Conditioned Attic

It has been standard practice for many years to place insulation on the ceiling of the living area below and have the attic space above the living area vented to the outside.  In recent years building scientists have determined that including the attic in the building envelope by placing the insulation at the roof line and not venting the attic is a superior method of building construction. The International Residential Code (2006 IRC Section 806.4)  recently began allowing unvented attics.  These unvented attics are now becoming much more common.  

With the insulation placed on the back side of the roof decking, the attic is included in the building envelope. There are numerous reasons why this is a more desirable situation than having a vented attic.  There are many penetrations between the living area and the attic.  Fiberglass bats or blown in cellulose simply cannot fill all these penetrations.  These penetrations allow warm air from the attic to move into the conditioned area of the house in the summer and allow the warm air from the house to migrate into the attic in the winter.  Both of these situations lead to increased heating and cooling energy usage.

In the winter this warm, moisture laden air migrating into the attic will lead to many problems.  As it comes into contact with the cold roof decking it may condense causing liquid moisture to form. This liquid moisture can lead to mold, mildew and even cause rotting of the structural framing members.  The warm air migrating into the cool house in the summer will carry dust and fiberglass fibers.  Some studies have indicated fiberglass fibers to be carcinogenic. 

When heating and air conditioning equipment (HVAC) is located in the attic, an unvented attic will have major ramifications.  A typical house may have several hundred feet of duct work.  In the summer the temperature differential between the conditioned air in the duct and the hot air in the vented attic may be in excess or one hundred degrees.  There may also be leaks in the ducts.  These factors can cause the air conditioner to work longer and harder than necessary.  In an unvented attic the air conditioner doesn't have to work against this temperature differential and conditioned air leaking from ducts is leaking into the conditioned envelope of the house.

Closed cell sprayed polyurethane foam (ccSPF) is the superior product for insulating the back side of the roof deck and bringing the attic into the building envelope.  ccSPF has the highest R-value per inch of any of the common insulating materials. It adheres to the roof decking and rafters extremely well.  In fact, it can increase the structural stability of the framing up to 3 times and is now being used in hurricane areas specifically because of its structural enhancement capabilities.

ccSPF provides an air and moisture barrier so that during the winter there is no interface where warm air from the interior of the house will come into contact with a cold exterior surface and cause condensation.  Another benefit of this moisture barrier is that if there were ever a major roof failure such as high winds ripping off a portion of the roof, the ccSPF would act as a secondary roof and prevent major damage to the interior of the house.
Thermal Roof Systems, Inc. • 6750 Florin Perkins Road, Suite 400 • Sacramento, CA 95828
Phone:(916) 387-1300 • Fax: (916) 387-1302
Toll Free: (877) 387-1320
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