In Latin, Lex means “Law” and Constructionis means “Construction”. With the two words combined, the phrase refers to “Construction Law”. Lex constructionis is often used in the context of international law.
Lex constructionis is very specific as it addresses issues only about construction. But in the bigger picture, lex constructionis can be described in the context of “Lex Mercatoria” or the mercantile law in the present.
How lex mercatoria retains its value in legal systems is still controversial. On the positive note, lex mercatoria is often perceived as an autonomous legal order drawing own character from legal pluralism which stems from customs and traditions in trade; therefore, Lex mercatoria is not bound to national law. In contrast, lex mercatoria is arguably nonexistent. Lex mercatoria may legally exist only by virtue of state laws. By itself, lex mercatoria is vague, incomplete, and void of biding force.
Lex mercatoria is important in the field of international law especially in decision process for an arbitration. Occasionally, engaged parties do not wish to have their contracts governed by any of their national laws, parties can instead choose lex mercatoria. Arbitrators may also opt for lex mercatoria when the arbitral tribunal is to decide as amiable compositeur or ex aequo et bono.
Lex construtionis is part of lex mercatoria that is calibrated for construction industry (so called “Lex mercatoria constructionis”). Lex constructionis in international practice is influenced by FIDIC contract. FIDIC is the federation of consulting engineers who provide templates for construction contracts, which are commonly used in the world today to the extent that the World Bank standardizes all contracts for projects it finances by using FIDIC contracts.
FIDIC contract is based on many principles that are considered lex constructionis, as it integrates principles used in some other international commercial contracts such as Pacta sunt servanda (promise must be kept) or Rebus sic stantibus (change in circumstances). These concepts are lex mercatoria by nature and also found in other international laws such as UNCRITAL and UNIDROIT.
Examples of lex constructionis principles in FIDIC contract are variation (not considered a breach of contract); compensation for inaccurate data provided by employer in good faith; and extension of time for project completion.
Moreover, FIDIC contract has one Golden Principle that forms the basis of a contract—that is, the balance of right and duty, no ambiguity, reasonable time to perform dictated tasks, and procedure for dispute resolution. Such is also part of Lex Mercatoria Constructionis.