Building Envelope: 

…is the principles of energy efficiency, durability, health, comfort, and environmental responsibility. The result synthesizes beauty, function, economy, and performance into a structure, when Guarding Against The Elements is your goal.

The building envelope is a total system of construction materials and design components that control the temperature, movement of air, and moisture both into and out of the building. A building’s insulation, air barrier and vapor barrier all need to work together to achieve a more stable, comfortable and healthier indoor environment. Many new materials and design practices are being implemented to extend the sustainable service life of buildings and homes.

Here is the old train of thought:

Ventilating the Attic and the Crawl Spaces has long been the traditional and code required method of home design and building. However, ventilation of these spaces was required because standard materials and building design practices were not capable of addressing radiant heat transfer, condensation, and the results of “stack-effect” issues.

In order to address heat transfer from weather issues, utilities, and the formation of moisture due to condensation and air infiltration, the only option was to ventilate the attics and crawl spaces. The major problem with ventilating these spaces is that the air brings moisture, pollution and other adverse problems and challenges with it. Furthermore, the vents and other permeations, create voids in the building for insects and rodents to enter, and allows our nice, conditioned air to escape, or is being pulled from the living spaces.

When our heating/cooling utilities and ducts are located in the attic and/or crawl spaces, their radiant contact with the ducts will cause them to lose 10% (or more) of the hot or cold air flowing through them due to radiant transfer. Worse yet, moisture and mold can also form within the ducts during certain temperature conditions, causing adverse health affects to the building occupants or your family.

Another major reason that traditional methods call for attic ventilation is that during the hot summer months, heat from the sun builds on the roof and radiates into the attic space. In fact, it can build to upwards of 130 to 150 degrees or more. (see our section on Urban Heat Islands). This extreme heat radiates throughout the attic and the living space causing condensation and the potential for mold. Our air conditioning systems also need to work harder and consume more energy with all this heat directly above our heads. The extreme heat also makes it very uncomfortable to enter these spaces.

Most builders and design professionals are not familiar with modern materials and progressive building science techniques that can virtually eliminate all of these problems that force the traditional, less effective requirement for ventilation in these building spaces.

Builders and design professionals will also make the argument that your home needs to breathe. Well, they are absolutely correct. But why rely on cracks, gaps and holes in your building for passive ventilation, when you can build your home tight, healthy and energy efficient, and let the mechanical ventilation systems due the job properly.

Spray foam insulation can provide benefits far greater than traditional materials such as fiberglass and cellulose, regardless of whether you decide to ventilate these spaces or not. By using spray polyurethane foam insulation you can increase your home’s energy performance, structural integrity and air quality.

This section will highlight further advantages of spray polyurethane foam insulation, methods of construction and its specific use in the Building Envelope.

Heat

…is a form of energy and always seeks a cooler area—in your home this means it flows outward in winter, and inward in summer. Insulation slows this heat flow, so your heating and cooling system requires less operation to maintain your desired temperature.

Stack Effect

• Air Infiltration is caused by wind, stack effect, and mechanical equipment in the home.
• The “stack effect” is when warm air moves upward in a building. This happens in summer and winter but is most pronounced in the winter because indoor-outdoor temperature differences are the greatest. Warm air rises because it’s lighter than cold air. So, when indoor air is warmer than the outdoor air, it escapes out of the upper levels of the building, through open windows, ventilation openings, or penetrations and cracks in the building envelope. The rising warm air reduces the pressure in the base of the building, forcing cold air to infiltrate through open doors, windows, or other openings. The stack effect basically causes air infiltration on the lower portion of a building and exfiltration on the upper part. Mechanical equipment such as fans and blowers cause the movement of air within buildings and through enclosures, which can generate pressure differences. If more air is exhausted from a building than is supplied, a net negative pressure is generated, which can induce unwanted airflow through the building envelope. Bathroom exhaust fans, clothes dryers, built-in vacuum cleaners, dust collection systems, and range hoods all exhaust air from a building. This creates negative pressure inside the building. If the enclosure is airtight or the exhaust flow rate is high, large negative pressures can be generated.