A building envelope is the physical separator (barrier) between the conditioned (interior) and the unconditioned (exterior) environment of a building. Both commercial and residential buildings (including homes) have a building envelope.
The elements of the building envelope are designed to maintain a dry, heated or cooled indoor environment and facilitate its climate control. Building envelope design is a specialized area of architectural and engineering practice that draws from all areas of building science and indoor climate control.
Building Envelope Categories
The building envelope has many elements, which can be divided into three primary categories:
- The Roof—simply put, it’s the waterproofing overhead that also resists the transfer of heat.
- The Foundation—this includes anything underground (below grade) plus the flooring elements. Moisture vapor barriers resist the transfer of moisture vapor/water ingress.
- The Wall System – this includes water resistive facades and coatings, along with air barriers.
The individual parts of the building envelope face different challenges, but collectively function to achieve the same goals of stopping or slowing the flow of air, water, noise and heat; while still allowing the inevitable intrusion of water a way to dry out.
The effectiveness of the building envelope is the primary determinant of the amount of energy required to heat, cool and ventilate a building. In the United States, air leakage accounts for 10 percent of energy that buildings consume (or 4 quadrillion BTU).
Types of Air Barriers
As more focus continues to be placed on the air barrier to address air and energy leakage, air barrier products and innovations have been increasing. The types of air barriers include:
- Self-adhered sheet membranes
- Fluid-applied membranes (coatings)
- Sprayed polyurethane foam
- Mechanically fastened commercial building wrap
- Boardstock (rigid cellular thermal insulation board)
- Factory-bonded membranes to sheathing
- Adhesive-backed commercial building wrap
To be effective, air and moisture vapor barriers must be continuous throughout the entire envelope so there is no point of failure from the roof to the wall transitions to the windows/doors to the foundation. The use of fluid-applied air and vapor barriers are recommended for a number of construction conditions and provide significant performance advantages, most importantly being an effective way to block air leakage, reduce energy costs and increase occupant comfort.
Unlike building wrap which has seams and can fail in preventing air passage, continuous coatings also reduce condensation through the wall, provide a seamless barrier with no tears, holes or gaps, protect the sheathing and rough openings from weather damage during and after construction, and don’t blow away during installation. The right type of coatings will not lose effectiveness from long-term weather exposure and they involve less labor to apply than other types of air barriers, making them more cost effective.
Lubrizol has developed two fluid-applied air and vapor barrier coatings that will be commercialized in 2019 – an elastomeric terpolymer emulsion and a high solids acrylic emulsion that offers excellent adhesion to a variety of building materials. Both coatings deliver the performance needed to meet the Air Barrier Association of America (ABAA) requirements in formulations designed for application as a liquid applied air-barrier. The coatings also meet multiple ASTM standards to enable the air barrier to meet AAMA standards.
For roofing, Lubrizol offers well-established products, like Carboset® AE-960 resins that perform to all the criteria required by UL, FM, ASTM and Miami-Dade. For vertical elastomeric applications, like concrete block, Carboset® SA-850 keeps water and air from moving through the cavities of the block.
Lubrizol has an extensive line of high-performing coatings and a long history in the dynamic coatings market to understand the applications and industries where they are applied, using considerable R&D and coatings expertise to meet the needs of formulators.
Contact your Lubrizol account manager to learn more.