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# Calculate Wind Loads - Components and Cladding (NBCC 2025)
> Peak local wind pressures for walls, roofs, overhangs and parapets on the NBCC 2025 1-in-500 hazard basis, from your tributary areas and building geometry.
CanadaNBCC 2025Division BPart 4
Wind Loads - Components and Cladding (NBCC 2025)
Run the calc
Determine peak local wind pressures on cladding and secondary members of low-rise buildings to NBCC 2025 (Subsection 4.1.7), on the 1-in-500 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.
Peak local wind pressures for walls, roofs, overhangs and parapets come from your tributary areas and building geometry, on the NBCC 2025 1-in-500 hazard basis. Site parameters carry over from project defaults, and ULS and SLS pressures are reported for every zone.
## Method & scope
| Property | Detail |
| ------------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| Design standards | NBCC 2025, Division B, Part 4, Subsection 4.1.7 (Wind Load) |
| Regions | Canada |
| Who it's for | Structural engineers computing C\&C wind pressures in Canada under the new NBC 2025 hazard basis (1-in-500), avoiding accidental reuse of unconservative 2020-basis (1-in-50) values. Available now to Core Calcs users (beta). |
| What it helps with | Replaces roughly 1 to 3 hours per building of manual figure reading, log interpolation and ULS/SLS bookkeeping across all wind zones, overhangs and parapet faces, and eliminates the cross-edition data-entry error that manual workflows have to police by hand. |
| 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 under the NBCC 2025 hazard basis, where reusing a 2020-era 1-in-50 reference pressure would leave the design unconservative. Wall, roof, overhang and parapet zones are each returned at ULS and SLS from one set of tributary areas.
Replaces roughly 1 to 3 hours per building of manual figure reading, log interpolation and ULS/SLS bookkeeping across all wind zones, overhangs and parapet faces, and eliminates the cross-edition data-entry error that manual workflows have to police by hand.
#### 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 2025 (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 2025 is the 1-in-500 annual probability value, q500. 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 × q500 × 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).
## Common questions
It applies the static procedure of the National Building Code of Canada 2025, 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.
NBCC 2025 moves the reference velocity pressure to a 1-in-500 annual probability of exceedance, q500, where NBCC 2020 used the 1-in-50 value, q50. The pressure equation and coefficient tables are otherwise applied the same way. Carrying a 2020-basis reference pressure into a 2025 design underestimates the load, so the two editions are kept as separate calculators rather than one with a toggle.
The reference velocity pressure q500 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
Calculate wind pressures on components and cladding to NBCC 2020 and NBCC 2025.
Complete list of Calcs.com design calculators available for Canadian projects (CSA O86, CSA S16, NBCC, and related standards).
MWFRS wind pressures for Load Case A and Load Case B on the NBCC 2025 1-in-500 hazard basis, from your building geometry, terrain exposure and roof slope.
Get balanced, unbalanced, drift, and sliding roof snow loads to NBCC 2025 Cl. 4.1.6, including the new thermal factor CT and winter wind factor Fws.
Design base shear and story forces to NBCC 2025 Cl. 4.1.8 from the six-period hazard values, site class and seismic force-resisting system.
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.