When it comes to air sealing and ventilating, new residential building codes are now in place to ensure energy efficiency as well as the comfort of the homeowner. In many existing homes, there can be a number of uncontrolled air leaks that add up to the equivalent of leaving a window open 24/7.
While its been reported that air sealing uncontrolled leaks can reduce energy bills anywhere from 10-20 percent or more in some cases, its important to understand a home’s ventilation before undertaking any project. The advice of a certified home contractor may even be needed to avoid creating an unhealthy and potentially-life threatening environment.
With indoor air pollutants such as carbon monoxide, dust mites, pollen, radon, mold, excessive carbon dioxide, volatile organic compounds and other chemicals identified by the EPA as contributing to poor indoor quality that causes or contributes to health concerns such as asthma, headaches, dry eyes, nasal congestion, nausea and fatigue, it’s extremely important to understand the role of proper ventilation or air exchanges. Indoor air is on average two to five times more polluted than the air outdoors and can be up to 100 times more.
A lack of ventilation traps indoor air pollution, while too much ventilation wastes energy and reduces comfort. When a home’s air leaks are sealed well, mechanical ventilation may need to be installed to remove pollutants generated in the home and provide outdoor air in a controlled manner. Whether a mechanical ventilation system makes sense in an existing home depends on the structure, its heating, ventilation and air-conditioning (HVAC) system, and the air-sealing changes.
To get started, the Department of Energy has identified the following common air-sealing trouble spots:
• Air barrier and thermal barrier alignment - air barrier is in alignment with the thermal barrier (insulation)
• Attic air sealing - top plates and wall-to-ceiling connections are sealed
• Attic knee walls - air barrier is installed at the insulated boundary (kneewall transition or roof, as appropriate)
• Shaft for piping or ducts - openings from attic to conditioned space are sealed
• Dropped ceiling/soffit - air barrier is fully aligned with insulation; all gaps are fully sealed
• Staircase framing at exterior wall - air barrier is fully aligned with insulation; all gaps are fully sealed
• Porch roof - air barrier is installed at the intersection of the porch roof
• and exterior wall
• Flue or chimney shaft - opening around flue is closed with flashing, and any remaining gaps are sealed with fire-rated caulk or sealant
• Attic access - attic access panel or drop-down stair is fully gasketed for an air-tight fit
• Recessed lighting - fixtures are provided with air-tight assembly or covering
• Ducts - all ducts should be sealed, especially in attics, vented crawlspaces, and rim areas
• Whole-house fan - an insulated cover is provided that is gasketed or sealed to the opening from either the attic side or ceiling side of the fan
• Exterior walls - service penetrations are sealed and air sealing is in place behind/or around shower/tub enclosures, electrical boxes, switches and outlets
• Fireplace wall - air sealing is completed in framed shaft behind the fireplace or at fireplace surround
• Garage/living space walls - air sealing is completed between garage and living space. Pass-through door is weather stripped
• Cantilevered floor - air sealed and insulated at perimeter or joist transition
• Windows and doors - space between window/door jambs and framing is sealed
• Rim joists, sill plate, foundation, floor - rim joists are insulated and include an air barrier, junction of foundation and sill plate is sealed, penetrations through the bottom plate are sealed, all leaks at foundations, floor joists and floor penetrations are sealed and exposed earth in crawlspace is covered with Class I vapor retarder overlapped and taped at seams
• Common walls between attached dwelling units - the gap between a gypsum shaft wall (i.e., common wall) and the structural framing between units is sealed
Air sealing an existing home can involve much more than merely caulking and weather-stripping, Any changes to the building envelope may affect your home’s ventilation and could potentially create health risks. Done properly, a well-sealed, well-ventilated home will maximize your return on investment when paired with other improvements such as new energy-efficient appliances.