The energy efficiency of the building envelope is critical to the overall energy efficiency of a building—especially in homes and smaller commercial buildings, in which heating and cooling loads come primarily from heat loss or gain through the skin.
Energy efficiency is also linked closely with moisture management. As we reduce the amount of heat and air moving through the building envelope we reduce the ability for the envelope to dry out after getting wet. Our choices of materials—insulation, cladding, vapor retarders, flashing—are important, but even more critical in terms of overall performance is how all those materials are combined into a high-performing assembly.
Some insulation products do a better job than others at blocking air leakage, while others are less expensive or easier to install without specialized equipment. Insulation products come in many forms, each with its own advantages and disadvantages. How well the insulation does the job of slowing heat transfer is the critical variable (commonly known as R-value), but what it’s made of and how those ingredients affect the environment are important as well.
Cladding options vary widely, offering a range of environmental and functional performance choices. The best systems are mounted as part of a rain screen assembly, in which an air space is behind the cladding helps protect the wall assembly from rain penetration.
Roofing (sloped and low-slope, including green roofs)
Roofing choices are generally divided into those intended for low-slope roofs, and those designed to go on pitched roofs, although there is some overlap between the two.
In addition to shedding water and withstanding the attack of ultraviolet radiation in sunlight, roofing might be called upon to allow foot traffic (for maintenance of equipment), to reflect heat, and even to generate power. Rainwater collecting on roof surfaces might also be stored, typically only for irrigation or toilet flushing. All these functions affect the optimal choice of roofing material.
Water running off of roofs is a major source of stormwater, which can cause erosion and flooding, so cisterns that can store runoff or vegetated roof systems that hold some water and delay the flow of runoff offer important benefits in densely populated areas.
Below-grade water is also a significant source of moisture problems in buildings, and a combination of good drainage around the foundation and effective waterproofing on walls below grade are important to keep that moisture out. Tar is commonly used for that purpose, but it’s better to use products that don’t release toxic chemicals to the air or water.
Any weather barrier is only as good as its weakest link, and that weak link is often at the joints. Joint sealants have to keep water out while allowing for expansion and contraction of the surrounding materials.