The emergence of institutions in Hayek's theory: two views or one?

Hayek opposes the explanation of the emergence of institutions as "spontaneous (unintentional) order'', which he considers correct, against "constructivism'' (viewed as erroneous). This dichotomy exhibits some inconsistencies, for, on Hayek's account, constructivist ideologies seem able both to prevent the evolutionary emergence of norms and to generate institutions coherent with deliberate, intentional, purposes. If this is so, are there then two views on the emergence of institutions in Hayek's theory? The paper consequently discusses whether constructivism and evolution of norms are two alternative kinds of explanation, and in particular whether the former can be interpreted in evolutionary terms.