The data presented here is derived from whole-building life cycle assessment (LCA) models of typical ("archetype") buildings in British Columbia, Canada. As such, Pathfinder is intended to be used as an educational tool only and does not represent any particular building or design.
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The tool is intended to provide higher level guidance on the potential effect of design choices on embodied carbon. It uses building archetypes and explores variations in design on that archetype.
Three separate building archetypes were considered: A high-rise residential building, a mid-rise residential building, and a stacked townhome. All archetypes are assumed to be located in Vancouver BC. Building archetype designs were selected after review of multiple building permit applications for similar buildings and using our knowledge of the building industry in the region. The designs selected for each archetype are fictional but are believed to be representative of what might be expected for these archetypes in these regions.
Variable types and iterations explored were developed with the intent of achieving realistic possible changes and/or changes that could result in significant change in embodied impact. These were selected based on review of existing building permit applications, using our knowledge of the building industry and embodied impacts, and with the input of others in the LCA and design industries.
|Description||High-Rise Residential||6-Storey Mid-Rise Residential||Stacked Townhomes|
|Building Length (m)||25||75||12|
|Building Width (m)||25||25||6|
|Floor to Floor Height (m)||3||3||3|
|Number of Floors||30||6||3|
|Gross floor area (m2)|
|Floor Live Load (kPa)||2.4||2.4||2.4|
|Service Life (years)||60||60||60|
|Window to Wall Ratio||40%-60%||30%-60%||10%-25%|
|Beam Span (m)||8||6||6|
|Joist Span (m)||6||3||3|
|Footing||300mm x 100mm below columns and perimeter walls|
|Slab on Grade||100mm concrete slab|
|Below Grade Walls||200 mm concrete|
|LVL (with load bearing walls)||x||Baseline|
|None (load bearing walls)||x||Baseline|
|Exterior Wall Types|
|Wood Stud (infill)||x||x|
|Wood Stud (load bearing)||x||Baseline|
|Wood Stud OVE||x|
|Precast Concrete Sandwich Panel||x|
|Hollow Core Precast Concrete||x|
|OWSJ with Steel Deck and Concrete Topping||x|
|Wood Joist with Plywood||x||Baseline|
|Wood I-Joist with Plywood||x||x|
|Exterior Cladding Type|
|Fiber Cement Panel||Baseline||Baseline|
|Exterior Wall Insulation Type|
|EPS||Included in EIFS||Included in EIFS||Included in EIFS|
|Mineral Wool Batt||Baseline||x||x|
|Mineral Wool Batt (medium density)||x|
|Fiberglass Batt (medium density)||x|
|Spray Polyurethane Foam||x||x||x|
|Roof Insulation Type|
|Mineral Wool (medium density)||x||x||x|
|Roof Membrane Type|
|Modified Bitumen (SBS)||Baseline||Baseline||Baseline|
|Double Glazed (low-E, Argon Filled)||Baseline||Baseline||Baseline|
|Triple Glazed (single low-E, Argon Filled)||x||x|
|Window Frame Type|
|None (Street Parking)||x||Baseline|
|2 Level Parkade||x|
|4 Level Parkade||x|
|6 Level Parkade||Baseline|
|SCM Content in Concrete|
The LCA modelling focused on the building structure and envelope above and below grade. It included the following:
Main structure including beams, columns, floor slabs, load bearing walls, shear walls foundation walls, and footings,
exterior walls and windows, including insulation and cladding, roofing membrane, vapour and air barriers, window framing and glazing.
Parking garages including structure and membranes
It did not include ceiling or floor coverings, finish materials, paint, interior walls, mechanical or electrical systems, or site components.
The system boundary for the LCA models included the product, construction, use and end of life stages excluding operational energy and water. This includes stages A1-A5, B1 to B4, and C1 to C4.
The Athena Building Impact Estimator (Version 5.4.0103) was used to model the impact of most of the various design iterations on embodied carbon (ie. embodied global warming potential). (For more information on the background material data and assumptions, see the Impact Estimator User Manual.) The impact estimator was used to estimate both material quantities and their embodied impacts. Exceptions and work-arounds are presented below:
Insulation: There was some concern that the Athena Impact Estimator would incorrectly estimate the embodied GWP of foam insulations due to the change in blowing agents mandated by recent legislation in Canada. Our approach regarding insulation was as follows:
Available EPDs were used to estimate the GWP of all insulations (not just foam). All insulation types were reviewed to allow a more fair comparison of insulations.
For GWP estimates of foam insulations, we used only EPDs associated with HFO blowing agents. Any EPDs with HFC blowing agents were not included.
Where available, industry wide EPDs were used. Industry wide EPDs were used for polyisocyanurate and loose fill cellulose
When industry wide EPDs were not available, product specific EPDs or averages of product specific EPDs were used.
Wall insulation fibrous and foam boards were medium density, typical for commercial walls
Roof insulation fibrous and foam boards were higher density, typical for commercial roofs
EPDs were not available for medium density rock wool and medium and high-density fiberglass. For these insulations GWP was estimated by factoring similar low-density insulation GWP by the differences in density.
For all insulation types in the High-Rise archetype R-15 nominal insulation was assumed and all insulation quantities were adjusted.
For all insulation types in the 6-Storey Mid-Rise and Stacked Townhomes archetypes, 4 inches (102 mm) of insulation was assumed.
Note that it is acknowledged that relying on EPD results is not ideal, as the scope and boundary conditions may be different and EPDs are often based on singular products that may not represent a typical value. To reduce this risk each EPD was carefully reviewed to confirm similar scope and boundary conditions are similar to other LCAs in this tool. In addition, the methodology was provided to a number of LCA practitioners and specialists in the Vancouver area for comment.
Supplementary Cementitious Materials (SCMs): SCMs created an issue as a change in SCMs could potentially impact many assemblies within a building. To resolve this issue, we compared the GWP of several different SCM ranges for several different concrete based building assemblies. More specifically, we reviewed the following assemblies: Slab on grade, footings, beams and columns, concrete walls, and concrete in extra basic materials within the software. For each of these assemblies we compared 0, 20%, 30%, and 40% SCM contents. We found that changing from 0 to 20% SCM content resulting in a reduction in GWP by between 3.6 and 5.2% for the various assemblies. Similarly, changing from 0 to 30% SCM content resulting in a reduction in GWP by between 10.4 and 12.2% and changing from 0 to 40% SCM content resulting in a reduction in GWP by between 15.5 and 20.1%. For this tool, we used the average change of impacts for the different assemblies. More specifically, the following factors that were applied to all concrete based assemblies to estimate the impact of different SCM contents:
|SCM content||SCM mult factors from base case|
Concrete Columns: The software did not factor in the additive load on columns in taller buildings: In a building, columns support not only the floor immediately above, but also the load of a column immediately above. As such, columns effectively support loads from all floors above, so lower floor columns are typically larger than upper floor columns. To determine the real impact on column design, three real designs of tall residential buildings were reviewed (between 30 and 37 stories) and take-offs were performed for concrete columns. These take-offs were factored according to the tributary area that they support and into three categories based on floor number (1-10, 11-20, and 21-30). An average of these values resulted in a volume of concrete per m2 of tributary area. Concrete strength was also factored in by converting all columns to 30 MPa concrete, using a simple multiplication factor (ex. A 40 MPa concrete volume was multiplied by 40/30 to estimate an equivalent 30 MPa column size). Reinforcing steel within the columns was assumed to be 1% of the mass of the equivalent 30 MPa concrete.
Wood Frame Load Bearing Walls: The software did not factor in the additive load on load bearing walls in multi-story buildings: load bearing walls support not only the floor immediately above, but also the load of any load bearing walls above it. This resulted in a significant underestimation of lower floor load bearing walls in the six-story design. To resolve this issue, the wood framing for the bottom three floors of the 6-storey archetype was increased by an additional 25% to account for extra studs at window openings and interior partition walls. Note this was not considered a significant error in the stacked townhouse design as the additive effects are small and it would not be typical to change the stud spacing across the height of this type of building. These decisions were made based on a review of multiple real designs and our knowledge of the industry.
The Morrison Hershfield team involved in the development of the tool, and this document are:
By nature, whole-building LCA results are uncertain and should be used as a guidepost and not an absolute. Although the archetype designs are believed to be typical for the region, actual designs will vary. The further a real design strays from the archetype design the less reliable the results.
The LCA results are specific to the region presented. Actual results can vary significantly for other regions, particularly outside of B.C.
For project-specific results, a custom whole-building LCA is needed. Access the free Impact Estimator for Buildings software tool at www.athenasmi.org.