Building Science
The History of Insulation
Have you ever wondered why your inside air conditioning system is located in that hot box on top of your living area called a ventilated attic? The temperatures can often reach 150°F in August. It just does not make sense does it? We arrived at this point by adapting building science that was never meant to include air conditioning. In the late 1930’s insulation as we know it today first came into residential use in the northern United States for heating purposes.
Moisture Problems - Furnaces are located in the basements and they carried warm air laden with moisture up through the living areas into the attic assembly where the moisture vapor condensed against the cold roof deck causing roof rot.
The Solution - The industry came up with attic ventilation as the solution to the condensation problem and it became a building code requirement in the late 1940’s.
New Building Science
The Challenge – In 1996 the Department of Energy commissioned Oak Ridge National Laboratories to develop a more energy efficient building envelope. Their findings indicated that up to 50% of energy loss comes from air leakage; a physical property of insulation known as convection. The popular method of rating an insulation performance is the “R” value which only measures conduction, however the true performance of an insulation must take into consideration both convection and conduction.
3” of Icynene has a prescriptive R value of 11.1 but when using DOE approved software which takes into consideration convection, it has a performance value meeting or exceeding R19 and 5” R30.
Conditioned Attic Assembly – through this research a new building envelope was designed, it consists of a near air tight building with a conditioned attic assembly. A conditioned attic assembly moves the insulation from the floor of the attic to the underside of the roof deck forming a thermal break, preventing the sun’s heat from entering your attic. An example of a thermal break we are all familiar with is a foam cup being filled with hot coffee; you feel no heat when holding the cup.
The requirements for a conditioned attic assembly using Icynene® spray foam insulation are no ridge vents, soffit vents, radiant barrier, the entire attic floor cannot have insulation or a vapor retarder. The roof insulation is tied to the vertical wall insulation.
Benefits of the Conditioned Attic – The temperature & humidity conditions in the attic can be kept reasonably close to those in the conditions within the occupied space in the building. The HVAC system can be sized properly without having to overcome the latent heat loads in a ventilated attic and in many cases resulting in a 50% reduction in energy consumption.
21st Century Building Science
In 2006 the Conditioned Attic Assembly, also known as the unventilated attic, became part of the 2006 building code giving you the choice between 1940’s old technology and 21st century energy efficient technology. The decision is yours; unfortunately, insulation is not something you can change after your home is built.