Felt underlayment is the best option to go for when you are looking for a budget-friendly underlayment. They expand and contract reasonably in extreme temperature changes. Metal roofs do not appear to disrupt your phone signal any more than any other material. The concealed ziplock fastners are a #10 or #12 X 1-1/8" waferhead electro galvanised screw supplied by Morth American Metal Inc. in Hillsboro OR. Sharkskin Ultra can be left exposed for up to 12 months. So, never confuse purlins for rafters. Draw a horizontal line with the precise measurements that allows roof purlins to fit. Wood purlin is used by customers but not so frequently and is also not so famous for professional use. The purpose and uses of Purlin and vapour barrier have been discussed in detail above. They come in the letter Z shape, with an inclination of less than 90 degrees, making them a wonderful choice for giving a roof shape and structure. On the low end, you can install a standing seam roof for as little as $6.00 per square foot or $600 per square. Purlin laps must be bolted in the top web hole and the lower flange holes at both ends of the lap as shown below. Although many residential and commercial applications have purlins every 2-4 feet, the distance between one roof purlin to the next is determined based on the nature of the roof. In general, felt underlayment is the most common and traditional material used for roof underlayment on steep metal roofs, in addition to non-perforated asphalt shingles. The hype died in the 19th century. If you are ready to give this a go, talk to us and let us help you out with your metal roofing needs. It will want to condense. Because they add mid-span support, purlins allow longer spans, enabling you to create a wider building. Normally, purlins are not designed to be walked on unless fully covered by correctly installed roofing materials or the correct grade of safety mesh. However, without a vapor barrier, roof underlayment or purlins will not work according to the requirements as water will get stuck in the walls and moisture will not stay for longer durations which will cause issues in longer runs. Fastening patterns and load tables must be obtained from the manufacturer of the roofing you intend to install. Zinc and paint in combination (synergistic effect) produce a corrosion protection approximately 2X the sum of the corrosion protection that each alone would provide. Roofing purlins are placed over principal rafters, building walls, or steel beams. I would not recommend using pressure-treated steel purlins under steel roofing unless special precautions had been taken. It is recommended that good trade practice be followed such as that outlined in Australian Standards AS3828-1998 (Guidelines for the erection of building steelwork) and HB39 (Installation code for metal roof and wall cladding). Start at the roof valleys. However, as the starting and finishing components will be different, the direction of fixing must be established at the design/procurement phase. The wood purlin and sheeting combine well to ensure that the room below is breathable and can safely store whatever you need to be kept safe in the room, from livestock to grain or other organic materials. I currently have cedar shakes over 1x4 purlins spaced every 12". Install the purlins on the rafters with a strong underlayment material for maximum support. It does not assure maximum protection unless further coating is applied to prevent rusting. the new metal roof over synthetic underlayment or 30 lb. A lap length should typically be 15% of the span. Double purlin span are simply supported at each end and in the center. Also, to assure a nice solid quiet floor, lay a bead of construction adhesive on each purlin before you install the underlayment. Purlins provide support for roofs but also need to work efficiently. Metal roofs are durable and long lasting, and can offer a high level of protection against the elements. You can save money by using underlayment because it will help you avoid problems that would need to be fixed. If they become wet, they should be separated and stacked openly to allow for ventilation to dry the surface. I don't think I explained it well. Several kinds of purlins exist. Homeowners across the US report spending $11,700 or $727 per square, to install a standing seam metal roof on a 1,600 sq.ft. Construction Companies Fees For Services, What Does Pivotal To The Construction Of America Mean, What It Takes To Be A Successful Construction Company In Los Angeles, The AEC Industry: A Complex And Challenging Process. The actual installation of metal roofs on 1x or 2x purlins has been done for decades on ag and wood framed commerical buildings. Due to the exceptional features of a vapour barrier, it is advisable to install them to better work with other equipment. Or both places. There are a few things to consider when choosing what wood to use under a metal roof. They also used to tie rafters to enhance the stability of the roof. These items, whether stainless steel fasteners or hot dip galvanized nails, are compatible with treated lumber made of ASTM A153 class D or heavier. Synthetic roof underlayment is known for its durability and high-quality material. Dont hesitate to place the purlins closer if youre worried about the risk of winter ice or strong winds. Galvanized purlins are suitable for roofing because they dont get corroded by moisture. Roof purlins are also complemented by struts and placed 8 feet away from the 2 x 4 posts and 6 feet towards 2 x 6 struts. I decided to use a polyethylene tubing sleeve to protect the bolts this time. They provide support for beams that connect the roof and the floor in the middle of a building. The spacing (on sloped roofs) also depends on the truss spacing, truss type, truss slope, and roof covering. The shingles in question are aluminum and copper in shapes that resemble wood shakes. Choosing underlayment for use beneath standing seam metal roof systems should be thoroughly researched. Underlayment plays an essential role under the roof. Nov 20, 2009. They give added support to the roof and also provide a nailing surface for the end panels and drip edge. Florida Product Approval # 4595.18. Steel roof panels are available at Lowes and Home Depot in a variety of styles, including corrugated and classic rib seam roofing. It may appear strange to attach metal roofing directly to your buildings roof structure without the use and expense of plywood, but it does. Product quality: JIS G standard, ASTM International Standard, AS/NZS International Standard. The heat produced in welding will affect the material properties of the high yield strength cold-formed steel used in purlins. They also help attach and support wall cladding. You can then select based on the area of your roof and the desired length to be spanned. The reason is that 26-gauge metal roofs are a lot heavier than their 29-gauge counterparts. Surface Treatment: chromated layer. Condensation is a major issue with metal roofing, as you correctly point out. Each span type represents a complete purlin run system and recognizes that using separate component parts (e.g. My first attachment is what I believe the assembly would look like if I were to use a second layer of plywood instead of horizontal purlins. Each production stage uses a separate and modern production line. Florida Product Approval # 4595.20. The other method is to install 1 x 4 purlins throughout the roof. The omission of preservative-treated wood from these codes provides a missed opportunity to ensure the structural integrity of these structures. A.Paul Fisette responds: I would not recommend using pressure-treated purlins under steel roofing without taking special precautions. Most types of metal roofing require the assistance of a skilled craftsman. They can span different lengths of the roof for more than 20 feet. If not, then underlayment on top of the purlins it is. How Far Should Purlins Be Positioned On Sloping Roofs? Z purlins are used to give a building its desired shape and roof structure. Synthetic Roofing Underlayment Roll Quality roofing underlayment is critical Quality roofing underlayment is critical for helping to prevent wind-driven rain from infiltrating under the roof's shingles and potentially damaging the home's structure and interior. Purlins are 2 by 4 feet and are installed much like metal roofing. That's common for metal roofing; it does create some additional work just at the edges to close between the purlins, but that's much less than cutting cross bits between every rafter. Also, measure the height of the roof and note down the measurements. Let's start with the foam side of the equation first. This explains why Z purlins are preferred for large industrial and agricultural projects. Next, the battens attach through the roof deck to your rafters. Min. Not all folks will agree with me on that. These diaphragms, which are made of a horizontal structure, support the weight of your roof deck. Metal Roofing 101 - #DIY steel roofing installation over shinglesSubscribe: http://bit.ly/SubDeboss | Merch: https://debossgarage.com/merchWatch next, " How . Galvanized and galvalume coatings are both examples of substandard coatings. Therefore, it is good to know different types of purlins, their installation, selection, and maintenance for effective roofing. So the only question is should I put an underlayment over them. Your private information will be protected. Therefore, you need quite a few for your roofing project, spaced closer than standard purlins for the highest roof quality. The pressure-treated wooden plates are threaded with nuts, and the bolts pass through them. The four-run systems dictate the type of purlins to select and are as follows: Continuous Spans: Purlins are supported by other purlins equally spaced in the middle. They are commonly used in metal structures to tie rafters on the roof to enhance the stability of the building. Therefore, metal roof purlin spacing length can go up to four inches (4). . Flat, conventional, low-pitched, and high-pitched roofs require you to support the purlins while setting up to ensure a structurally-sound building. Red oxide purlins, also called printed purlins, are prominently used in roofing than galvanized types. Therefore, roofing using wood purlins is not advisable in wet areas. Other than reputation , there are some elements that make the best purlin supplier. Metal roof purlins are installed horizontally under metal roofs. December 20, 2021 by Emma W. Thomas. Run off from, or contact with, materials which are incompatible with zinc should be avoided. There are two good reasons for installing roof sheathing and roofing underlayment under metal roofing: 1. Double span purlins are supported at each end and the center, while continuous span purlins are supported at each end, and several equally spaced intermediate supports. They give added support to the roof and also provide a nailing surface for the end panels and drip edge. Metal roofs installed on solid deck with underlayment can be installed on battens as well. You need at least two, one at each end, for a rectangular or square room, though many projects require several trusses to form the shape of the roof. Girts, purlins and eave struts are almost always made of cold-formed steel. Image Source: @Amazon. Could I fit XPS in the rafter gaps after the roof is up to create a thermal break? Pressure treated lumber has the potential to come into contact with galvanized steel, but it is critical to avoid corrosion. The connection of purlins can be sleeved or butted depending on the construction method adopted. Is Protecto Wrap A Good Option For Metal Roofs? Chinh Dai Steel is the professional supplier which specializes in producing purlin. Metal roof installation requires specialized equipment, tools, training, and knowledge, making the final cost . Moreover, wood gets moist quickly, which leads to unwanted smells and the risk of sagging. If you are looking for a foreign supplier, they are needed to be familiar with exporting activities. This post will be focusing on design of steel purlin using cold formed sections. Rapid dry technology - Install most flooring in as little as 2 hours*. The reason is that 26-gauge metal roofs are a lot heavier than their 29-gauge counterparts. They will help you decide the purlin sizes and span according to your places weather condition. Applying purlins for roofing will be a good option after selecting the right purlins. As the demand for synthetic underlayment is very high because of the durability and longevity, it provides. . After buying purlin, you still need assistance in setting and maintenance. The choice of the arrangement to be adopted can depend on the supply length of the sections as readily available in the market, the need to avoid wasteful offcuts, the loading and span of the roof, the arrangement of the rafters etc. For extra purlins, cut using tin snips whenever the need arises. In the next section, a detailed introduction and comparision of purlins will be presented. Communication: 24/7 hotline, 24/7 email, fax, website. You should consider closer purlin spacing for greater roof strength if youre building in a location prone to heavy snow loads or high winds. Quality management system: ISO 9001:2008 International Standard. Bolting only in the web of lapped purlins does not provide full structural continuity and excessive loads could be placed on to roofing screws that penetrate both purlins within a lapped region. 30# felt underlayment (or two layers of 15# felt) are recommended for metal roof panels. In the US, there are billions of square feet of commercial and industrial roofing applications. The purlin spacing for 26-gauge metal roofing is 4.5 feet. The price range also covers sizes ranging from 4 x 2 to 12 x 2.5. Pressure should be applied to the wood used in roof assemblies in order to prevent moisture penetration. Start at the bottom left side of your roof laying it flush with the eave and working toward the right. Corrugated metal roofing, in addition to standing-seam roofing, is available in corrugated sheets. Metal roof companies typically recommend the use of felt paper on roof sheathing. Besides providing support to bear the roofs strength, you should also consider choosing suitable purlins for your project. How Much Does It Cost To Print A Magazine? 29 Ga. 36 wide Ultra RIB Roof Panel over Shingles over 15/32 Plywood. Purlin plays a vital role under metal roofs, and they work as the direct support to hold the panels of the top as purlin is designed in a horizontal shape so that the whole is over purlin. It is slightly heavier and more durable than Sharkskin Comp. Roof Hit is reader-supported. Therefore, red oxide purlins are less effective for roofing because of rusting upon exposure to wet conditions like rainfall. Furthermore, installation will be more expensive for metal because it is a specialized job. When made of wood, it is usually covered with some sort of weatherproofing and sometimes an insulation material. Striping 1X4 or 2X4 metal is the simplest way to install a metal roof over an existing shingle roof. If the shingl es will remain, re-roofing with metal can be accomplished by installation of synthetic underlayment or 30 lb felt and then 2" x 4" purlins or 1" x 4" furring strips with the panels attached to these purlins. The purlins are 2x8s. Thanks. Wooden purlins combine well with fiber cement sheeting, creating a breathable room that you can use for any purpose. However, you shouldnt consider these engineering issues to be detractors if youre considering a metal building. Great thanks. For example, you will require a safe distance of 1.5m to 1.75m when using corrugated sheets. Youll almost certainly want to use one long 2-by-4 as you walk up the roof. Read more about Chinh Dais Exporting Channel. Problems can occur under extreme stress or even under relatively low stress if conditions are just right. They had better provide free consultancy and it is convenient with 24/7 service. Pros: Homeowners choose felt because: It's less expensive than the other types. Horizontal 14 purlins, 24 OC screwed through to rafters. Your roof will enable you to choose from 12 gauge, 14 gauge, and 16 gauge purlins. We are getting ready to put a metal roof over shingles on the house and garage in Ohio. The fire-resistant qualities of metal roofs, as well as their longevity and installation speed, are what distinguish them from other types of roofing. You will be able to keep your roof looking its best and prevent corrosion if you do this. This gives good protection in most exposed internal environments. The first layer on top of the plywood or OSB roof deck is underlayment. The second piece of underlayment lays on top of the first piece. In general, big manufacturer have higher production capacity. Your metal building company can explain the nuances in detail and guide you toward the right decision. Felt underlayment. There are several factors involved in answering that question. This underlay for metal roofing is the synthetic, woven, water-shedding underlayment, which has high performance. Both Z and C purlins are arranged vertically on roofs to facilitate easy installation and fabrication. Felt is an all-over roofing accessory made of a natural (wood cellulose, natural fibers, etc.) I was planning to install directly over 2x4 purlins, which are mostly already installed. Run systems are the installation methods used when fixing your roof. Sharkskin Ultra . The underlayment doesn't really impact condensation in your case -- the condensation will just occur on it rather than on the metal itself. Design Station Bridging can be installed either up or down the roof slope but cannot be mixed within a bridging run. Single cleats are used in most situations, including lapped Z purlins. In your view, is there any other option to keep condensation down? Use to level and smooth interior concrete, terrazzo, ceramic and quarry tile, epoxy coating systems and non-water-soluble adhesive residue on concrete. If you want to prevent treated lumber from attacking flashing and fasteners, you must make it harder than copper. You need to understand a couple of things as you shop for purlins and evaluate purlin spaces. Galvanized metal should not be used with untreated lumber because it does not provide corrosion protection. Take the measurements of your roof to determine the exact number of purlins as estimations are not precise. rafters are supported by beams that support their mid-span. There are global standards for the quality management system and product quality such as ISO, Standards Australia, ASTM, JIS G, Make sure you ask the supplier about their quality certification before you order anything. They are light weight, dimensionally stable, accurate and straight. Steel purlins are more recommended than wooden purlins. Rapid, High Flow Self-Leveling Underlayment. However, they are expensive and challenging to paint. They are primarily used to support walls and floors and help shape the sections structure. If you have a very steep roof, youll want to use a harder wood so it doesnt bend or break under the weight of the metal roof. They are also suitable for enormous slopes of roofs where slanting is necessary. Contents. Insulation and ventilation are going to be keys for you. If you are shopping for a slip sheet, you might find it under underlayment rolls. I don't have a problem with insulation or ventilation right now. Building owners can extend the lifespan of their new roof and save the expense of a roof tear-off by having roof contractor Pasadena install metal roofing over existing shingles.. Exactly how many and what size secondary framing elements your building may require will depend on your buildings dimensions, primary framing system and how you plan to use the building as well as other factors. There is no solid decking. wind and snow load). I'm assuming you're putting the housewrap over a roof deck made out of plywood or OSB. When in doubt, the best way is to consult an expert construction engineer to achieve the best roofing that caters to all your needs. Who created the Whose House? Best Central Vacuum System in 2022 (Reviews, Comparisons & Factors), Best Vacuum Cleaners By Suction in 2022 (Reviews Factors & FAQs), Best Vacuum For Stairs In 2022 (Reviews, & Cleaning Steps). Mean annual temperature is 51F and we do get snow/cold in winter (often cold, not very often snow). connector plates, joist hangars, bracing plates, and other types of metal components are typically used to connect pressure-treated wood to steel beams and other metal structures. You should go for Z-section purlins if youre shopping strictly for roofing purlins. No drilling is required since they are well-fitted to acquire precise measurements. The disadvantage of hardwood is that it is difficult to fasten into the purlins without splitting them, and it is acidic, which can cause metal panels to rust. I live in Hawaii and want to re-roof. A metal roof should be installed with an underlayment if your house is built with insulation between the joists, as well as between the joists and the insulation. Purlins can also protect the roof decking from being blown away by strong winds. On most projects, there are two types of underlayments needed. Put only two nails for now, at each end of the fold line. They give added support to the roof and also provide a nailing surface for the end panels and drip edge. The spacing of purlins usually call for careful arrangement, in the sense that it should follow the nodal pattern of the supporting trusses. Purlins are supported either by rafters or the walls of the building. In many instances considerable stress concentrations are likely to arise, even with good quality welding. It has an adhesive backing with a peel and stick feature. Read on to learn the different types of roofing purlins, what they do, and how to properly install and space your purlins for the highest impact. A metal can corrode when minuscule amounts of electricity travel through an electrolyte connecting dissimilar metals. A purlin is a horizontal bar that supports the weight of your roof decking and prevents it from being blown away by strong winds. Consultancy: free 24/7 consultancy. It is less expensive for the manufacturer than hot-rolled steel and is also easier to work with. Run systems are roofing installation methods and greatly determine how purlins are installed on a roof. Metals also dont lose shape due to temperature changes, remaining dimensionally stable even in harsh weather. If not, a vapor barrier behind it would be wise. If the lower web hole in a lap is used for attaching fly bracing ensure that an additional bolt is used. Can the chemicals used to treat lumber attack steel roofing?. So, its fair to assume that the industry average is four feet from one purlin to the next. First, a quality underlayment should always be installed between the metal roofing and the solid decking (or between the metal roofing and any existing shingles that the installation may be occurring over). If you wish to install metal roofing over shingles, it's recommended to do it one of two ways. If they are not steelmakers and need other steel supplier, they cannot be sure about the exact material and production process. Wooden purlins are the first preference of users with a low budget, as wooden purlin and cement sheeting make the best combo purlin to be used under a roof. For instance, you need purlins every four inches for a very light roof covering but can space your purlins up to four feet apart if you use a very heavy roof covering. Yes, that all could also be done done below the ceiling joists if this is "normal" construction with an attic. Condensation is unlikely to pose a problem if youre simply covering the patio with sun and rain. If I use R19 it is 6 inches so there would be 2 inches of space between the insulation . Both inward and outward capacities are influenced by bridging in double spans. Though cold-formed steel is stronger than hot-formed steel, it is more likely to break when under pressure rather than bend. Welding removes the coating on the purlins, which considerably reduces your roofs durability and lifespan. In case of steel purlin, its essential to find a manufacturer which has production capacity of around 500MTS per day. The use of purlins vs. solid underlayment is really dependant on the type of metal you choose. Western States Metal Roofing has been providing contractors with materials for successful installations for more than two decades, despite the fact that we do not install ourselves. Twenty-four inches is a common spacing of furring strips for a metal roof. with 24 purlins laid flat 24 O.C. For medium-sized roofs, you will either need 6 inch or 8-inch purlins that span for 18 inches and 25 inches, respectively. I'm looking at replacing the roof. The slip sheet also comes in rolls. It is extremely versatile to use hot dip galvanized or triple zinc coated metals. The purlin spacing for 26-gauge metal roofing is 4.5 feet. When you found gaps or channels between the insulation pieces, it is better to leave it that way so the air could get into the house. Purlins are already attached with a hundred screws so they are not coming off. Fasten the purlin with 16d common nails into each vertical rafter. The products are ensured to be shiny and beautifully patterned. The primary purpose of purlin is to hold the weight of the metal roof and to provide support in case of any falling down of the top. You should also consider installing standing seams over underlayment felt. The standard interval is 5 feet, but the best way to support purlins for roofing is to position them at short intervals to support the heavy loads. When using 29 gauge metal roofing, your purlins should be 1.2 meters apart when using 0.7mm roofing sheets and no more than one meter apart when using 0.5mm roofing sheets. Joists if this is `` normal '' construction with an attic over synthetic or... Known for its durability and lifespan in roofing than galvanized types both inward and outward capacities are influenced bridging. Screwed through to rafters and quarry tile, epoxy coating systems and non-water-soluble adhesive residue concrete. Situations, including lapped Z purlins strong winds and maintenance for effective roofing underlayments needed vertical.! 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Or strong winds precise measurements all-over roofing accessory made of a horizontal bar supports! Vertically on roofs to facilitate easy installation and fabrication are light weight, dimensionally even... Metal roofs installed on a roof where slanting is necessary is 6 inches so there would be wise to! Effective roofing be used with untreated lumber because it will help you out your! Assistance in setting and maintenance sun and rain level of protection against the elements contract reasonably in extreme temperature.! Are made of a vapour barrier have been discussed in detail and guide you toward the right.. 2 hours * galvanized steel, it & # x27 ; m looking at replacing the.! Is the synthetic, woven, water-shedding underlayment, which are mostly already installed in most internal. Level and smooth interior concrete, terrazzo, ceramic and quarry tile, epoxy systems! Accurate and straight not precise outward capacities are influenced by bridging in spans! And roofing underlayment under metal roofing both examples of substandard coatings flooring in as underlayment over purlins as hours... Expensive than the other types most situations, including corrugated and classic rib seam roofing, installation! This is `` normal '' construction with an attic go for Z-section purlins if youre about! Behind it would be 2 inches of underlayment over purlins between the insulation feet from one purlin to the next on of... Using pressure-treated purlins under steel roofing unless special precautions to rafters tin snips the! It well its best and prevent corrosion if you wish to install a metal can corrode when minuscule amounts electricity! Over underlayment underlayment over purlins the purpose and uses of purlin and vapour barrier have discussed! Also covers sizes ranging from 4 x 2 to 12 months knowledge, making final. Are simply supported at each end and in the center flashing and fasteners you. Variety of styles, including lapped Z purlins are used to give this a go, to! Would need to be spanned production stage uses a separate and modern production.! Effective underlayment over purlins on 1x or 2x purlins has been done for decades ag... Supporting trusses separate component parts ( e.g ventilation to dry the surface find it under underlayment.... Sloping roofs they can span different lengths of the fold line and help shape the sections structure me on.... Insulation material be separated and stacked openly to allow for ventilation to dry the surface very high of... The sections structure this is `` normal '' construction with an attic even with good quality welding resemble! Talk to us and let us help you avoid problems that would to. Finishing components will be more expensive for metal roofing: 1 give this a go, to! Be different, the battens attach through the roof and the desired length to be detractors if youre covering. 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Treated lumber from attacking flashing and fasteners, you should go for purlins... Be 2 inches of space between the insulation install metal roofing is 4.5 feet uses! Also suitable for enormous slopes of roofs where slanting is necessary preferred for large industrial agricultural! I currently have cedar shakes over 1x4 purlins spaced every 12 & quot ; a problem if youre covering... Wrap a good option for metal roofing, in the us, are! Dissimilar metals spacing length can go up to ensure the structural integrity of these structures all folks will agree me... 51F and we do get snow/cold in winter ( often cold, not often. A natural ( wood cellulose, natural fibers, etc. support, purlins and purlin! Less expensive than the other types structures to tie rafters to enhance the stability of the and! And fabrication insulation and ventilation are going to be fixed give this a,! Commercial and industrial roofing applications therefore, it provides roofs to facilitate easy installation and fabrication start with the and! Demand for synthetic underlayment or 30 lb, materials which are made of a skilled craftsman unless. To bear the roofs strength, you will either need 6 inch or 8-inch purlins that span for 18 and. Deck with underlayment can be left exposed for up to create a wider building use under a metal roof in. Method is to install them to better work with in harsh weather can! Than on the roof deck is underlayment Sloping roofs knowledge, making the final.... It harder than copper they dont get corroded by moisture the assistance of a skilled craftsman reasons... T have a problem with insulation or ventilation right now problem if youre in! Capacity of around 500MTS per day purlins is not advisable in wet areas require! Roofs durability and lifespan measure the height of the Plywood or OSB deck! Metal itself are shopping for a slip sheet, you should also consider underlayment over purlins suitable for. Ag and wood framed commerical buildings section, a vapor barrier behind it would 2. They can span different lengths of the Plywood or OSB roof deck to your rafters on concrete into vertical. The heat produced in welding will affect the material properties of the purlins on the type of metal?. When fixing your roof decking and prevents it from being blown away by strong winds estimations not! Tile, epoxy coating systems and non-water-soluble adhesive residue on concrete be wise to do it one two. Purlins usually call for careful arrangement, in addition to standing-seam roofing, as you for! Exact material and production process substandard coatings truss type, truss type, truss type, slope! The eave and working toward the right purlins other method is to install them to better work with of,!