Building Envelope/Building Science

Cellulose insulation is made from recycled paper that is applied as either loose fill into attics and closed wall cavities or damp-sprayed into open wall cavities. Due to its recycled content and potentially higher energy and acoustic performance, cellulose is an environmentally preferable product.

Cotton insulation comes in batts that are comparable to fiberglass in ease of installation, fire resistance, and energy efficiency. However, it has better sound dampening qualities and avoids some of the potential health problems of fiberglass.

Fiberglass insulation is composed of commonly found minerals-primarily silica-that are spun from a molten state into fibers. From an environmental perspective, there are some significant drawbacks to fiberglass. However, some manufacturers have made noteworthy strides to address some of the problems. "Green" fiberglass insulations are made with recycled content materials and may have better indoor air quality properties than conventional fiberglass.

Insulation and a tight exterior seal are two of the most important components of a home's protection against outside conditions, often called its "thermal envelope". This envelope consists of all six sides of the home, the four walls, roof, and foundation. All envelope components interact as a system to affect the flow of heat, air, moisture, and sound into or out of a home. The better the thermal envelope performs, the better the health and comfort of occupants and the lower their utility and maintenance bills.

Passive solar design is the process of creating a home that provides both shelter and comfort year-round while responding to regional climate conditions and minimizing dependence on energy-consuming mechanical systems. The goal is to build and occupy a home that a) utilizes solar heat gain in the winter to warm the interior of a home, b) controls solar heat gain in the summer, and c) facilitates daylighting, natural ventilation, and nighttime cooling to keep a home comfortably cool in the summer.

Moving on from Passive Solar Design, Part 1, the interior of the home, surfaces and building materials must be carefully chosen and strategically placed to perform as absorbers and thermal mass storage of solar heat gain in winter and convective cooling breezes in summer. In addition, window coverings for preventing heat loss in winter and heat gain in summer are recommended. Finally, fans and controls for air distribution from one room to another can provide supplemental heating and cooling to the entire home.

A radiant barrier system (RBS) is comprised of a sheet of reflective foil placed next to an air space, the combination of which discourages radiant heat transfer. In a hot climate, an RBS properly installed beneath a roof blocks up to 95% of the heat transfer from the roof to the attic insulation, resulting in a cooler living space and less cooling load.

Today, wood framing is the most common construction method for residential and small scale commercial buildings. However, environmental concerns, and volatile fuel and lumber prices are driving the quest for high performance building envelope systems such as Structural Insulated Panels (SIPs) and Insulated Concrete Forms (ICFs). In addition, natural disasters throughout the U.S. and large payouts for insurance companies are motivating builders to consider more robust and durable building material.

The underlying principle of water management is to layer materials from roof to foundation in such a way that water is always directed downward and outward from the building. Good water management practices require good drainage details. The typical building envelope is subject to water entry in numerous locations. Keeping water out of a building envelope is the primary line of defense against mold and a necessary condition for durability.

Inefficient windows can account for 9% of all residential energy consumption. Energy performance in windows can be improved through multiple panes of glass, low conductivity gasses (Argon and Krypton) between panes to boost R-value, and low emissive (Low-E) coatings of tin and silver oxide to block radiant heat gain. Window frame materials such as wood, fiberglass, composites, vinyl, and metal, are also a consideration for conductivity and environmental impact.