GENERAL ATTIC INSULATION REQUIREMENTS
AT 2.0—Introduction
In attics with no pre-existing insulation, vapor retarders shall face the heated area of the building. Do not install new insulation with a vapor retarder on top of pre-existing insulation. There should only be one vapor retarder in the assembly and it should be in contact with the heated ceiling. If existing attic insulation has a vapor retarder on top surface, slash with razor knife every six inches before adding more insulation.
Attic insulation shall be in contact with the heated area of the home and shall be installed so there is no air space between the insulation and the heated area.
If the added attic insulation compresses the existing insulation, the final R-value shall be R-38, or greater. After installing the insulation, eave and soffit vents shall remain unblocked.
Kraft facing (commonly attached to batt-type insulation) is a vapor retarder. If kraft facing is attached, it must be in contact with the heated ceiling of the home.
AT 2.1—Installing
Loose-Fill Insulation
Loose-fill insulation shall be level and smooth, with a uniform R-value. The number of bags used to attain the added R-value shall reasonably match manufacturer’s estimated bag count. Baffling and damming requirement, as defined in AT 1.4, 1.5 and 1.6, shall be reviewed prior to installing loose-fill insulation.
AT 2.2—Installing Batt-Type Insulation
If batt-type insulation is installed, prepare the attic in the same way as for loose-fill insulation. As stated in section AT 2.0 above, do not install vapor retarders over existing insulation. In attic areas where no insulation exists, batts with vapor retarders may be used. The vapor retarder shall be in contact with the ceiling.
Batts shall be cut to fit and placed tightly together with no gaps except those required for clearance around heat-producing fixtures. Where practical, place one row of batts between the joists and another row of batts on top of the first row and at right angles to the joists. When lower ventilation exists, baffling is required to ensure effective R-value and prevent windwashing of insulation. See AT 1.4 for baffling requirements for fiberglass batt-type insulation installation.
AT 2.3—Installing Foam Insulation
Spray or rigid foam are acceptable types of insulation, provided they meet the requirements for R-value, are installed in contact with the heated surface and comply with thermal and ignition barrier requirements for foam plastics, as defined by the prevailing jurisdictional building code.
When installing foam-insulation products, the manufacturer’s name, product identification and information to determine the end-use shall be left with the homeowner and presented to an Existing Homes representative for review during the QC process. Contact the trade ally coordinator at existinghomesta@energytrust.org or call 1.866.365.3526 option 9, to request support for insulating sloped cavities with foam insulation.
AT 2.4—Floored Attics
Cavities below decked storage areas above a conditioned space shall be insulated to the highest practical level. When decked storage areas exceed five percent of the attic area, or 64 sq. ft., whichever is greater, they shall not be included in the square footage calculation of the insulation incentive. When decked storage areas are less than five percent or 64 sq. ft., they may be included in the incentive area calculation. When unusual circumstances allow only for the cavity to be filled, contact the Existing Homes program for incentive information. See AT 1.5 for damming requirements for decked storage areas.
Insulation shall be installed under the boards of floored attics. To fill the cavities, the boards can be lifted or holes can be drilled into them no more than 4 feet apart. Joist cavities shall be tightly packed with insulation.
Areas with loose-fill insulation next to a floored attic shall be dammed to prevent insulation from falling onto the floored attic.
AT 2.5—Vented Vaulted Ceilings
If insulation is added to a vented vaulted ceiling, a 1-inch air space shall be maintained above the insulation. Each cavity shall have an upper and lower vent.
AT 2.6—Unvented
Vaulted Ceilings
If insulation is added to an unvented vaulted ceiling, it shall be filled with tightly packed insulation. Contact the trade ally coordinator at existinghomesta@energytrust.org or call 1.866.365.3526 option 9, to request support insulating sloped cavities with foam insulation.
AT 2.7—Insulating
Rake and Crown Attics
When insulating rake attics, floor cavities from adjacent heated spaces shall be sealed with an air barrier. Rake insulation shall be in full contact with the plug(s) with no gaps or voids. See illustration below for suggested plug locations.
Illustration AT 2.7
Sloped cavities between rake and crown attics shall be insulated unless physical barriers exist. If loose-fill insulation is used, the lower opening of each cavity must be dammed to prevent insulation from falling out of the cavity.
Knee walls shall be insulated to maintain a consistent thermal envelope separating conditioned and unconditioned spaces. Accessible knee walls shall be insulated to meet the complete measure requirements listed in AT 1.0.
Knee wall insulation shall be installed prior to installing ceiling insulation. All penetrations through the knee wall shall be sealed with caulk or foam. Knee walls shall be insulated to a minimum of R-15 in a 2x4 cavity, and R-21 in a 2x6 cavity. When adding new insulation over existing knee wall insulation, the cavity shall be completely filled. Do not install new insulation with a vapor retarder on top of pre-existing insulation.
Existing condition must be R-4, or less, to qualify for an Existing Homes Knee wall incentive.
Illustration AT 2.7B
New or pre-existing Knee wall insulation shall be covered with a durable, vapor-permeable air barrier material to prevent air penetration of the insulation and to ensure insulation is held in full contact with the wall cavity. The air barrier material shall be permanently fastened to support the Knee wall insulation.
Knee wall accesses shall be insulated to R-15 and weatherstripped to create an effective air seal. If Knee wall is used for storage, fibrous Knee wall door insulation shall be covered to prevent human contact (see section IN 1.7). Foam core doors with a minimum R-5 insulation rating (manufactured for exterior use) and used in Knee wall access door installations will be permitted, provided gaskets or weatherstripping prevents air infiltration around the entire door perimeter.
Uninsulated skylight or pony walls between conditioned and unconditioned spaces within the attic area shall be sealed for air leaks, insulated to a minimum of R-15 and create a continuous thermal boundary. When no wall exists, one shall be constructed and an effective air and thermal barrier shall be installed.
AT 2.8—Low-Sloped and Flat Roofs
Insulating low-sloped or flat roofs is technically difficult. Plans for insulating these types of roofs should be reviewed by the local building jurisdiction. Building permits and code compliance are the responsibility of the homeowner and contractor. A waiver is required for all low-sloped and flat roofs cannot be insulated to R-38. Contact the trade ally coordinator at existinghomesta@energytrust.org for a waiver.
Exterior applications
When installing rigid insulation on top of the roof sheathing, all ceiling cavities shall be insulated to highest possible R-value with tightly-packed insulation. The overall insulation assembly shall equal or exceed R-19.
Ceiling cavity applications
Ceiling cavity insulation shall achieve a minimum of R-19, or fill cavity.
Preparation
• Recessed lights in insulated cavities shall be IC or ICT rated.
• All plumbing vents, kitchen fans, bath fans, wood stoves and other fixtures shall vent to the outside of the new roof and be adequately flashed and sealed.