“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 http://www.drexmet.com

Posted by Bill Dooley ASCE, CSI  Director of Architectural Sales

Tips regarding bare metal finishes, paint finishes, and the handling and repair of them.

Natural finishes of various metals have differing characteristics. Copper is bright and polished when new, but quickly oxidizes to a deep brown. Fingerprints and surface scratches are quite conspicuous at first, but do the finish no harm, because they become invisible as the metal weathers. Still, it is customary when working with copper to wear cotton gloves to minimize fingerprints during installation. The material can be easily spot cleaned with an abrasive pad , or metal cleaner/polish. In contrast, bare “Galvalume” steel will retain fingerprinting indefinitely, permanently staining the finish. Most other staining from foot traffic, power cords, tools and such will also cause indelible stains. “Galvalume” should never be spot cleaned with any kind of abrasive material, nor any cleaners that contain strong alkali or acid. Pressure washing and mild soapy solutions are the sole remedies. “WD-40” and similar solvents, which clean most metals quite satisfactorily, will cause permanent staining of “Galvalume”. Fingerprinting will be minimized if installers wear gloves. Use of an acrylic coated material (“Galvalume Plus” “Zincalume Plus”) will be more effective in minimizing the effect of installation staining, than anything else the installer can do.
Other metals and finishes all have their own idiosyncrasies, which should be learned from their manufacturers or distributors.
Some paint types are more fragile than others, and often painted steel and aluminum surfaces are protected with a strippable plastic film. This film is applied during coil processing, and intended to help protect the finish during transit and installation. It is critical that the installer strip this film prior to prolonged exposure to sunlight, as it will become brittle and very difficult to remove after such exposure. Care should always be exercised in handling painted finishes and foot traffic should be minimized or eliminated, or surface scratching is almost certain to result.
In the event of surface scratching during installation, touch-up paints are usually made available by the panel system manufacturer. Discretion should be exercised in their use. Because they are often different resin types than the coil-coated material, they will weather quite differently. Although the color match may be perfect at the time of installation, the air-dried paint will fade more quickly and may be unsightly after a number of years. For this reason, they should only be used in the event of a severe scratch, and then applied only to the scratch itself, with a small artist’s brush or a “paint pen”. Remember that from an aesthetic standpoint, over use of touch up paint will be much more conspicuous than the untouched scratch in several years time. If surface scratching is excessive, the material should be replaced, rather than touch-up painted.

The same principals as stated above apply to the painting of other components to match prefinished metal panels and flashings. Most such paint applications will have very different weathering effects than the factory finishes, and will mismatch in a few years, even when the initial match is perfect. Whenever possible, use prefinished sheet metal flat sheets to color match other components and roof accessories, rather than air dried paints. Often this practice is also more economical, as the cost of field painting can be substantial.

Occasionally, a paint finish is used which is “directional”. Which means that the finish will reflect light differently from different angles, giving a different appearance. Metal flake finishes are usually directional. The installer must exercise extreme caution during installation of such finishes to be sure that the direction of the finish is consistent. Reversal of the finish direction may not be obvious at first, but quite consspicuous when viewed at a distance, and under different lighting conditions. Normally “directional” finishes are marked with arrows printed on the non-weather side so that installers can keep them consistent in installed direction.

It was discussed above that in the event that touch-up of the paint is required that either an small artist’s brush or a paint pen be used. Drexel Metals Inc. was the first to introduce such a tool (paint pen) for touch-up for metal roofs.
The Drexmet Paint Pen is the first of its kind in the industry and utilizes a Fluoropolymer Air Dry System. Developed with the contractor in mind, the Drexmet Paint Pen is the lower cost and more efficient alternative to other touch up systems. The Drexmet Paint Pen allows contractors to quickly and easily touch-up scratches on the metal panels, saving time, money and future potential problems. No waste, no spillage, no brushes, no cleanup. The Drexmet Paint Pen is available in all of our 30 stock colors and has a shelf life of up to six years.
For more information regarding paint finishes or any questions concerning standing seam metal roofing systems contact Drexel Metals at 888-321-9630 or visit us at http://www.drexmet.com
This article and others in the drexelmetalsretrofitroofing.wordpress.com Blog are written by
Bill Dooley, ASCE, CSI
Director of Architecture Sales Drexel Metals Inc.

Sealant Applications and Placement

Proper execution of field applied sealants is vital to the finished weather integrity of any low slope, hydrostatic roof system. In principal, each panel is gasketed 360 degrees around its perimeter. Along the sideseams, sealant is mechanically applied by the roll forming machine. At all other panel termination points, it is the duty of the installer to apply sealant beads that marry into and establish the continuity of this gasketed seal between factory applied sealant beads. These sealant locations and procedures are described in the manufacture’s installation manual. Each is critical, and must be followed. Some of the usual areas for critical sealant applications include:

Eave: Panel to eave flashing or gutter. Panel rib closure to eave flashing or gutter. Panel to rib closure. Panel seam end.
Endlap: Panel flat to panel flat. Panel rib area to panel rib area (and into seam)
Ridge: Panel to closure components. Closure component to ridge flashing.
Terminations: Panel to flashing at rakes or gables. Panel to flashing at longitudinal expansion joints. Panel to flashing at parapet conditions.
Penetrations: Panel and ribs to preformed curbs. Panel and ribs to other roof penetrations.
Flashings: Laps of adjacent flashing segments. Flashings to panels.

In addition to the above, in some cases, panel attachment clips require wetting with sealant. This is because the clip tab interrupts the seam sealant, creating a dry joint between clip and male seam component. Some clips do not interrupt the seam sealant, and some manufactures do not deem clip wetting necessary. The manufacturer will note such a requirement in the installation manual, if clip wetting is necessary. If so specified, it is another critical aspect of installation.

Sealants are used within low slope, hydrostatic roof systems for several reasons, among them, to protect joints should they become periodically submersed (pressure); and to prevent capillary action from pulling moisture through the system. These are demanding circumstances for any joint. In order to perform and not leak, sealant continuity is the primary concern. The installer must be sure to “marry” (or meld) adjacent sealant beads one to the next.
For instance, when using vertical rib panels, the panel is normally sealed at the eave, through its flat area to the eave flashing, gutter leg or some other flashing component. This is usually done with a butyl tape. Of course, sealant seals the top of the seam. Where the seam terminates (at the panel end) there is a discontinuity of sealant in the vertical portion of the seam between the seal and the tape seal at the panel flat. It is not only vital that the installer seals the two rib surfaces together, but that he marry this vertical bead of sealant to both the eave tape, and the seam sealant. When properly done, this will create a continuous gasketed seal at the eave area.

One of the most frequent mistakes made by installers of low slope roofing, is the misplacement of sealant relative to related mechanical fasteners. In lap joints that do not involve cinching hardware, it is important that the fastener is on the “dry” side of the sealant, or alternatively through the sealant. The screw hole in the upper lapping component is sealed by the rubber washer on the screw. The hole in the lower joint component is sealed only by the joint sealant. If that sealant is upslope of the hole, then moisture drawn into the joint will migrate down the screw shank and drip into the building interior.
On joints where cinching hardware is used, the fastener must be through the sealant bead. Such a joint relies upon the sealant to swell into the threads of the screw and the upper joint component as it is tightened. The washer beneath the screw head is really of no effect, since the joint between cinch hardware and upper joint component is dry. Once installed, removal of a screw in such a joint is risky as the sealant may not “re-bed” upon reinstallation of the screw. Installing a small patch of sealant tape between the cinch hardware and the upper joint component can restore weathertightness in such a case.

It is rarely acceptable practice to use externally applied sealants on low slope, hydrostatic roofing. No sealant will have the same life expectancy as the roof material when exposed to ultra-violet light from the sun. Additionally, precipitation and particulate matter will continually abrade, wear away and deteriorate exposed sealants. In freezing climates, ice and snow will pull and tug at external sealants until their adhesion is lost and they peel from the roof.

Because of the numerous types of sealants on the market and the different types of materials they are used upon, its always best to contact a professional who’s knowledgeable in sealant application. To learn more about sealants and panel installation call 888-321-9630 or visit http://www.drexmet.com
By: Bill Dooley ASCE, CSI.
Director of Architectural Sales Drexel Metals Inc.

Job Site Manufacturing

Job site manufacturing finally has gained the industry respect it so rightly deserves.

Manufacturing roof and wall  panel products on site eliminates the delivery, unloading and shake-out issues that come with factory preformed panel orders. Job site manufacturing (JSM) virtually eliminate all bulky site storage issues. JSM frees up that storage space and gives all construction trades more room for vehicles, equipment and area to perform their work. With factory preformed panels a contractor must move the panels from a storage site to the building then lift them up to the roof. With JSM the contractor can position the roll forming machine where the work needs to be done and run the panels to the lengths the project requires. Manufacturing on site at either ground level or roof level eliminates delivery and handling problems, and increases the installation process. JSM also means that panel lengths of more than 300+ l.f. can be installed without any swedges.

Lets visit these Job Site Manufacturing benefits:   No costly crating and shipping of panels. No potential shipping and handling damage, the more you handle the panels the more potential for damage. Less waste, manufacture each panel to the exact length. Manufacture your panels to any length. No need to install expensive swedge end laps.

Are you a SSR roofing installer with out portable roll forming capability? Contact Drexel Metals Inc. and ask for information regarding our DM-ARM program. Visit us at http://www.drexmet.com or call toll free 888-321-9630

Drexel Metals offers a common sense approach to storm related power outage solution.

Drexel Metals Inc.

If you have solar-powered lights outside your home, these can be brought indoors at night to use if you have lost electricity. Depending upon the number of lights you might be able to light your entire home. The solar-powered light should be able to light your home for the entire night. Put them back in the yard the next morning to “re-charge” and use again the next evening if needed.

Drexel Metals’ Metal Roof Systems…Tornado Proof vs Tornado Resistant?

Is it possible to build a “tornado-proof” home? For a home to be “tornado-proof” the walls, roof, windows, doors and garage door would have to be “missile-resistant” to halt penetration by flying debris, and the connections of the structural elements would need to be capable of withstanding 250 mph wind pressures. In most cases this type of design consideration would be a drain on a construction budget. A more reasonable goal would be to design towards a “tornado resistant” structure. Tornado’s are rated on scale called a “Enhanced Fujita” scale, 0 thru 5. An EF0 is measured winds 65-85 mph. EF1 winds are 86 – 110 mph. EF2 winds 111 – 135 mph. EF3 136 – 165 mph. EF4 166 – 200 mph. EF5 over 200 mph. The best defenses against a tornado is an underground cellar. If an in ground shelter is not practical, improving the most vulnerable parts of your home is the next best option. Those vulnerable parts are openings such as windows and doors. Garage doors are an expecially weak link in a home when it comes to strong winds. If your garage door fails due to high winds you get a increase of internal pressure that can blow out walls and roofs. A wind rated garage door is one of the better investments you can make. Double-pane windows seem to fare reasonably well in tornadoes. A top quality roof is also paramount to the structures success in holding up to high winds. Poorly installed roofs can rip off in high winds exposing the structure to an increase in internal pressures, as discussed above can blow out walls, windows and cause a total lose of structure. As you can see it is possible to up grade your existing structure to withstand weaker tornadic winds and most hurricanes winds at a reasonable cost.

Drexel Metals Inc. is available to offer you design solutions regarding high winds, weather tightness, solar generation, thermo-solar and rain water harvesting.

By: Bill Dooley ASCE, CSI

For more information visit http://www.drexelmetals.com

Building a slope build up framing system – Drexel Metals offers a helpful solution.

Do you know you can grow your business in today’s economy? Increase opportunities, create jobs, and add valuable skills to your company.

Tap into the conventional and flat roof market. Using a roofing system that can be designed with consideration of LEED compliance, sustainable and renewable energy, as well as high material recyclable content.

A slope build up framing design with a standing seam roof (SSR) can do that and more to capture that re-roofing project.

First it must be determined if your existing roof can support the new load. The building must be capable of supporting the increased load and its structural adequacy should be verified. In most cases the cost to inspect and certify the structural integrity of the roof is minimal.

Next you must prepare the existing flat roof deck to accept the sub-structural supports. If your roof has a gravel ballast cover you should consider removing as much of the gravel as possible, as the spec for ballast cover is normally 6 lbs. per sq. ft. coverage. If you manage to get one half of the gravel removed the reduction in weight will be equal to the total additional load of the new framing and roof panels. It is a good idea to take core samples of your roof in a few areas to determine if the existing membranes are holding moisture. If excessive moisture is found it will be necessary for you to incorporate a venting method into your new roof design. It may be necessary to cut out wet or soft membrane and insulation to establish a firm bearing surface for the framing.

Configuration. Now you must decide how you want your new roof to look. Gable, hip, any roof elements such as dormers and also what do you want your roof pitch to be? When this has been determined, its time to start laying out/designing your framing system. With the information you received while doing your structural analysis you have knowledge of your deck and secondary member orientation, spacing and attachment methods. This is important as we will be attaching our new structural framing thru the existing roof membrane and decking into those secondary members.

Design considerations. Normal support spacing for a structural roof panel is five feet. The panels (particularly 22 gage) in many instances can carry uniform design loads for greater spans. Minimum roof slope is 1/4:12 care must be taken with slopes less than 1/2:12 to make sure structural’s are placed and designed to prevent undue deflection, and even slope is maintained throughout. It will usually be necessary to fasten the re-roof framing to the existing joist or other secondary structural. Deck fastening to the structural is usually not satisfactory. However some decks such as concrete construction may permit fastening to the deck.

Post & Beam. There are two types of sub-structural support systems. Post and beam and sleeper. The sleeper system is a continuous spanning member that is used for low slope applications where your existing deck has a minimal (1/4:12) slope and no greater pitch is desired. It is used for your top chord connection. Or it can be a transverse sub-structural member used to transfer sleeper or post loads to existing framing. Post and beam construction is used for requirements of greater slope than your existing roof deck provides. Post and beam is comprised of the following: A base component. The base can be either a 6″ angle plate or a continuous length depending on the economics of insulation. An extension post. The extension post can be angle, cee or zee shaped, it is used to transfer loads to the base angle as well as establish height. Bracing. Bracing in the form of strapping is utilized parallel to the roof slope and perpendicular to the roof slope. This bracing is designed to stabilize the support structural’s as well as brace it against wind and design loads. Top chord support (purlin).This is used to support “Drexel 200 SS” roof panel. Design of this member is based upon loads, spacing between top chord members and spacing between the extension posts.

Now that you have built the base to install an attractive longer lasting SSR, are there any other considerations you might propose to your client?

Insulation and vapor retarders. Earlier I talked about saturated roof decks and membranes and how it might be necessary to cut into the membrane to let the roofing materials dry out. In re-roofing applications the existing vapor retarder and/or existing roof membrane may serve as an adequate vapor retarder. The effectiveness of the later will be voided if cut or removed for the purpose of drying of the roof membranes. If no insulation is being added a vapor retarder should not be installed. Remember now is the time to consider your options for your roofs performance other than weather tightness. Adding blanket insulation at this time is a very inexpensive proposition that will ROI immediately upon completion of the roof work. Insulation can be easily added in the cavity created between the old roof and the new re-roof, or installed over the top chord of purlin. an un-faced fiberglass blanket utilizing the existing roof as a vapor barrier can nominally provide R-10 for each 3 inch’s of thickness.

Re-roofing is like remolding no two applications are ever the same. That’s why the use of standard components that can be utilized for non-standard applications offers you the most flexibility at the very best price. Drexel Metals Inc. offers many roof covering options to finish off your new slope build-up system.

Bill Dooley is the Director of Architectural Sales for Drexel Metals Inc.

For more information visit www.drexelmetals.com

The Benefits of RetroFit Roofing – a Drexel Metals solution

Tapping into the conventional and flat roof market utilizing metal roofing products.

Understanding how to develop new opportunities for utilizing Sanding Seam Roofing products on existing conventional and flat roofs

Many metal roofing contractors felt their only source for applying their trade skills was on new, sloped construction projects.

Drexel Metals Solution

We shall take an in-depth look into the process of transforming an existing flat roof into a sloped roof by adding a light gage framing system to the structure.

Benefit 1

By understanding how to design and install slope build up retrofit roof framing you increase awareness of your company’s expertise and creativity as a leading SSR contractor in your market.

Benefit 2

The ability to increase the existing roofs structural integrity by designing and installing a frame that has greater up lift resistance than the flat surface.

Benefit 3

*Environmentally friendly. Reductions in land fill waste due to the fact that the majority of the existing membrane will remain in place.

* Increased curb appeal with gables, hips, dormers or other roof elements.

*LEED compliance with use of high performance panel coatings, recyclable and sustainable material content.

*Energy efficient.

For more info contact Bill Dooley at bdooley@drexmet.com

Drexel Metals helps to navigate the credits a SSR System that may contribute towards LEED Certification

Division 7 Manufactured Metal Roofing can contribute as many as 30 credits towards a projects LEED certification. There are two major categories that these credits fall into:  Direct LEED Credits and Indirect LEED Credits.

LEED DIRECT CREDITS; *Energy & Atmosphere: 1 to 3 credits. *Material Recyclability: 1 to 2 credits. *Regional Manufacturing: 1 to 2 credits. *Building Re-use: 1 to 2 credits.

INDIRECT LEED CREDITS; *Water Efficiency: 1 to 4 credits, *Water Reduction: 1 credit. *Energy / Atmosphere: 1 to 3 credits. *Optimize Energy Efficiency: 1 to 10 credits. *Solar Thermo Energy: 1 to 3 credits.

Lets look at each of these categories, both direct and indirect and define what they represent.

DIRECT CREDITS:

Energy & Atmosphere, sometimes referred as Heat Island Effect by definition is a “dome” of elevated temperatures over an urban area caused by structural and pavement heat fluxes and pollutant emissions.

Material Recyclability. Purpose to increase demand for building products that incorporate recycled materials. Post consumer recycled content is any material that was used by a consumer and then recycled for use in a new product. Post consumer materials indicates the product was made with materials that were recycled by residents and businesses. Pre consumer recycled content is recycled materials made with industry scraps.

Regional Materials / Manufacturing. Purpose to reduce energy usage and pollution in the movement of goods to a construction site. One LEED credit for Regional Materials where 10% of the materials is extracted, processed and manufactured regionally within 500 miles of the project. Two credits if 20% is extracted.

Building Re-use. Purpose to extend the life cycle of existing building stock and reduce waste and the environmental impacts of new buildings as they relate to materials, manufacturing and transport. One LEED credit if the owner or developer maintains at least 75% of the surface area of an existing building structure including structural floor and roof decking and the envelope including structural roofing materials. Two credits if 95% of the surface area is maintained.

INDIRECT CREDITS:

Water Efficiency. Purpose to retrieve and conserve water for water efficient landscaping. One LEED credit for the reduction of potable water by 50% for project landscape irrigation. Two LEED credits for reducing potable water consumption by 100% for project landscaping irrigation. One LEED credit for reducing 20% potable water use by reusing storm water for non-potable applications such as toilet and urinal flushing and custodial uses. Two LEED credits for reducing 30% potable water.

Water Reduction. One LEED credit for reducing the generation of wastewater and potable water demand through a number of processes, including captured rainwater.

Energy & Atmosphere. Purpose to use photovoltaic technology to reduce conventional energy consumption. Obtain up to 3 LEED credits for generating 5%, 10% or 20% of the building’s energy use with renewable power.

Optimize Energy Efficiency Credit. Awards up to 10 LEED credits based on percentages of energy cost reductions. For example, a 60% reduction will earn the maximum 10 points. A project gains a credit for energy cost savings of 10.5% and one point for each additional 3.5% of savings.

Solar Thermo Energy. Purpose to gain efficiency through solar thermo technology that heats water for domestic use or space heating. Obtain up to 3 LEED credits for generating 5%, 10% or 20% of the building’s energy use with renewable power.

Drexel Metals Inc. is available to assist with all of your Standing Seam Roofing design, questions or concerns. Please visit us at www.drexmet.com.

Drexel Metals Inc.. addresses Insulation and moisture concerns within a Standing Seam Metal Roofing System.

Energy conservation is an important consideration for building owners and roof designers. There are many different methods for insulating metal roofing systems, but the most common are blanket insulation and rigid board insulation. In addition, there are several proprietary systems available on the market, which may be more suitable for specific applications.

I will attempt to walk you through the importance of understanding the steps necessary in keeping a building envelope dry, comfortable and insuring a long life for the building materials used in its construction.

Heat transfer is the term commonly used to indicate the movement of heat (energy)  from one area to another. Minimizing heat transfer is the role that insulating materials play in conserving energy. The driving force for heat transfer is the difference in temperature between two areas, or surfaces and will occur in a direction from hot to cold.

The three basic mechanisms of heat transfer are as follows:

1: Conduction, the process by which heat will transfer through a solid material. Heat will transfer through the material from hot to cold by means of molecular contact.

2: Convection, the transfer of heat by means of a moving fluid such as air or water. Heat is picked up by a moving fluid and transported to another area.

3: Radiation, the transfer of heat by means of electromagnetic waves.

Now that we know the fundamentals of heat transfer. How is it measured? The amount of heat transferred is measured in British Thermal Units (BTU). One BTU is equivalent to the amount of energy required to raise one pound of water by one degree Fahrenheit (F). Several interrelated properties are used to measure the ability of a material to permit heat flow through it.

Thermal conductance (C) is a measure of the rate (measured in BTU’s per hr.) that heat will flow through an insulating material. Materials that have lower conductance values will allow less heat to flow through them.

Thermal resistance (R) is a measure of a material’s ability to resist the passage of heat. Materials with higher resistance values allow less heat to flow through them. Thermal resistance is the reciprocal of the thermal conductance.

Thermal transmittance (U) is the total rate that heat will flow through a given roof or wall assembly including the effects of surface air film resistances. A lower U-value indicates that less heat will flow through an assembly. Thermal transmittance (U) is the reciprocal of the total resistance,(R).

Condensation is another concern and needs to be addressed when designing a successful SSR system. The condensation process occurs when warmer moist air comes in contact with cold surfaces such as framing members, windows and other accessories, or the colder areas within the insulation envelope (if moisture has penetrated the vapor barrier). Warm air, having the ability to contain more moisture than cold air, loses that ability when it comes in contact with cool or cold surfaces or areas. When this happens, excessive moisture in the air is released in the form of condensation. *If this moisture collects in the insulation, the insulating value of the insulation is decreased as wet insulation has about the same heat conductance value as water. In dealing with condensation, air may be considered to be a mixture of two gases, dry air and water vapor. One thousand cubic feet of air at 75 degrees F can hold up to 1.4 pints of water. At 45 degrees F, it  can hold only 0.5 pints.

Relative humidity is a percentage measurement of the amount of water vapor present in the air in relation to the amount it is capable of holding at that temperature. Therefore 50% relative humidity would mean that the air is carrying only one half of the total amount of moisture that it could be holding at that particular temperature. Cold outside air is usually much drier than warm inside air. Therefore, the indoor relative humidity can be lowered by bringing in outside air to mix with and dilute the moist inside air. At 100% relative humidity, the air is “saturated”. The temperature at which the air is saturated and can no longer hold the moisture is called the dew point temperature. Whenever air temperature drops below its dew point, excess moisture will be released in the form of condensation.

A vapor retarder (barrier) is used to inhibit the passage of warmer moist air into the inner areas of a roof or wall system. The proper selection and installation of the vapor barrier can help control condensation problems in a building. Vapor barriers are rated by the amount of moisture that can pass through them. The lower the rating, called a perm rating, the less vapor transmission will occur and the more effective the vapor barrier will be. Materials with perm ratings of 1.0 or above are considered to be at the high-end of vapor barrier performance.

I hope you now realize how important your understanding of what your design will clad, and how that cladding will impact temperature and moisture contents within the structure. Gone are the days of metal roofing and siding being nothing other than a shade and shelter structure. Our roofs and wall are now sheltering all types of hi-tech buildings.

Drexel Metals Inc. welcomes all inquiries regarding roof design. Please visit us at www.drexmet.com