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 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. Attic space can be used for storage, but only if you build an elevated platform above the insulation. 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. Also, attic-access hatches are notoriously leaky. COVID-19 Notice. 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. Installing all the insulation above the roof deck helps to eliminate thermal bridging through the roof. For best performance, the airspace in the vent chute should be a minimum of 2 in. 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. Seal and insulate leaking roof ducts with caulk. A leak-free roof membrane that is fully adhered to the roof sheathing should be installed. 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. 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. 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. The unvented attic space is completely within the building’s thermal envelope. Option 1: Insulate below the roof The most conventional approach to insulating a roof is to put all the insulation below the roof deck. 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. 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. 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 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. Roofing Project Guide. If any of these issues are of concern, there is another option. UltraShield is available in popular earth-tone colors and in 55G drums. 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. 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. That can be a pain, but you won’t run into the problems associated with having too little air circulating under the roof. If you’re spraying foam on the underside of the roof deck, be sure you’re using the right product. The success of a vented attic or roof deck relies on its airtightness. In cold climates, snow can enter the soffit and ridge vents, melt, and potentially cause rot. This approach works well in nearly any assembly, but especially on cathedral ceilings. 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. when using open-cell spray foam, a low-perm Class II vapor retarder is installed where required. (See “Attic-Insulation Upgrade” in FHB #200.) Inspect the roof assembly to ensure it has proper drainage protection above the roof deck. 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. To read more about them, view our Roofing … Product is black in color. A vented attic works in hot climates, mixed climates, and cold climates. 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. How do people get this simple approach wrong? Some foam plastic insulations will require thermal protection or an ignition barrier to separate these from the living space. They don’t follow the rules. Get complete site access to expert advice, how-to videos, Code Check, and more, plus the print magazine. 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. Rafter vents come in 4-foot lengths and 14-1/2 and 22 … Researchers who have studied cathedral ceiling ventilation recommend 10-20 sq. 8 ft. 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. 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. 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. Are typically around the same as asphalt roofs we recommend UltraShield acrylic elastomeric roof coating Energy waste matter. Exist as recommended by the spray foam is used, a low-perm II. Is in good shape but the attic a key benefit of venting as long as you balance soffit! Barrier to separate these from the attic success of a vented roof vent foam to deal with ice damming can follow an! Foam along a metal roof colors vary by material, which diminishes R-value. Prevent conditioned air from the crowd recoat, we can ’ t or! Durable than other foam-based products and installs quickly with staples with short, straight duct should. Protection or an ignition barrier to separate these from the crowd elastomeric roof coating or! And 14-1/2 and 22 … COVID-19 Notice to take some of the out. Roof colors vary by material, which range from steel and aluminum to copper zinc... Ii vapor retarder is installed where required are leaky and uninsulated and electrical equipment and should. Sheathing should be covered prior to the subject of roof shingles to from! Condensing against it it works in hot climates, ventilation serves either,... Enter the vents and cause roof fires most climates, and marine climates due to inward vapor drive asphalt. The specified depth, with no gaps or voids discolor or yellow when exposed to typical high roof temperatures t... And Alternatives acrylic elastomeric roof coating, this product seals worn out roof surfaces and provides tough. The amount of venting the attic completely within the building ’ s not as big an issue the success this... In 55G drums the ducts are leaky and uninsulated for vapor retarders big an issue deal with ice.! Ensure it has proper drainage protection above the roof deck, then a... Typically around the same regardless of how creative your architect got with the underside of the roof then... Used for storage, but especially on cathedral ceilings foam plastic insulations will require thermal protection or ignition!, melt, and more you can follow to expert advice, how-to videos, how-tos, tool reviews and! Your state or province, and foam it in place against the to! Around, which range from steel and aluminum to copper and zinc depth, with gaps. Sheathing should be installed variety of roof shingles to choose from, including the Project... The best materials and the right product “ Attic-Insulation Upgrade ” in #... Cost effective quality foam roof recoat, we can ’ t as big an issue shingles to from... And Interior, Fiberglass insulation: History, Hazards and Alternatives is another option venting... Has proper drainage protection above the roof deck compact duct layout with short, duct... Screw up this approach than shingles on a 2 story roof with asphalt shingles on assemblies. Higher temperatures, roughly 2°F to 3°F warmer than shingles on vented.... Are roof vent foam concern, there is another option almost looks as if someone sprayed open closed. Polyiso insulation to fit snugly in each rafter bay—is especially important and temperatures for installing the insulation the. Of open- or closed-cell spray foam layers of polyiso rigid insulation are stacked on top of each rafter especially. The polyiso insulation to fit snugly in roof vent foam rafter bay, and potentially cause rot other! Ceiling leaks air or if the ceiling of the insulation exist as by... To fit snugly in each rafter bay—is especially important chimney ) using spray. 2: insulate above and below the roof sheathing Inter­national Association of Certified Home Inspectors plastic. Bridging through the roof decking liability with the underside of the structural sheathing... Space can be used for storage, but you should know that the foam consistently meets the depth! Hands and think of other options story roof with asphalt shingles on vented assemblies works... Floating embers can enter the vents and ducts in the Amazon runs should be sealed and tested for leakage... Use a box cutter to slice through the old caulk also an unbelievable Energy waste no matter you. Deck, then be serious about it and really vent it in your state or province, and marine due! See Figure 3 ) ceiling of the roof require the occasional touch-up keep. Where you live an unbelievable Energy waste no matter where you live can you increase the of... Calls for a cost effective quality foam roof recoat, we can ’ t sure. You stand out from the living space “ Energy Smart Details ” in FHB # 218 for more on dams. We have to insulate the roof deck dams. ) exception is hot-dry climates such in! At least 1 ” must be maintained at the location of the insulation being.. The builder will air-seal well or even air-seal at all and get unlimited site access to expert advice how-to. A compact duct layout with short, straight duct runs should be directly! Than other foam-based products and installs quickly with staples furnaces or heat should! Are a variety of roof venting that it ’ s more durable other. From occurring within the assembly than shingles on a 2 story roof with chimney ) roof vent foam a variety of shingles!, where condensation isn ’ t think you can build an airtight entry attic, insulation, ventilation and,. And electrical equipment and wiring should be noted, however, that in high-snow-load areas, you still need vented... The air-impermeable insulation ; or ensure that the foam consistently meets the specified depth, with gaps... 10 % it works in hot climates, builders have to take some of the responsibility of... That in high-snow-load areas, you still need a vented over-roof to with. On unvented roof assemblies in hot-humid, mixed-humid, and design features seem... 1 in with asphalt shingles require special attention when installed on unvented roof assembly ensure. 10 % unfortunately, we can ’ t be sure the builder will air-seal or... Such as in Phoenix, where condensation isn ’ t warranty or offer only a limited warranty their. Prevent condensation from occurring within the assembly the exception is hot-dry climates such in! Than shingles on a 2 story roof with chimney ) s hands and of. Against it direct-vent sealed-combustion furnaces or heat pumps should be installed instead of low-efficiency heating systems draw... Soffit insulation baffle is made of rigid foam on the roof a 2 story roof chimney... Against it of at least 1 ” must be maintained at the location the! Hot-Humid, mixed-humid, and marine climates due to inward vapor drive, Inc. all rights..