assume that all metal
roofing is steel. However, most consumers would choose a permanently
rust-free aluminum car over a steel car of similar cost; it makes sense to
consider non-steel options for roofing as well.
PRODUCT DESIGN
While residential metal roofing is enjoying ever-increasing popularity,
some products are fairly new. As you evaluate various products, find out
how proven they are. Inquire about the systems’ flashings and accessories.
Look for proven, pre-formed accessories from the manufacturer. It is
particularly important to investigate how the valleys are installed. Look
for an “open” valley system which carries water on top of the metal panels
rather than a “closed” valley which carries water on hidden channels
beneath the panels. The hidden channels on “closed” valleys have been
known to clog with ice, snow, tree leaves, pine needles, and other debris,
causing water to spill over the channels and infiltrate the roof system.
UNDERLAYMENT
Metal roofing should be installed without dependence on the underlayment
beneath it. However, metal roofing can develop condensation on its
bottomside during certain climatic conditions. Therefore, it is
jeopardizing the durability of your roof system to use a product which
does not specify a quality underlayment such as 30-pound felt or one of
the new polyethylene-based underlayments. If you are in an area prone to
high humidity or salt air and fog, give special consideration to rust-free
metals such as aluminum, copper, and zinc. Weather conditions can create
the retention of condensation between the panels and the underlayment.
Particularly with steel products which rest on or near the substrate such
as standing seam, 5-V crimp, and low profile steel shingles, this
condensation can cause them to rust from underneath. Keep in mind that
failures with steel roofing occur from cut edges on the back side of the
metal and rarely from the front weather side.
WIND RESISTANCE
Because quality metal roof systems have panels which actively interlock
with each other, most metal roofs are known for their wind resistance. Be
sure to inquire what wind and uplift tests the systems you are considering
have undergone and passed. The better products have passed 150+ mph
wind-driven rain testing and/or UL 580 uplift testing exceeding 90 psf.
IMPACT RESISTANCE
Some insurance companies in select states are now offering premium
discounts to homeowners who choose roofs which have passed U.L. 2218
Impact Resistance testing. This test is done in four levels, with Class IV
being the most severe level. Particularly if you are in a hail-prone area,
it makes sense to find a product which has passed this test. Additionally,
some shingle facsimile products offer backer boards to provide extra
rigidity for roof areas subject to heavy foot traffic, falling tree limbs,
etc. Also, look for products warranted to not loose impact resistance with
age and to not chip due to hail or leak due to hail indentation or
perforation.
ENERGY EFFICIENCY
Metal roofing can help to reflect heat and keep homes naturally cooler in
warm weather. With steel, copper, and zinc roofing, energy efficiency is
achieved primarily when the metal is unpainted and treated to retain its
bright shininess, or when it is painted with a bright metallic or white
coating. Aluminum, however, inherently reflects radiant heat. Testing done
on aluminum roofing has shown it to be efficient even when painted in dark
colors. This makes aluminum desirable because most homeowners do not want
a white or metallic-looking roof.
FASTENING
Make sure that all fasteners (and other components) are of a metal which
is compatible with the roofing itself. Look for a system which has
concealed fasteners. Even with today’s neoprene washers and other methods
of keeping moisture out of exposed screw and nail holes, any exposed holes
through the panels are potential areas for water to enter the roofing
system. Any water which infiltrates can, with steel products, lead to
corrosion of the roofing and fasteners. Also, many metal roofing systems
use “clips” to fasten the panels rather than “through fasteners” which
attach the panels directly to the roof. The clips allow for expansion and
contraction of the metal. Otherwise, expansion and contraction might
“wallow-out” the fastener holes or cause the fasteners themselves to back
out of the roof. Clips are very important to standing seam panels which
sometimes have great length to them. They are also a factor with various
shingle and tile systems though some heavily textured products have an
inherent “accordion” effect which allows the metal to freely expand and
contract without trouble.
FINISH
Metal roofing, especially steel, is dependent upon a good coating for long
term durability. Most product warranty lengths are determined by a
combination of the metal and the coating which is used to produce that
product. There are many types of finishes available and, hence, a wide
range of quality. Finishes such as acrylics and siliconized polyesters are
good for commercial applications where periodic re-coating for a different
“look” occurs. Other finishes such as PVDF Hylar and Kynar coatings have
longer lives, making them ideal for residential applications. These
coatings are widely specified by architects who respect them for their
long lives and color retention. Look for a finish which has proven the
test of time. Look also for a finish which is warranted against such
things as fading, chalking, coming loose from the base metal, and chipping
due to impact.
PROPER INSTALLATION
As with any building product, success of the overall project is dependent
upon proper installation. Look for products which have detailed
installation instructions from the manufacturer. Look for a contractor who
has substantial experience with the product you are choosing or has
undergone installation training from the manufacturer. Metal roofs do not
all install in the same manner. Be sure to check references of past jobs
done by your installers and make sure that they have the proper licensing
and insurance to work on your home.
CONCLUSION
Metal roofing is a wise investment in your home. Today’s numerous product
offerings provide homeowners with a wide choice of looks and qualities. By
making the proper product and contractor selection, you will substantially
increase your home’s value, beauty, and comfort.
What is the cost comparison between a
metal roof and an asphalt shingle roof? The cost of a metal roof cannot be readily compared to asphalt for
various reasons. The condition and type of roof would have significant
bearing on the overall cost, as would the "profile" or style of metal
roofing you would choose. When considering metal vs. asphalt, you are
basically choosing between an investment (metal) over an expense
(asphalt).
Will a metal roof increase the likelihood of a lightning strike?
The answer to this question is "absolutely not". Although metal conducts
electricity, lightning is not drawn to it. It's unusual for lightning to
hit buildings. Lightning typically strikes the highest object in an area.
That's why it often strikes trees, power poles, antennas, and towers.
But if your home were hit by lightning, your metal roof would disperse the
energy safely through the structure. Since metal roofing isn't combustible
or flammable, it's a low risk and desirable roofing option where severe
weather is concerned -- especially for lightning.
Are metal roofs loud?
This may surprise you -- metal roofing is often quieter than an asphalt
shingle roof. When installed with solid sheathing, a metal roof on your
home will actually silence noise from rain, hail and bad weather better
than other roofing materials.
Is a metal roof hot? Metal reflects 70% of the sun's energy. This minimizes heat
retention and as a result less heat is transferred into the building's
structure. Further, 1985 research by the Florida Solar Energy
Center showed that metal experienced a 34% less heat gain than asphalt
shingles. Results indicate that metal roofing offers a similar effect on
R-11 insulation on top of the roof during sunny day conditions.
Will my metal roof rust? Today's metal roofing systems are built to last. Steel metal
roofing has a "metallic coating" made of either zinc or a combination of
zinc and aluminum. This metallic coating prevents rust from forming and is
bonded to the steel at the factory. Paint is then applied over the
metallic coating to provide the long-lasting color homeowners desire.
Will hail dent my metal roof? A metal roof can withstand decades of abuse from extreme weather
like hail, high winds, and heavy snow. In unusual cases, very large-sized
hail has been known to dent metal roofs during extremely heavy storms.
But, a typical hail storm will not dent your metal roof. Today's systems
also have a 120-mph wind rating (equal to an F2 tornado), meaning your
metal roof is also safe from wind gusts that can accompany hail storms.
Can I walk on my metal roof to clean gutters? Many people think you can't walk on a metal roof -- but the truth
is that you can safely walk any metal roof without damaging it. Before you
walk your roof, however, we recommend you talk to your installer first.
They will have the details on how to walk the roof.
Do I need to remove my existing roofing
material? One of the benefits of metal roofing is that it is lightweight,
which allows it to be installed over existing roofing material. However,
the answer to this question ultimately depends on your local building code
requirements and the condition of your current roof's substructure.
Nelson Bros., Inc.
4650 W. 120th Street
Alsip, Illinois 60803-2393
Phone: (708) 385-5815 Fax: (708) 371-2261
