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Hot Roof vs. Cold Roof: Attic Insulation Options for Homeowners

Posted on Thu, Aug 02, 2012

insulation, attic insulation, insulation tech

Inadequate insulation and air leakages are often the key factors that waste energy in homes, and can add substantial heating and cooling costs for homeowners. Because heat always moves toward cooler areas, homes tend to lose heat to the exterior of the house in the winter through the attic, walls, and basement, and gain unwanted heat during the summer adding an unnecessary load to the HVAC (heating, ventilation, air conditioning) equipment. Given that insulation acts as the thermal barrier between the heated/cooled and unconditioned space in the average home, increasing thermal resistance of the building by adding insulation not only can help homeowners significantly cut back on utility bills, but also make their homes more comfortable year-round.  


Attics are often the easiest places in a house to insulate, especially for retrofitting existing homes that need added insulation. However, depending on the type of the attic a house might have, homeowners sometimes need to consult with a insulation professional to determine where in the attic to add insulation, as well as the type of material used. Our experts here at 360Chestnut recommend homeowners consider factors such as the type of roof venting and whether the attic is part of the unconditioned or conditioned space before choosing an attic insulation project apporiate for their home. In an unconditioned attic, insulation and air barriers are in the ceiling that separates the conditioned living space of the house from the attic. On the other hand, if the attic is used for space storage or components of the HVAC system, the thermal barrier and insulation should move to the roof line, making the attic an unvented and semi-conditioned space. This type of attic or roof is known as hot roof, as opposed to an unconditioned attic, or cold roof. 


For unconditioned attics, proper ventilation is important because it helps to maintain a cold roof temperature to control ice dams created by melting snow and remove moisture moving from the conditioned space to the attic. This type of roof, traditionally known as cold roof, calls for both proper ventilation and insulation. While ventilation keeps the roof deck cool, insulation protects the house from heat loss. In this case, it is recommended that you have insulation installed on the attic floor rather than between the rafters. Laying down fiberglass batts or blowing cellulose between the joist of the attic floor can be the fastest, easiest, and most affordable way to insulate a vented and unconditioned attic. 


attic insulation

Cellulose insulation on attic floor



When the attic is part of the living space (used for space storage or HVAC equipment such as the air handler and ductworks), it is recommended that the vents be sealed, and the attic be treated as a semi-conditioned space (insulated but not heated). For this type of attic, open or close-cell polyurethane foam can be sprayed directly on the underside of the roof deck to act as an air and thermal barrier. Closed-cell foam is denser and has a higher thermal resistance value than open-cell foam.

spray foam insulation 3Spraying foam insulation on the underside of the roof deck 


Below, 360Chestnut's founder, Harold Simansky, explains attic insulation. Check out our Insulation Basics page to learn more about other types of insulation in your home. Let us connect you with a trusted local contractor for your insulation projects. 


 Tung Huynh