Air Infiltration - Insulation Performance and Testing

 

Minimizing air infiltrationAir that unintentionally leaks into a building. is dependent on the sealantSealants in insulation function primarily as water and vapor seals. They may also be used as adhesives, and for expansion joints for metal, masonry, cellular glass, etc. They must exhibit low shrinkage, excellent adhesion and permanent flexibility. package, not the insulation.

 

Air infiltration is driven by wind, temperature differences, or HVACAcronym for heating, ventilation, and air-conditioning systems. appliance induced pressures. Research has shown that up to 35% of the heat loss in a home can be attributed to air infiltration.¹ Most of the air that passes through the exterior wall assembly of a home does so by way of jointsThe place where two adjacent pieces of material or jacketing meet. They may be overlapped, sealed, filled (pointed) or finished by the application of tape, cement, mastic, coatings, additional layer of insulation materials or other compounds. and interfaces between rigid framing and sheathing components where the infiltrating air never encounters insulation.

Numerous claims have been made about the superiority of other types of insulation products which ‘limit’ air leakage in a home. The fact is that cavityThe empty space between studs or joists typically filled with insulation. insulation, whether it is cellulose, spray foam, fiber glassA material consisting of glass fibers used in making various products, including yarns, fabrics, insulation, and structural objects or parts. Fiber glass is resistant to heat and fire., rock woolA synthetic vitreous fiber insulation made by melting predominantly igneous rock and other inorganic materials, and then physically forming them melt into fibers. See Mineral Wool., or slag woolMan-made material made primarily from iron ore blast furnace slag., plays virtually no role in blocking air infiltration through the walls of a home. The only way to stop air infiltration is to properly sealTo make water-tight or airtight. the building envelopeThe exterior assembly that encloses the interior space of a building. It serves as the outer shell to protect the indoor environment as well as to facilitate its climate control. Building envelope design is an application area that draws from all areas of building engineering, especially building science and indoor climate control. Building envelope design includes four major performance objectives: Structural integrity; Moisture control; Temperature control; and control of air pressure boundaries (this includes air movement into and out of the interior space and through the components of the building envelope-interstitial). The physical components of the envelope include the foundation, roof, and walls, along with the insulation encompassed in these components, as well as the doors and windows..

Tests conducted over a number of years have concluded that all common insulations (fiber glass, rock wool, slag wool, cellulose and spray foam) perform equally when it comes to reducing air infiltration when properly installed and used with a suitable air barrier material applied to joints, seams, and penetrations. The differences between them is insignificant when compared to the overall leakage through the other components of a home.

1.http://homerepair.about.com/od/heatingcoolingrepair/qt/heat_loss.htm

• The Truth About Air Infiltration (BI499)
• Let's Set the Record Straight (BI500)
• Facts #15: Achieving Expected Thermal Performance (BI461)
• Facts #24: The Facts About Insulation And Air Infiltration (BI480)
• NAHB Field Study Assesses Alternative Wall Insulation Products (RP043)
• Alternative Insulations Show Little Reduction in Air Leakage (RP041)
• Effect of Cavity Insulation, Vapor Retarders, and Air Retarders on Air Infiltration of Residential Walls (RP016)