An Indian structural team that designs for US clients works in two wind codes every week. The equations look alike, so people copy factors across. That is how a design ends up with the wrong return period or a load factor applied twice.
This comparison is for engineers who already know one code and need to work in the other. It maps each step of ASCE 7-22 to its IS 875 (Part 3):2015 counterpart. For a full walk-through of each code alone, see our ASCE 7-22 wind load guide and our IS 875 Part 3 guide.
Quick answer. ASCE 7-22 and IS 875 (Part 3):2015 both start from a 3-second gust at 10 m. They differ in return period, units, exposure terms and load factors. ASCE 7-22 maps strength-level speeds by risk category and uses a 1.0 wind load factor. IS 875 uses a 50-year speed, then IS 800 applies a 1.5 factor. Never mix factors between the two chains.
TL;DR
- Both codes use a 3-second gust at 10 m as the base speed.
- ASCE 7-22 speeds are strength-level; IS 875 speeds are 50-year values.
- ASCE 7-22 moved the directionality factor Kd out of the velocity pressure equation.
- IS 875 has a minimum design pressure of 0.7 pz.
- Neither code has a full chapter for ground-mounted solar, so coefficient choice needs a stated basis.
How do ASCE 7-22 and IS 875 compare at a glance?
| Item | ASCE 7-22 (USA) | IS 875 (Part 3):2015 (India) |
|---|---|---|
| Base speed | 3-s gust at 33 ft (10 m), Exposure C | 3-s gust at 10 m, Terrain Category 2 |
| Return period | Mapped by risk category (strength level) | 50 years, adjusted by k1 |
| Units | mph, psf | m/s, N/m² |
| Speed adjustments | Kz, Kzt, Ke inside qz | k1, k2, k3, k4 inside Vz |
| Pressure equation | qz = 0.00256 Kz Kzt Ke V² | pz = 0.6 Vz² |
| Directionality | Kd in pressure equations | Kd in pd = Kd Ka Kc pz |
| Area reduction | Through GCp by effective wind area | Ka, from 1.0 to 0.8 |
| Floor on pressure | Code minimum loads apply | pd not less than 0.7 pz |
| Steel load factor | 1.0W (LRFD) | 1.5WL (IS 800 limit state) |
| Rooftop solar rules | Section 29.4 | No solar-specific clause |
Sources: GAF on ASCE 7-22 changes; Bentley on the IS 875 Part 3 method.
What is the difference in basic wind speed?
Both codes define speed as a 3-second gust at 10 m in open terrain. That shared base is why the equations look interchangeable. The difference is the return period behind the number.
IS 875 (Part 3):2015 gives a 50-year basic speed, Vb, across six zones from 33 m/s to 55 m/s (InfraLens IS 875 walkthrough). The risk coefficient k1 then adjusts it for design life and return period.
ASCE 7-22 maps speeds by risk category. These are strength-level speeds with long return periods, so the map value already includes the margin that IS 875 adds later through load factors.
How do the pressure equations compare?
The two equations do the same job in different units.
- ASCE 7-22: qz = 0.00256 Kz Kzt Ke V², in psf with V in mph.
- IS 875: pz = 0.6 Vz², in N/m² with Vz in m/s, where Vz = Vb k1 k2 k3 k4.
The constants 0.00256 and 0.6 are both about half the air density, in each code’s units. So the physics is the same. The factors around it are not.
| ASCE 7-22 factor | Meaning | Closest IS 875 factor |
|---|---|---|
| Kz | Exposure and height | k2 (terrain and height) |
| Kzt | Topography | k3 (topography) |
| Ke | Ground elevation | No direct equivalent |
| Risk category map | Return period and importance | k1 (risk), k4 (cyclone importance) |
| Kd | Directionality | Kd |
| GCp by effective area | Pressure and area effect | Cp or Cf, with Ka |
The mapping is approximate. Kz and k2 use different terrain definitions, so do not convert one table into the other.
Where did ASCE 7-22 move the directionality factor?
ASCE 7-22 moved Kd out of the velocity pressure equation. It now sits in the pressure and force equations of Chapters 27 to 30 (MECA on ASCE 7-22 wind changes). For most structures, the final pressure does not change.
The risk is in old spreadsheets. An ASCE 7-16 sheet that already includes Kd in qz will count it twice if you add Kd again in the 7-22 pressure step. IS 875 keeps Kd in the design pressure equation, pd = Kd Ka Kc pz. Teams moving from IS 875 often get this right by habit.
Why the load factors matter most
This is where cross-code designs go wrong. Each code’s wind number belongs to its own load-factor system.
- ASCE 7-22 speeds are strength-level, so the LRFD combination uses 1.0W, for example 0.9D + 1.0W for uplift.
- IS 875 speeds are 50-year values. IS 800:2007 limit state design then applies a partial safety factor of 1.5 to wind load.
A simple check shows the effect. Multiplying a 50-year pressure by 1.5 equals the pressure at a speed about 1.22 times higher, because pressure scales with speed squared and √1.5 ≈ 1.22.
Watch out. Applying 1.5 to an ASCE 7-22 wind load, or 1.0 to an IS 875 wind load, gives a wrong design. Keep each code's speed, pressure and load factor together as one chain.
How does each code treat solar arrays?
Rooftop arrays. ASCE 7-22 has rooftop solar provisions in Section 29.4, covering arrays on low-slope roofs and arrays parallel to the roof. IS 875 (Part 3):2015 has no clause written for solar, so designers adapt coefficients for inclined surfaces or canopies.
Ground-mounted arrays. Neither code has a full chapter for ground-mounted solar. Engineers commonly adapt open-structure or canopy coefficients, or use wind tunnel data from the racking supplier. Our comparison of wind tunnel and code-based wind loads covers when each is justified.
Trackers. Trackers add dynamic effects that static coefficients do not capture. The tracker foundation loads guide covers how stow loads reach the piles.
Whatever basis you use, state it in the calculation report. A reviewer can check a stated assumption. They cannot check a hidden one.
Worked factor map: converting a design between codes
Use this sequence when a project moves from one code to the other. It avoids hybrid calculations.
- Confirm the governing code and edition for the site. In the US, check state adoption in our ASCE 7-22 adoption matrix.
- Take the basic speed from that code’s own map. Never convert one code’s speed into the other’s.
- Apply that code’s terrain, height and topography factors.
- Compute pressure with that code’s equation and units.
- Select coefficients and state their source.
- Apply that code’s directionality and area factors once.
- Combine with the load factors of the matching design code: ASCE 7-22 with AISC LRFD, IS 875 with IS 800.
- Record every factor in the report.
The STAAD Pro guide for solar structures shows how load cases enter the model. STAAD.Pro supports both codes, but the engineer still picks every factor.
How Heaven Designs helps
Our structural team prepares wind calculations under ASCE 7-22 and IS 875 (Part 3):2015 for rooftop and ground-mounted arrays. The work is delivered through our STAAD Pro reports and calculations and civil and structural engineering services.
Where a US jurisdiction requires a stamp, the stamp comes from a professional engineer licensed in that state. We do not promise AHJ acceptance.
To see a sample STAAD report, download design samples. To scope a project, get a project quote.
FAQ
Is ASCE 7-22 more conservative than IS 875?
Not as a rule. The answer depends on site wind speed, exposure, coefficients and load factors together. Compare complete factored loads for the same structure, not basic wind speeds alone.
Can I use IS 875 for a US solar project?
No. US jurisdictions adopt a building code that references a specific ASCE 7 edition. The structural design must follow the adopted edition and any local amendments.
What return period does IS 875 Part 3 use?
The basic wind speed in IS 875 (Part 3):2015 is a 50-year value. The risk coefficient k1 adjusts it for a different design life or return period.
Why did ASCE 7-22 remove Kd from qz?
Kd depends on the shape of the structure, and one structure can have several shapes. Moving Kd into the pressure equations lets each part use its own factor. For most structures, final pressures do not change.
Does STAAD Pro handle both codes?
Yes. STAAD.Pro includes wind load generators for ASCE 7 and IS 875 Part 3. The engineer must still choose coefficients, check the generated loads and apply the right load combinations.