The stairs are one of 2 exits from a basement but are not enclosed and the staircase construction is wood.
Residential or commercial?
Check out NFPA 1 2015 ED. Chapter 14 Usable Space Sections 14.6.3 - 18.104.22.168 and Section 14.3.3, Appendix A 14.3.3. NFPA 101 2015 ED. Chapter 7 Usable Space Sections 22.214.171.124.3, 126.96.36.199.3, 188.8.131.52.3.1, 184.108.40.206.3.2. In general there is no storage allowed under wooden staircases. The above NFPA Codes should answer your question. Just my opinion . Hope this was helpful to you.
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