Assumptions || BuildCarbonNeutral.org - A CO2 calculator for your whole building project.

Assumptions

Buildings, sites and construction processes vary widely — we've done our best to create an easy to use calculator for generating an estimate from averaged data. This will provide a rough approximation of the carbon load - not an exact one. Here are the assumptions made for the current iteration of the Construction Carbon Calculator. We welcome your feedback!

The calculator is accurate to about 25%, plus or minus. (This is similar to most operational carbon calculators.)
Landscape data are for soil organic carbon (SOC) only and do not include above ground biomass (trees, shrubs and grasses).
Disturbed soil retains an amount of residual carbon. This carbon factor has been accounted for in both the disturbed soil and the installed landscape accounting.
The land use categories are very broad and refer largely to mature natural landscapes - 5 years for grasslands, 10 years for shrublands and 30 years for forests.
The data are taken from a number of published references. Where there is a range for any vegetation type/ecoregion cell, the mid point is taken.
This takes no account of the variation of soil characteristics within each ecoregion.
This does not include data for conventional landscaped systems, which can vary considerably depending on inputs - the nearest vegetation type should be used (e.g. for a urban park use savanna/parkland; lawns use shortgrass/lawn).
Numbers have been built from a combination of project cost estimates including quantities and available web-based resources of embodied carbon intensity ratios of different building materials.
The building data takes into account site excavation, shell and core (structural systems, building envelope and building systems). Tenant improvements, interiors or furniture, fixtures or equipment have not been included in version 0.01.
These carbon cost estimates are based primarily on commercial or multi-family projects. Residential projects may vary from these results.
The building data is based on Life Cycle Balancing: Building Shell, Interiors, & Furnishings Sub-Systems: Nursing and Biomedical Sciences Building, the University of Texas at Houston Health Sciences Center from the Center for Maximum Potential Building Systems. They had the following factors for different building elements: Shell - 24%, Service Systems - 22%, Service Sector - 14%, Substructure - 5%, Other/ Miscellaneous - 17%. This is 70% of the total for a complete building including interiors, but covers the materials being quantified in our analysis. Our breakdown was slightly different, taking into account the specific building elements for which we were able to accumulate data, and extrapolating the unknown factors. Our factors were as follows: Shell Known - 12%, Shell Unknown - 12%, Service Systems - 22%, Service Sector - 14%, Substructure Known - 2%, Substructure Unknown - 3%, Other/ Miscellaneous - 5%.
Building square footage intensity values have been generated from cost estimate data for excavation, steel, concrete and wood and material carbon intensity ratios.
Wood values assume non-certified wood sources. The values for the wood represent the carbon released converting the wood from a natural forested state to an installed condition. Certified wood will compensate for the carbon released and allow the wood in a building to count as a carbon sink.
Some data sets used in developing version 0.01 were smaller than others. Averaged values were available for certain building structural types, but for others it was based on one or two actual buildings.

If you have some good ideas for improvements, we'd like to hear about it!

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Assumptions