Post-frame construction is suitable for a wide range of low-rise commercial building applications. Compared to buildings with concrete-block, stud-wall or steel framing, post-frame buildings can be better insulated, resulting in an elimination of drafts, energy savings, and occupant comfort.
Characteristics of a properly insulated post-frame structure that will provide optimal energy efficiency include: wood framing that is an insulator, not a conductor; insulation that fills the cavity from column to column and is continuous from grade to ceiling; an air barrier; vapor retarder; deep truss heel; and a well-ventilated attic.
Air Barriers
Air barriers retard exterior air movement through building cavities and are an important component in an energy-efficient design. Heat is transferred through convection, such as infiltration of heat flow through gaps in the building envelope. Moisture-laden air or water vapor can infiltrate gaps. When water vapor cools and condenses, structural damage and mold growth can result. Installing a continuous air barrier material is imperative and is typically place on the exterior of the building envelope. All joints in air barrier should be sealed. All joints or seams should be covered with tape specified by manufacturer. The air barrier must be carefully inspected after installation to see if there are any tears, punctures, or seams.
Vapor Retarders
Often referred to a vapor barriers, these restrict moisture-laden air movement from inside the building to the attic, floor, and exterior wall spaces. However, the term, “vapor barrier” is not accurate since materials allow some moisture to penetrate through them. Moisture or water vapor can be transferred in and out through air movement, diffusion through materials, or heat transfer. The temperature at which a particular concentration of moisture condenses is called the “dew point.” Two factors that will greatly decrease moisture condensation and “dew point” are the wall cavity’s insulation R-value, and proper placement of the vapor retarder. Installing a vapor retarder, along with sealing gaps to resist moisture transmission, is very important, and usually come as either membranes or coatings. Common types of vapor retarder membranes include: polyethylene plastics; paper-faced insulation; rigid-foam insulation; and foil-backed wallboard. Paint is a common retarder coating.
Deep Truss Heel
A deep truss heel allows the ceiling insulation to continue to the exterior wall without disrupting the airflow from the soffit. Some methods reduce or compress the ceiling insulation at the eave due to the small heel depth, creating a lower thermal resistance over a portion of the ceiling.
A Well-Ventilated Attic
Proper ventilation of the attic will prevent moisture from condensing on the insulation and building components. Attic ventilation also decreases roof temperatures, which will help lengthen the life of the roof. In attics, vent openings must be placed as to allow air to flow from one opening, across the insulated area and out the other opening. Air deflectors move air up through the attic and out through the peak, not through the insulation. Ventilation prevents condensation build-up at the roof.
Utilizing these recommendations will ensure a comfortable environment that can be heated and cooled efficiently for the life of your building.
