Energy Code Changes: What the Design Team Needs to Know: Session 2 -- Building Envelope
Session 2 of the Energy Code Series dealt with the building envelope and how the code changes affect this area. Michael Waite, LEED AP from Simpson Gumpertz and Heger was the presenter.
Mr. Waite emphasized, that from the earliest phase of planning and design it is a MUST to reference the energy code. This is where Integrated Building Design excels. The code should really be used as a guide from this point onward. As mentioned earlier, it is really the ASHRAE Standard 90.1 that comprises the New York State Energy Code, but any locality such as NYC can adapt a more stringent code.
Some general definitions:
R-value, which is the measure of heat (or cold) resistance.
U-value is the measure of heat transfer through a system.
The C-factor is a measure of thermal conductance, and is used below grade, while the F-factor is used as measure of conductance for slab or grade floors.
SHGC, Solar Heat Gain Coefficient is the measure of solar source heat gain through the envelope system.
The Window to Wall Area is the ratio of the vertical fenestration (window or door opening area) to that of the gross wall area.
There are several compliance methods here, and they include both a prescriptive and performance pathway. In the prescriptive path, one just simply follows allowed R- and U-Values for a given area; while in the performance path, one will calculate them, and trade back and forth between components to arrive at the allowable total R- or U-Value. Both methods contain mandatory provisions, such as air leakage and window to wall ratios. For smaller or less complex buildings, a design team will often just use RES Check (for residential) or COM Check (for commercial) These are free software programs that allow for all R and U values, gross areas, cavity spaces, window and door schedules, type of heating system to entered in spreadsheet form, and the program will calculate whether the building meets the code, if so, by how much beyond code compliance.
Climate Zone is a major factor here, and the correct zone MUST be entered. Also, it is VERY important to enter the correct code, as each state differs.
Residential is defined as low rise limited to less than three stories; all other buildings are classified as commercial. R and U values are needed to be entered for all envelope assemblies, but there is NO SHGC requirement at the residential level; SHGC IS needed for commercial.
There is a mandatory provision in the code that now specifies the maximum allowable air leakage to be complied with. This is defined as less than 5.5 air changes per hour at a pressure of five Pascals, and can be confirmed with an ASTM E-799 Blower Door Test.
A vapor barrier on the warm side in winter is now needed.
For the UA calculations, the lower the number the better the building performs.
Commercial Code is far more complex in scope of required data. Once again, in New York State, ASHRAE Standard 90.1 is used, but ECCNYS Chapter 8 can also be followed. For commercial, most prefer to follow ASHRAE 90.1, as it allows for more flexibility and area trade-offs.
If a building will have more than 50% of its Window to Wall ratio, it is mandatory to use simulation modeling to comply; simple UA calculations will NOT surfice. In this case, shading devices are needed here. The mandatory provisions are still the same here, and include air leakage, recessed light fixture limits.
There is a need to define walls in commercial building submittals, but orientation is optional. R and U values are input, as well as SHGC, Roof Type, Cavity Insulation type, basement walls and their height of grade level. If the basement is unheated, the values for the floor of the first floor are used.
For U values, care is really needed here. Many mistakes are made by using the Center of Glass U Value for a window rather then the required total U-Value for the complete assembly. The same is true for walls; one MUST factor in the framing schedule, as thermal bridging plays a BIG role! U-Values can also be modeled, as can fenestration.
The Projection Factor plays a big role in the performance of a window. If the window sits inside of the outer wall (recessed), and is located over the insulation, the R-Value is increased.
Once again Mr. Waite emphasized the need for proper care to be taken when making the submittal to the Department of Buildings. The following are needed here:
In future, we will be seeing increased R-Value levels, decreased U and SHGC values, as well as more restrictions on glazing areas. We will also see envelope provisions that take into account the benefits of day lighting. As we know, LEED addresses this very well.
Mr. Waite emphasized, that from the earliest phase of planning and design it is a MUST to reference the energy code. This is where Integrated Building Design excels. The code should really be used as a guide from this point onward. As mentioned earlier, it is really the ASHRAE Standard 90.1 that comprises the New York State Energy Code, but any locality such as NYC can adapt a more stringent code.
Some general definitions:
R-value, which is the measure of heat (or cold) resistance.
U-value is the measure of heat transfer through a system.
The C-factor is a measure of thermal conductance, and is used below grade, while the F-factor is used as measure of conductance for slab or grade floors.
SHGC, Solar Heat Gain Coefficient is the measure of solar source heat gain through the envelope system.
The Window to Wall Area is the ratio of the vertical fenestration (window or door opening area) to that of the gross wall area.
There are several compliance methods here, and they include both a prescriptive and performance pathway. In the prescriptive path, one just simply follows allowed R- and U-Values for a given area; while in the performance path, one will calculate them, and trade back and forth between components to arrive at the allowable total R- or U-Value. Both methods contain mandatory provisions, such as air leakage and window to wall ratios. For smaller or less complex buildings, a design team will often just use RES Check (for residential) or COM Check (for commercial) These are free software programs that allow for all R and U values, gross areas, cavity spaces, window and door schedules, type of heating system to entered in spreadsheet form, and the program will calculate whether the building meets the code, if so, by how much beyond code compliance.
Climate Zone is a major factor here, and the correct zone MUST be entered. Also, it is VERY important to enter the correct code, as each state differs.
Residential is defined as low rise limited to less than three stories; all other buildings are classified as commercial. R and U values are needed to be entered for all envelope assemblies, but there is NO SHGC requirement at the residential level; SHGC IS needed for commercial.
There is a mandatory provision in the code that now specifies the maximum allowable air leakage to be complied with. This is defined as less than 5.5 air changes per hour at a pressure of five Pascals, and can be confirmed with an ASTM E-799 Blower Door Test.
A vapor barrier on the warm side in winter is now needed.
For the UA calculations, the lower the number the better the building performs.
Commercial Code is far more complex in scope of required data. Once again, in New York State, ASHRAE Standard 90.1 is used, but ECCNYS Chapter 8 can also be followed. For commercial, most prefer to follow ASHRAE 90.1, as it allows for more flexibility and area trade-offs.
If a building will have more than 50% of its Window to Wall ratio, it is mandatory to use simulation modeling to comply; simple UA calculations will NOT surfice. In this case, shading devices are needed here. The mandatory provisions are still the same here, and include air leakage, recessed light fixture limits.
There is a need to define walls in commercial building submittals, but orientation is optional. R and U values are input, as well as SHGC, Roof Type, Cavity Insulation type, basement walls and their height of grade level. If the basement is unheated, the values for the floor of the first floor are used.
For U values, care is really needed here. Many mistakes are made by using the Center of Glass U Value for a window rather then the required total U-Value for the complete assembly. The same is true for walls; one MUST factor in the framing schedule, as thermal bridging plays a BIG role! U-Values can also be modeled, as can fenestration.
The Projection Factor plays a big role in the performance of a window. If the window sits inside of the outer wall (recessed), and is located over the insulation, the R-Value is increased.
Once again Mr. Waite emphasized the need for proper care to be taken when making the submittal to the Department of Buildings. The following are needed here:
- Professional Statement
- Energy Analysis and drawings signed and sealed by a licensed professional
- Compliance Certificate for New and Alterations that includes the correct climate zone
- Supporting documentation, such as construction drawings, descriptive properties about door and window assemblies, among other items, as deemed necessary for the project.
In future, we will be seeing increased R-Value levels, decreased U and SHGC values, as well as more restrictions on glazing areas. We will also see envelope provisions that take into account the benefits of day lighting. As we know, LEED addresses this very well.
Posted by Alan L. Englander at 1/9/2010 11:57 PM 
Categories: Window to Wall Area, R-Value, Mandatory Provisions, Prescriptive and Performance Compliance, Thermal Bridging, Simulation, UA Calculations, Projection Factor, Fenestration, U-Value, Climate Zone, Submisson of Data, F-Factor, SHGC, C-Factor, Trade-Off Options
Categories: Window to Wall Area, R-Value, Mandatory Provisions, Prescriptive and Performance Compliance, Thermal Bridging, Simulation, UA Calculations, Projection Factor, Fenestration, U-Value, Climate Zone, Submisson of Data, F-Factor, SHGC, C-Factor, Trade-Off Options
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