InterNACHI® can help you get licensed in your state or province, When open-cell spray foam is used, a low-perm Class II vapor retarder is installed where required. Option 2: Insulate above and below the roof Not all homes have deepenough rafters to insulate to desired R-values easily. Find here detailed information about roof replacement costs. UltraShield is available in popular earth-tone colors and in 55G drums. 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. You can only hope you’re doing a good-enough job. 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. It almost looks as if someone sprayed open or closed so insulating foam along a metal roof ridge vent. An unvented roof assembly is possible only if you keep the roof sheathing warm enough to prevent conditioned air from condensing against it. If any of these issues are of concern, there is another option. A key benefit of venting the attic is that the approach is the same regardless of how creative your architect got with the roof. Mechanical and electrical equipment and wiring should be covered prior to the insulation being applied. The space above the top plate of exterior walls—at the bottom of each rafter bay—is especially important. Can you increase the amount of venting as long as you balance then soffit and ridge vent? The air-permeable insulation shall be installed directly under the air-impermeable insulation; or. November 17, 2020. It works absolutely everywhere—when executed properly. Seal and insulate leaking roof ducts with caulk. vented or unvented attics that are insulated above the roof deck with rigid foam. chute or baffle. The thickness of the insulation will vary depending on the type. 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. © 2021 The Taunton Press, Inc. All rights reserved. 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). Don’t think you can get away with putting ductwork in an unconditioned attic just because you sealed and insulated it. The air-impermeable insulation shall be applied in direct contact with the underside of the structural roof sheathing for condensation control. On 2019-02-27 by Pretty Mhlongo. You can build an airtight entry attic, but you should know that the more it is used, the leakier it gets. It’s more durable than other foam-based products and installs quickly with staples. 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. Metal roof costs are typically around the same as asphalt roofs. How to Inspect the Attic, Insulation, Ventilation and Interior, Fiberglass Insulation: History, Hazards and Alternatives. 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. Some manufacturers don’t warranty or offer only a limited warranty when their products are used over an unvented roof assembly. Unfortunately, we can’t be sure the builder will air-seal well or even air-seal at all. So much information has been devoted to the subject of roof venting that it’s easy to become confused and to lose focus. 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. 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. A leak-free roof membrane that is fully adhered to the roof sheathing should be installed. of airspace between the top of the insulation and the back of the roof sheathing. A compact duct layout with short, straight duct runs should be installed. 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. This approach works well in nearly any assembly, but especially on cathedral ceilings. As a roof coating, this product seals worn out roof surfaces and provides a tough flexible waterproof seal. air space under the sheathing for ventilation, 2 in. roof with asphalt shingles on a 2 story roof with chimney). This way, it’s not as big a deal if the ceiling leaks air or if the ducts are leaky and uninsulated. Get complete site access to expert advice, how-to videos, Code Check, and more, plus the print magazine. 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. 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 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. 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. The exception is hot-dry climates such as in Phoenix, where condensation isn’t as big an issue. 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. In most climates, builders have to insulate the roof sheathing to prevent condensation from occurring within the assembly. Because the roof isn’t in play here, it doesn’t matter how many hips, valleys, dormers, or gables there are. 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. 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. It’s hard to screw up this approach. Also, attic-access hatches are notoriously leaky. Here, I’ll explain how to construct a vented attic properly. 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. of open- or closed-cell spray foam in their roof or to stack a half-foot of rigid foam on the roof deck. After all, the shingle color and the roof orientation are much more significant concerns when it comes to shingle life. and provides certification to help you stand out from the crowd. They don’t follow the rules. Finally, in wildfire zones, floating embers can enter the vents and cause roof fires. 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? It works in the Arctic and in the Amazon. Beyond the decreased capacity for insulation when venting the roof deck, venting the roof deck or the attic has some other drawbacks worth considering. 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. If you choose to vent the roof deck, then be serious about it and really vent it. Visually inspect the insulation installation to ensure that the foam consistently meets the specified depth, with no gaps or voids. 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. 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. Researchers who have studied cathedral ceiling ventilation recommend 10-20 sq. 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. 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. 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. Roofing Project Guide. 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. 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. March 27, 2017 . 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. Attic space can be used for storage, but only if you build an elevated platform above the insulation. 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. Through provision R806.4, the IRC also allows you to build an unvented roof assembly. Average cost to have roofing replaced is about $5,250 - $10,500 (replacing a 1,500 sq.ft. if possible. Proper ventilation in the work area should exist during application. layers of polyiso rigid insulation are stacked on top of each other with their seams staggered and taped. 8 ft. It’s also an unbelievable energy waste no matter where you live. Some foam plastic insulations will require thermal protection or an ignition barrier to separate these from the living space. 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. Similarly, not everyone can afford to spray nearly 10 in. 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. 1 1/2 in. It should be noted, however, that in high-snow-load areas, you still need a vented over-roof to deal with ice damming. Become a member and get unlimited site access, including the 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 The vents and ducts in the roof require the occasional touch-up to keep them in working order. So we have to take some of the responsibility out of the builder’s hands and think of other options. Three 2-in. As a foundation coating, this product seals masonry, foam board insulation, wood and metal surfaces to protect, preserve and damp-proof, below grade surfaces. 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. In cold climates, snow can enter the soffit and ridge vents, melt, and potentially cause rot. Inspect the roof assembly to ensure it has proper drainage protection above the roof deck. They recommend a min. 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%. 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 approach also remedies thermal-bridging issues. 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. COVID-19 Notice. Scrape away the debris, then spread a bead of caulk around the duct or vent … In mixed climates, ventilation serves either role, depending on the season. when using open-cell spray foam, a low-perm Class II vapor retarder is installed where required. Ductwork should be sealed and tested for air leakage. ... .3 Vent and insulation clearance. 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. 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. A vented attic works in hot climates, mixed climates, and cold climates. deep. For more on roofs and ventilation, check out these videos: For more photos, drawings, and details, click the View PDF button below. 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. 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.”. The success of a vented attic or roof deck relies on its airtightness. Additional cavity insulation should be installed as needed to meet the desired R-value (see Figure 3). in. A complete resource that includes the best materials and the right techniques to build a sturdy, leak-free, attractive roof on any house. 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. Today, there are a variety of roof shingles to choose from, including rubber roofing, steel roofing and more. of open- or closed-cell spray foam in their roof or to stack a half-foot of rigid foam on the roof deck. Also, check to be sure that you are in compliance with the manufacturer warranties when installing shingles over an unvented roof in all climates. Start your subscription today and save up to 52%. 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. Atlas Signature Select: A Comprehensive Roofing System. 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. For a cost effective quality foam roof recoat, we recommend UltraShield acrylic elastomeric roof coating. 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. 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. 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. A vent space clearance of at least 1” must be maintained at the location of the vent and between insulation and roof sheathing. 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. How does one vent a lower roof that has no ridge? 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. To install the rafter vents, staple them directly to the roof decking. The success of this approach hinges on the ceiling of the top level of the house being absolutely airtight before any insulation is installed. Similarly, not everyone can afford to spray nearly 10 in. Rafter vents come in 4-foot lengths and 14-1/2 and 22 … 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. (See “Energy Smart Details” in FHB #218 for more on ice dams.). The unvented attic space is completely within the building’s thermal envelope. 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. 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. 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. 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