What Is Roof Decking?

As it gets colder, you might wonder: does moss on a roof die in winter like other pesky plants? It's a common myth. However, while you might hope winter weather will eliminate the moss, this isn't the case. Even if the moss looks dried out when temperatures drop, it goes dormant and absorbs water like a sponge. Before long, it will continue growing and become more difficult to get rid of as it spreads across your roof, even after the winter season.Why You Should Remove Moss from Your RoofIf you don't remove moss from your roof, it can wreak havoc on shingles, eating away at their protective coating. Moss roots also grow in between shingles and underneath the structure. This can degrade the shingles and push them apart as temperatures drop, allowing water to penetrate and leak into your home.Moss growth can also prevent proper water drainage and result in bacteria or mold growth, rotten underlayment, and damaged framing. It compromises the roof's ultraviolet protection, too. Left to grow into a thick layer, moss can reduce your roof's lifespan.The Difference between Moss and AlgaeIt's also important to know the difference between moss and algae, and how to prevent or remove both to extend the life of your roof. Moss is a herbaceous plant that absorbs nutrients and water through its leaves, producing spores to reproduce. It spreads across your roof as it grows. Algae are flat, slimy, green aquatic plants that lack leaves, stems, or flowers. They tend to grow on moist areas of your roof, causing dark stains. Algae are usually found in areas where water drips overhead. If you suspect algae on your roof, consider installing algae-resistant shingles.How to Remove Moss from Your RoofSince the answer to 'does moss on a roof die in winter?', is no, now's a good time to hire a professional roofer to get rid of it. Moss is resilient, and you can't simply remove it by hand. They'll remove the moss using a chemical solution, and they can replace any damaged shingles to restore your roof's integrity.It's best to rely on a professional who can eliminate the moss while also inspecting your roof for damage. Don't try to use a pressure washer or any weed killers not designed for moss, as these can stain or damage your roof.How to Prevent Moss GrowthSince moss thrives in damp, shady spots, trimming trees to allow more sunlight onto your roof can help deter its growth. Also, regularly clear away leaves, twigs, and other debris, which helps moss grow, and clean your gutters frequently to prevent water buildup. In addition to these tasks, scheduling regular roof inspections can help you catch any issues early.You can also install a zinc strip, such as GAF Master Flow® Zinc Moss & Mildew Preventer, near the roof ridge to help protect your roof against moss, algae, and mildew growth. The metal strip oxidizes over time, and as water washes over the roof plane, it creates an undesirable environment for moss.By proactively removing moss and preventing its return, you'll protect your biggest investment: your home. Contact a GAF-certified roofing contractor* to ensure it's removed effectively.*Contractors enrolled in GAF certification programs are not employees or agents of GAF, and GAF does not control or otherwise supervise these independent businesses. Contractors may receive benefits, such as loyalty rewards points and discounts on marketing tools from GAF for participating in the program and offering GAF enhanced warranties, which require the use of a minimum amount of GAF products. Your dealings with a Contractor, and any services they provide to you, are subject to the GAF Contractor Terms of Use.

If every day was sunny, mild, and a pleasant 75 degrees, there'd be little reason to wonder about the best time to replace a roof. Of course, not everyone lives in areas with ideal weather conditions, as climates vary greatly across the country.So if a client ever asks, "When is the best time to replace a roof?" your answer will likely vary based on where they live and what each season is like. However, you can share some general pointers in response. Here's what to consider for each season to help answer the question, "when is the best time to replace a roof?"SpringSpringtime is traditionally recognized as the kickoff of roofing season, as outside temperatures begin to warm and activity increases. Thanks to melting ice and snow, it's also the time of year that homeowners may want to have their roofs checked out for damage.While spring offers outdoor temperatures that are more friendly for workers, the season also typically comes with an increased chance of severe thunderstorms (and potentially tornados, depending on the region). Spring is usually a good time to schedule a roof replacement if you just monitor the weather forecast for major events to help reduce the chance of delays.SummerWith spring showers in the rearview, most areas of the country see longer stretches of nice weather during summertime, which lends itself well to working outside. Accordingly, summer tends to be the most ideal time for installing a new roof.But with potentially hot days, when is the best time to replace a roof in the summer? Workers will need to start as early in the day as possible because temperatures are usually cooler in the morning. Depending on the forecast temperatures, the job may need to be spread over a few days, so most of the work can be done in the morning hours before it gets too hot. It's also wise to remind customers that workers will need to have breaks in the shade and access to water to stay hydrated.FallThe autumn months can be an equally good time for a roof replacement as summer, as the hot and hazy days have passed, and severe weather isn't as common. The only exception to this is if you're working in an area prone to hurricanes. Hurricane season runs through the end of November and can cause project delays.In addition to the favorable weather, fall is a popular season for roof replacement because many property owners want to fortify their homes and buildings with a new roof before the winter months.WinterIn some areas of the country, it may be possible to continue roofing installations year-round, including during the winter. In southern regions, for example, roofing replacements can often be completed in the winter, as there's less chance of inclement weather. Temperatures may drop, but not as drastically as in areas that see ice and snow more regularly. Of course, it's still important to reference the relevant local forecast when scheduling upcoming work.Sustained stretches of very cold weather does not constitute suitable weather for the installation of asphalt shingles. All self-sealing shingles must be exposed to warm, sunny conditions for several days before they completely seal. Before sealing occurs, shingles are vulnerable to blow-offs and wind damage. Shingles installed in fall or winter may not seal until the following spring. Shingles that are not exposed to direct sunlight, adequate surface temperatures, or that are not fastened or installed properly may never seal. Failures to seal, blow-offs, and wind damage under these circumstances result from the nature of self-sealing shingles, and are not covered under most manufacturer's warranties. Be sure to follow the manufacturer's instructions for proper installation. While most provide guidance about cold weather installations, it will ultimately be up to you to exercise discretion about when to move forward with an installation vs. postponing the work until more favorable weather conditions are present.Other Factors That May Affect Project TimingWhile weather is likely the leading factor that can disrupt scheduled roofing work, if you want to best answer your client's question of "when is the best time to replace a roof?" you'll need to take other factors into account when setting timeline expectations for property owners. One such consideration is the lead time needed for materials. If your customer chooses an uncommon color or a specialty product, it may take longer for materials to arrive.Another factor to weigh is your own backlog. If your production calendar is booked weeks out, clearly communicate the timing to your customers with the knowledge that weather events could impact the schedule. Regularly communicating with customers and setting accurate expectations are key to a positive experience.Looking to learn more roofing best practices and further expand your knowledge base? Check out GAF's CARE Contractor Training Center to help build your skill set and receive valuable training.

A common question being asked in the roofing industry is whether or not the 2016 version of ASCE 7 is going to increase the design wind pressures acting on a building. The answer is "yes" in many cases. So, the follow up question is "by how much?" And, that leads to the next question, "how much more capacity will roof systems be required to have when wind design follows ASCE 7-16?"This blog looks at 2 buildings of different sizes and heights in two cities in the U.S., one centrally located and one along the Gulf coast, and compares design wind pressures based on ASCE 7-10 and ASCE 7-16. By assessing the required roof-system capacity for all roof zones in conjunction with the increases in the size of roof zones, we can begin to put some real numbers to the question "by how much will ASCE 7-16 affect the low-slope roofing industry?"While analysis of two building types in two cities doesn't represent a significant study, this study offers an example of how the 2016 version of ASCE 7 is going to affect installed roofing systems over the next decade.Case StudiesDesign wind pressures (DWP) were determined for two building types in two cities. DWPs were based on varying the Risk Category and Exposure. The following table shows the building types, cities, variables, and constants.The big box store is 290' long x 169' wide x 24' tall, and the apartment building is 100' long x 40' wide x 55' tall. Wind speeds were determined using an online tool.DWPs can be determined by using proprietary third party methods (e.g., RoofNav), simplified calculation tools (e.g., RoofWindDesigner), or hand calculations following the methods within the ASCE 7 standard.For this case study, DWPs were determined using hand calculations via an Excel spreadsheet. The DWPs are slightly more refined since there was no rounding of wind speeds for ASCE 7-16. Both RoofNav and Roof Wind Designer round to the nearest 5 or 10 mph. The maps in ASCE 7-16 have been revised, not only from a wind speed perspective but from the number of wind isobars on the maps. The ASCE 7-16 maps are more refined which allows for more exact wind speed values.ASCE 7-10 Map, Risk Category II, showing a limited number of wind-speed isobars.ASCE 7-16 Map, Risk Category II, showing many additional wind-speed isobars relative to the ASCE 7-10 wind map shown in the above figure.In total, 72 different sets of DWPs were calculated. Buildings over 60' tall are designed the same in ASCE 7-16 as in ASCE 7-10; therefore, this article focuses on buildings less than 60' tall.Design Wind Pressure ResultsThe following charts provide the DWPs for each of the scenarios that were analyzed for this article.Design wind pressures based on ASCE 7-10 and ASCE 7-16 for a big box store in Kansas City, MO that is 24' tall.Design wind pressures based on ASCE 7-10 and ASCE 7-16 for a big box store in Mobile, AL that is 24' tall.Design wind pressures based on ASCE 7-10 and ASCE 7-16 for a 5-story apartment building in Kansas City, MO that is 55' tall.Design wind pressures based on ASCE 7-10 and ASCE 7-16 for a 5-story apartment building in Mobile, AL that is 55' tall.Comparing the 2010 and 2016 versionsThe primary intent of this article is to start generating data to help answer the question "how much did the DWP increase from the 2010 version to the 2016 version of ASCE 7?" Using the DWP calculated for each roof zone within each of the four scenarios, we calculated the percent increase in DWP per zone. The percent increases in DWP were calculated by dividing the ASCE 7-16 value with the corresponding ASCE 7-10 value for each roof zone. However, because there are 4 roof zones in ASCE 7-16 (and 3 roof zones in ASCE 7-10), both Roof Zones 1' and 1 were divided by the value for ASCE 7-10 Roof Zone 1 to determine the percent increase. Values in the following charts that are below 100% (shaded gray) indicate a reduction in DWP from ASCE 7-10 to 7-16.Percent increases in DWP per roof zone for a big box store in Kansas City, MO that is 24' tall, focusing on Exposure C values.Percent increases in DWP per roof zone for a big box store in Mobile, AL that is 24' tall, focusing on Exposure C values.Percent increases in DWP per roof zone for a 5-story apartment building in Kansas City, MO that is 55' tall, focusing on Exposure C values.Percent increases in DWP per roof zone for a 5-story apartment building in Mobile, AL that is 55' tall, focusing on Exposure C values.For the big box store scenarios, the percent increases in DWP per roof zone varies from 84% to 178%. The percent reductions (values less than 100%) are all in Roof Zone 1' while Roof Zones 1, 2, and 3 have increased DWP. As seen in the Figures, Roof Zone 1 percent increases are greatest while Roof Zone 3 increases are smallest.For the 5-story apartment building scenarios, the percent increases in DWP per roof zone varies from 84% to 177%. The percent increases in Roof Zone 1 are the largest. The percent reductions are all Roof Zone 1'.It is worth noting that the increases in Pressure Coefficients from ASCE 7-10 to 7-16 are, in fact, relatively indicative of the increases in DWP. For more on Pressure Coefficients and the wind design process.The case studies in this blog also show that the 2016 version of ASCE 7 imposes higher DWPs in Roof Zones 1, 2, and 3. However, given some of the substantial reductions in Roof Zone 1', it could be expected that installed roof system capacity may be lower. While that is hopeful, the roofing industry has a minimum-capacity backstop of 60 psf. This means that any calculated DWP at or below 60.0 psf (even for DWP values as low as 23 psf) will have a 60-psf-capacity roof assembly installed to meet building code requirements. The reality is many buildings are required to use a 60-psf-capacity roof system when in fact '60 psf' is more capacity than needed based on calculated DWPs.Let's take a closer look at one subset for each of the 4 scenarios.Example 1: Big Box; Central USThe big box store in KC, MO (Risk Category II, Exposure C) saw the DWP increase from 38 psf to 56 psf in Roof Zone 1 per ASCE 7-10 vs ASCE 7-16; and reduce to 32 psf in Roof Zone 1'. Regardless of the increases or decreases, a 60-psf-capacity roof should be installed in both Roof Zone 1 and Roof Zone 1' per 7-16, which is unchanged relative to ASCE 7-10.Roof zones and pressures for a 24' tall big box store in Kansas City, MO based on ASCE 7-10 using Risk Category II and Exposure C.Roof zones and pressures for a 24' tall big box store in Kansas City, MO based on ASCE 7-16 using Risk Category II and Exposure C.For Roof Zones 2 and 3, the DWPs are not only increased, but the sizes of the roof zones that require higher capacity are also increased. Roof Zone 2 per ASCE 7-10 required a 75-psf-capacity roof, and a 75-psf-capacity roof will be needed per ASCE 7-16. However, approximately 9% of the roof area will need a higher capacity because of the increase in roof zone size. The following chart shows roof area percentages based on the required roof system capacity for this scenario.Chart showing required roof capacity and the roof area (%) where each is required.Example 2: Big Box; Gulf CoastA big box store in Mobile, AL (Risk Category II, Exposure C) saw the DWP increase from 69 psf to 109 psf in Roof Zone 1 per ASCE 7-10 vs ASCE 7-16; and reduce to 63 psf in Roof Zone 1'. A 75-psf-capacity roof should be installed in Roof Zone 1', and higher-capacity roofs will be required in Roof Zones 1, 2, and 3 relative to ASCE 7-10.Roof zones and pressures for a 24' tall big box store in Mobile, AL based on ASCE 7-10 using Risk Category II and Exposure C.Roof zones and pressures for a 24' tall big box store in Mobile, AL based on ASCE 7-16 using Risk Category II and Exposure C.For Roof Zones 1, 2, and 3, the DWPs are not only increased, but the size of the roof zones that require higher capacity are also increased. A larger perimeter roof zone (combining Roof Zones 1 and 2) with higher required capacity is created (relative to 7-10). Approximately 30+% of the roof area will need a higher capacity. The following chart shows roof area percentages based on the required roof system capacity for this scenario.Chart showing required roof capacity and the roof area (%) where each is required.Example 3: 5-story; Central USThe 5-story apartment building in KC, MO (Risk Category II, Exposure C) saw the DWP increase from 45 psf to 66 psf in Roof Zone 1 per ASCE 7-10 vs ASCE 7-16; and reduce to 38 psf in Roof Zone 1'.However, because the method used to determine the sizes of roof zones in ASCE 7-16 is changed, Roof Zones 1' and 1 do not exist on this building! Decreases of DWP in Roof Zone 1' are rendered meaningless, and the lack of a Roof Zones 1' and 1 means the entire roof consists of only Roof Zones 2 and 3, the perimeter and corner roof zones.Roof zones and pressures for a 55' tall apartment building in Kansas City, MO based on ASCE 7-16 (top) and ASCE 7-10 (bottom) using Risk Cat II and Exposure C.The increases in DWPs for the roof zones significantly increase the roof system capacity requirements for this scenario. Almost the entire roof area will need a higher capacity roof. The following chart shows roof area percentages based on the required roof system capacity for this scenario.Chart showing required roof capacity and the roof area (%) where each is required.Example 4: 5-story; Gulf CoastThe 5-story apartment building in Mobile, AL (Risk Category II, Exposure C) saw the DWP increase from 81 psf to 129 psf in Roof Zone 1 per ASCE 7-10 vs ASCE 7-16; and reduce to 74 psf in Roof Zone 1'. Similar to Example 3, due to the size of the roof zones relative to the size of the roof, Roof Zones 1' and 1 do not exist in this scenario.Roof zones and pressures for a 55' tall apartment building in Mobile, AL based on ASCE 7-16 (top) and ASCE 7-10 (bottom) using Risk Cat II and Exposure C.The increases in DWP for the roof zones significantly increase the roof system capacity requirements for this scenario. The entire roof area will need a higher capacity. The following chart shows roof area percentages based on the required roof system capacity for this scenario.Performance versus PrescriptiveThe case studies in this analysis are presented using a performance method for wind design. That is, a specific DWP is determined for each roof zone and a roof system with appropriate capacity is selected for use in the associated roof zone. Another method that is often used in the roofing industry is a prescriptive method for wind design. The DWP for Roof Zone 1 (or Roof Zone 1' in certain localities) is used to select a roof system with an appropriate capacity for Roof Zone 1 (similar to a performance method), and then Roof Zones 2 and 3 use an installation method/layout that is prescriptively increased relative to Roof Zone 1 installation methods. Prescriptive installation methods for Roof Zones 2 and 3 are regularly used with mechanically attached (MA) roof systems, and for MA roofs, Roof Zone 2 increases are commonly 50% and Roof Zone 3 increases are commonly 100%.ConclusionASCE 7-16 DWPs are generally increasing relative to ASCE 7-10, but this impact is better understood by comparing the required roof system capacity for different building types and dimensions in different cities. Looking only at DWPs does not provide enough information; a comparison of required roof system capacities is needed. Not only did the DWPs change, but the methodology for determining the size of the perimeter and corner roof zones changed significantly in the new ASCE 7-16 version; the amount of roof area contained by the perimeter and corner roof zones increased. The case studies—of two buildings less than 60 ft tall in two cities—and corresponding analysis in this blog are just one additional small step to understanding how the ASCE 7-16 will affect wind design over the next decade.