BASC Search | Building America Solution Center

Wrong: Ducts are not laid across the lower truss cords or ceiling, but are hung from the rafters by straps. As a result, ductwork is not buried

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Second layer of rigid insulation is adhered with foam

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Two pieces of flex duct are spliced together with a metal sleeve, nylon draw bands, mastic, metal tape, and more mastic

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Unvented, Insulated Crawlspaces

Guide

Guide describing method for insulating an unvented crawlspace or conditioned basement with rigid foam on the interior side of the walls.

Cut fiber board with a red V-groove tool and a gray shiplap tool to create mitered corners and a shiplapped edge for duct sections

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Boot has been covered with insulation and sealed with mastic

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Inadequate amount of insulation installed with compression, misalignment, and voids

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Right - The rigid metal HVAC ducting is installed between the floor joists rather than in an unconditioned attic or crawl space to minimize heat loss.

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Right – R-25 of open-cell spray foam lines this new home’s attic ceiling, to protect HVAC ducts from heat and cold.

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Seal bottom layer of rigid insulation with adhesive, tape and nails

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Wrong – Fibrous insulation does not air seal

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Step 5. Install sheathing tape flashing over the duct or pipe and wood blocking on either side for later attachment of trim.

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Why Are Attics Insulated With Open-Cell Spray Foam So Damp?

Presentation

Presentation describing issues with condensation in unvented attics insulated with open-cell spray foam.

A second layer of rigid insulation is installed over the 2 in. by 4 in. retaining strip

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Blown Insulation for Existing Vented Attic

Guide

Guide describing how to insulate a vented attic in an existing home using blown insulation added to the attic floor.

Seal all joints and seams in the metal ductwork with mastic before installing insulation

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Attic Air Sealing, Insulating, and Ventilating for Ice Dam Prevention

Information Guide

Information guide describing proper attic air-sealing, insulation, and ventilation to combat ice dam formation on roofs in cold climate zones.

Right- This flue pipe has been air sealed with sheet metal and fire-rated caulk and an insulation dam has been constructed to keep insulation from touching the hot flue pipe

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Batt Insulation for Existing Vented Attics

Guide

Guide describing how to increase insulation in existing homes by installing batt insulation on the ceiling plane of a vented attic.

Form an insulation dam of heat-resistant insulation with at least 3 inches of clearance around a flue pipe in the attic after air sealing around the pipe with sheet metal and fire-rated caulk or canned foam

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A box was constructed of rigid foam and sheathing tape to insulate this return plenum in the attic.

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Wrong: This exhaust fan duct is too long and terminates in the attic instead of going through the roof and it is improperly supported; it needs straps all along its length to prevent sagging.

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Air Sealing, Insulating, and Venting Attics and Roofs to Reduce Heat Gain

Information Guide

Information guide providing links to guides describing specific ways to air-seal, insulate, and ventilate attics and roofs to minimize heat gain in new and existing homes.

Spray Foam Insulation Applied to Existing Attic Floor

Guide

Guide describing how to apply spray foam insulation to the floor of the attic in existing homes.

Attic Eave Minimum Insulation

Guide

Guide providing guidance on insulating attic eaves in new and existing single-family homes and multifamily buildings.

The inner liner of the flex duct is fastened to the collar with a tension tie, the connection is sealed with mastic, then the outer layer is pulled over and sealed with mastic or foil tape (Steven Winter Associates 2013).

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Attic Air Sealing and Insulation

Home Improvement Expert™ Checklist

Many home have inadequate insulation and excessive holes, cracks, and missing air barriers resulting in unwanted heat loss in cold weather, heat gain in hot weather, and infiltration of moisture, dust, pollen, and pests year-round. Air sealing leaks and adding insulation between the attic and the home is one of the most cost-effective measures to improve your home’s energy performance. However, critical installation best practices need to be followed to ensure a successful project. Use this checklist to get the significant energy savings, enhanced comfort, and health benefits possible with quality installed attic air sealing and insulation.

Cavity used for return is not insulated and is not air sealed, which will pull in air from outside

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Unvented Conditioned Attic with Spray Foam Insulation Below Roof Deck

Guide

Guide describing a method for insulating an unvented attic by spraying foam insulation along the underside of the roof deck.

Right - The energy recovery ventilator ducts supply filtered outside air to multiple locations in the home and continuously exhaust stale air to provide clean, balanced ventilation.

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