Notes

• (SB-1) Structure and Basement:

  (SB-1) Note: An exterior wall of a building should be properly sealed, protected from moisture, and insulated properly to increase comfort, reduce noise, and save on energy costs. An exterior wall is complex; one of the most complex systems in a building is the building envelope. An effective wall should have the following characteristics:

  • airtight: all air leaks should be sealed in the wall during construction and before the insulation is installed in the wall;
  • moisture-controlled: an exterior rain drainage system, an air barrier, and a vapor diffusion retarder should be installed on the wall on the correct side of the wall; and
  • complete insulation coverage: the wall framing should provide enough room for complete, maximum insulation coverage and reduce thermal bridging, with no open gaps or compressed insulation, and continuous insulated sheathing.

• (SB-2) Structure and Basement:

  (SB-2) Note: How Insulation Works

  Insulation provides resistance to heat flow. The more heat flow resistance the insulation provides, the lower the heating and cooling costs.

  Heat flows naturally from a warm to a cool — from a warmer space to a cooler space. In the cold winter, this heat flow moves directly from all heated living spaces to adjacent unheated spaces, such as attics, garages, basements, under-floor crawlspaces, and even to the outdoors. Heat flow can also move indirectly through interior ceilings, walls and floors — wherever there is a difference in temperature. During the cooling season, heat flows from the exterior to the interior of a building.

  To keep the occupants of the building comfortable, the heat lost in the winter must be replaced by the heating system, and the heat gained in the summer must be removed by the cooling system. A properly insulated home will decrease this heat flow by providing an effective resistance to the flow of heat.

  Batts, blankets, loose-fill and low-density foams all work by limiting air movement. The still air inside the insulation is an effective insulator because it eliminates convection. Still air also has low conduction, so heat doesn’t flow very well via conduction through insulation. Some foams are filled with special gases that provide additional resistance to heat flow.

  Reflective insulation limits heat that travels in the form of radiation. Some reflective insulation also reduces air movement, but not as much as other insulation types.

  Don’t confuse insulation’s ability to limit air movement with “air sealing.” Insulation reduces air movement only within the space it occupies. It cannot limit air movement through other pathways nearby. For example, the insulation in the wall cavity does not affect the air leakage that may take place around a window frame. Adding insulation will not likely have the same effect as air sealing.

  Insulation's resistance to heat flow is measured or rated in terms of its thermal resistance, better known by inspectors as the “R-value.” Let’s learn about R-value.

• (SB-3) Structure and Basement:

  (SB-3) Note: Thermal Bridging

  Insulation in between studs in a wall does not restrict the heat flow through those studs. This heat flow is called “thermal bridging.” The overall R-value of that wall may be different from the R-value of the insulation itself. 

  It is recommended that the insulation installed in an attic covers the tops of the attic floor joists. And it is also recommended that insulation sheathing be installed on stud walls. Wood studs can transfer energy through the wall assembly. Metal studs can transfer energy much better than wood studs can. As a result, the metal wall’s overall R-value can be as low as half of the insulation’s R-value.

• (BD-1) Blower Door:

  (BD-1) Note: A blower door is a diagnostic tool designed to measure the airtightness of a building and to help locate air leakage sites. The blower door has a variable-speed fan and meters to measure airflow and pressure. Blower doors are used for a variety of purposes, including:

  • documenting the construction airtightness of buildings;
  • estimating natural infiltration rates in houses;
  • measuring and documenting the effectiveness of air-sealing activities; and
  • measuring duct leakage in forced-air distribution systems.

  A building can lose energy by the transfer of heat via conduction, radiation and convection. Convection loss deals with air movement. Almost all buildings have some air movement through the building envelope. Where there is a driving force or a pressure difference across the envelope, air moves. If there is air moving into a dwelling through an open gap, then there is also air moving out of the dwelling through another open gap located somewhere else. 

  Pressure can cause air to move. Pressure differences can be caused by wind, exhaust fans, or the venting of combustion appliances. 

  Temperature can cause air to move. The stack effect is a powerful force that can cause convective losses in many homes, particularly during the cold winter months.

  Stack Effect

  Stack effect, in relation to residential energy audits, is the movement of air into and out of a house. It is driven by buoyancy.  Buoyancy occurs due to a difference in indoor-to-outdoor air density resulting from temperature and moisture differences. The result is either a positive or negative buoyancy force. The greater the thermal difference and the height of the structure, the greater the buoyancy force.

  Since houses are not completely sealed, the stack effect can cause air to infiltrate. During the heating season, the warmer indoor air rises up through the structure and exits through open windows, vents and air leakage points. The rising warm air drops the pressure in the lower part of the building, forcing cold air to infiltrate through open doors, windows and other openings and air leakage points.

  When there is only a temperature difference causing the air to move and leak, there exists what is called the neutral zone of a building (or the neutral pressure level or NPL). It is where the interior and exterior air pressures are equal. At all other areas above and below, the pressure differences between the interior and exterior depends on the distance from the neutral zone and the difference between the air densities of the inside and outside air. At the neutral zone, there is neither infiltration nor exfiltration of air in significant amounts. The neutral zone is typically located in the middle of a building where the pressure differences are at a minimum. 

  It is important to understand the significance of sealing the air leakage points at the top and bottom portions of a building, rather than anywhere else. 

  Usually, the natural air movement in a house depends on a combined force of wind and stack effects. Pressures continually change as the temperatures and wind forces change.

  The wind and stack pressures in a house depend on the house’s height, resistance to air flow through the house interior, the air leakage openings, the local terrain, and the immediate shielding of the house’s structure.

  How a Blower Door Works

  The blower door is a tool used to exaggerate pressure differences on a building. The blower door is made up of a powerful fan that is temporarily installed inside an exterior doorway opening. The fan blows air into or out of the building to create a slight pressure difference between the inside and outside. This pressure difference forces air through holes and penetrations in the exterior envelope.

  By simultaneously measuring the air flow through the fan and its effect on the air pressure in the building, the blower door system measures the airtightness of the entire building envelope.

  The tighter the building (e.g. the fewer the holes), the less air you need from the blower-door fan to create a change in building pressure.

  Blower Door Test

  A typical blower door test will include a series of fan-flow measurements at a variety of building pressures ranging from 60 pascals to 15 pascals. One pascal (Pa) equals approximately 0.004 inches of water column.

  During a blower door test, the fan is on at a high speed. The door needs to create significant pressure differences in order to create results that are measurable. Tests are done at relatively high pressures to also mitigate the effects of wind and stack-effect pressures on the test results.

  Oftentimes, a simple “one-point” test is conducted where the building is tested at a single pressure (typically, 50 pascals). This is done when a quick assessment of airtightness is needed. 

  How Long Does it Take?

  It takes about 20 minutes to set up a blower door, conduct a test, and document the airtightness of a building.

  The blower door can be used to estimate the amount of leakage between the conditioned space of a house and attached structural components, like a garage.

  It can also be used to estimate the amount of leakage in forced-air duct systems.

  The blower door forces air through holes and gaps. And these problem spots are easier to find using chemical smoke, an infrared camera, or by simply using the sensitive backside of your hand.

  The blower door can also help investigate backdrafting and help determine the need for mechanical ventilation.

  Wind and Temperature Can Affect a Test

  Wind blowing on the house can significantly affect the blower door test. Wind has the largest impact on blower door tests. If the wind is blowing at 20 mph against the house, it can create an indoor-outdoor pressure difference as much as 50 pascals. A measurement of a house using a blower door during a time of high wind pressures can affect the test, the flow rate of the blower fan itself can be changed, and the measurement accuracy of the fan flow will be affected.

• (BD-3) Blower Door:

  (BD-3) Note: Each Image was taken in the home to look for large air gaps in the building or areas where air sealing is needed. The format of the photos will be: (1) infa-red image followed by a normal picture of the area being documented.

• (EG-4) Exterior/Garage:

  (EG-4) Note: The chimney was not finished at the time of inspection and was sealed to conduct the blower door test. The chimney cladding should be airtight when completed. Remember to close the damper when the chimney is not in use.