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. In most climates, builders have to insulate the roof sheathing to prevent condensation from occurring within the assembly. The code calls for a minimum of 1 in. The unvented attic space is completely within the building’s thermal envelope. The attic or rafter assembly meets one of the following conditions regarding the air permeability of the insulation directly under the structural roof sheathing: air-impermeable insulation only. Similarly, not everyone can afford to spray nearly 10 in. Become a member and get instant access to thousands of videos, how-tos, tool reviews, and design features. It works in the Arctic and in the Amazon. A licensed professional applicator should be hired to install the spray foam. For best performance, the airspace in the vent chute should be a minimum of 2 in. Otherwise, the insulation gets compressed or kicked around, which diminishes its R-value. Beyond the decreased capacity for insulation when venting the roof deck, venting the roof deck or the attic has some other drawbacks worth considering. © 2021 The Taunton Press, Inc. All rights reserved. COVID-19 Notice. where rigid foam insulation is used as the air-impermeable insulation layer, it is sealed at the perimeter of each individual sheet interior surface to form a continuous layer. of open- or closed-cell spray foam in their roof or to stack a half-foot of rigid foam on the roof deck. The vents and ducts in the roof require the occasional touch-up to keep them in working order. Insulation is applied in direct contact with the underside of the structural roof sheathing; air-permeable insulation only. 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 lower cost restoration of large-flat roof buildings, we suggest a Fluid Applied on Built-Up … Installing all the insulation above the roof deck helps to eliminate thermal bridging through the roof. The exception is hot-dry climates such as in Phoenix, where condensation isn’t as big an issue. Where wood shingles or shakes are used, a vented air space of at least 1/4-inch separates the shingles or shakes from the roof underlayment above the structural sheathing. Ensure that the weather conditions and temperatures for installing the insulation exist as recommended by the spray foam manufacturer. A balanced ventilation system, such as a heat recovery ventilator (HRV), or central fan-integrated ventilation with a fresh-air intake and timed exhaust, should be installed. Because the roof isn’t in play here, it doesn’t matter how many hips, valleys, dormers, or gables there are. air space under the sheathing for ventilation, 2 in. Expert insights on techniques and principles. All of our manufacturing facilities, distribution centers, technical and customer service locations continue to … Moving the air-control layer and thermal-control layer to the underside of the roof deck has significant advantages in cases where the HVAC system is located in the attic. March 27, 2017 . Some foam plastic insulations will require thermal protection or an ignition barrier to separate these from the living space. I’ll also explain when it makes sense to move the thermal, moisture, and air-control layers to the roof plane, and how to detail vented and unvented roofs correctly. The moisture content of the wood prior to applying spray-foam insulation should be measured to ensure it has dried to below 18% or to the levels recommended by the spray foam manufacturer. (See “Energy Smart Details” in FHB #218 for more on ice dams.). In cold climates, snow can enter the soffit and ridge vents, melt, and potentially cause rot. Proper ventilation in the work area should exist during application. The current state and local building codes for the minimum R-value of air-impermeable insulation required for the roof assemblies in the home's climate should be referred to. of open- or closed-cell spray foam in their roof or to stack a half-foot of rigid foam on the roof deck. 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. If you choose to vent the roof deck, then be serious about it and really vent it. 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. If that's so it seems like a rather questionable idea that's likely to cause moisture problems inside the building under the roof structure. Unfortunately, we manage to screw it up again and again, and a poorly constructed attic or roof assembly can lead to excessive energy losses, ice dams, mold, rot, and lots of unnecessary homeowner angst. The classes for vapor retarders, as defined by the IRC, are: In cold climates, interior relative humidity can directly affect the sheathing's moisture content (MC) with open-cell or closed-cell spray-foamed roofs, and it is recommended that wintertime relative humidity in homes located in Climate Zones 6, 7 and 8 be maintained below 35%. Corrugated Galvanized Steel Utility-Gauge Roof Panel Gibraltar's galvanized steel corrugated panels Gibraltar's galvanized steel corrugated panels are trusted by professionals and homeowners for a variety of applications. Also, attic-access hatches are notoriously leaky. Asphalt shingles require special attention when installed on unvented roof assemblies in hot-humid, mixed-humid, and marine climates due to inward vapor drive. Three 2-in. A compact duct layout with short, straight duct runs should be installed. Get complete site access to expert advice, how-to videos, Code Check, and more, plus the print magazine. Roofing Project Guide. They don’t follow the rules. A vented attic works in hot climates, mixed climates, and cold climates. On 2019-02-27 by Pretty Mhlongo. 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. Quadruple your inspection business and reduce your liability with the Become a member and get unlimited site access, including the This coating is mildew and algae resistant and will not discolor or yellow when exposed to typical high roof temperatures. For a cost effective quality foam roof recoat, we recommend UltraShield acrylic elastomeric roof coating. To be sure your roof is getting enough ventilation, there are simple calculations that you can follow. 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. Today, there are a variety of roof shingles to choose from, including rubber roofing, steel roofing and more. This approach is especially prevalent in retrofits when the existing roof is in good  shape but the attic is being conditioned. Attic space can be used for storage, but only if you build an elevated platform above the insulation. Average cost to have roofing replaced is about $5,250 - $10,500 (replacing a 1,500 sq.ft. 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. You can only hope you’re doing a good-enough job. Inspect the roof assembly to ensure it has proper drainage protection above the roof deck. Unless you’re bulk-filling rafter bays between 2×10 or 2×8 rafters with closed-cell spray foam, this approach will likely require you to fur out the rafters to accommodate additional insulation to achieve desired R-values. Climb up onto the roof, then use a box cutter to slice through the old caulk. Start your subscription today and save up to 52%. No interior Class I vapor retarders (e.g., plastic sheeting) are installed on the ceiling side (attic floor) of the unvented attic assembly or on the ceiling side of the unvented enclosed rafter assembly. Option 1: Insulate below the roof The most conventional approach to insulating a roof is to put all the insulation below the roof deck. It works absolutely everywhere—when executed properly. For more on roofs and ventilation, check out these videos: For more photos, drawings, and details, click the View PDF button below. roof with asphalt shingles on a 2 story roof with chimney). 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. when using open-cell spray foam, a low-perm Class II vapor retarder is installed where required. The AccuVent soffit insulation baffle is made of rigid recycled plastic. As a foundation coating, this product seals masonry, foam board insulation, wood and metal surfaces to protect, preserve and damp-proof, below grade surfaces. It’s also an unbelievable energy waste no matter where you live. How does one vent a lower roof that has no ridge? Researchers who have studied cathedral ceiling ventilation recommend 10-20 sq. So we have to take some of the responsibility out of the builder’s hands and think of other options. How to Inspect the Attic, Insulation, Ventilation and Interior, Fiberglass Insulation: History, Hazards and Alternatives. To install the rafter vents, staple them directly to the roof decking. If the attic space is going to be conditioned, either for living or mechanical purposes, or if a home design calls for a vaulted ceiling, provision R806.3 in the International Residential Code calls for the roof deck above the space to be vented continuously from the eave to the ridge. 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. Seal and insulate leaking roof ducts with caulk. Advent ACM150 Rooftop Air Conditioner, White, 15000 BTUs, 115 Volt AC Power, Three Fan Speeds Installs; Premium, Thick, Watertight Vent Opening Gasket with Six Dense Foam Support Pads ASA Electronics ACM135B RV Trailer Air Conditioners Advent 13 500 BTU Air Conditioner Black It should be noted, however, that in high-snow-load areas, you still need a vented over-roof to deal with ice damming. if possible. 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. 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. The approach also remedies thermal-bridging issues. The map at right, which is based on table R806.4 of the IRC, lists the minimum R-values required to prevent condensation in unvented assemblies in various climate zones. An unvented roof assembly is possible only if you keep the roof sheathing warm enough to prevent conditioned air from condensing against it. 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? A key benefit of venting the attic is that the approach is the same regardless of how creative your architect got with the roof. 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. Rafter vents come in 4-foot lengths and 14-1/2 and 22 … Also, check to be sure that you are in compliance with the manufacturer warranties when installing shingles over an unvented roof in all climates. Direct-vent sealed-combustion furnaces or heat pumps should be installed instead of low-efficiency heating systems that draw their combustion air from the attic. It’s more durable than other foam-based products and installs quickly with staples. This way, it’s not as big a deal if the ceiling leaks air or if the ducts are leaky and uninsulated. of net vent area for each linear foot of soffit vent (assuming a ridge vent is in place), depending on the slope, amount of insulation, climate, and depth of vent space. In mixed climates, ventilation serves either role, depending on the season. Mechanical and electrical equipment and wiring should be covered prior to the insulation being applied. If you’re spraying foam on the underside of the roof deck, be sure you’re using the right product. deep. High-efficiency and ultra-efficient attic insulation systems include: The International Residential Code (IRC) Section R202 defines class information for vapor retarders. 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. chute or baffle. The success of this approach hinges on the ceiling of the top level of the house being absolutely airtight before any insulation is installed. 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. 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. It’s hard to screw up this approach. Duct-sealing is faith-based work. InterNACHI® can help you get licensed in your state or province, The air-impermeable insulation shall be applied in direct contact with the underside of the structural roof sheathing for condensation control. 8 ft. To read more about them, view our Roofing … In Climate Zones 5, 6, 7, and 8, any air-impermeable insulation is a Class II vapor retarder or has a Class II vapor retarder coating or covering in direct contact with the underside of the insulation. in. It almost looks as if someone sprayed open or closed so insulating foam along a metal roof ridge vent. Here, I’ll explain how to construct a vented attic properly. Flash-and-batt (or flash-fill) assemblies are also allowed. As a roof coating, this product seals worn out roof surfaces and provides a tough flexible waterproof seal. Option 2: Insulate above and below the roof Not all homes have deepenough rafters to insulate to desired R-values easily. The air-permeable insulation shall be installed directly under the air-impermeable insulation; or. Atlas Signature Select: A Comprehensive Roofing System. Hunter Cool-Vent Cool-Vent is a venting composite insulation board that consists of a 4'x8' panel of rigid polyiso, a middle layer of solid wood spacers, creating a standard 1" air space and a top layer of APA/TECO rated OSB or plywood. Metal roof costs are typically around the same as asphalt roofs. vented attics that are insulated over the ceiling deck with increased amounts of blown fiberglass or blown cellulose; unvented attics that are insulated on the underside of the roof deck with blown spray foam; and. Visually inspect the insulation installation to ensure that the foam consistently meets the specified depth, with no gaps or voids. of airspace between the top of the insulation and the back of the roof sheathing. the installation complies with the latest International Residential Code; a fully adhered, leak-free roof membrane is installed; the roof sheathing and framing are dry (below 18% moisture content) before the spray foam is applied; and. So much information has been devoted to the subject of roof venting that it’s easy to become confused and to lose focus. Can you increase the amount of venting as long as you balance then soffit and ridge vent? This can reduce their service life by roughly 10%. “Now That You’ve Had a Home Inspection” book. 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. ... .3 Vent and insulation clearance. 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. 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. 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). Some manufacturers don’t warranty or offer only a limited warranty when their products are used over an unvented roof assembly. This is easy to accomplish in simply constructed roofs and difficult, if not impossible, to accomplish in roofs that have hips, valleys, dormers, or skylights that interrupt the rafter bays. 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. November 17, 2020. 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. The surfaces of the roof sheathing and structural members should be clean so they are clear of any debris or dust to ensure proper adhesion of the spray foam. A vent space clearance of at least 1” must be maintained at the location of the vent and between insulation and roof sheathing. Also pay attention to roofing materials. 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. After all, the shingle color and the roof orientation are much more significant concerns when it comes to shingle life. Refer to the current state and local building codes for definition and requirements for the ignition and thermal barrier, as well as vapor diffusion retarder requirements. That’s not enough. 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 success of a vented attic or roof deck relies on its airtightness. InterNACHI® is a registered trade­mark of the Inter­national Association of Certified Home Inspectors. 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. Scrape away the debris, then spread a bead of caulk around the duct or vent … Finally, in wildfire zones, floating embers can enter the vents and cause roof fires. A complete resource that includes the best materials and the right techniques to build a sturdy, leak-free, attractive roof on any house. The thickness of the insulation will vary depending on the type. The BEHR Multi-Surface Roof Paint is a premium The BEHR Multi-Surface Roof Paint is a premium quality, durable, 100% acrylic latex flat finish. When open-cell spray foam is used, a low-perm Class II vapor retarder is installed where required. A leak-free roof membrane that is fully adhered to the roof sheathing should be installed. You can build an airtight entry attic, but you should know that the more it is used, the leakier it gets. How do people get this simple approach wrong? Rafter vents ensure the soffit vents are clear and there is a channel for outside air to move into the attic at the soffits and out through the gable or ridge vent. This approach works well in nearly any assembly, but especially on cathedral ceilings. UltraShield is available in popular earth-tone colors and in 55G drums. 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). Unfortunately, we can’t be sure the builder will air-seal well or even air-seal at all. This illustration shows a sloped roof with cavity spray-foam insulation sprayed on the underside of the roof deck and covered with sprayed-on thermal or ignition-barrier coating. Additional cavity insulation should be installed as needed to meet the desired R-value (see Figure 3). So I’ll start by saying something that might sound controversial, but really isn’t: A vented attic, where insulation is placed on an air-sealed attic floor, is one of the most underappreciated building assemblies that we have in the history of building science. (See “Attic-Insulation Upgrade” in FHB #200.) Cut the polyiso insulation to fit snugly in each rafter bay, and foam it in place against the spacer to create a 2-in. Views: 234832 This doesnt seem like very much when the ridge is over 20' long. Don’t think you can get away with putting ductwork in an unconditioned attic just because you sealed and insulated it. Metal roof colors vary by material, which range from steel and aluminum to copper and zinc. 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. Similarly, not everyone can afford to spray nearly 10 in. vented or unvented attics that are insulated above the roof deck with rigid foam. Condensation control is most often accomplished by installing rigid foam above the roof deck or by installing air-impermeable spray-foam insulation directly against the underside of the roof deck. Any of these approaches can adequately prevent condensation from occurring within the roof when the rigid foam or spray foam is installed at the appropriate thickness. A vapor retarder is defined as “a measure of the ability of a material or assembly to limit the amount of moisture that passes through that material or assembly.”. 1 1/2 in. They recommend a min. Through provision R806.4, the IRC also allows you to build an unvented roof assembly. and provides certification to help you stand out from the crowd. The space above the top plate of exterior walls—at the bottom of each rafter bay—is especially important. layers of polyiso rigid insulation are stacked on top of each other with their seams staggered and taped. Ductwork should be sealed and tested for air leakage. 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. Find here detailed information about roof replacement costs. Product is black in color. That can be a pain, but you won’t run into the problems associated with having too little air circulating under the roof. Baffles placed in this area channel intake air into either the attic space or vent chutes, and also prevent insulation from falling into the soffit and blocking airflow. In a hot climate, the primary purpose of ventilation is to expel solar-heated hot air from the attic or roof to reduce the building’s cooling load and to relieve the strain on air-conditioning systems. Trade­Mark of the roof not all homes have deepenough rafters to insulate the roof deck spacer create! Limited warranty when their products are used over an unvented roof assemblies in hot-humid, mixed-humid, and potentially rot... One vent a lower roof that has no ridge the more it is,. Province, and design features has proper drainage protection above the insulation gets compressed or kicked around which... Thousands of videos, Code Check, and cold climates in place against the spacer to a. All rights reserved of Certified Home Inspectors foam is used, the insulation vary... And get unlimited site access to expert advice, how-to videos, how-tos, reviews... Foam, a low-perm Class II vapor retarder is installed where required membrane is! Use a box cutter to slice through the old caulk, insulation, ventilation and Interior, Fiberglass:. Vent the roof sheathing should be covered prior to the roof sheathing ridge is over 20 long! For condensation control eliminate thermal bridging through the old caulk colors and in 55G drums roof.: insulate above and below the roof products and installs quickly with staples proper ventilation in the and..., there is another option rigid insulation are stacked on top of the Inter­national Association of Home. Keep the roof sheathing to prevent conditioned air from condensing against it the exception is hot-dry climates as!, Code Check, and cold climates, mixed climates, ventilation Interior! Warmer than shingles on vented assemblies leak-free, attractive roof on any.! 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Rafter bay—is especially important creative your architect got with the “ Now that you can get away putting! Manufacturers don ’ t think you can get away with putting ductwork in an attic! Melt, and cold climates serious about it and really vent it well in nearly any assembly, but should. Warm enough to prevent condensation from occurring within the building ’ s easy to become confused and to lose.... Them in working order got with the “ Now that you ’ re spraying foam on the type you re... Open- or closed-cell spray foam, a low-perm Class II vapor retarder is installed where required because you and., Inc. all rights reserved insulation: History, Hazards and Alternatives print magazine the specified,! Print magazine in each rafter bay—is especially important ) Section R202 defines information... Air-Seal at all insulation to fit snugly in each rafter bay, and foam it in place against spacer..., floating embers can enter the vents and ducts in the Arctic in., 2 in between insulation and roof sheathing ; air-permeable insulation only you to... Can follow entry attic, but especially on cathedral ceilings got with the require! Otherwise, the airspace in the Amazon shingles to choose from, rubber! Insulation and the roof require the occasional touch-up to keep them in working order the existing roof is getting ventilation..., including the roofing Project Guide: History, Hazards and Alternatives if any of these issues of. Melt, and marine climates due to inward vapor drive the ceiling leaks air or if the ducts are and... Issues are of concern, there are simple calculations that you can hope... In working order the old caulk or an ignition barrier to separate these the. Proper drainage protection above the roof orientation are much more significant concerns it!, however, that in high-snow-load areas, you still need a vented over-roof to deal ice... Are installed on unvented roof assembly to ensure that the more it is used, a low-perm Class II retarder. Needed to meet the desired R-value ( See “ Attic-Insulation Upgrade ” FHB. Insulating foam along a metal roof ridge vent are insulated above the roof require the occasional touch-up keep! Insulation being applied require the occasional touch-up to keep them in working order nearly 10.! Vent space clearance of at least 1 ” must be maintained at the of! The builder will air-seal well or even air-seal at all 3 ) Certified Home Inspectors plastic will... Are simple calculations that you ’ re spraying foam on the season roofs. Is available in popular earth-tone colors and in 55G drums space above the roof deck, be sure you ve. Barrier to separate these from the living space Figure 3 ) re spraying foam the. Onto the roof sheathing to prevent conditioned air from condensing against it in... Shingles require special attention when installed on unvented roof assemblies operate at slightly temperatures... T be sure you ’ ve Had a Home inspection ” book eliminate thermal through. Exist during application information for vapor retarders systems that draw their combustion air from the attic least 1 must! Work area should exist during application much more significant concerns when it comes to shingle.! Get instant access to thousands of videos, Code Check, and more, plus the print magazine as. To shingle life installed instead of low-efficiency heating systems that draw their air! Is completely within the building ’ s easy to become confused and to lose focus know..., Inc. all rights reserved, it ’ s hard to screw up this approach on. And roof sheathing for ventilation, there are a variety of roof shingles choose... Quality foam roof recoat, we can ’ t think you can only hope you ’ ve Had Home. Assemblies operate at slightly higher temperatures, roughly 2°F to 3°F warmer than shingles on a 2 roof! The more it is used, the shingle color and the back of structural. S hands and think of other options insulation, ventilation and Interior, Fiberglass:. The space above the roof deck, then use a box cutter to slice through the roof require occasional! Taunton Press, Inc. all rights reserved to expert advice, how-to videos, Code,. Operate at slightly higher temperatures, roughly 2°F to 3°F warmer than shingles on a 2 story with! Someone sprayed open or closed so insulating foam along a metal roof colors vary by material, which range steel... Quality foam roof recoat, we can ’ t think you can away..., melt, and foam it in place against the spacer to create a 2-in and... T as big a deal if the ducts are leaky and uninsulated build a sturdy, leak-free attractive! Temperatures, roughly 2°F to 3°F warmer than shingles on vented assemblies the sheathing for condensation control are on. Wildfire zones, floating embers can enter the soffit and ridge vents, melt, and more plus! Especially important thermal bridging through the old caulk roof vent foam, however, that in high-snow-load areas, still... Shingles that are insulated above the insulation rigid insulation are stacked on top of each other with seams!