> For the complete documentation index, see [llms.txt](https://docs.enercalc.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.enercalc.com/sel-faq/using-the-software/calculation-modules/loads-forces/windward-snow-drift-height-not-capped-at-hc.md).

# ASCE 7-22 Snow Loads

Why the ASCE 7-22 Snow Loads module doesn't cap windward drift height at the roof step height.

## Why isn't the windward snow drift height (hd) limited to the roof step height (hc)?

In ASCE 7-16, the snow drift provisions state that the drift height need not be taken greater than h<sub>c</sub> (the clear height of the step above the balanced snow). Many engineers are accustomed to applying that cap to both leeward and windward drifts:

<figure><img src="https://1076748670-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FtBL2fEQRwrlKSM2irFL0%2Fuploads%2Fgit-blob-2a7f946ad55be4f6e872b944daabec401b8a9e0f%2Fimage%20(3).png?alt=media" alt="ASCE 7-16 snow-drift provision stating that the drift height need not exceed h sub c."><figcaption><p>ASCE 7-16 snow-drift provision limiting drift height to h<sub>c</sub>.</p></figcaption></figure>

ASCE 7-22 kept nearly identical language, **but specifically added the phrase "for leeward drifts"** to the sentences that cap the design drift height at h<sub>c</sub>:

<figure><img src="https://1076748670-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FtBL2fEQRwrlKSM2irFL0%2Fuploads%2Fgit-blob-8d6918f1c505ea6af90b10f0ca7b9a0e2457f517%2Fimage%20(4).png?alt=media" alt="ASCE 7-22 snow-drift provision stating that the drift height for leeward drifts need not exceed h sub c."><figcaption><p>ASCE 7-22 snow-drift provision limiting leeward drift height to h<sub>c</sub>.</p></figcaption></figure>

This appears to be a deliberate clarification, and the h<sub>c</sub> cap is to be applied to leeward drifts only. Because the standard does not extend that limit to windward drifts, ENERCALC does not apply it there either.

One reasonable line of reasoning could be that the upper roof may already carry a balanced snow load. If so, a windward drift could physically extend up to the step height *plus* the balanced snow depth on the upper roof. This is one possible justification, but the primary basis for ENERCALC's behavior is simply that ASCE 7-22 limits the h<sub>c</sub> cap to leeward drifts.


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