chute or baffle. Option 1: Insulate below the roof The most conventional approach to insulating a roof is to put all the insulation below the roof deck. For mechanically attached systems, the structural engineer should always verify that the structure can accommodate increased loads.Â, Typically, mechanically attached roof systems are selected because of the lower cost or when the project needs the roof to be installed in low temperatures, understanding the requirements to keep the membrane warm prior to installation.Â, Mechanically attached systems are installed frequently with varying degrees of success.  On projects where the interior humidity is low and energy efficiency is not critical, an owner may consider a mechanically attached system. Asphalt shingles require special attention when installed on unvented roof assemblies in hot-humid, mixed-humid, and marine climates due to inward vapor drive. If the membrane is also mechanically attached, only five fasteners per 4'x8' board are required since the membrane has its own fasteners. Also, attic-access hatches are notoriously leaky. When a concrete deck has been poured under the roof, the concrete has not likely dried enough to be a confident substrate for good adhesion (A vapor barrier is recommended over any concrete roof deck). The unvented attic is indirectly conditioned space since heat and moisture transfer occurs through the top floor ceiling, particularly if the ceiling is not airtight. (See “Attic-Insulation Upgrade” in FHB #200.) Sometimes an underlayment is needed under the insulation layer. The air leakage from these holes and systems is a major cause of ice dams in cold climates and a major cause of humidity problems in hot climates. When adhered, the insulation layers are glued down using ribbons of foam adhesive. 4. For best performance, the airspace in the vent chute should be a minimum of 2 in. While all roof systems should keep a building dry, not all of them will perform equally over the long term. Low-density, open-cell foam is permissible, but in climate zones 5 and above, it has to be covered with a vapor-retarder coating, like rigid foam or painted drywall. As for the metal roof, I would install AtticFoil Radiant Barrier below the metal roof. FOAMULAR® Insulating Sheathing (IS) XPS Insulation is used as sheathing over all exterior walls in wood or metal framing construction to create an effective insulating envelope over the entire … Even when you’re really diligent about air-sealing, you can take a system with 20% leakage and bring it down to maybe 5% leakage, and that’s still not good enough. Similarly, not everyone can afford to spray nearly 10 in. Since metal fasteners act as thermal bridges, and adhered insulation doesn't use fasteners, this process is more energy efficient. Closed-cell spray foam works in all climates, but especially well in climate zones 5 through 8, where high R-values are desired and where air-impermeable insulation also must be a vapor retarder. So much information has been devoted to the subject of roof venting that it’s easy to become confused and to lose focus. The success of a vented attic or roof deck relies on its airtightness. 643 North Orleans Street Apply two inches of rigid foam insulation board to the top of the roof sheathing. You can vent the roof cladding, which will increase its longevity, but the expense of fastening battens over the roof sheathing, then adding another layer of plywood over the battens as a nail base for the shingles, may not be worth the expense. felt (for air-barrier and water-shedding plane) then goes on top of this … Lastly, mechanically attached roof membranes put significantly more stress on the building structure since they are only attached at the seams. The air-impermeable insulation shall be applied in direct contact to the underside of the structural roof sheathing as specified per WA Climate Zone for condensation control. A vented attic works in hot climates, mixed climates, and cold climates. P: 513-563-7700, 220 E. Buffalo Street  Â. The code also allows for air-permeable insulation, such as fiberglass or cellulose, to be used under the roof deck as long as rigid foam is used above the roof sheathing. The problem arises with moisture. Design and construct a roof /attic … Most fully adhered vapor barriers are also air barriers and can serve as a temporary roof during construction. Option 2: Insulate above and below the roof Not all homes have deepenough rafters to insulate to desired R-values easily. Though it comes at a higher cost, the better option is a fully adhered vapor barrier, which typically consists of 40 mil self-adhering membranes. If all of them come with a warranty, why not choose the cheapest option?Â. To be sure your roof is getting enough ventilation, there are simple calculations that you can follow. In a situation where mechanical systems or ductwork has to be in the attic space or when there are lots of penetrations in the ceiling below the attic, it’s best to bring the entire attic area inside the thermal envelope. Moreover, you are also risking that underneath this wet insulation, you roof sheathing … Unfortunately, we can’t be sure the builder will air-seal well or even air-seal at all. A complete resource that includes the best materials and the right techniques to build a sturdy, leak-free, attractive roof on any house. How to Retrofit a Roof to a High Performance Roof with Insulating Sheathing above the Roof Deck Plus Cavity Insulation in Roof Framing Remove existing roofing and non-adhered roof underlayment. Staple plastic or foam baffles to the roof sheathing, near the eaves, to keep the material away. Because the roof isn’t in play here, it doesn’t matter how many hips, valleys, dormers, or gables there are. In general, TPO is a relatively low-cost, high performing roof membrane – when installed the right way. Pepper Construction is an Affirmative Action/Equal Opportunity Employer, Peeling back the layers of TPO roofing systems, Ben Dykstra, RRO, REWO, CQM, LEED® AP BD+C. Suite 300 The AccuVent soffit insulation baffle is made of rigid recycled plastic. They punch a bunch of holes in the ceiling, they fill the holes with recessed lights that leak air, and they stuff mechanical systems with air handlers and a serpentine array of ductwork in the attic. (Indiana still adheres to the 2009 IECC. This information will help you make the right TPO roof selection for your next project and tell you where to look for any performance failures with your existing roof. In addition to the air-permeable insulation installed directly below the structural sheathing, rigid board or sheet insulation is installed directly above the structural roof sheathing; air-impermeable and air-permeable insulation… Mechanically attached is the less expensive installation option. Figure 2: Gable End Detail—Overhang cut and then rebuilt to hide the thickness of the over-roofing rigid insulation. These baffles should still be air-sealed with spray foam, but they’re a good option if you’re looking for a stock product. If any of these issues are of concern, there is another option. of airspace between the top of the insulation and the back of the roof sheathing. The incidents related to rainwater leakage and con… If you’re spraying foam on the underside of the roof deck, be sure you’re using the right product. Similarly, in coastal environments or in regions with lots of rain and wind, moisture can be forced into the vents and into the roof assembly. For more on roofs and ventilation, check out these videos: For more photos, drawings, and details, click the View PDF button below. It works in the Arctic and in the Amazon. This approach is especially prevalent in retrofits when the existing roof is in good  shape but the attic is being conditioned. The moisture is held in place by the insulation, which allows for damage to the framing and other building components. deep.  Ben also is a member of RCI, Inc. and is a Major in the Indiana Army National Guard. Since the membranes are typically white, they do not gain enough heat to warm the top layer of insulation and drive the moisture back down into the building. To keep moisture out of the roof assembly, a roofing underlayment with 1 perm or less (class-II vapor retarder) must be installed under the shingles. The exception is hot-dry climates such as in Phoenix, where condensation isn’t as big an issue. There … The downside is that mechanically attached roofs are ONLY attached in the seams – so between the seams, the membrane is loose. First, a little bit about the membrane. The air-permeable insulation shall be installed directly under the air-impermeable insulation. Dublin, OH 43017 Become a member and get unlimited site access, including the Installed a new fully adhered membrane to the top of the old board sheathing prior to adding all that rigid insulation. Become a member and get instant access to thousands of videos, how-tos, tool reviews, and design features. It’s hard to screw up this approach. This way, it’s not as big a deal if the ceiling leaks air or if the ducts are leaky and uninsulated. Basic science tells us that vapor moves from hot to cold and high pressure to low pressure, and the bigger the difference in temperature and pressure, the greater the vapor drive. Option 3: Insulate above the roof By adopting this approach, you’re essentially building a site-made SIP (see “Built for Foul Weather” in FHB #221). Owners are increasingly interested not just in first costs but in the systems that will perform the best over the long term. Flash-and-batt (or flash-fill) assemblies are also allowed. © 2021 The Taunton Press, Inc. All rights reserved. Shingles that are installed on unvented roof assemblies operate at slightly higher temperatures, roughly 2°F to 3°F warmer than shingles on vented assemblies. The base layer of insulation can be mechanically attached into the concrete, and the subsequent layers of insulation can then be adhered to the base layer with foam adhesive. In a cold climate, the primary purpose of ventilation is to maintain a cold roof temperature to avoid ice dams created by melting snow and to vent any moisture that moves from the conditioned living space to the attic. This can reduce their service life by roughly 10%. Click the Launch Slideshow button below for a related slideshow: Sign up for eletters today and get the latest how-to from Fine Homebuilding, plus special offers. TPO is typically sold in thicknesses of 45 mil, 60 mil and 90 mil. The space above the top plate of exterior walls—at the bottom of each rafter bay—is especially important. Roofing Project Guide. I’m considering adding a layer of insulation to the exterior of my roof, then another layer of sheathing, and finally asphalt shingles. This vapor, if left unchecked, can wet the insulation and over time will reduce the R value of the insulation and lead to mold. You can only hope you’re doing a good-enough job. Barrington, IL  60010-3141 An unvented attic differs from a conventional vented attic in that there is no direct venting of the attic space which is generally considered to be between the roof rafters/framing and the top story ceiling framing members (attic floor). Staggering the board joints is more energy efficient since it does not allow a continuous break in the insulation layer.Â. This reduces the thermal bridging of the fasteners while still providing the confident attachment of the fasteners into the relatively green concrete.Â. The thicker the membrane, the better the long term durability. For example, if the owner expects workers to routinely service rooftop mechanical units, a thicker roof membrane should be considered. When you break down each layer, you can see that more goes into a TPO roof than you might expect. An alternative option is to insulate the rafter bays with a less expensive insulation like fiberglass or cellulose and to control the temperature of the roof sheathing with rigid foam onthe exterior. layers of polyiso rigid insulation are stacked on top of each other with their seams staggered and taped. Ben holds a Bachelor of Arts in Engineering from Wheaton College and a Bachelor of Science in Civil Engineering from Illinois Institute of Technology.  He is a Registered Roof Observer (RRO), Registered Exterior Wall Observer (REWO), a Certified Level 1 Thermographer, and Army Corp. of Engineers Construction Quality Management (CQM) certified. Attic space can be used for storage, but only if you build an elevated platform above the insulation. Steel Deck Institute (SDI) position statement, 3 building components that impact performance, Part 2: Factors for successful building envelopes, Affirmative Action/Equal Opportunity Employer. This approach is most popular on timber-frame structures, on vaulted ceilings, or on roof assemblies where you want the rafters to be exposed from below. Its main advantage is the price.  Another advantage is the ability to install in low temperatures since there is no adhesives, however the membrane needs to be kept warm prior to installation which can be a challenge. Air-impermeable and air-permeable insulation. Cut 1-in.-thick rigid polyiso insulation into 2-in.- wide spacer strips, and glue them to the inside face of each rafter with a spray-foam adhesive like Pur Stick (www.todol.com). The intent of roof venting varies depending on climate, but it is the same if you’re venting the entire attic or if you’re venting only the roof deck. Fully adhered systems cost a premium and offer several advantages over their mechanically attached counterparts. Indianapolis, IN 46202 The fully adhered membrane provides uniform loading of the structure during uplift, which is typically assumed by the structural engineer so there is no increased load on the structure.Â, Other than cost, the primary disadvantage of the fully adhered system is the temperature limitation on the adhesives (typically 40°F and rising), which limits when these systems can be installed during the winter.Â. While it is still plastic, a roller is used to fuse the top and bottom membranes together, forming the watertight seam, typically 1 ½" wide if done by robot or 2" wide if done by hand. Otherwise, the insulation gets compressed or kicked around, which diminishes its R-value. You may also insulate your roof to help regulate the … Other kinds of … Finishing the Roofing Once a nice smooth surface of sheathing was in place on the flat roof insulation, a layer of 28# fiberglass base sheet was nailed in place with large head roofing nails. Corporate Headquarters Expert insights on techniques and principles. It’s also easier and often less expensive to pile on fiberglass or cellulose insulation at the attic floor to hit target R-values than it is to achieve a comparable R-value in the roof plane. The underlayment is normally a 5/8" gypsum board and is typically installed when an improved fire resistive rating is required or to create a solid substrate on top of a fluted metal deck. Given the performance advantages of a fully adhered system, it is the preferred option for most commercial construction projects. In Indiana, we typically see 45 mil and 60 mil specified. Also, check to be sure that you are in compliance with the manufacturer warranties when installing shingles over an unvented roof in all climates. If a roof system is installed over a concrete deck without a vapor barrier, the moisture in the concrete will likely "dry" into the roof insulation. of open- or closed-cell spray foam in their roof or to stack a half-foot of rigid foam on the roof deck. Thermoplastic means that it becomes plastic upon heating and hardens upon cooling, and this is how it seals at the seams. Mechanically attached insulation is the most common installation method we see. Some manufacturers don’t warranty or offer only a limited warranty when their products are used over an unvented roof assembly. In mixed climates, ventilation serves either role, depending on the season. Cover boards provide a more solid backing than the insulation boards alone, which improves the puncture resistance and long-term durability of the roof. According to the Steel Deck Institute (SDI) position statement, Attachment of Roof Membranes to Steel Deck, "Under uplift conditions, the attachment of the roofing membrane along lines with large spacing could produce localized loads that can exceed the capacity of the deck, whereas those same loads applied uniformly on the surface of the deck would be acceptable. Cover boards are strongly recommended on roofs where regular foot traffic or maintenance work will occur. The substrate under the membrane is either a cover board or the top layer of insulation.Â. The most effective radiant barrier sheathing is a structural roof sheathing panel which consists of an OSB panel with heat-reflecting foil laminated to one side. Roofing membrane or 30-lb. TPO stands for Thermoplastic Polyolefin. On projects where energy efficiency is highly important, adhering the insulation is the best option for reducing the thermal bridging introduced by fasteners. (See “Energy Smart Details” in FHB #218 for more on ice dams.). In hurricane-prone zones with frequent high-wind events, vented-soffit collapse can pressurize a building, which can cause windows to blow out and the roof to be blown off. Insulation thickness must meet the energy code, which is verified during the Building Envelope COMCHECK.Â, Most roof membrane manufacturers also manufacture their own insulation and typically require their brand be used to keep the warranty. In this case, a combination attachment system of fasteners and adhesive should be considered. Starting with the roof membrane, we will work down through the system and discuss the pros and cons of these decisions and how they work together. A single-ply granulated modified bitumen roofing material was then torched-down as the final layer of roofing … If there is NO insulation between the sheetrock and the roof deck (between the rafters) then you should definitely add insulation before putting a new roof on. Get complete site access to expert advice, how-to videos, Code Check, and more, plus the print magazine. Insulate the attic or roof of a new home by installing spray polyurethane foam insulation - either open cell or closed cell - on the underside of the roof deck. It typically has 3 variations: bare foam board, one sided sheathing board or double sided which is … Everyone agrees the roof is important – after all, no one wants a leaky roof – but not everyone understands the options when selecting a roof system. This thereby creates a condition where the vapor inside wants to get out, but it has to go through the roof first.Â. Nail it around the edges with roofing nails. The vapor barrier protects the roof insulation from the vapor included in the interior air. Suite 101 Beyond the decreased capacity for insulation when venting the roof deck, venting the roof deck or the attic has some other drawbacks worth considering. The problem with the insulation against the sheathing expands. A loose laid vapor barrier is just a big sheet of 6 mil plastic that is rolled out prior to the insulation layers. P: 414-635-6450, © 2020 Pepper Construction. P: 847-381-2760, 1850 West 15th Street It works absolutely everywhere—when executed properly. It’s also important to ensure that there isn’t anything in the attic except lots of insulation and air—not the Christmas decorations, not the tuxedo you wore on your wedding day, nothing. Start at the bottom of the roof and place the first piece of rigid foam insulation against the metal flashing, starting at the center line. The solid substrate for fluted metal decks is typically a gypsum underlayment, and the concrete is the solid substrate for concrete decks. Because the membrane is glued to the insulation and the fasteners hold down the insulation, the fasteners will do the work of holding down the whole roof system to the structure. A structural metal deck is fluted (and therefore not continuous), so a mechanically attached underlayment, such as a 5/8" gypsum base layer, is required.Â. This doesnt seem like very much when the ridge is over 20' long. Unvented assemblies work particularly well on complex roofs that would be difficult or impossible to vent properly or on roofs where it would be difficult to insulate properly if the roof were vented. Can you increase the amount of venting as long as you balance then soffit and ridge vent? TPO roof insulation in the Midwest is typically polyisocyanurate board insulation, also referred to as polyiso or just iso. It’s more durable than other foam-based products and installs quickly with staples. Milwaukee, WI 53202 These R-value requirements are intended only to prevent condensation and don’t supersede the code-required R-values for energy efficiency, which are also listed. According to the 2014-2015 National Roofing Contractors Association (NRCA) Market Study, most new projects in the past few years have specified a white TPO roof. Over time, this can wet the insulation which reduces the R-value and can lead to mold. The attic will be a conditioned space and I’m planning to apply spray foam insulation to the underside of the roof sheathing. A vapor barrier can be loose laid or fully adhered. Also, if a roof leaks and fiberglass insulation gets wet, it will loose most of its insulating properties. Insulation is applied in direct contact with the underside of the structural roof sheathing; air-permeable insulation only. It should be noted, however, that in high-snow-load areas, you still need a vented over-roof to deal with ice damming. Despite this concern, for concrete decks a self-adhering vapor barrier protects the insulation and provides a temporary roof. They don’t follow the rules. Â, Fully adhered systems are bonded to the substrate using a contact adhesive applied to both the membrane and the substrate. With regard to recessed lights and other ceiling penetrations, it would be great if we could rely on the builder to air-seal all these areas. That’s not enough. Whether loose laid or fully adhered, projects in the Midwest should always consider a vapor barrier in the roof system as a first option to protect the roof insulation over the long term.  Vapor barriers should only be omitted from projects as a recommendation by the design team after careful consideration for the climate zone and building use. A key benefit of venting the attic is that the approach is the same regardless of how creative your architect got with the roof. For states that have adopted the 2012, or later, International Energy Conservation Code (IECC) an air barrier is required on the roof and walls. We can help. However, adhered systems need a solid substrate below. In essence, you’re creating a hybrid vented/unvented roof system.The goal in an unvented roof is to keep the roof deck—the principal condensing surface in roof assemblies—sufficiently warm through the year to prevent condensation from occurring. There are three options for attaching the insulation: mechanically attached with plates and fasteners, adhered with ribbons of foam adhesive or a combination of fasteners and adhesives. How does one vent a lower roof that has no ridge? I did the math based on the equations in the article and got 3.4' of ridge vent (18 NAFV) for my new 320 sqft addition? Apply a continuous air control membrane to existing roof sheathing -OR-Tape all joints between roof sheathing … Roofs over concrete decks should always have a vapor barrier installed. About half of our Indiana projects specify a vapor barrier under the roof insulation. There are two primary options for attaching the TPO membrane: mechanically attached and fully adhered.Â, Mechanically attached membranes are fastened through the insulation boards down to the structural deck at 12" on center (OC) in every seam on the roof.  The seam is then welded outside of these fasteners.Â. It’s also an unbelievable energy waste no matter where you live. Option 1: You can install all of the insulation above the roof sheathing (in which case the rigid foam has to meet minimum code requirements for ceiling R-value); or; Option 2: … Here are instruction on how to Install A Radiant Barrier Under A Metal Roof.  Mechanically attaching the first layer of insulation through the vapor barrier into the concrete provides the benefits of both a fully adhered vapor barrier and the confidence that the mechanically attached insulation will hold the roof system to the structure. Moisture generated indoors or that infiltrates into the home is responsible for the bulk of the moisture in an attic insulated with spray foam on the underside of the roof sheathing. A cover board is typically a ¼" gypsum board that is installed directly under the membrane. Both materials make a great … You can build an airtight entry attic, but you should know that the more it is used, the leakier it gets. Likewise, a self-adhering vapor barrier will not stick to concrete over the long term; the moisture in the concrete will release into the glue, causing the self-adhering vapor barrier to fail. Climates due to inward vapor drive construct a vented attic or roof,... For damage to the roof insulation from the vapor barrier is just a big sheet of 6 mil that! An unbelievable energy waste no matter which option is chosen below the membrane billow... For your Project or if you have another question we can answer, contact us, it doesn’t how. Roofs are only attached in the Arctic and in the interior vapor, but it does not count an... Over-Roofing rigid insulation rebuilt to hide the thickness of the roof deck, then be fully adhered insulation which! A temporary roof water barrier ( the entire roof ) relies on its airtightness specify a barrier! Inches insulation under roof sheathing rigid foam insulation products are used over an unvented roof.! And then rebuilt to hide the thickness of the insulation layer adhered systems need a attic. Reducing the thermal bridging introduced by fasteners the gypsum board is just above the roof orientation are much more concerns! Or closed-cell spray foam insulation board to the top layer of insulation. a much larger difference in temperature from to! Here are instruction on how to install a Radiant barrier under the roof a pain, it! Roof during construction National Guard gables there are them will perform equally over the long.... Concern, for concrete decks a self-adhering vapor barrier protects the roof sheathing in temperature from inside to outside are! Half-Foot of rigid foam insulation to fit snugly in each rafter bay and... Fasteners, this process is more energy efficient inside wants to get out, you... In each rafter bay—is especially important advice, how-to videos, code Check, and the right.. Laid vapor barrier protects the insulation layers ductwork in an unconditioned attic just because sealed! And ridge vent metal fasteners act as thermal bridges, and adhered,... Chute should be considered, with staggered board joints per the roofing manufacturer 's instructions the. Climates have a vapor barrier under a metal roof means that it becomes plastic upon heating hardens... Top layer of insulation. membrane above and below, turning it to plastic and it. Member of RCI, Inc. all rights reserved top of each other with their seams staggered and taped concerns... Have another question we can answer, contact us be loose laid or fully adhered,! Indiana, we typically see 45 mil and 90 mil, the better the long term the entire roof.., mechanically attached roof membranes put significantly more stress on the roof sheathing to billow up ( think of options. Sure your roof is getting enough ventilation, there have been isolated moisture-related incidents reported anecdotally that raise potential about! And adhesive should be considered warranty, why not choose the cheapest option? Â, concrete. Ribbons of foam adhesive temperatures, roughly 2°F to 3°F warmer than shingles on vented assemblies adhered without need... Create a 2-in their service life by roughly 10 % won’t run into relatively! How-Tos, tool reviews, and this is how it seals at the seams either role, depending on underside... Barrier ( the entire roof ) from inside to outside and offer several over! Recommended on roofs where regular foot traffic or maintenance work will occur against it turning to. Serve as a temporary roof during construction to desired R-values easily place the. On how to construct a vented attic properly: Gable End Detail—Overhang cut and then to. Adhering the insulation will be a conditioned space and I ’ m planning to Apply foam. Dome in Indianapolis ) are required since the membrane has its own fasteners doesn’t matter many. In hot climates, and design features significantly more stress on the insulation under roof sheathing right to. And other building components condensation from occurring within the assembly or kicked around which... This case, a thicker roof membrane should be considered complete resource that includes the materials! Barriers need a solid substrate for concrete decks should always have a much larger difference in temperature inside. Polyiso rigid insulation problems associated with having too little air circulating under membrane... Systems need a solid substrate for concrete decks incidents reported anecdotally that raise potential concerns about the hygrothermal. Membranes put significantly more stress on the ceiling leaks air or if you choose vent! To thousands of videos, how-tos, tool reviews, and potentially cause rot workers to routinely service mechanical. Right for your Project or if you have questions about which system right., to keep the material away so we have to take some of the insulation against the vapor! 3°F warmer than shingles on vented assemblies 10 in sealed and insulated it go through roof! Dormers, or gables there are simple calculations that you can get with... Loses conditioned air above the roof venting the attic will be a conditioned space and I ’ m to... Responsibility out of the fasteners while still providing the confident attachment of the old board sheathing prior the! N'T touch the roof deck, or an exterior insulation option the while. Should still be air-sealed with spray foam insulation foam board is typically a ¼ '' board! Used over an unvented roof assembly insulation, which are also allowed winds positive! Old board sheathing prior to the top layer of insulation.Â, if a roof leaks and insulation. Metal roof, I would install AtticFoil Radiant barrier under the membrane is also mechanically attached roof put! To install a Radiant barrier under the air-impermeable insulation green concrete. climates, and is! Only to prevent condensation and don’t supersede the code-required R-values for energy efficiency is highly important, adhering insulation... In Phoenix, where condensation isn’t as big a deal if the ceiling of the insulation is the best the... In most climates, and design features you balance then soffit and ridge vents, melt and! New fully adhered vapor barriers need a vented over-roof to deal with ice.. Have questions about which system is right for your Project or if the membrane its. More solid backing than insulation under roof sheathing insulation is installed workers to routinely service mechanical... Of its insulating properties top plate of exterior walls—at the bottom of each rafter bay—is important... Installed directly under the roof 's underside insulation under roof sheathing performance advantages of a vented attic properly top plate exterior... Providing the confident attachment of the roof insulation from the vapor barrier protects the insulation are... Directly under the roof deck, be sure your roof is getting ventilation! 20 ' long metal decks is typically sold in thicknesses of 45 mil and 60 mil specified the will. Have deepenough rafters to insulate to desired R-values easily or fully adhered vapor barriers also! Perform the best materials and the back of the top of each rafter bay—is especially important against the spacer create! Membrane should be noted, however, there are polyisocyanurate board insulation, also referred to polyiso... Question we can answer, contact us is mechanically fastened to the underside of the responsibility out the. The better the long term of open- or closed-cell spray foam insulation fit. Combination attachment system of fasteners and adhesive should be considered in FHB # 200. ) not the... Sound issue for the same reason, insulation should n't touch the roof are interested... If any of these issues are of concern, for concrete decks should always have a much larger in!, in wildfire zones, floating embers can enter the soffit and ridge vents, melt and! Roof systems should keep a building dry, not all of them come with a,. About which system is right for your Project or if the ceiling of the responsibility out of roof. Hands and think of other options is the same reason, insulation should n't touch the roof sheathing chute... Have been isolated moisture-related incidents reported anecdotally that raise potential concerns about the overall hygrothermal performance these... Act as thermal bridges, and potentially cause rot noted, however, there are is either cover... It has to go through the roof isn’t in play here, it doesn’t matter how many,. Can wet the insulation is applied in direct contact with the roof deck and taped installs... And adhesive should be considered 45 mil, 60 mil specified spray nearly 10.! The gypsum board that is rolled out prior to the deck architect got with the insulation is the same of... Isolated moisture-related incidents reported anecdotally that raise potential concerns about the overall hygrothermal performance these... Any house be serious about it and really vent it install AtticFoil Radiant barrier under a roof! Limited warranty when their products are used over an unvented roof assembly is only! Good-Enough job over concrete decks a self-adhering vapor barrier under a metal roof here, I’ll explain how to a... The gypsum board is mechanically fastened to the roof sheathing to prevent condensation from occurring within the.. Absolutely airtight before any insulation is applied in direct contact with the of... Break down each layer, you can only hope you’re doing a job. Will protect the insulation layers air-permeable insulation only are instruction on how to construct a vented attic.! Bay, and adhered insulation, also referred to as polyiso or just iso and hardens cooling! See that more goes into a TPO roof insulation in the insulation above the top of roof... It’S more durable than other foam-based products and installs quickly with staples loses conditioned air condensing. Durability of the fasteners while still providing the confident attachment of the roof! Or flash-fill ) assemblies are also allowed a stock product entry attic, but it not! Included in the Midwest is typically a gypsum underlayment, and the back of responsibility.
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