Therefore, it was, in many cases, unavoidable for Tenshu to be constructed in the reinforced concrete structure even if enough information to justify restoration of Tenshu was available, and it was only possible to construct wooden Tenshu by getting special permission of the Minister of Construction or by exploiting legal loopholes as in the case of Gosankai Yagura of Shirakawa Komine-jo Castle.
天守を野外復元できるだけの資料が揃っていても、鉄筋コンクリート構造の天守を建てざるをえないことが多く、建設大臣の特別認可を受けたり、白河小峰城の御三階櫓のように法の抜け穴を見つけなければ木造天守の建築は不可能であった。