What is the Building Envelope? According to popular definition, a building envelope is the separation between the interior and the exterior environments of a building. It serves as the outer shell to protect the indoor environment as well as to facilitate its climate control. In general, the building envelope is the entire exterior building system. It may include the building's: windows, doors, roof, foundation, siding, floor, sidewalls, and all components thereof, such as insulation, bricks and structural masonry.

Energy efficiency is one of the most pressing concerns for today's property owners, and with mighty good reason. Energy costs are rising with no end in sight, and tenants are demanding lower energy bills. Municipalities are increasingly regulating the energy efficiency of buildings, and owners are becoming more aware of their responsibilities to reduce their buildings' energy consumption.

As a result, many property owners are scrambling to do whatever they can to make their buildings more efficient. In the mad rush of updating and making changes, many fail to realize a building system that can have a huge impact on a building's energy efficiency. The building envelope plays a critical role, as it forms the barrier between a building's interior and exterior environments. And with proper management, the building envelope can significantly slash a building's energy demand.

The All-Important Envelope

Many property owners are aware of the obvious ways to save energy, such as replacing incandescent light bulbs with more energy-efficient options and updating mechanical systems. But what about the building envelope? A building's windows, doors, walls, roof, foundation and other structures comprising the envelope system can waste tremendous amounts of energy, if not properly attended.

Deteriorated sealants and masonry.

An energy-efficient building envelope provides numerous benefits to property owners. First, it reduces the load on the mechanical systems in the building. When the heating and cooling systems don't have as much variation in temperature(s) to regulate, energy consumption naturally drops. For tenants, this translates to lower heating and cooling bills, which increase a property's attractiveness and value.

Beyond the benefits to owners, an energy-efficient building envelope is becoming increasingly important to owners due to stricter governmental regulations. Across the country, jurisdictions are updating building codes and mandating higher levels of energy efficiency. For example, in Virginia as counties adopt the revised State Building Code, (effective May 1, 2008 in Henrico County, already adopted in other Virginia counties) new fenestrations are required to meet U factor of .40, basement walls R-10 to R-13 for new and retrofit construction - recognition that energy efficiency is now a permanent requirement. These changes in building codes point to the government's expanding attention to sustainable design and construction, a trend that will likely continue far into the future.

Open cavities filled properly and sealed prevent infiltration.

What Needs Attention?

A building envelope is a system of interdependent parts. Like other types of systems, the whole unit functions only as well as the least effective component. When making improvements, the system should be considered as a whole. For example, if a property owner replaces every door in a building with the most energy-efficient model, while leaving drafty, ineffective windows in place, the efforts only improve the building's efficiency to a minimal degree. If the entire system is not working at maximum effectiveness, conditioned air inside a building will find a way to escape; unwanted outside air will find a way to enter.

When considering the envelope system, property owners should consider the following elements.

• Caulking and weather stripping - The least expensive to update, these seals will suffer the most abuse. As the least durable element of the envelope, caulking and weather stripping also wears out more quickly than other elements. They're small components, so property owners may not give them much thought. But in the aggregate, they can have a massive impact.
• Windows and doors - Many windows and doors in today's properties were designed for an era when energy was less expensive to purchase. As energy costs increase, windows and doors play a critical role in the envelope system.
• Exterior wall, fascia and trim - In many buildings, the fascia and trim are often not insulated properly or not insulated at all. These elements are designed to allow adequate ventilation into and out of the building. Property owners should see that their ventilation is being maintained at the rate at which it was originally intended. Repair contractors on the cutting edge of technology have access to newly designed mechanisms to properly monitor ventilation, such as plastic honeycomb vents to control the flow of moisture into and out of the wall, masonry sealers, wall flashings, control vents, and new sealants. All are part of materials industries that have developed new products and technologies to improve building energy performance and product durability. These honeycombs, for example, don't deteriorate like original methods and materials, and they offer dramatically longer service life.
• Wall system - Wall systems include the brick, wood, siding or concrete and the joints that connect these building materials. A wall system should have a very long life expectancy, depending on the materials used for construction. However, if a property owner notices water intrusion or cracks in the exterior wall, the wall system may need repair sooner than expected. Walls address the issue of infiltration - such as air, water or insects that can infiltrate the building -- and transmission of the temperature differences into the interior of the building through the solid wall. The deterioration of the construction materials over time can also compromise a wall system's ability to protect the building against infiltration and transmission.

When property owners understand the importance of the building envelope, the next step is taking action. But where should property owners go for help? The next article in this series will discuss how to evaluate and investigate your property's building envelope in conjunction with mechanical upgrades. The article will also take a look at choosing the right consultant, engineer, design professional or contractor and working as a team to update or increase the building's energy efficiency.