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. 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