Step 1: Load Minimization - Architectural Elements & Building Envelope

The building shape and its envelope, which comprises building geometry, orientation, thermal performance of walls, windows and roofs, window coatings which will determine their solar heat gain coefficient (SHGC) or shading coefficient (SC) and finally, shading strategies are the most important components that will determine the energy use of a building, irrespective of climate.

These elements are the foundation of a good design and their proper specification and selection can significantly reduce building energy use. In fact, the potential energy reduction, can be as much as a third to half of a building's energy use according to architects Ed Mazria and William McDonough and further demonstrated via analytical means in this page. [1] [2]

The 435,300 ft² (40,400 m²) Ottawa Courthouse built in 1986 represents a readily quantifiable example of the potential impact that architectural design can have on building energy performance. Built at a time when the term “Low Energy Design” had not yet been defined, this building exhibits an energy performance of 12 ekWh/ft².yr (465 MJ/m².yr), which is better than some low energy buildings thanks to mundane architectural features that include a very well insulated building envelope, very tight construction that almost eliminates infiltration and use of few windows. The design was described in a 1991 Centre for the Analysis and Dissemination of Demonstrated Energy Technologies (CADDET) profile. [3] The Mt. Airy Library previously mentioned in the "Principles of IBD" page is another example of the impact that proper architectural design can have on building energy performance.

Such large reductions in energy use are possible because space heating and space cooling account for 30 to 40% of total energy use in a typical commercial building and 50 to 55% in buildings located in heating dominated climates. Thus, efforts to optimize the architectural design elements will affect a significant portion of a typical building energy use and as further illustrated in this page, reduce the size of heating, cooling and air handling equipment by an even larger amount.

Six architectural elements that have the largest impact on building energy use are separately examined in the following sections and the effect on building energy use and size of HVAC equipment illustrated via energy simulations and load calculations.

1. Optimized Building Shape: A building shape close to a cube exhibits the lowest surface to floor area (S/F) ratio and, in theory, energy use would be minimized since heating and cooling requirements are affected by the total building surface. [4] This however only applies if the building walls and roofs have a uniform thermal resistance. Under such conditions, a reduction in surface area would be accompanied by a reduction in heating energy use. In practice however, modern buildings do not exhibit uniform thermal resistance of their walls and roofs making the surface to floor area ratio a less important design element that may exhibit a small reduction in energy use in some climates, but a net increase in others.

The graphic at right provides an illustration using three different building configurations with roughly the same floor area of 29,000 to 30,000 ft² (~2,700 to ~2,800 m²). All buildings assume a 12 ft (3.6 m) floor-to-floor height, 35% window-wall ratio an R20 (RSI 3.5) roof and R12 (RSI 2.1) wall. As shown in the tables at the bottom of the graphic, the more compact, 3-storey square building has one-third less surface area compared to the single storey building. However, it has significantly more wall area and window area than the other two buildings, resulting in a lower overall thermal performance and higher heat transfer, which are also shown in the table and highlighted in red. In contrast, the single storey building exhibits the highest overall R value and lowest heat transfer (values highlighted in green) despite having a significantly higher surface area. The whole building energy intensity (calculated using eQUEST) for a Toronto location is also shown in the table with the single storey building displaying the lowest energy intensity. The scenarios illustrated are restricted to square buildings because rectangular buildings would introduce an additional variable that affects energy use as a function of orientation.

The above behavior holds true in different geographical locations as shown in the table of energy intensities provided below. It shows that the single storey building exhibits a 4% reduction in whole building energy intensity in cooling only locations and a much smaller difference in mild climates such as Houston, Rome, Atlanta and San Francisco. In colder locations such as Frankfurt and Chicago the single-storey building exhibits a 4 to 6% reduction in energy use compared to the three-storey building. There is however no difference in energy use between the 2-storey and 3-storey buildings in mild climates, or as in the case of Houston, the 3-storey building actually shows a small reduction in energy use relative to the 2-storey building.

This variability in energy use from different S/F ratios occurs due to the many variables that affect building energy performance including the geographical location, the ratio of wall to roof thermal performance, the amount of sunshine, the solar heat gain coefficient (SHGC) and even the ratio of interior areas to perimeter areas (which affects fan energy use). To add further complication, different energy analysis tools can potentially provide significantly different results than what is illustrated above and show a compact building design with a lower S/F ratio exhibit a lower building energy use. [5]

Designers therefore need to look at the building shape on a case by case basis to best fit their particular location. This should sound familiar to readers, since it is essentially what Vitruvious stated approximately 2000 years ago in the following passage:

We must at the onset take note of the countries and climates in which they are built. One style of house seems

appropriate to build in Egypt, another in Spain, a different kind in Pontus,.....Thus, we may amend by art to

correspond to the position of the heaven and its effect on climate”

2. Building Orientation: A building with its long axis running in an east-west direction will generally display a lower building energy use, lower electrical demand and reduced space peak cooling load. The potential energy reduction can be less than 1% as shown in the accompanying table of energy intensities for different geographical locations, but it can also be negative as shown by the values in red (San Francisco, Atlanta and Houston). The peak electrical demand reduction can be in the range of of 1 to 6% and the space peak cooling load reduction in the range of 0.4% to as much as 10%. These results are based on energy simulations of a hypothetical 36,000 ft² (3,345 m²), five-storey commercial office building with a 60 ft x 120 ft (18 m x 36 m) floor plate, a WWR of 45% and SHGC of 0.4 for buildings in heating dominated climates and SHGC of 0.25 for Singapore, Houston and Atlanta (ASHRAE 90.1 Envelope Requirements). The simulations were performed using eQUEST.

The use of windows with lower SHGC values would make the building less responsive to orientation as shown by the negative energy savings in Houston and Atlanta, although there still is some reduction in peak electrical demand and space peak cooling loads. San Francisco appears to be an outlier with negative energy savings, as well as a higher electrical demand. The degree of variability in the results suggests that optimum orientation and building performance depend on a number of variables including the geographical location, amount of glass and length to width aspect ratio and designers need to review their design for their particular location to determine the optimum building orientation.

3. Thermal Performance of the Building Envelope: A highly insulated building envelope is a key design element to achieve a low energy building design in heating dominated regions and at the same time reduce the size of the central heating plant and distribution system (perimeter heating equipment).

As described in the “Building Energy Use Statistics” page, heating is the largest end-use, accounting for approximately 32% of the total building energy use in the U.S. and 50% in Canada and also reported to be the largest end-use in the six largest world markets surveyed by the World Business Council for Sustainable Development (WBCSD). [6] As a result, good thermal performance of the building envelope is one of the most important foundations of low energy buildings.

Energy standards for new construction such as those published by ASHRAE continue to increase the envelope thermal performance requirements, driven by the goals towards low energy buildings and net zero buildings. This trend is illustrated below in graphical and tabular form for the ASHRAE 90.1 Standard Series, Standard 189.1 and the Advanced Energy Design Guides (AEDGs) in ASHRAE defined climate Zone 5 and Zone 6. [7] [8] [9] The tables show an approximate doubling in the thermal performance requirements between the 90.1-2004 Standard and the AEDG50 Standard, which is a stringent standard designed to achieve 50% savings over ASHRAE 90.1-2004. For Zone 5, which includes cities such as Chicago and Denver, the Southern Ontario City of Hamilton and the European cities of Berlin and Prague, the AEDG50 calls for performance levels of R30 (RSI 5.3) for the roof, an R13 (RSI 2.3) for mass walls or an R28 (RSI 4.9) for steel stud walls and finally, an overall glazing Uvalue of 0.39 Btu/hr.ft².ºF (2.2 W/m².ºC). Interestingly, the difference in thermal requirements between Zone 5 and Zone 6 are very small and so colder cities such as Minneapolis-St. Paul or the Canadian cities of Toronto and Montreal require essentially the same thermal performance targets.

Some industry practitioners are calling for even higher levels such as R40 walls and R60 roofs or even higher levels that would have been viewed as excessive a few years ago. As an example, Robert Bean, a high performance building consultant in Alberta, Canada stated in a recent article on high performance construction that: [10]

“If you want to set an example of high performance construction and beat ASHRAE 90.1 by 50% or more, we will need

insulation and lots of it placed on the outside of the mass by subscribing to the 10-20-40-60 rule of insulation, meaning

R10 for under slabs, R20 below grade walls, R40 above grade walls and R60 roofs.”

Given the industry objectives towards transforming the market to consistently design net zero energy buildings within the next 10 to 20 years [11] [12], very high levels of insulation are an implicit requirement for energy efficient new construction and yet there is significant debate on the amounts needed to achieve large reductions in energy use. An illustration that provides one answer is presented below in two tables that include the thermal performance of the walls, roof and glazing, the peak heating load and the predicted natural gas use and finally, the energy intensities. The predicted natural gas use and whole building energy intensities are based on energy simulations performed with eQUEST for the same hypothetical 5-storey, 36,000 ft² (3,345 m²) commercial office building used in the previous section in a Toronto location. Three different levels of thermal performance are shown including a 90.1-2004 reference, an intermediate efficient design and a low energy building (LEB) design that displays thermal performance levels beyond the most stringent standards mentioned above.

As shown in the outputs, the significantly better thermal performance of the LEB design achieves a 47% reduction in peak heating load and a 46% reduction in natural gas energy use relative to the 90.1-2004 Reference. The reported natural gas energy use is equivalent to a low space heating energy intensity of 7.7 ekWh/ft².yr (298 MJ/m².yr) compared to the 90.1-2004 Reference space heating intensity of 14.4 ekWh/ft².yr (558 MJ/m².yr). Overall, the whole building energy intensity is reduced by 27%.

The second table shown below includes the required plant size to meet the design heat loss assuming two boilers, each sized to meet 65% of the peak load. The peak hot water flow is also included based on the installed plant capacity. The size of the heating plant, peak hot water flow and circulating pump for the LEB design is reduced by 50% and shown to be approximately proportional to the reduction in peak heating load.

From a practical perspective, walls with large amounts of insulation need to be thick, which can be a design challenge. The location of the insulation and the design of the wall structural elements are equally important in order to minimize thermal bridging and ensure that the effective thermal performance of the wall is as close as possible to its nominal thermal performance. The examples used in this section assume that the wall Rvalues used in the energy models and load calculations are effective Rvalues, but the vast majority of wall construction used in commercial buildings exhibits significant thermal bridging and achieve much lower effective Rvalues. Designing a wall with an effective R32 such as what is used by the LEB is not easy and this is especially true for steel stud cavity walls and spandrel glass panels, which exhibit significant thermal bridging to the point of cutting their effective thermal performance by as much as 50% or more. [13] [14] [15] [16]

The best approach to minimize thermal bridging in an exterior wall construction is via placement of the insulation as a continuous layer to the exterior of the wall as opposed to the stud cavity. [17] Doing so will also provide additional benefits including better sound attenuation, increased durability (cracks in back-up and cladding due to thermally induced expansion and contraction are minimized), condensation of moisture will occur in the exterior and finally, the internal mass of the building is able to function as heat storage. [18]

4. Downsizing of Perimeter Heating Systems: A wall that is highly insulated has the added ability to maintain more even interior space temperature throughout the seasons. In winter, the surface temperature of exterior walls will stay warmer with a corresponding increase in comfort and more importantly, the rate of temperature drop during the unoccupied period will be slower, allowing the building to “ride-through” or coast with minimal or no heating. In milder climates where winter design temperatures are above 23 ºF (-5 ºC), it may be possible to reduce the size of perimeter heating. This potential downsizing is something that is not typically considered by designers since steady state calculations of design heat loss explicitly requires that thermal storage effects be ignored. [19] Yet, there is evidence in the form of operational performance data of existing buildings showing that they maintain the interior temperature during the unoccupied period better than predicted, especially in the cases where there are constant internal heat gains such as office equipment and other plug loads. Additionally, there are anecdotal reports of some buildings designed with no perimeter heating systems and research work including one study completed in 2009 that measured the indoor temperature in a building in Montreal, which concluded that the use of a high performance building envelope could potentially eliminate the need for perimeter heating. [20]

Space temperature can be used as an indicator of the required capacity of the perimeter heating system. However, there is almost no technical information on the subject of calculating rates of temperature drop, as it is not an important consideration when sizing heating equipment. In addition, prediction of indoor space temperatures requires dynamic, non-steady state calculations that are based on sets of differential equations or hourly computer programs in order to consider thermal mass and thermal inertia. To illustrate this behavior, two computer-based approaches that take into account the building thermal mass were used to create the indoor space temperature profiles presented below. The profiles represent a perimeter zone of a typical multi-storey, commercial building that goes on temperature setback for 9 hours starting at 10:00 PM and assumes a space that is sandwiched between two 8 inch (200 mm) concrete slabs. One set of results were derived using the Passive Design Assistance (PDA) computer program. [21] [22] [23] This program uses the CIBSE Admittance Method developed in the 1960s to predict the thermal performance and indoor space temperature taking into account dynamic effects of heat storage in a building. [24] The second set of results were derived with DOE 2.1E by requesting hourly reports of the “average perimeter zone temperature”. DOE 2.1E uses a weighting-factor technique to calculate thermal loads and heat flow from the building mass. [25]

The results are presented as three sets of data and graphs that are arranged in two separate columns. The three graphs on the left column display temperature profiles created with the PDA program at different outside air temperatures (OAT) while the graphs on the right column show the temperatures calculated by DOE 2.1E. Each graph displays multiple curves for the different levels of thermal performance used in the previous examples and show that the higher the level of insulation, as depicted by the LEB scenario, the lower the rate of temperature drop. The first graph is for an OAT of 14 ºF (-10 ºC) and shows the final indoor temperature of the 90.1-2004 Reference scenario to be between 48 and 56 ºF (9 to 13 ºC), depending on the analysis tool used. In contrast, the LEB displays a final interior space temperature of approximately 55 to 57 ºF (13 to 14 ºC). At a warmer OAT of 28 ºF (-2ºC), the final interior temperature for the highly insulated walls is estimated to be in the range of 59 to 62 ºF (15 to 17 ºC), meaning that the perimeter is almost able to ride through the unoccupied period with no need for heating. Finally, at an OAT of 36 ºF (2ºC), the final temperature of the space is estimated to be in the range of 60 to 66 ºF (16 to 19 ºC), again indicating minimal need for heating.

The above temperature profiles suggest that a heavily insulated building located in a mild climate where the winter design temperature is above 23 ºF (-5 ºC) has very little need for space heating and designer can potentially consider reducing the size of the perimeter heating system since the unoccupied temperature stays within less than 10 ºF (5 ºC) of the occupied period setpoint.

5. Windows: Windows are the weakest thermal component of a building envelope and their selection and size will significantly affect building energy use and the required capacities of the heating, cooling and air handling equipment. In the past, size and window placement was optimized to minimize winter heat loss and summer heat gain while maximizing the need for natural lighting by locating windows high so that natural lighting could penetrate into the far recesses of a building. Today’s architecture trend of gleaming steel and glass that started sometime in the 1960s ignores this concept with the result of all glass buildings with window to wall ratios (WWR) that exceed 50% and even go as high 60%. Joseph Lstiburek referred to this trend in a March 2009 ASHRAE Journal article as: [26]

“The architectural glass and curtain wall disease”

While there are reasons that can justify the use of high WWR beyond the aesthetic, such as the cost effectiveness of curtain wall construction in some markets relative to other wall types, large expanses of glass weakens the overall thermal performance of the envelope, especially in heating dominated climates. More importantly, a high WWR contributes to excessive solar heat gain in both heating and cooling dominated climates and increases the size of HVAC equipment. It also creates unwelcome glare and high illuminance levels, even when the glass has low solar heat gain coefficients (SHGC) or shading coefficients (SC). The result is the common sight of an all glass building with all the blinds down. Additionally, a building with higher WWR has less mass and is more susceptible to temperature swings and reduced comfort compared to a building with more mass and smaller windows.

Even from a style or aesthetic perspective, striking and beautiful architecture is possible without resorting to an all-glass, curtain wall design as shown by the countless high rise buildings around the world with masonry wall construction and punched windows that are designed in the Postmodernist style and to a lesser extent Neoclassical and Georgian styles. As shown in the examples at right, there are many recently constructed buildings, especially in Europe that follow a design of “Mass and Less Glass” because of the stringent European energy performance requirements since as Joseph Lstiburek stated in one of his blogs [27]:

“If you want to save serious energy use less glass; windows

and curtain walls provide the worst energy performance, so limit

the glazing area to 30% and use really good glass and frames”

The energy performance of a building with a curtain wall design and high WWR is doubly penalized because curtain wall construction exhibits significant thermal bridging with the very best curtain walls only able to achieve an effective thermal performance of R9 (RSI 1.6). [28] From an energy performance standpoint then, the amount of glass should be limited and efficient design guidelines from multiple ASHRAE Standards and publications including Standards 90.1, 189.1 and the AEDG guidelines supports this by limiting WWR to a maximum of 40% [29] [30] [31]. Older design references suggest even lower glass percentages stating that 25% WWR is near ideal to achieve optimum energy performance and not just in heating dominated climates [32] and there are countless of professionals and advocates of true energy efficient construction that question so called “Green Designs” with all-glass facades including Ed Mazria who stated:

“Many Green Buildings Don’t Save Energy. Why? They have too much glass,

they are over-ventilated, they are leaky to air, they are fraught with thermal

bridges and they rely on gimmicks and fads rather than physics.”

Some will argue that large expanses of glass are a requirement of designs that emphasize natural lighting, reinforcing the trend of high WWR. However, good designs that provide ample daylighting do not require more than 40% WWR and this is supported by the guidelines in the Lawrence Berkeley National Laboratories (LBNL) report Tips for Daylighting with Windows which states:[33]

“Keep window area to a 30 – 40% WWR and don’t’ waste glazing

area where it can’t be seen such as below desk height ”

An indication of the potential savings in energy use and HVAC loads from reducing the WWR are shown in a series of tables and graphs presented below. The results are based on parametric energy simulations of the same hypothetical 5-storey, 36,000 ft² (3,345 m²) commercial office building used in the previous sections. The simulations were performed with eQUEST for the same eight geographical locations also used previously and assume an envelope and window thermal performance that meets ASHRAE 90.1-2004. The results are presented in multiple formats to show the relationship of energy use and HVAC loads against different WWR and varying SHGC selections.[34] As shown in the first graph and table, decreasing the WWR from 55% to 25% in a cooling dominated climate such as Singapore translates into a total building energy use savings of approximately 7% (these small savings are due to the low SHGC of 0.25 required in ASHRAE Zone 1). Intermediate climates such as Atlanta, Houston and Rome could achieve building energy use savings of approximately 17 to 20% and finally, colder climates such s Frankfurt, Chicago and Toronto would experience savings of 18 to 19%. As expected, the reduction in building energy use from lower WWRs would be in the form of decreased heating, cooling and fan energy use, particularly in milder climates where the decrease in solar heat gain from less window area requires lower volumes of air with a significant reduction in the size of air handling equipment.

A further relationship of energy use against WWR and SHGC is illustrated in the series of 3-D bar graphs shown below. In cooling dominated climates the lowest energy performance is achieved at a low WWR and low SHGC, which is consistent with the recommendations from typical design standards to keep WWR and SHGC to a minimum. In intermediate and heating dominated climates though, a higher SHGC results in a minimum energy use with identified savings in the range of 20%. The additional savings in building energy use at high SHGC is the result of increased winter solar heat gain, which offsets the space heating energy use. However, this occurs at the expense of potential space overheating which has to be countered with larger air volumes and slightly bigger air handling equipment and cooling plants.

The impact on the size of the heating and cooling loads from varying the WWR and SHGC is shown in the next set of tables. In a cooling dominated climate, decreasing the WWR from 55% to 25% decreases the cooling load and the size of the air handling equipment by 20% to 25%, which is significantly more than the potential energy use reduction of 7%. In milder and heating dominated climates, the heating and cooling load decrease from the lower WWR is even larger, with savings of 25 to 35%. Readers will notice that the heating plant reduction is constant across all geographical locations due to the same thermal performance applied to all regions.

The series of results presented suggest that optimum selections of WWR and SHGC can in general, achieve a reduction in building energy use of 7% to 20%, depending on geographical location with a corresponding 20 to 35% reduction in the size of the heating and cooling loads.

6. Shading Strategies: The use of shading elements such as a window recess or other external shading can have a small impact on building energy use that can be positive or negative depending on the climate, the type and amount of glazing, its SHGC and the design of the shading device.

In heating dominated climates, shading devices can reduce the summer solar heat gain and the cooling load, but will also reduce the winter solar heat gain with a consequent increase in overall building energy use. This behaviour is illustrated below in two separate sets of tables and graphs for a 4” (100 mm) window recess, which would act as a horizontal shading device. The results were derived with eQUEST for the same hypothetical 5-storey building used throughout this page. [35]

As shown in the first set of results, adding a window recess while keeping a constant window SHGC (0.4 in heating dominated climates and 0.25 in Atlanta and Houston) will increase total building energy use by less than 0.5% (negative values shown in red font). However, the peak electrical demand and the space peak cooling load will be reduced by an average of 1% and 2%, respectively.

In a cooling dominated climate such as Singapore, the window recess will reduce the building energy use, as well as, the peak electrical demand and space peak cooling load by 0.3%, 0.4% and 1.5% respectively.

Adding the window recess and simultaneously increasing the SHGC will help reduce the building energy use in heating dominated climates by as much as 2% as shown in the second set of results, but at the expense of increasing the peak electrical demand and space peak cooling load by 3% and 7%, respectively.

Different combinations of window SHGC values applied to each building orientation in combination with shading elements will produce results that would be in-between the two sets of outputs presented above. Depending on the project objectives, designers can focus on minimizing energy use while incurring a penalty on equipment size and peak electrical demand or employ the opposite design approach. However, as a general rule, optimum design practices for heating dominated climates should typically consist of shading elements coupled with the use of windows with higher SHGC values selected for southern exposures and windows with lower SHGC values selected for the east and west exposures to minimize the afternoon solar heat gain during the summer period. In cooling dominated climates the design practice should consist of shading elements and windows with low SHGC selected for all orientations.

7. Putting it All Together: The graphic shown below provides a summary that compares the design specifications of a 90.1-2004 design with a WWR of 45% against a low energy building design that incorporates the architectural elements covered in the previous sections. These elements include a highly insulated envelope, high performance glazing, a close to ideal WWR of 30% based on punched windows and finally, recessed windows to control the summer heat gain.

By combining all the architectural design elements illustrated in this page, the low energy building design achieves energy savings of 30 to 35% in heating dominated climates and 25% in a milder climate such as San Francisco compared to the ASHRAE 90.1-2004 Reference Building. Additionally, the highly insulated envelope contributes to cutting the design heat loss by half while the reduced WWR and use of recessed windows cuts the space peak cooling load and required air flow by approximately one-third and peak electrical demand by approximately 10%. These results pointedly illustrate the concept of “bundling” of design features in order to magnify the energy savings and achieve very large reductions in equipment size discussed in the “IBD Process” page.

In cooling dominated climates such as Singapore, the energy savings and space peak cooling load reduction are significantly smaller and in the order of 6% and 13%, respectively since the savings are only from the reduced WWR and recessed windows.

[1] Architecture and Climate Change: An Interview with Ed Mazria. January 29, 2007.

[2] Lovins, A. 1992. Energy Efficient Buildings: Institutional Barriers and Opportunities. Boulder, Colorado: Competitek.

[3] A copy of the CADDET profile is available in the “References” page.

[4] Energy Conservation Design Resource Handbook, Royal Architectural Institute of Canada. 1979. Ottawa, Ontario: Section

[5] Energy & Economics: Strategies for Office Building Design; A Guidebook for Architects, Engineers, Developers, Facility Planners and Owners. Northeast Utilities. 1987. Chapter 4, Site, Orientation, Configuration and Program.

[6] Energy Efficiency in Buildings - Trasnforming the Market. World Business Council for Sustainable Development, 2009. Accessed at

[7] ASHRAE 90.1-2004, 2007 and 2010 Energy Standard for Buildings Except Low-Rise Residential Buildings.

[8] ASHRAE Standard 189.1-2011 Standard for the Design of High-Performance Green Buildings Except Low-Rise Residential Buildings

[9] ASHRAE Advanced Energy Guide Series Achieving 50% Energy Savings Toward a Net Zero Energy Building. There are currently four guides that cover small & medium office, medium and big box retail, K-12 schools and large hospitals. They can be downloaded free at:

[10] Bean, R. 2011. “Are Your Clients Going Green? The Ontario Technologist. Aurora, Ontario: OACETT. Vol. 53, No 5, September/October.

[11] Peterson, K.W. 2007. “Greater Efficiency Today, Blue Skies Tomorrow” ASHRAE Journal. Atlanta, Georgia: ASHRAE. Vol. 49, No. 8, August, pp. 12-15.

[12] Directive 2010/31/EU of 19 May 2010 on the energy performance of buildings. Accessed at According to Article 9, by 2020 all new EU buildings are to be “nearly zero energy” while goverment buildings are required to meet this criteria by 2018.

[13]1996 Model National Energy Code for Buildings (MNECB). Appendix C: Method for Calculating the Thermal Properties of Building Assemblies contains a description of the degree to which steel studs and similar structural elements derate the thermal performance of an insulated wall. A procedure to calculate the effective thermal performance is also illustrated that relies on a parallel calculation of the Rvalue of the insulated wall section and the structural wall section. This procedure has been implemented in NRCan’s EE4 program, which permits the creation of a layer-by-layer wall detail that takes into account thermal bridging. This is unique to EE4 while other energy models require this calculation to be done outside the model.

[14] The procedure to calculate the effective Rvalue of a non-uniform wall with sections having different construction elements is also described in other publications including the ASHRAE 2009 Fundamentals Handbook Chapter 27, Zone Method Calculation, pages 27.5 to 27.7 and in other publications.

[15] Lstiburek, J. 2007. “A Bridge Too Far: Thermal Bridges-Steel Studs, Structural Frames, Relieving Angles and Balconies” ASHRAE Journal. Atlanta, Georgia: ASHRAE. Vol. 49, No. 10, October, pp. 64-68.

[16] Straube, J. Building Science Insights “BSI-006: Can Highly Glazed Building Facades Be Green?”. 9/11-08. Accessed at

[17] Lstiburek, J. 2007. “The Perfect Wall” ASHRAE Journal. Atlanta, Georgia: ASHRAE. Vol. 49, No. 5, May, pp. 74-78.

[18] Energy Conservation Design Resource Handbook, Royal Architectural Institute of Canada. 1979. Ottawa, Ontario: Section 3.6.4.

[19] 2009 ASHRAE Fundamentals Handbook, Chapter 18, Nonresidential Cooling and Heating Load Calculations, page 18.28.

[20] Tzempelikos, A. et all. “Investigation of thermal and airflow conditions near glazed facades using particle image velocimetry and CFD simulation--eliminating the need for secondary perimeter heating systems”. ASHRAE Transactions, 2009. Accessed at

[21] De Saulles, T. 2012. “Learning Tool” CIBSE Journal, March, pp.606-62.

[22] The PDA program was developed by a United Kingdom (UK) consortium that includes ARUP, the Concrete Centre and AHMM Architects. It is available as a free download at

[23] In free running mode (passive analysis only), heating is inactive, and so the curves were created using the final temperatures predicted by the PDA.

[24] Chartered Institution of Building Services Engineers (CIBSE)

[25] See DOE 2 Engineers Manual, Version 2.1A, Section 2 Weighting Factors, pages II.30 – II.49 and II.88 to II.94. DOE-2 uses the weighting factor technique introduced by Mitalas and Stephenson. The average perimeter zone temperatures were created by defining operating schedules set with a 55 ºF (13 ºC) temperature setback to allow the space to “coast” and illustrate the temperature decay.

[26] Lstiburek, J. 2009. “Extreme Heat: Tale of Two Cities” ASHRAE Journal. Atlanta, Georgia: ASHRAE. Vol. 51, No. 3, March, pp. 75-79.

[27] Lstiburek, J. Building Science Insights “BSI-007: Prioritizing Green – It’s the Energy Stupid”. 10/28/08. Accessed at

[28] Straube, J. Building Science Insights “BSI-006: Can Highly Glazed Building Facades be Green?”. 09/11/08. Accessed at

[29] ASHRAE 90.1-2004, 2007 and 2010 Energy Standard for Buildings Except Low-Rise Residential Buildings. The tables of envelope requirements state that vertical glazing should have a WWR of 0-40%.

[30] ASHRAE Standard 189.1-2011 Standard for the Design of High-Performance Green Buildings Except Low-Rise Residential Buildings. The tables of envelope requirements in Appendix A state that vertical glazing should have a WWR of 0-40%.

[31] Advanced Energy Design Guide for Small and Medium Office Buildings: Achieving 50% Energy Savings Toward a Net Zero Energy Building. Chapter 5, pages 121 to 122 and page 131 states that “for office buildings to achieve a 50% savings the overall WWR should not exceed 40%”.

[32] Energy Conservation Design Resource Handbook, Royal Architectural Institute of Canada. 1979. Ottawa, Ontario: Section Daylighting and Building Geometry.

[33] O’Connor, J., et al. 1997. Tips for Daylighting with Windows: The integrated Approach. Berkeley: Lawrence Berkeley National Laboratory, pages 3-3 and 3-10.

[34] The DOE2.2 engine used in eQUEST uses SC where: SHGC = SC x 0.87.

[35] This was achieved in eQUEST by specifying a 0.33 ft window setback.

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