About & Disclaimer
This web tool enables designers of multi-storey buildings to easily estimate the embodied carbon footprint of the superstructure.
There are two ways to use the tool. In ‘Auto generate’ mode, the basic building geometry, structural grid and chosen floor system are used to estimate structural material quantities using algorithms developed by the Steel Construction Institute (SCI) for common structural steel solutions. Alternatively, a user may use the ‘Manual input’ mode to enter the actual material quantities for their building.
Whichever mode is used, appropriate carbon emission factors are then applied to the material quantities to estimate the overall carbon footprint of the building. The results are presented as a single CO2e figure for the building, a CO2e figure per m2 of floor area, and a bar chart illustrating the contributions to the total made by the various elements of the building, i.e. frame, concrete cores, floors, roof, fire protection and void walls.
Although care has been taken to ensure that the material quantities and associated embodied carbon impacts calculated by the tool are accurate. The Steel Construction Institute and other parties associated with this software and website assume no responsibilities for errors or misuse of this software, or damage arising from use of this software.
In 'Auto generate' mode, specify the upper floor area, number of floors, type of floor construction, the structural grid, vertical bracing, fire protection, void area, void walls, roof structure and a factor to reflect the building complexity.
For the 'Manual input' mode, data may be entered for a broad range of construction materials including; structural steel, intumescent paint, board fire protection, in-situ concrete, precast concrete floor units, bar and mesh reinforcement, plywood formwork, steel floor decking, steel stressing tendons, light steel framing, blockwork and plasterboard.
Methodology and assumptions
Auto generate mode
The material quantities derived in the ‘Auto generate’ mode are based on a series of algorithms developed by SCI that encompass the steel frame including bracing and fittings, fire protection, cores, upper floors, roof structure and void walls.
The algorithms cover a range of common structural steel floor systems. For each system, designs for a range of typical floor grids in a rectangular building were produced, and structural steel weights estimated per m2 floor area. A factor is included to increase the steel weight (beams and columns) for buildings with more complex forms.
Column sizes were calculated as a function of the floor grid and the number of storeys. In the designs, the imposed load reduction factor with number of storeys was used and the storey height was taken as 4m for buckling checks. Column sizes were reduced at higher floors, every 3 storeys, and the average size used.
Key assumptions made in the designs were:
- Imposed loading of 4 kN/m2 (+1 kN/m2 for partitions)
- Cladding load of 8 kN/m (used to design the edge beams)
- Services and other loads of 0.6 kN/m2
- Fire resistance of 90 minutes
- Bracing and connection weights are assumed to be 10% of the weight of steel in the columns
- Design limit of span/250 or 60 mm maximum on total deflection
Full details of the derivation of the algorithms used to estimate the structural steel quantities used in this web tool are given in SCI report RT1585.
Where concrete cores are employed for lateral stability, these are assumed to comprise 200 mm thick reinforced concrete walls. If default cores are selected, one core (7 x 6.5 m in plan) is assumed for every 800m2 of floor area. Alternatively, users may input the dimensions of up to three concrete cores.
The quantities of all materials used to construct the upper floors are based on the net upper floor area, i.e. the gross upper floor area less the area of any cores and other voids in the upper floors, e.g. staircases, lifts and service cores. The area of void walls is estimated based on the perimeter length of the voids and the fixed 4 m high storey height. Void walls are either 140mm thick blockwork or proprietary dry-lining comprising plasterboard on light steel framing.
For the fire protection of beams, the quantity of intumescent paint is estimated based on the total weight of beams as follows:
- for downstand UKBs an average surface area of 22 m2 per tonne
- for cellular beams an average surface area of 15 m2 per tonne
- for slim floor beams an average surface area of 2.5 m2 per tonne.
For the fire protection of columns, the intumescent paint quantity is based on an average surface area of 13 m2 per tonne. Alternatively, for boards, 305 x 305 UKCs are assumed to be fully boxed-in.
Options for the roof level structure include the same structure as for other upper floors, for example if plant were to be placed on the roof, or alternatively, a lightweight steel structure comprising hot-rolled steel beams supporting light gauge steel purlins. The weight of steel for the lightweight option is calculated using an algorithm based on the span and spacing of the steel beams assuming an imposed load of 1.5 kN/m2 (for maintenance access), and a self-weight of 0.8 kN/m2, including the weight of the steel beams. A total deflection limit of span/250 is used for roofs. Note that only the structure supporting the roof is included; the roof envelope, membranes, ballast, etc. are not included.
Embodied carbon calculations
For all materials included in the scope of the web tool (either auto-generated or manually input), site wastage rates are applied to derive gross weights of materials. Embodied carbon impacts associated with the processing, transport and disposal of construction site waste are not included within the scope.
To account for the embodied carbon impacts, the modular approach prescribed in relevant CEN standards (BS EN 15804 and BS EN 15978) is adopted in the web tool. Where relevant, the following impacts are included:
- Modules A1 to A3 – the production stage including raw material supply, transportation and manufacturing. For steel products, additional impacts are included to take account of secondary processing such as fabrication, in the case of hot-rolled structural steel, and roll-forming, in the case of decking and light gauge steel. In addition, transport impacts from the steel mill to the secondary processing facility are included.
- Module A4 – transport to site – based on average UK road trip distance and average UK HGV emissions.
- Module A5 – on-site impacts. On-site impacts are based on an SCI study which quantified the construction impacts associated with the erection of the above ground structure (frame and upper floors).
- Module C1 – deconstruction/demolition impacts.
- Module C2 – transport of materials from the deconstruction/demolition site.
- Module C3 – waste processing.
- Module C4 – disposal.
- Module D – benefits and loads beyond the system boundary including reuse and recycling potential.
Modules B1 to B7 relate to the use stage of the building. These impacts are, in general, not relevant to the structural elements of the building and therefore are not included within the scope of the tool.
The embodied carbon emissions factors for the materials and products included within the web tool are available here.