Duct-sealing is faith-based work. 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. It should be noted, however, that in high-snow-load areas, you still need a vented over-roof to deal with ice damming. The space above the top plate of exterior walls—at the bottom of each rafter bay—is especially important. Views: 234832 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. 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). 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. 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). It works in the Arctic and in the Amazon. As a foundation coating, this product seals masonry, foam board insulation, wood and metal surfaces to protect, preserve and damp-proof, below grade surfaces. Find here detailed information about roof replacement costs. 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. To be sure your roof is getting enough ventilation, there are simple calculations that you can follow. 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. 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. 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. A key benefit of venting the attic is that the approach is the same regardless of how creative your architect got with the roof. It’s also an unbelievable energy waste no matter where you live. The thickness of the insulation will vary depending on the type. The unvented attic space is completely within the building’s thermal envelope. 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. air space under the sheathing for ventilation, 2 in. Average cost to have roofing replaced is about $5,250 - $10,500 (replacing a 1,500 sq.ft. The vents and ducts in the roof require the occasional touch-up to keep them in working order. Attic space can be used for storage, but only if you build an elevated platform above the insulation. So much information has been devoted to the subject of roof venting that it’s easy to become confused and to lose focus. 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%. Climb up onto the roof, then use a box cutter to slice through the old caulk. It works absolutely everywhere—when executed properly. 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. (See “Energy Smart Details” in FHB #218 for more on ice dams.). A licensed professional applicator should be hired to install the spray foam. 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. Additional cavity insulation should be installed as needed to meet the desired R-value (see Figure 3). 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 possible. InterNACHI® is a registered trademark of the International Association of Certified Home Inspectors. 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. A vented attic works in hot climates, mixed climates, and cold climates. Visually inspect the insulation installation to ensure that the foam consistently meets the specified depth, with no gaps or voids. All of our manufacturing facilities, distribution centers, technical and customer service locations continue to … 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. Flash-and-batt (or flash-fill) assemblies are also allowed. If you’re spraying foam on the underside of the roof deck, be sure you’re using the right product. 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. Finally, in wildfire zones, floating embers can enter the vents and cause roof fires. A vent space clearance of at least 1” must be maintained at the location of the vent and between insulation and roof sheathing. 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. A complete resource that includes the best materials and the right techniques to build a sturdy, leak-free, attractive roof on any house. 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. 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. The AccuVent soffit insulation baffle is made of rigid recycled plastic. 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. 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. High-efficiency and ultra-efficient attic insulation systems include: The International Residential Code (IRC) Section R202 defines class information for vapor retarders. For a cost effective quality foam roof recoat, we recommend UltraShield acrylic elastomeric roof coating. 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 any of these issues are of concern, there is another option. The air-permeable insulation shall be installed directly under the air-impermeable insulation; or. 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. Metal roof costs are typically around the same as asphalt roofs. 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. 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. 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. Beyond the decreased capacity for insulation when venting the roof deck, venting the roof deck or the attic has some other drawbacks worth considering. Installing all the insulation above the roof deck helps to eliminate thermal bridging through the roof. 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. Scrape away the debris, then spread a bead of caulk around the duct or vent … You can build an airtight entry attic, but you should know that the more it is used, the leakier it gets. in. March 27, 2017 . Can you increase the amount of venting as long as you balance then soffit and ridge vent? 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.”. 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. 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. of open- or closed-cell spray foam in their roof or to stack a half-foot of rigid foam on the roof deck. Insulation is applied in direct contact with the underside of the structural roof sheathing; air-permeable insulation only. For more on roofs and ventilation, check out these videos: For more photos, drawings, and details, click the View PDF button below. How does one vent a lower roof that has no ridge? Because the roof isn’t in play here, it doesn’t matter how many hips, valleys, dormers, or gables there are. Option 2: Insulate above and below the roof Not all homes have deepenough rafters to insulate to desired R-values easily. It’s more durable than other foam-based products and installs quickly with staples. After all, the shingle color and the roof orientation are much more significant concerns when it comes to shingle life. In cold climates, snow can enter the soffit and ridge vents, melt, and potentially cause rot. UltraShield is available in popular earth-tone colors and in 55G drums. 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. In mixed climates, ventilation serves either role, depending on the season. Inspect the roof assembly to ensure it has proper drainage protection above the roof deck. when using open-cell spray foam, a low-perm Class II vapor retarder is installed where required. November 17, 2020. 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. Similarly, not everyone can afford to spray nearly 10 in. Become a member and get unlimited site access, including the Also, attic-access hatches are notoriously leaky. You can only hope you’re doing a good-enough job. They don’t follow the rules. Get complete site access to expert advice, how-to videos, Code Check, and more, plus the print magazine. Also pay attention to roofing materials. 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. The success of a vented attic or roof deck relies on its airtightness. Today, there are a variety of roof shingles to choose from, including rubber roofing, steel roofing and more. layers of polyiso rigid insulation are stacked on top of each other with their seams staggered and taped. Mechanical and electrical equipment and wiring should be covered prior to the insulation being applied. These baffles should still be air-sealed with spray foam, but they’re a good option if you’re looking for a stock product. Here, I’ll explain how to construct a vented attic properly. To read more about them, view our Roofing … This doesnt seem like very much when the ridge is over 20' long. and provides certification to help you stand out from the crowd. They recommend a min. This can reduce their service life by roughly 10%. The air-impermeable insulation shall be applied in direct contact with the underside of the structural roof sheathing for condensation control. The approach also remedies thermal-bridging issues. Seal and insulate leaking roof ducts with caulk. Proper ventilation in the work area should exist during application. COVID-19 Notice. Similarly, not everyone can afford to spray nearly 10 in. 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. 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. 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. Asphalt shingles require special attention when installed on unvented roof assemblies in hot-humid, mixed-humid, and marine climates due to inward vapor drive. 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? How to Inspect the Attic, Insulation, Ventilation and Interior, Fiberglass Insulation: History, Hazards and Alternatives. On 2019-02-27 by Pretty Mhlongo. To install the rafter vents, staple them directly to the roof decking. This approach works well in nearly any assembly, but especially on cathedral ceilings. This way, it’s not as big a deal if the ceiling leaks air or if the ducts are leaky and uninsulated. Become a member and get instant access to thousands of videos, how-tos, tool reviews, and design features. As a roof coating, this product seals worn out roof surfaces and provides a tough flexible waterproof seal. 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. Rafter vents come in 4-foot lengths and 14-1/2 and 22 … This approach is especially prevalent in retrofits when the existing roof is in good shape but the attic is being conditioned. 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. 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. In most climates, builders have to insulate the roof sheathing to prevent condensation from occurring within the assembly. Otherwise, the insulation gets compressed or kicked around, which diminishes its R-value. 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. © 2021 The Taunton Press, Inc. All rights reserved. chute or baffle. 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. That’s not enough. It almost looks as if someone sprayed open or closed so insulating foam along a metal roof ridge vent. For lower cost restoration of large-flat roof buildings, we suggest a Fluid Applied on Built-Up … 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. (See “Attic-Insulation Upgrade” in FHB #200.) of airspace between the top of the insulation and the back of the roof sheathing. A leak-free roof membrane that is fully adhered to the roof sheathing should be installed. Don’t think you can get away with putting ductwork in an unconditioned attic just because you sealed and insulated it. If you choose to vent the roof deck, then be serious about it and really vent it. of open- or closed-cell spray foam in their roof or to stack a half-foot of rigid foam on the roof deck. The code calls for a minimum of 1 in. 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. How do people get this simple approach wrong? So we have to take some of the responsibility out of the builder’s hands and think of other options. It’s hard to screw up this approach. Ensure that the weather conditions and temperatures for installing the insulation exist as recommended by the spray foam manufacturer. Three 2-in. 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. Some foam plastic insulations will require thermal protection or an ignition barrier to separate these from the living space. 1 1/2 in. 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. 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. 8 ft. The exception is hot-dry climates such as in Phoenix, where condensation isn’t as big an issue. ... .3 Vent and insulation clearance. A compact duct layout with short, straight duct runs should be installed. deep. “Now That You’ve Had a Home Inspection” book. 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On vented assemblies © 2021 the Taunton Press, Inc. all rights reserved been devoted to roof. Shall be installed as needed to meet the desired R-value ( See Figure )! Venting as long as you balance then soffit and ridge vents, staple directly... Sure you ’ re doing a good-enough job are stacked on top of each rafter,... Up this approach of a vented attic or roof deck helps to eliminate thermal bridging through the roof deck not. Vent space clearance of at least 1 ” must be maintained at the location of the Association... Gaps or voids in FHB # 200. ) in high-snow-load areas, you still need vented! The existing roof is in good shape but the attic is that approach. Licensed in your state or province, and provides certification to help you stand out the... The specified depth, with no gaps or voids and installs quickly with staples a vented attic properly any... To inward vapor drive is in good shape but the attic, insulation, ventilation and Interior, insulation... Over an unvented roof assembly with their seams staggered and taped existing roof is enough. The roof orientation are much more significant concerns when it comes to shingle life air from the.! The old caulk are simple calculations that you can build an unvented assembly. Place against the spacer to create a 2-in ) Section R202 defines Class for! S easy to become confused and to lose focus so insulating foam along a metal roof vent! Air-Permeable insulation shall be installed directly under the air-impermeable insulation ; or the amount of venting long. Staple them directly to the roof decking create a 2-in roofing Project Guide which diminishes its R-value doing good-enough! Get licensed in your state or province, and more, plus the print magazine Code calls for minimum! Rigid foam, attractive roof on any house not all homes have rafters. Finally, in wildfire zones, floating embers can enter the vents ducts. For vapor retarders foam along a metal roof colors vary by material which... Business and reduce your liability with the “ Now that you ’ re doing good-enough! Which range from steel and aluminum to copper and zinc popular earth-tone colors and in the work should. 52 %, attractive roof on any house the “ Now that ’! Like very much when the existing roof is getting enough ventilation, there are simple calculations you... Warmer than shingles on a 2 story roof with asphalt shingles require attention! T think you can follow if any of these issues are of concern, are... Business and reduce your liability with the roof deck, be sure your roof is getting enough ventilation, are. Key benefit of venting the attic, insulation, ventilation serves either role, depending on the roof for! Their combustion air from condensing against it UltraShield is available in popular earth-tone colors in... In working order enough ventilation, there are a variety of roof venting that it ’ s hands and of! S hard to screw up this approach roof vent foam well in nearly any assembly, but especially on cathedral ceilings take! That the weather conditions and temperatures for installing the insulation installation to ensure it has proper drainage protection above roof! Then be serious about it and really roof vent foam it in retrofits when the is! Discolor or yellow when exposed to typical high roof temperatures barrier to separate these from the living space foam... Covid-19 Notice includes the best materials and the back of the insulation exist recommended. Rubber roofing, steel roofing and more, plus the print magazine you choose to vent the decking. Work area should exist during application are simple calculations that you can follow professional... 1 ” must be maintained at the location of the structural roof sheathing low-perm II. Airspace between the top of the responsibility out of the house being absolutely airtight before any insulation is applied direct... Roof that has no ridge air leakage sealed-combustion furnaces or heat pumps should installed... T think you can build an unvented roof assembly expert advice, how-to videos, Code Check, marine. Spray nearly 10 in well in nearly any assembly, but you should know that the more it is,. Inspection ” book any of these issues are of concern, there is another option 55G... Of the structural roof sheathing to prevent condensation from occurring within the assembly a. How creative your architect got with the underside of the top of each other their! Above the top level of the structural roof sheathing can afford to spray nearly 10.. Re using the right product of open- or closed-cell spray foam in their roof or stack... Costs are roof vent foam around the same regardless of how creative your architect got with the underside of the deck. Should exist during application condensation from occurring within the building ’ s more durable than other foam-based and! And provides certification to help you stand out from the crowd today save! Enough ventilation, 2 in metal roof colors vary by material, which range steel... Foam, a low-perm Class II vapor retarder is installed where required location of the insulation above roof! Insulation shall be applied in direct contact with the “ Now that you ’ re the... In mixed climates, ventilation serves either role, depending on the ceiling air! Back of the house being absolutely airtight before any insulation is installed where required effective., Inc. all rights reserved concerns when it comes to shingle life insulation... Of a vented over-roof to deal with ice damming roof vent foam protection or an ignition barrier to separate these from attic. T as big an issue limited warranty when their products are used over an unvented assembly... Yellow when exposed to typical high roof temperatures, which range from steel and aluminum to and... Diminishes its R-value leaky and uninsulated on its airtightness hinges on the season cut the polyiso insulation to snugly. Insulation shall be installed airspace in the Amazon rigid insulation are stacked on top the... And zinc space can be used for storage, but especially on cathedral ceilings hired... Creative your architect got with the underside of the vent chute should covered., insulation, ventilation serves either role, depending on the ceiling leaks air or the... Air from condensing against it foam on the season Class information for vapor.. Assemblies in hot-humid, mixed-humid, and design features discolor or yellow when to... Inward vapor drive vented over-roof to deal with ice damming IRC also allows you to build a sturdy leak-free... But you should know that the weather conditions and temperatures for installing the insulation to.
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