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# Calculate Wind Loads - Components and Cladding (NBCC 2020)
> Calculate wind pressures on components and cladding to NBCC 2020 and NBCC 2025.
Determine peak local wind pressures on cladding and secondary members of low-rise buildings to NBCC 2020 (Subsection 4.1.7), on the 1-in-50 reference velocity pressure basis. Returns net ULS and SLS pressures for every wall and roof zone, plus overhang uplift and parapet member and cladding pressures, with logarithmic interpolation on tributary area.
## Method & scope
| Property | Detail |
| ---------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Design standards | NBCC 2020, Division B, Part 4, Subsection 4.1.7 (Wind Load) |
| Regions | Canada |
| Who it's for | Structural engineers computing C\&C wind pressures for low-rise buildings in Canada (walls, roofs, overhangs, parapets) under NBCC 2020, replacing manual figure-reading and interpolation. Available now to Core Calcs users (beta). |
| What it checks | Reference velocity pressure and importance factors, Exposure and topographic factors, External pressure coefficients, Internal pressure, Net design pressures, Overhangs, Parapets |
#### What it calculates
Canadian structural engineers sizing cladding and secondary members on low-rise buildings for projects still running under NBCC 2020, where the reference velocity pressure is the 1-in-50 value. Use the NBCC 2025 version for new work on the 1-in-500 hazard basis.
Saves roughly 1 to 2 hours per building of curve reading, interpolation and load-case bookkeeping, more when overhangs or parapets are involved. Replaces the per-project wind spreadsheet for low-building cladding design in Canada.
#### Calculation method
This calculator determines peak local wind pressures on components and cladding of low-rise buildings using the static procedure of the National Building Code of Canada 2020 (Division B, Part 4, Subsection 4.1.7). The workflow moves from the site reference velocity pressure, through exposure, topographic and pressure coefficients, to net design pressures reported per zone at both ultimate and serviceability limit states.
##### Reference velocity pressure and importance factors
The reference velocity pressure for NBCC 2020 is the 1-in-50 annual probability value, q50. It is taken from the project defaults for the site or entered directly as an override. The building importance category sets the wind importance factor, applied separately at ULS and SLS, so both limit states are produced from the same geometry and coefficient set rather than requiring a second run.
##### Exposure and topographic factors
The exposure factor Ce is computed from the reference height and the terrain condition, subject to the code floor on the factor for low buildings. Where a hill or escarpment is present, the speed-up ratio is evaluated from the hill height, the upwind horizontal distance and the shape, and combined with the gust effect factor to give the topographic factor Ct. When no topographic feature applies, Ct is unity and drops out of the pressure equation.
##### External pressure coefficients
Wall and roof surfaces are divided into the code zones: wall interior and wall end zone, and roof interior, roof edge and roof corner. Each zone carries a gust-pressure coefficient product CgCp that depends on the roof angle, which the calculator resolves into the NBCC bands of θ ≤ 7°, 7° \< θ ≤ 27°, and steeper roofs. Positive and negative coefficients are tracked separately so that both pressure and suction cases are reported.
The coefficient for a given member depends on its tributary area. Each zone defines a coefficient at a lower area limit and at an upper area limit, and the calculator interpolates logarithmically between them:
**CgCp** = CgCp,low − (CgCp,low − CgCp,up) × log(A / A,low) / log(A,up / A,low)
Tributary areas at or below the lower limit take the lower-limit value, and areas at or above the upper limit take the upper-limit value.
##### Internal pressure
The building opening condition selects the internal pressure coefficients Cpi, positive and negative, from the NBCC categories ranging from a sealed building with small uniformly distributed openings through to a building with large or dominant openings. The internal pressure is factored by its own exposure factor Cei and the internal gust effect factor Cgi.
##### Net design pressures
The net pressure on a component combines the external and internal contributions:
**p,net** = IW × q50 × Ct × (Ce × CgCp − Cei × Cgi × Cpi)
The positive net pressure pairs the positive external coefficient with the negative internal coefficient, and the negative net pressure pairs the negative external coefficient with the positive internal coefficient, so each zone reports the governing inward and outward case. Substituting the ULS and SLS importance factors produces both limit states.
##### Overhangs
Where roof overhangs are included, they are evaluated in their own interior, edge and corner zones using the overhang coefficients and the overhang tributary area, with the same logarithmic area interpolation. Overhang pressures are reported as net uplift at ULS and SLS, since the underside and topside contributions are already combined in the overhang coefficient.
##### Parapets
Parapets are handled as two separate cases. Parapet members take windward and leeward coefficients by region, General for the wall interior and roof edge combination and Corner for the wall end zone and roof corner combination. Parapet cladding is reported as an outer face positive pressure, an outer face negative pressure, and an inner and top face pressure, each combined with the parapet internal pressure coefficients. Both cases use the parapet height and the parapet member tributary area as inputs.
## How to use it
Open it from **Run calc** in the About this calculator panel above.
Work through the input sections from top to bottom. Click any input label to see its reference explanation, clause, conditions and assumptions. See [Checks, References, Conditions and Assumptions](/docs/running-calculations/checking-results/checks-references-conditions-assumptions).
Check the utilization of each governing check in the summary, then export a PDF report. See [Views and Export](/docs/running-calculations/exporting-reports/views-and-export).
#### Wind Loads Calculator: components and cladding pressures to NBCC 2020
#### Wind Loads Calculator: components and cladding pressures to NBCC 2025
## Common questions
It applies the static procedure of the National Building Code of Canada 2020, Division B, Part 4, Subsection 4.1.7, to determine peak local wind pressures on components and cladding of low-rise buildings. Pressures are built from the reference velocity pressure, exposure and topographic factors, external gust-pressure coefficients, and internal pressure.
Use this NBCC 2020 version for projects assessed under that edition, where the reference velocity pressure is the 1-in-50 annual probability value, q50. For new work under NBCC 2025, use the 2025 calculator, which uses the 1-in-500 value q500. The editions are kept separate because carrying a 1-in-50 reference pressure into a 2025 design underestimates the load.
The reference velocity pressure q50 and building importance category, which can flow from the project defaults or be overridden; the tributary area of the wall, roof, overhang and parapet member being designed; roof type, pitch, eave and top heights; building width and length; terrain exposure; topographic conditions; and the building opening condition that sets the internal pressure coefficients.
Net design wind pressures at both ULS and SLS for each wall and roof zone, positive and negative, plus separate tables for overhang uplift, parapet member pressures, and parapet cladding pressures on the outer, inner and top faces. The end zone width and the governing external and internal pressure components are reported alongside.
Yes. Roof overhangs are computed in their own interior, edge and corner zones with the appropriate uplift coefficients. Parapets are handled twice: once for parapet members using windward and leeward coefficients, and once for parapet cladding using outer face positive and negative pressures together with the inner and top face pressure, each split by General and Corner region.
Each zone has a coefficient at a lower area limit and at an upper area limit. Where your tributary area falls between the two, the calculator interpolates logarithmically between them, matching the log-scale axes of the NBCC figures. Areas at or below the lower limit take the lower-limit coefficient, and areas at or above the upper limit take the upper-limit coefficient.
## Next steps
Complete list of Calcs.com design calculators available for Canadian projects (CSA O86, CSA S16, NBCC, and related standards).
Calculate wind pressures on the main structural system to NBCC 2020 and NBCC 2025.
Get balanced, unbalanced, drift, and sliding roof snow loads to NBCC 2020 Cl. 4.1.6 from the 1-in-50-year ground snow basis, with each code clause shown.
Determine design base shear to NBCC 2020 (Art. 4.1.8) with the Equivalent Static Force Procedure, and distribute forces story by story.
Pull the reference wind pressure and climatic data for any Canadian site from the NBCC 2020 tables (Appendix C) as the basis for design wind loads.
