The DFARs requirement for peer reviews set a threshold of 1 Billion dollars and applies that to Major Defense Acquisition Programs.  So to answer your question, the threshold is, per DFAR 201.170(a)(1)(i)

(i) DPC will conduct the preaward peer reviews for competitive procurements prior to the in three phases of the acquisition (see (a)) for all procurements with an estimated value of $1 billion or more under major defense acquisition programs for which the Under Secretary of Defense for Acquisition and Sustainment (USD(A&S)) is the milestone decision authority or USD(A&S) designates as requiring a peer review regardless of value. DoD components may request DPC-led peer reviews for acquisitions valued below the $1 billion threshold. DPC will conduct these reviews upon approval by the Director, Defense Pricing and Contracting (Contract Policy).]

There is no additional guidance in FAR part 36 on peer reviews for construction contracts.