Modelling Wall Assemblies: Developing an objective database for performance

Photo © BigStockPhoto/Daniel Meunier
Photo © BigStockPhoto/Daniel Meunier

By Mark Driedger
Architects have traditionally been held at arm’s length when it comes to the performance of the assemblies they specify. The statistics regarding wall performance have always been provided by manufacturers or testing organizations. Values such as thermal resistance, fire rating, and acoustical performance for individual materials can be found from individual suppliers—still, an objective stance on how all the materials work together in an assembly is unavailable.

This author is part of ATA Architects, a design firm in Oakville, Ont. Using building information modelling (BIM) and energy analysis software, ATA has created a system that allows design professionals to make informed decisions regarding wall type use at the start of the drawing process.

One of the firm’s major philosophies toward energy conservation and sustainability focuses on effective production (and retention) of energy within the building envelope. Therefore, an understanding and subsequent design of high-performance building envelopes is essential to sustainability strategies.

Building façades and breaking down façades
Since buildings represent approximately 40 per cent of North America’s total energy consumption, educated decisions need to be made by architects at the design stage. This means priority should be given to reduce energy requirements rather than simply acquiring points under the Leadership in Energy and Environmental Design (LEED) program.

CC_April13.indd
The plans above represent three different wall types commonly used in Canadian construction—wood, steel, and insulating  concrete forms (ICFs). The isobars (lines) illustrate how effective the insulation is in the wall system. In locations where the isobars are closer together, the insulation is working more effectively to stop the cold transfer. Where the lines are farther apart, more heat loss is occurring.

Spent fossil fuels will have less negative impacts on the environment if more energy is contained within the envelope and not leaked into the environment through low-performing assemblies and misplaced glazing. This means using proven, durable details with special emphasis on higher insulation values and tighter wall construction.

The entire industry seems to be preaching green, yet most of what is being constructed can appear to be the opposite. Consumers are buying into glass towers and large expanses of glazing without considering the lifecycle costs associated with these designs. The focus of energy saving in Canadian buildings should be on using glazing in a smart manner, with more focus on the efficiency of wall systems.

From a pure energy standpoint, it makes little sense to build a wall out of traditional glass in cooler or cold climates. Glass performs at a fraction of the efficiency of a typical wall in both summer and winter. Even ‘fine-tuning’ a building to capture the sun in the winter via southern glazing does not make too much sense—a few hours of sun through glazing cannot possibly overcome the energy losses through that same glazing during long winter nights.

The exterior envelope’s performance becomes even more important as society evolves and generations consume more than their predecessors. In the suburbs, the average dwelling is increasing in size, as the availability of land gets smaller. The larger buildings create more exposed exterior walls, putting further pressure on infrastructure. The cost for energy will only get more expensive, bringing the subject again to the forefront as spaces become more costly to heat and cool.

Designing the database
Many architectural practices are under continuous pressure to specialize on a particular building type, thus keeping their overhead down by using the same proven details over and over. The specialization lowers costs for clients, and reduces the architect’s risks by using methods and details they have used before. Firms that work on various building types do not have that luxury. Every project has a different set of circumstances that needs to be adjusted to.

The research and time associated with developing, drawing, and annotating new assemblies used to take a lot of time for the firm. Now, a database assists in comparing the different thermal resistance values for entire wall assemblies, not just individual components, allowing designers to customize components to use in the wall.

This research project has also assisted with the co-ordination among the consultants. Previously, the mechanical engineer would usually design the HVAC system around the performance levels of the assemblies prepared by the architect. Disconnects constantly occurred in the co-ordination of these elements, as the wall assemblies were revised to meet mechanical requirements. In the new scheme, the design firm provides the mechanical engineer with the best possible performing assembly; in the end, this reduces HVAC size and saves money for the client.

To create the database, the firm began by developing a scalable categorization system to organize the walls. It was important the final database was organic in nature, allowing walls to be inputted and deleted when required, or when new materials became available. All types of walls were selected to be part of the research, including:

  • concrete masonry units (CMUs);
  • insulating concrete forms (ICFs);
  • light-gauge steel;
  • structural insulated panels (SIPs); and
  • wood studs. (Examples are shown in Figure 1.)

Many different types of exterior cladding—such as exterior insulation and finish systems (EIFS)—were also included, ensuring a variety of exterior finishes were possible.

Using BIM, the firm modelled the walls, taking care these assemblies followed the requirements of testing laboratories, such as Underwriters Laboratories of Canada (ULC). Acoustical performance information was also integrated with the system. The walls then went through a strict review to ensure all details were included in the database.

After this, the walls were exported out of the BIM program into a two-dimensional heat-modelling software called Therm, by the U.S. Lawrence Berkeley National Laboratory (LBNL). In this program, the typical wall sections were tested for their actual thermal resistance value, including the thermal losses associated with the individual structural members. The most recognized example of this is metal stud exterior wall construction. The insulation on the cold face of the metal stud is much more effective than insulation between the metal studs. The metal studs transfer cold in the winter through the wall if not adequately protected. Wall systems susceptible to moisture and dewpoint issues were then deleted from the database.

To organize the database, the firm has created a page within an internal intranet site (i.e. Confluence Enterprise Wiki), complete with each BIM file attached to a graphic of the wall assembly and key words allowing staff to search for specific walls. Staff can now select the desired wall and download it into the BIM building file, complete with all information relating to the wall. The wall is then automatically tagged in a wall schedule, and annotated within the drawings themselves.

For the modelling database, each wall assembly has fi re, insulation, and sound ratings embedded to allow users as much information available as possible.
For the modelling database, each wall assembly has fire, insulation, and sound ratings embedded to allow users as much information available as possible.

Applications present and future
By analyzing each wall in the exact same way, the firm can now make easy comparisons between the different systems and their performance qualities. Within each assembly, fire, insulation and sound ratings are embedded to allow users to have as much information available as possible while spending little wasteful time searching (Figure 2).

The purpose of the research was to verify wall performance in a comprehensive manner and to be able to inform clients as to the reasons for selection of particular wall systems. Additionally, when changes are prepared for reasons of cost or ‘value engineering,’ the implications to performance and operations costs can be evaluated almost immediately.

Since the database is scalable, other assemblies such as flooring, roofing, or ceilings are a possibility in the near future. The potential of including real-time costing of the system is also a very interesting part of the future plans for the firm.

Computers are already becoming more involved in the calculations within BIM. Analysis and testing programs are becoming mainstream, engaging in performance testing on the architect’s model in real-time. Instead of using theories to define a sustainable feature within a building, architects will soon be able to provide simulation data to prove or disprove the theory.

The building model or database is becoming more important to all players as the basis of their deliverables. The paper drawings in architecture will fall away as building departments and contractors start to work in digital environments.

Like all industries dealing with new technologies, it is important architects position themselves to stay relevant in the midst of these evolutionary technological changes. The firms able to adapt and anticipate in these technological revisions may be set to take an increased role in their field. Like the elevator or switchboard operator, the role of the architect could become extinct if firms do not anticipate these changes.

The architect profession developed from that of the ‘master builder’—the person most knowledgeable about the methods of construction. By using the database and software, the performance of specific conditions can be graphically modelled to illustrate which assembly performs best. For the authors’ firm, it is essential architectural research continue not only for social change, but also to keep up with the technical evolution.

Figure 3 illustrates two proposed foundation options at grade showing a typical thermal break in a foundation wall in section. The interior slab edge with the 12-mm (1/2-in.) thermal break is actually 5 C (9 F) colder than the 76-mm (1 ½-in.) model.

Two foundation options at grade showing a typical thermal break in a wall.
Two foundation options at grade showing a typical thermal break in a wall.
A computer model showing convective heat fl ow moving through a residence incorporating cutting-edge green technologies.
A computer model showing convective heat fl ow moving through a residence incorporating cutting-edge green technologies.

 

 

 

 

 

 

 

 

 

 

Moving forward
ATA is presently working on several buildings in the Toronto area, using a conglomeration of new technologies not yet seen on a large scale in the Canadian environment.1 Part of the goal is to show how today’s architecture should use leading technologies, and should not just be a nice-looking form with ‘green’ add-ons to score LEED points. A design should be integrated, logical, and proven in the realm of science. Taking from the design principle of biomimicry, nature fits form to function, not the reverse.

For this project, the firm is partnering with several high-profile team members, including Ryerson University, the National Research Council of Canada (NRC), and a BIM software company.

Figure 4 is a computer model showing convective heat flow moving through one of these residences. Interior and exterior environmental factors have had a significant role in shaping the building form. The model assisted in the refining of the design to ensure the building operated as planned.

As more Canadian design/construction firms begin to harness the potential of BIM to develop databases, these sorts of projects will hopefully become more common.

Notes
1 The process developing the buildings will be video-documented online and eventually made into a TV program for next year. (back to top)

Driedger copyMark Driedger is an associate at ATA Architects Inc. (Oakville, Ont.). After receiving his bachelor of architectural science from Ryerson University, he spent several years in construction as a site supervisor in Toronto, before pursuing an interest in architectural design and technology. Driedger is LEED-certified, and continues to push the limits, integrating science with design at ATA. He can be contacted via e-mail at mark@ataarchitectsinc.com.

 

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