成本法為估價三大方法之一，其中折舊率之掌握至今仍無定論，Malpezzi et al.（1987）、Smith（2004）指出，由於土地無實體損壞及功能性退化，故利用特徵價格法分析折舊時，分析主體包含土地，將造成折舊的低估，而國內先前研究亦指出，分析主體包含土地，可能是使其分析結果不合常理的原因。本研究採特徵價格法，以台南市透天建物為對象，實證結果與Malpezzi等之論點一致，即不包含土地之價格函數，確有較高的折舊率，且呈現凸向原點之折舊型態。不動產價格模型亦顯示，建物壽命前期價格逐年下跌，但至後期將反轉向上，反應出土地之再開發價值。 此外，依不動產估價技術規則之規定，求取建物價格時似乎未考慮外部性退化之價值減損，或將其視為與剩餘經濟耐用年數相關。然而Colwell and Trefzger（1994）指出負面外部性將同時影響土地與建物，本文實證結果發現，外部性退化除對土地價格造成影響外，事實上對建物價格亦產生價格減損效果。此外，外部性特徵對於建物價格之影響視兩者距離相鄰程度而定，故不應將外部性退化視為與屋齡相關，而於考量後推估建物剩餘經濟耐用年數。 / In this paper, we verify that estimated depreciation rate is higher when the land price has been extracted from single-family house prices in Tainan, and the depreciation pattern of building is convex to the origin. We also find that property prices will decrease in the early years and then turn to increase; this phenomenon may testify the benefit in land redevelopment. Moreover, this study shows that external obsolescence would reduce not only the land price but also the building price when the surrounding is unattractive, and the decreasing figures caused by external obsolescence shouldn’t base on house age, but distance between house and unattractive objects.