Wood and metal framed buildings often use blown in and batt insulations. Both insulations have adequate R-values; however, neither is airtight. Airtightness of a building is an essential factor in overall energy efficiency and moisture resistance. Energy efficiency saves money and energy. Moisture resistance improves and promotes the durability and sustainability of a building. Without moisture resistance, condensation may accumulate which can lead to mold, mildew, and rot. Mold, mildew, and rot significantly degrades the indoor environmental quality and can cause premature failure of a structure. Blown in and batt insulations provide adequate thermal controls but lack air and moisture resistance. 

Applying an air and moisture barrier to blown-in and batts insulation provides thermal control and airtightness. Blown-in insulation, often made of fiberglass, cellulose or rock wool, is blown into wall cavities, attics, and floors using an insulation blower. The insulation conforms to any space without disturbing the structure or finishes. This attribute makes blown in insulation well suited for retrofits and locations where installing paneled insulation might be difficult. Blown in cellulose is inexpensive and has R-values ranging from 3.1 to 3.7 per inch. Batt insulation is sold in rolls and pre-cut panels and often made from rock wool, fiberglass, and natural fibers. Batt insulation is flexible and easily installed between studs, rafters and joists block. Batts is also inexpensive and has R-values ranging from 3.2 to 3.8 per inch. The problem with both blown in and batts insulation is they are not airtight, which lowers the effective R-value1 and reduces the air quality and energy efficiency of a building.  Achieving adequate insulation in a building requires continuous insulation, sufficient R-values and air and moisture tightness. To attain effective insulation, blown in and batts insulations both need the application of an air and moisture barrier. 

Effective insulation requires a continuous layer of insulation around the building’s envelope, with adequate R-values and air and moisture resistance. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE 90.1) specifies the amount of insulation required to meet the minimum thermal requirements (R-value) for different climates. For instance, in coastal Texas, wood or steel-framed buildings must have a wall R-value of 13. So, if the insulation has an R-value of 3.0, the building will need about 4 to 5 inches of wall insulation. Additionally,  Energy Star recommends that in coastal Texas the attics of a wood-framed building should have R-values of 30 to 60 and the floors should have R-values of 13 to 19. Effective insulation is essential to the energy performance of a building and the health and comfort of the occupants. Effective insulation needs both continuous insulation and an air and moisture barrier, in accordance with ASHRAE 90.1 and 2015 IECC codes2 and standards.

Applying an air and moisture barrier over blown in and batts insulation minimizes air inflation and thermal convection3. The envelope of a high-performing building has four control layers: thermal, bulk water rejection, air infiltration, and water vapor permeability. Blown in and batts insulations have the thermal control but not the bulk water rejection, or resistance to air infiltration and water vapor permeability. Application of the an air and moisture barrier can provide the bulk water rejection and air and moisture resistance to a wall system. It also limits thermal convection. The an air and moisture barrier, applied over blown in or batts insulation, creates a healthy, comfortable, and energy efficient building. 

The an air and moisture barrier provides bulk water rejection and air infiltration protection control of a building’s envelope. It works well when applied to most above-grade exterior wall applications: the ICF Wall Systems, concrete masonry units, DensGlass® sheathing, wood sheathing and more. The application flexibility of an air and moisture barrier is what sets it apart from other barriers (commercial wraps, peel and stick membrane, laminated boards with the tape seams). Application of the an air and moisture barrier may occur either pre or post taping and caulking to the wall. For example, applying the barrier is possible if the project is only partially through the caulking process and the windows are not complete. Once the barrier is applied, it will accept whatever, tape, caulking or flashing goes into the window. The an air and moisture barrier exceeds the requirements of ASTM E2357 test for determining air leakage of air barrier products and ASTM 2178 test for air permeability of building materials. The an air and moisture barrier provides excellent air and moisture resistance to above-grade exterior wall applications and meets the 2015 energy codes

Blown in and batt insulations provide thermal control but both lack airtightness. Lack of airtightness lowers the effective R-value and reduces the air quality and energy efficiency of a building. Applying the an air and moisture barrier over blown in or batt insulation increases the effective R-value and creates a high-performing, energy-efficient,  healthy and comfortable building.

1The effective R-value of a building’s wall assembly is a measure of its resistance to airflow. The effective R-value includes all the materials used in its construction: the drywall, studs, fiberglass batts, plywood or OSB sheathing, water control plane, and siding. The lower the R-value, the higher the conductivities of the wall assembly and the more susceptible a wall assembly is to air infiltration.

2The ASHRAE 90.1 and the 2015 IECC requires continuous insulation in both residential and commercial structures. The 2015 IECC also requires air leakage testing of a building envelope in accordance with either ASTM E 779 or ASTM E 1827. ASTM E 779 test method quantifies the airtightness of a building’s envelope utilizing fan pressurization. ASTM E 1827 test method quantifies the airtightness of a building’s envelope utilizing an orifice blower door.3Thermal convection is the transfer of heat energy from a hotter place to a cooler place by the movement of fluids (usually liquids and gases).  For instance, if it is warmer inside a building, then it is outside the building, the hotter air will move towards the cooler air. Minimizing air infiltration (hot air flowing towards cooler air) is important for limiting the loss of heat energy inside the building. 

Editorial Contributors
Matt Greenfield

Matt Greenfield

Matt Greenfield is an experienced writer specializing in home improvement topics. He has a passion for educating and empowering homeowners to make informed decisions about their properties. Matt's writing focuses on a range of topics, including windows, flooring, HVAC, and construction materials. With a background in construction and home renovation, Matt is well-versed in the latest trends and techniques in the industry. His articles offer practical advice and expert insights that help readers tackle their home improvement projects with confidence. Whether you're a DIY enthusiast or a seasoned professional, Matt's writing is sure to provide valuable guidance and inspiration.

Learn More