違章建築交易問題已經困擾實務數十年。最高法院創造出事實上處分權之概念，並在一系列判決、判例、民事庭會議決議中，逐步填充其概念，並指出違章建築交易後各種具體問題之處理方式。然而，訴訟案件仍然層出不窮，法院也始終沒有釐清事實上處分權的本質與內涵。本文填補法院見解之空白，並指出實務看法值得商榷處：若違章建築仍會繼續存在，最理想的政策手段是讓違章建築辦理保存登記，且在主管機關依法拆除違章建築前，課予行政罰鍰。替代及備位方案則是將事實上處分權建構為習慣創設之物權，並以房屋稅籍登記作為公示與取得事實上處分權之必要條件。在現行法體系下，事實上處分權之最佳定位是一種特殊定限物權——永久使用、收益、處分權。

The legal issues regarding the transactions of unlawful buildings have persisted for decades. The Supreme Court of Taiwan invented the idea of “right of de facto disposal” and provided flesh and blood to this idea over a series of cases, precedents, and resolutions. Nevertheless, these judicial constructs still fail to solve the problem of unlawful buildings, as evidenced by the large number of lawsuits nowadays. Using economic analysis of law, I propose a new theory to construct the nature and contents of right of de facto disposal. Specifically, I argue that in addition to strictly enforcing the building code and tearing down all the unlawful buildings, the best solution is to include unlawful buildings in the real estate registry and impose civil fines to owners of unlawful buildings. The second best solution is to construe right of de facto disposal as a type of property rights created by custom, and to provide notice through the building tax registry. Tax registration would serve as a necessary condition for acquiring a full-fledge, in-rem right of de facto disposal, which resembles a permanent usufruct. Holders of rights of de facto disposal are also subject to civil fines.