In plain English
FAR 52.226-4, Notice of Disaster or Emergency Area Set-Aside, is a contract clause prescribed at FAR 26.206(b), most recently dated Nov 2007. The complete official text is reproduced below, verbatim, from GSA's published FAR source files.
Its text contains no sentence requiring insertion into subcontracts; see the flowdown section below for what that does and does not mean.
Does it flow down to subcontracts?
No flowdown mandate found in the clause text
We scanned the full clause text and found no sentence directing the contractor to insert this clause into subcontracts. That is a statement about the text, not legal advice: a prime contractor may still flow terms down contractually, an agency supplement (DFARS, VAAR, …) may add requirements, and clauses listed below (if any) may order this clause into subcontracts from the outside.
Where it's prescribed
As prescribed in 26.206(b), insert the following clause:
Prescribing reference: FAR 26.206(b).
The official text, verbatim
As prescribed in 26.206(b), insert the following clause:
Notice of Disaster or Emergency Area set-Aside (Nov 2007)
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(a) Set-aside area. Offers are solicited only from businesses residing or primarily doing business in ________________________________________________ [Contracting Officer to fill in with definite geographic boundaries.] Offers received from other businesses shall not be considered.
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(b) This set-aside is in addition to any small business set-aside contained in this contract.
(End of clause)