Who’s responsible for weathertight integrity during a re-roof?

Responsibility for temporary waterproofing during the re-roofing process can be a complex issue. This is because it is likely that the roof is leaking before the contractor ever sets foot on the job. Should the contractor, by the act of commencing work, suddenly become responsible for leaks that existed before he got there? On the other hand, in the case of slope build up retrofit work. New attachments will be made which involve multitudes of penetrations through the existing membrane which were not there prior to the contractor performing his work. Should he be exonerated if they all leak during construction? Should the contractor be responsible for holes that he makes, and should the owner be responsible for pre-existing leaks? If so, who decides which is which?

It is highly advisable that this aspect of re-roofing is discussed prior to contract award,and then addressed contractually. The cleanest approach is a specification and contract provision which states that temporary repairs to pre-existing leaks are included in the scope of work, and to be performed by the contractor upon commencement of the project. This eliminates disputes if during construction there are leaks. It also, however may add cost to the project , which would otherwise be avoided. An alternative is that the contractor is responsible only for new leaks which he creates as a result of the re-roofing work. If the nature of the work is such that waterproofing during construction is either not possible or not included in the scope of work, then the contractor should be sure to so state in the contract.

In lieu of contractual provisions designating responsibility, the owner would continue to be responsible for pre-existing conditions, and the contractor would generally be responsible for any new conditions which arise due to his performance of the work. It is also normally understood by the owner that there are risks associated with a re-roofing project, and the contractor may not be able to guarantee complete freedom from leakage during the course of work. He would however, always have a responsibility to take reasonable percautions to waterproof his construction during the course of the work, and to minimize the risk of leak potential.

Because systems and attachment methods vary, as do existing roof and deck conditions, temporary waterproofing techniques also vary.
My next article will address temporary waterproofing techniques. In the mean time should you have any questions or concerns regarding this posting or other roofing issues please call 888-321-9630 or visit www.drexmet.com
Posted by: Bill Dooley ASCE, CSI
Director of Architectural Sales Drexel Metals, Inc.

Roof Penetration, how best to handle them and keep your SSR weathertight.

Round penetrations are best handled with EPDM (
ethylene propylene diene monomer) rubber pipe flashings with a moldable
aluminum compression strip laminated to there base. These are quite
available from multiple sources and in a variety of sizes. Black rubber
is strongly preferred to other colors due to its superior ultraviolet
radiation resistance. The hole for the pipe through the metal panel
should be cut oversized to allow for the panel’s thermal movement. Butyl
tape should be used between flashing base and metal panel, and a small
fillet bead of polyurethane can be used as well, if desired, neatly
finger-wiped around the base. Both types of sealant are compatible with
EPDM. Screws or watertight bulb rivets should be used to secure the
base, spaced about two inches on center. The top of the rubber flashing
is cut a bit smaller than the pipes outer diameter for a snug, forced
fit. In snow country, the addition of a stainless steel drawband to
cinch the rubber to the pipe is a wise addition to prevent the peel back
of the cone-shaped rubber under the weight of roof snow.
Although the base of these flashings is moldable and can creep part way
up the slope of a trapezoidal rib, care should always be taken that the
base of the pipe flashing does not intersect the seam itself. It is also
important that waster can freely drain around it. In the case of
vertical-rib panel profiles, the base cannot contact the rib are at all.
If necessary, these criteria may mean closely coordinating such
locations with mechanical contractors. If such a location does interfere
with a panel seam, it is best to relocate the pipe. Alternatively, a
pre-formed metal curb must be employed. This is also true when the pipe
diameter is such that the base of the flashing would exceed the panel’s
flat width dimension.
In most cases, prefabricated equipment curbs used in conjunction with
roof mounted mechanical units, skylights or smoke vents are of
“floating” design. As the roof moves thermally, the curb moves with it.
It is imperative that these thermal movement characteristics be
preserved with the installation of such a unit. Often, sub-framing
components are used beneath such a curb to help distribute its weight.
They also provide a termination point for insullation, or can serve as a
back-up compression plate for the marriage of the curb flange to the
roof panel. Different curb designs and manufactures utilize different
shaped components and proprietary details to accomplish these
objectives. It is important for the installer to be sure that when these
various sub-framing components are attached to the panels and curb
flange, they are not also attached to the building structure. The
reciprocal statement is also true. Attachment of certain sub-framing
components to the structure is permissible and sometimes necessary, but
when doing so, the same member should not be attached to the panels.
In some cases, a prefabricated curb is of a design that it does not
actually carry th weight of the rooftop unit. In such cases, the curb is
serving only as a flashing component, although it may still utilize
some of the sub-framing components mentioned above. When the curb serves
only as a flashing, then the unit is stationary, and rigidly attached
to the building structure in some other fashion. Such is often the case
with larger, heavier units. The unit is sometimes mounted on a separate
structural curb, which is rigidly anchored to the structure beneath the
roof. In other cases, the unit may be mounted on a structural steel
frame above the roof.The frame is in turn supported by steel pipe which
extends upward through the roof from the structure below. In either
case, the curb flashing will be tied to the panels, and move thermally
while the unit (and/or support structure) will not. This means the curb
flashing must be sized somewhat larger than the unit or duct that it
surrounds to allow differential thermal movement between the two. The
space allowed between the curb flashing and the unit, or duct is then
closed off with sheet metal flashings, or with flexible membrane
flashings and sealant.
In many instances involving skylights or smoke vents, the exact curb
location is not critical. The installer merely coordinates an
approximate location with architectural drawings, and locates the curb
for convenience with respect to panel layout and geometry. In other
cases, the exact location of a curb (and roof opening) may be critical
to a fraction of an inch. Depending upon the curb style, it may have a
predetermined point of integration with panel ribs. Additionally, it
should be ordered and delivered to the job site well in advance of the
roofing crew reaching its location on the roof.
In any case, where other trades are involved with the installation, the
same must be closely consulted to effect a successful installation. When
frame mounted equipment above the roof is used, for instance, it will
be much easier to flash a round pipe support through the roof than a
square or I-beam shape. The roofing and flashing work around those
supports will be much easier to accomplish before horizontal components
of the support frame are added. The installer who is on guard for such
small details and coordinates work closely and carefully with these
other trades can make the job not only easier for himself, but also for
others who follow.
Rules of sealants as earlier posted on 8-18-12 “Sealant Applications and
Placement” should be carefully followed at curb locations. Well placed
sealant is the key, and more is not necessarily better. At some
curb-to-panel rib and seam interfaces, it may be necessary to supplement
butyl tapes with butyl tube grade as well, in order to achieve good
sealant flow and a positive seal. At some junctures, it may be
advantageous to filley and finish the joint with one part polyurethane,
outside the primary butyl seal. Such a fillet is done as a finishing
touch, such as a crack filler, and never relied upon as a primary seal.
Because of the numerous types of roof top equipment and different types
of installation requirements, its always best to contact a professional
who’s knowledgeable in roof top penetrations and equipment installation.
To learn more about roof top flashings call 888-321-9630 or visit
www.drexmet.com
Posted by: Bill Dooley ASCE, CSI
Director of Architectural Sales Drexel Metals, Inc.

Choosing a substrate for your standing seam roof system.

Metal standing seam roof (SSR) and through fastened roof panel systems can be supported on either open framing or structural decking. The considerations and reason for one system over the other is what I’ll attempt to explain in this posting.
Open Framing:
During the early days of metal building development, roof and wall sheets were attached to the secondary framing by means of through-fastened screws. This method of attachment provided a positive, non-moving connection between the panel and its underlying support. The rigidity of the panels with this type of system provides stabilization to the secondary structural system. The purlins and girts are therefore designed with the assumption that the exterior flange is fully supported.
As the nature of wind loading was better understood, questions arose concerning the structural stability of the inside flange of the purlin and girts, especially under uplift loads. In response to these concerns, the American Iron and Steel Institute (AISI) developed the provision for determining the flexural design strength for members when the tension flange is fully supported and the compression flange is not supported.
With the introduction of panel clip attached standing seam roof systems, the question has been raised whether these systems do, in fact, provide the assumed positive support to the secondary system. Sliding clips were developed to allow panels to move relative to their secondary support. If this type of movement is allowed, then it is only logical that the secondary member is allowed to translate under load. To measure the restraints provided by the cladding system to the secondary members, the “Base Test Method for Purlins Supporting a Standing Seam Roof System” was developed by AISI. It is the responsibility of the cold-formed steel designer to incorporate these factors into the design in accordance with the AISI specifications.

Structural Deck:
Metal roof deck is the structural component that provides support and mounting surface for roof building materials (i.e. insulation, membrane, modified bitumen, and SSR panels). This deck provides resistance to the positive and negative building loads. The most common deck material is carbon steel with a galvanized coating.

Wood Substrates:
Plywood is a popular construction material for both residential and non-residential roof sheathing. Plywood is made from thin plies that are shaved from logs. These plies are then laminated together using heat, pressure and glue with the grains aligned perpendicular to each other to provide strength from both directions. This is because wood has its greatest strength along the grain. The proper rating and thickness depends on the design roof loads and spacing of the supporting framing. The size and spacing of the nails used to attach the plywood to the supporting framing depend on the design roof loads and whether the roof deck is designed to function as a diaphragm. The selection of the size and spacing of the nails must be made by the design engineer. The minimum recommended thickness for plywood in roofing applications is 15/32 inches thick.

Oriented Strand Board (OSB), like plywood is often used in both residential and non-residential roof sheathing applications. OSB is composed of rectangular-shaped wood strands, which are cross-oriented, compressed and glued together with waterproof adhesives. The cross orientation of the strands is what gives OSB it’s strength and rigidity in both directions. The edge of OSB panels are often treated to retard any moisture penetration. As with plywood, the selection of the size and spacing of the nails must be made by the design engineer. The minimum recommended thickness for OSB in roofing applications is 15/32 inches thick.

Wood Plank Decks:
Wood plank decks are primarily selected for their appearance from the inside of the building. They may be made from solid-sawn lumber or from laminated lumber. The solid sawn planks may have square edges, ship lapped edges, or tongue-and-groove edges. The thickness of the planks depend on the roof design loads, the spacing of the supporting framing, and the species and grade of the wood used. The size and spacing of the nails is determined by the design engineer.

Cementitious Wood Fiber Deck Board:
Cementitious wood fiber deck panels are composed of aspen wood fibers bonded with hydraulic cement, and formed into a structural lightweight panel by a continuous process under heat and pressure. The physical characteristics obtained by this process include insulation, sound absorption, and a decorative textured interior finish, and by itself forms a limited combustible roof deck system. These panels can be bonded to urethane foams or naiable OSB to form composite roof deck panels.

For more information regarding the selection of, and or specifications for a roof substrate contact Drexel Metals Inc. at 1-888-321-9630.
Or visit us on the web at www.drexmet.com

Posted by Bill Dooley, ASCE, CSI
Director of Architectural Sales

Cool Roof and its contribution towards reduction of heat island effect and energy consumption.

Architectural professionals have embraced the concept of sustainability and energy conservation in their building designs. The U. S. Green Building Council’s LEED program is an economic and environmental standard for measuring construction products conducive to green building. The LEED program uses a point system to establish an overall building performance. Rating points are given for various sustainable features in five categories: building site; water efficiency; energy; materials; and indoor environmental quality.
Metal roofing products are an important element to building environmentally sound structures. Metals energy efficiency, high recycled content and total recyclability qualify it for points in the LEED rating program.
Urban areas produce what is called the heat island effect, with dark heat absorbing roofs being a major contributor to this heat gain. The temperatures in the air above heat absorbing roofs can be as much as 12 degrees Fahrenheit warmer than surrounding undeveloped areas. This elevation in temperature leads to higher air conditioning costs, and unhealthy levels of ozone and smog. Reduction of heat island effect will lessen impact on human and wildlife habitat as well as reduce energy usage.
Cool Roofs can help in the reduction of heat island effect. Cool roof materials have two important surface properties: a high solar reflectance and a high thermal emittance. Solar reflectance is a measure of the ability of a surface material to reflect sunlight. This includes the visible, infrared, and ultraviolet wavelengths on a scale of 0 to 1. Solar reflectance is also called “albedo.” Thermal emittance is defined as the percentage of energy a material can radiate away after it is absorbed. Solar emittance of a material refers to its ability to release absorbed heat. Scientists use a number between 0 and 1, or 0% and 100%, to express emittance. Cool roofs reflect heat well across the entire solar spectrum, especially in the infrared and visible wavelengths. The less solar radiation materials absorb, the cooler they are. In addition to absorbing less heat, cool roofing materials radiate away any absorbed heat.

Energy Star’s roof product program has a cool roof specification for low slope and sloped roofs. Low slope roofs, must have a average initial albedo of at least 0.65. Steep sloped roofs must have an average initial albedo of 0.25 or more. Department of Energy research has shown that one additional percent of reflectivity in a coating will reduce the roof temperature on average by one degree. When heat is reflected away from buildings, smog is reduced, energy costs are lowered and the life expectancy of the roof will be increased due to less expansion and contraction.

New infrared reflective pigments incorporated into paints used on architectural metal roofing products allow them to achieve higher reflectivity values, even in darker colors. This improved reflectivity allows designers to select a sustainable roof without have to sacrifice color choices and the reduction in heat energy means less demand for air conditioning and lower energy usage.

Whereas emissive and reflective properties of a roof are important design considerations, there other areas to investigate in achieving a energy efficient roofing system. Insulation, attic ventilation, roof slopes, and roof orientation render a huge roll in building efficiency.

Drexel Metals Inc. is an industry leader in  engineered metal roofing systems. Drexel Metals welcome any questions you may have regarding Cool Roofs or any other topic involving metal roofing. Visit us at www.drexmet.com, to review our complete product offering.

by: Bill Dooley ASCE, CSI. Director of Architectural Sales

“Fundamentals of Coil Coating”

This posting will focus on exploring the history, features and benefits of metal roof coatings. Since the beginning of metal panel usage the industry has used a number of different types of coating systems. Early on, painting of panels was done as a way to protect the metal from corroding. With the creation of Galvalume, Aluminized Steel, and Galvanized alloy coatings, painting was no longer needed for corrosion protection. The painted panels we use today still protect the panels core material but they have additional benefits that now make the metal panel the best choice for residential and commercial roof coverings. Aside from offering a wide range of colors to choose from and being more durable and fade resistant today’s painted panels offer superior reflective and emissive properties. In the architectural world, metal roofing systems are often the feature elevation element adding shape and color to the building design. However for years there has been concerns that the paint finish would dull out making the building look old before its time. A paint needed to be developed that would holdup against ultraviolet radiation, acid rain and other adverse atmospheric conditions.

The “High Performance”painted metal panels we see today are the byproduct of 60 years of development in the coil coating industry. Prior to the development of the “Paint Line” field applied paint was the norm in coating mil finished roof and wall panels. The invention of the paint line elevated the production level and enhanced the quality of painted coil products. In the following years, the coating industry developed a number of different types of paint material for coating applications including polyesters, siliconized polyesters, acrylics, polyurethane and fluoropolymers.

Coatings are divided into categories. Inorganic coatings typically found on ceramic products have a brittle film and require a thick substrate. Organic coatings are used on metal coil and contain carbon materials. Organic paints have three basic components. Resin binds the pigment and forms a barrier over the substrate. Pigment absorbs the ultraviolet radiation and is the ingredient that creates the color. Solvent is the transfer device used to disperse the resin and pigment. The solvent evaporates during the curing process. Paints generally are identified by resin types such as latex, urethane, polyester, siliconized, etc.

There are three traditional resins used in the coil coating industry. Polyesters are thought of as the lesser quality finish due to chalking when exposed to sunlight. However polyesters offer a hard, scratch resistant finish and a wide range of gloss. Siliconized also known as siliconized polyesters or silicone protected. Siliconized polyesters improved polyester by increasing chalk resistance, better gloss retention however had a tendency to fade. Polyvinyl idene fluoride PVDF is known as the premium resin in coil coating. PVDF includes teflon and halar ingredients. PVDF resin has superior gloss retention and chalk resistance. It is softer than polyester meaning it is susceptible to scratch, but this softness allows the film to be highly formable without risk of cracking making this the ideal choice coating for hydrostatic type roof systems.

Drexel Metals Inc. is a leader in the  painted metal standing seam industry. In a future posting we will visit new infrared reflective pigments incorporated into paints used on architectural metal products allowing them to achieve higher reflectivity values, without sacrificing color choices. In the mean time should you have any questions regarding coatings or any other metal roofing concerns please visit our website www.drexmet.com

Posted by Bill Dooley ASCE, CSI  Director of Architectural Sales

Maintenance and cleaning proceedures for your roof.

Items on your “Standing Seam Metal Roof”, just as items inside your structure occasionally need attention to keep them in good condition. The purpose of this article is to offer suggestions of recommended maintenance steps designed to keep your roof in proper working condition.
Mill finished or painted roofing and siding should be washed with soap and water as necessary to maintain appearance. A 5% solution of commonly used commercial and industrial detergents will not harm your panel surface. Always rinse thoroughly with water. Do not use wire brushes, steel wool, sandpaper, abrasives or similar cleaning tools which will mechanically abrade the coating surface. Use a cloth, sponge or a soft bristle brush for application. Cleaning should be done in the shade or on a mildly cloudy day.
Once a year inspect the panels for rust staining. Should any rust stain be found, determine the source, (such as steel filings from drilling) and remove them. The rust stain can generally be cleaned off with one of the following: soap and water, mineral spirits, “Soft Scrub”, or a mild polishing compound as used on a automobile finish.
Scratches to the paint should be repaired using a “Drexmet Paint Pen”. The Drexmet Paint Pen is available in all Drexel Metals standard non-metallic colors. If the scratched area has not rusted, the paint may be applied without surface preparation. If the area is rusted, remove the rust, prime the affected area and touch up with the color matched Drexmet Paint Pen. Primer and paint pens are available from your authorized DM- ARM member.
Mildew can be expected in areas of high humidity. Mildew is more of an appearance problem than an actual threat to the paint finish. Mildew can be removed by using a basic solution of the following: 1/3 cup detergent, 2/3 cup trisodium phosphate (TSP), 1 qt. sodium hypochloride (5% solution), 3 qts. water. Rinse with clean water immediately after use.
Non water soluble deposits on Kynar finishes may be remover by use of solvents on the Kynar paint finish. Alcohols, petroleum solvents and aromatic cleaners may be used however contact time to less than 5 minutes. Test a small sample area before venturing into a larger surface. Do not use acetone paint remover, Methyl Ethyl Ketone, or Methyl Isobutyl Ketone on Kynar surfaces. Continued contact with these products could result in loss of gloss or other blemishes detrimental to the aesthetics of the roof or siding surfaces.
Precautions should be made to prevent sealants from getting on the painted surface of your panels as the sealant may be difficult to remove. Sealant should be removed promptly with a solvent such as alcohol or a naphtha type solvent. Caution needs to be taken to not damage the sealants that installed into panel joints. Clean all debris from gutters and downspouts as requires. The frequency required is dependent on the building’s surroundings.
Should your roofing system have roof mounted mechanical equipment the roof curbs need to be inspected. Vibration from a mechanical unit can cause water leakage around a roof curb. Should this occur, check the sealant and fasteners around the curb. Any loose fasteners should be tightened or replaced with the next larger size. Any sealant or mastic that has deteriorated should be removed and replaced with new.
Roof traffic is a leading cause of roof leaks. If routine traffic is unavoidable, have your Drexel Metals authorized dealer install a walkway system designed for use with your roof panel. When walking on the roof is required: Avoid stepping on ridge caps. Avoid stepping on lap joints in panels and flashings. Avoid walking near roof curbs or other roof penetrations. Avoid stepping on panel ribs. Do not step in or on gutters. Do not step on or near skylights.
While bushes and trees enhance the appearance of any building, their contact with panel surfaces can produce scratches which will eventually cause problems. Keep bushes and tress trimmed back from the panel surfaces.
This article was prepared by Bill Dooley ASCE, CSI. Director of Architectural Sales Drexel Metals. Bill can be reached at 407-403-4130 0r bdooley@drexmet.com.
Visit Drexel Metals @ www.drexmet.com

Trust Not The Truss

When your flat roof finally fails (patches upon patches type failure) its not just the roof membrane that has failed, the total roofing system has failed. Your insulation most likely is saturated, and the additional water weight in the saturated insulation may have caused your roof deck to deflect. If so this deflection has left your roof surface having ups and downs (undulations). Depending upon the type of roof system you choose for your replacement roof these undulations can cause your roofing contractor additional labor and materials, meaning additional costs to you.

Improving your buildings appearance is an important consideration in your selection of a re-roofing system. You’ve also decided that getting as much heating and cooling cost savings while being a responsible “Green Citizen” is another factor to consider in your selection process. Installing a metal standing seam roof is the ideal solution for you.
Designing retrofit slope build up framing for the new standing seam metal roofing system and associated components is the next step. As a first thought a light gauge truss appears to be an easy solution to your creating slope for your new SSR. Build the trusses on the ground, and raise them to the roof for attachment. What could be easier? A post and beam design is easier, neater and less costly to install, and here’s why. Remember when we inspected our roof and determined it had failed we observed that the roof surface was no longer a flat smooth surface. It had numerous raised patches and undulations. This condition would require that the installing contractor would have to either dig a channel or shim up to the bottom cord of the truss throughout the entire length of each truss set. This step is critical in that the truss needs to be set properly to insure that the fastening of the bottom cord of truss be per design and that the elevation of the top cord be level with all of the other trusses. I said using a post and beam design was easier and here’s why.
The three major components of the system are a angle base clip, a post and a top purlin. The angle clip is set and fastened through the membrane into the sub structural member. A post is cut to a measured height that is equal to the height required for its location and fastened to the base angle. A continuous length purlin is set and fastened to the post. No digging, no shimming, no wasted time or repairs repairing the dug out membrane. Hence the Trust not the truss, its not what it had appeared to be when we first thought of it.
Everything else from this point forward remains the same for either system. Install cross and transverse bracing. Install blanket insulation if desired. Install Drexel Metals DM-200 roof panels and trim.
For more information regarding converting a flat roof into a long life, energy efficient, attractive standing seam roof contact a Drexel Metals representative at 888-321-9630 or visit us at www.drexmet.com
This article produced by Bill Dooley ASCE, CSI Director of Architectural Sales, Drexel Metals Inc.