This is for multi family structures.
Sorry That was NFPA 1 Chapter 1.... Not 101.
Check chapter 5
more than likely the same in NFPA
CHAPTER 5 EXHAUST SYSTEMS | 2015 International Mechanical Code | ICC publicACCESS
Might be in NFPA 96
Missed the multi family, any way besides the link above if you are looking at NFPA
Check 2012 NFPA 54 starting at 10.4, but I do not see anything about length.
Also, it goes back to the manufacture requirements, which is a little hard with multi family.
You may also want to check NFPA 211, 10.7.3.7. It covers dryer exhaust duct requirements.
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