The boundary between the conditioned, indoor living spaces and the unconditioned and outdoor spaces is referred to as the “building envelope” and consists of the walls, floor, and ceiling or roof. An airtight building envelope contributes directly to the energy efficiency and comfort of a home.
Air leakage accounts for 25 percent to 40 percent of the energy used for heating and cooling and also reduces the effectiveness of other energy-efficiency measures such as increased insulation and high-performance windows. Thus, a tightly sealed house envelope results in lower utility bills.
There are hundreds of penetrations through a typical home’s building envelope. These include gaps in framing members and penetrations for wiring, plumbing, and ducts. Tightly sealing the house’s envelope, combined with proper ventilation, can reduce energy bills and eliminate unwanted drafts and pollutants.
Reduced air infiltration combined with proper ventilation not only reduces energy bills but also improves the quality of your indoor air. Outdoor air that leaks indoors makes it difficult to maintain comfort and energy efficiency. In addition, heated or cooled indoor air leaking outdoors can account for 25 – 40% of the energy used for heating and cooling in a typical home.
There are a number of ways to construct a tight thermal envelope including house wraps like Tyvek or Typar and spray foam. One of the most effective ways is to use a double air-barrier system.
Installing STYROFOAM™ Residential Sheathing, Tongue & Groove, DURAMATE™ Plus, TUFF-R™, Super TUFF-R, THERMAX™ or STURDY-R™ over the OSB structural sheathing provides a thermal break to reduce heat loss and heat gain through thermal conductance. The vertical joints of the insulation board are tongue and groove and the horizontal joints are flashed with poly z-flashing. This allows the insulation board to act as an exterior air barrier as well as a drainage plane for rain control. This exterior sheathing eliminates the need for building paper or housewrap thus reducing construction costs.
Windows are set in sealant and flashed on all four sides.
Benefits of a tightly sealed thermal envelope
A tighter building envelope reduces the amount of unconditioned air, drafts, noise, and moisture that enter your home. Proper air sealing will also minimize temperature differences between rooms. As a result, tight envelopes can maintain a more consistent level of comfort throughout a house.
Improved indoor air quality
A tighter building envelope reduces the infiltration of outdoor air pollutants, dust and radon as well as eliminating paths for insect infestation. Properly sealing the building envelope will also reduce moisture infiltration from outdoor air in humid climates.
Fewer condensation problems
Moisture and condensation on cold surfaces inside wall cavities can lead to mold problems and structural damage. Exterior air barriers and drainage planes prevent moisture from entering wall cavities eliminating or significantly reducing these problems.
Reduced heating and cooling loads
A tightly sealed thermal envelope helps reduce heating and cooling loads, enabling the use of smaller “right-sized” heating, ventilation, and air-conditioning (HVAC) systems. The cost savings from using smaller HVAC equipment are used to offset the additional cost of high efficiency heating and cooling equipment.
Lower utility bills