Know your barriers Understand the difference between air, vapor and water-r€sistive barriers

f, rR nnnnnRs ARE Nor to be confused with vapor barrilA.ers or water-resistive barriers-although individual materials may provide all three functions. Each barrier has a different function to perform in a building assembly. Dealers and distributors should understand the separate functions their materials provide to sell the right product for each job.

Vapor barriers are materials used to slow or reduce the movement of water vapor through a material (water vapor is also transported by air leakage but this can be resolved by installing an air barrier). Vapor barrier materials are typically installed on the warm side of the insulation in a building assembly.

The position of the vapor barrier in a building assembly will be determined based on the climatic conditions. In warm climates, it will typically be on the exterior and in cold climates, it will be on the interior.

Vapor barrier materials can be self-adhered membranes (depending on composition), fluid-applied materials, rigid cellular thermal insulation board, or medium density spray polyurethane foam (SPF). The thickness of the material will impact whether it is vapor penneable or not.

Water vapor transmission is the measurement of water vapor through a material.In most cases, the results are expressed as vapor permeance. The most common test method for measuring water vapor permeance is ASTM E96. It can be tested using either the desiccant or water method, and typically the results are reported in the units of ng/(Pa.s.m2) or US Perms. Keep in mind that these test methods are different and results from both methods of testing are not comparable. Check your local building code for the method that is referenced in the glossary.

The test measures the water vapor that passes through a material. Proper specimen preparation is critical and experience has shown that if there are pinholes in the material or if the specimen has not been properly sealed into the apparatus using the correct mixture of wax, the results are not repeatable or reproducible.

Water-resistive barriers are materials on the exterior of a building that are intended to resist liquid (bulk) water that has leaked, penetrated or seeped past the exterior cladding from absorbing into the exterior sheathing or concrete wall (depending on the application) and further into the wall assembly.

Water-resistive barrier materials can be mechanicallyfastened building wraps, self-adhered membranes (depending on composition), fluid-applied materials, rigid cellular thermal insulation board, medium density spray polyurethane foam, or any other material that has been designed to resist liquid water.

Water-resistive barriers are combined with flashing and other supporting materials to ensure that there is a shingled effect to direct liquid water away from the exterior sheathing.

Testing the water resistance of a material is normally done using the "boat method" (ASTM D719), the "water ponding" method (CCMC 07lO2 section 6.4.5), or the hydrostatic head method (AATCC 127).

Air barrier materials are used anywhere in a building assembly to stop the movement of air into or out of the conditioned space (water vapor can also be transported by air). Air barriers can be mechanically-fastened building wraps, self-adhered membranes (depending on composition), fluid-applied materials, rigid cellular thermal insulation board, medium density spray polyurethane foam, poured concrete, metal, or a host of other materials.

Air permeance is the amount of air that permeates through a material, whereas air leakage is the air that passes through holes or gaps. Any material that has an air permeance no greater than 0.02 L/(s.mz), at a pressure difference of 75 Pa (0.004 cfm/sq. ft. at a pressure difference of 1.56 lb./sq. ft.) when tested in accordance with ASTM E 2178, is an air barrier material.

Air barrier assemblies are a collection of air barrier materials and air banier accessories (such as sealants, tapes and transition membranes) assembled together to form a continuous barrier for air filtration into and out of the environmental separator.

The performance of an air barrier assembly is of far greater importance that the air permeance of the material. When materials and accessories are installed proficiently, the benefits of the assembly have positive benefits for the entire life cycle of the building.

Multi-Function Materials

Materials can provide an air barrier, a vapor barrier, a water-resistive banier, or any combination of these three functions. Some materials can provide all three, plus the function of a thermal insulation. Other materials may provide all three functions, and some materials may provide two functions. It would be unusual for a material to only provide one function.

By understanding these principles, an effective building separator can be provided to professionals to create effective barriers that help increase building occupant comfort, reduce energy bills, and prevent future moisture and airrelated concerns.

- Colin Szewaqa, C.E.T., is technical services advisnr for the Air Barrier Association o.f America. He can be reached via www.airbarrier.org.

Siding, Trim to Post Big Gains

Demand for residential siding and trim will reach $9.1 billion by 2014 from $7.2 billion in 2011, according to a new study by Principia.

Siding demand will increase 'l%o from 58 million squares valued at $5.8 billion in 201 I to 7 | .6 million squares with a factory gate value of $7 .2 billion in 2014, based on projected unit shipments.

Exterior trim will increase lj%o from 1.7 million linear ft. in 20l l to 2.3 million linear ft. in2014.

"The residential siding and trim market is expected to see steady growth over the next few years due to the increasing need for re-siding and repair along with increased activity in new construction," said Ken Jacobson, partner at Principia. "Manufacturers are improving existing products so that they are more cost effective, easier to install, and align with existing and upcoming codes and standards."

Ogden Lumber, ogden, ta., has been acquired by Amanda and Joel Benbow from John and Joan Sutton, who are retiring after 26 years of ownership.

Spalln & Rose, Dubuque, la., has purchased the former Barker Lumber Co. iite in Byron, ll., and wiil reopen the yard by next month as its 27th location.

McGarty Lumber Co., Muncie, tt., ctosed Oct. 31 after 82 years.

Owners Sue Earls and Greg Barnard aftributed the closure primarily due to the national housing downturn and resultant decrease in local building projects.

ProBuild is closing its yards in Pittsburgh, pa.; Morgantown, W.V., and Hagerstown, Md.

DeckStore, Simpsonville, S.C., has been opened by David and Rachel Elenbaum.

MaxYield Lumber, Garner, la., was destroyed by a late-night fire Sept. 26.

Arrowhead Building Supply moved its Springfietd, Mo., branch to a new 42,000-sq. ft. complex on 5 acres in Strafford, Mo.

Marlowe's Ace Hardware, Hampshire, ll., is closing at the end of the month after 31 years, with the retirement of owners Dean and Marge Marlowe.

Tart Lumber Co., Sterling, Va., unveiled a new 9,000sq. ft. millwork design center.

Ace Hardw?ro, Daleville, Pa., suffered extensive damage in a Sept. 29 fire.

True Value Hardware is opening a new store in Farmington, Mi.

Newtown Hardware House, Newtown, pa., has closed after 37 years.

Ragsdale Ace Hardwar€, Marietta, Ga., this month is adding a 9,000-sq. ft. sister store, East Cobb Ace Hardware. East cobb, Ga.

Knotts Hardware, Tampa, Fl., closed Oct. 12 after nearly 60 years.

Habitat for Humanity opened severat ReStore discount LBM outlets over the last two months, including a 40,000-sq. ft. store in Opelika, Al.; a 4,000-sq. ft. unit in Exmore, Va., and a location in Lancaster, 0h. (Miranada Reason, mgr.). Another opens next month in Woodstock, ll.

The Akron, Oh., store added 15,000 sq. ft. to grow to 42,000 sq. ft., while Cleveland, Tn., was expanded to 8,000 ft.

The Morgantown, W.V., ReStore reopened at a new location, while relocations are also planned for Rockford, ll., and Wichita, Ks. The unit in North Beach, Md., closed Sept. 22, in hopes of eventually reopening in a larger space.