Building Envelope

The following came from the EPA’s web site: 

http://energystar.gov/ia/new_homes/features/VEFraming1-17-01.pdf 

An effective building envelope is a key element for an energy –efficient home.  Value-engineered framing increases the thermal resistance of the building envelope without compromising structural integrity by eliminating unnecessary framing members.  This can result in up to 25 percent reduction in the amount of wood used.  With lumber prices high, optimizing the use of wood can significantly lower the framing cost and reduce the resource impact of new home construction. 

Wood loses or gains heat more quickly than insulation.  In frame construction, studs, joists and rafters are placed at regular intervals throughout the building envelope.  The cavities formed by these framing members are filled with insulation.  The unnecessary use of wood displaces insulation and degrades the thermal efficiency of the building envelope. 

Standard construction practice places framing members at 16 inches on center.  Most building codes allow this spacing to be increased to 24 inches by using deeper framing members (i.e. 2×6’s instead of 2×4’s).  This also reduces labor costs.  

The size and location of doors and windows has an impact on the thermal efficiency of the building envelope.  Figure 1 shows a window opening in standard framed wall.  The location of the window opening requires the installation of additional studs to support the frame.  By utilizing value-engineered framing and adjusting the location of the window opening as shown in Figure 2, unnecessary studs are eliminated. 

At exterior corners and the intersection of interior partitions and exterior walls, additional studs are required to support the drywall.  Figures 3 and 4 show how these studs create pockets that are difficult to insulate and air seal.  By making the modifications shown in Figures 5 and 6, these pockets are eliminated.  Using “drywall stops” can further increase the thermal efficiency at these locations. 

Look for Energy Star labeled homes to include value-engineered framing for improved thermal performance of the building envelope. 

Value-engineered framing can provide many benefits including:

  1. Improved Comfort:  By increasing wall insulation and eliminating air spaces, value-engineered framing increases the overall R-value and integrity of the building envelope.  This results in walls that are warmer in winter and cooler in summer.  This is important because approximately 40 percent of our physical comfort is due to the radiant heat exchange between our bodies and the surrounding interior surfaces.  Value-engineered framing reduces this radiant heat exchange, thus maintaining a more consistent level of comfort throughout a house.
  2. Reduced construction cost:  Value-engineered framing can reduce the amount of lumber and labor needed to construct a home.  This results in construction cost savings.
  3. Lower utility bills:  Value-engineered framing reduces the amount of heat and air that flows through the building envelope.  This results in lower utility bills, making homes less expensive to operate.
The exterior walls and roof of the American Ingenuity dome contain no wood to interrupt the insulation.  The seven inch thick blocks of Expanded Bead Polystyrene that Ai uses is comparable to eleven inches of fiberglass insulation. During the shell kit assembly, a temporary wooden rib system is used to support the component panels until the seams between the panels and all the entryways and dormers are concreted…then the rib system comes down.  There is no wood in the exterior walls and roof of the Ai dome to interrupt the insulation…no wood to burn…no wood to rot and no wood for termites to eat.  The exterior of the Ai dome is steel reinforced concrete that does not contain shingles.
So the Ai dome exterior is a tight envelope because it does not have wood interruping its insulation and the insulation is super-thick; as a result the Ai dome saves its clients 50% to 70% on their heating and cooling bills.  For example, American Ingenuity can cool its 3,700 sq.ft. office domes to 76 degrees during work times for less than $133 a month in the hot Florida summer months.
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