有別於市場比較法與收益法,成本法為不動產估價技術中,能夠直接針對不動產中之建物進行估價。以成本法為基礎的建物估價,主要透過建物重建成本的求取並考量建物折舊對於價值的減損據以推估。也因此,當建物折舊無法被準確估算時,將影響歷經不同屋齡的建物價值評估。 在台灣,房屋稅的稅基便依據成本法概念評定出房屋現值。然而,過往研究鮮少針對房屋稅中,法令折舊是否與真實市場折舊產生落差做出實證。過去文獻曾提及折舊存在空間上變異的可能,但並未進一步解釋造成折舊於空間上變異的原因。透過台北市公寓住宅交易資料,本研究將同時推估市場建物折舊,展現出其空間上的變異,並採用空間遞延與空間誤差模型,避免因空間效果存在所造成衡量建物折舊上的偏誤。實證發現公寓建物的折舊速度,隨著屋齡上升逐漸和緩而呈現凸型折舊路徑,且區位條件較佳(差)之建物,折舊帶來對於建物價值的減損較小(大)。我們認為,造成折舊存在空間上的變異,主要是區位條件使外部性退化產生差異所致。此外,當市場折舊情形高於法令規範折舊時,將使得房屋稅稅基被高估。我們發現,在房屋現值其他評定因素正確的前提下,低估建物折舊率將造成房屋稅稅基被過度評定達45%。
Unlike market comparison and income approach, cost approach is one of the three primary appraisal approaches which can estimate structure value directly. Its accuracy depends upon the satisfactory estimates of land value, replacement or reproduction costs and building depreciation. The lack of figures for building depreciation in Taiwan has led to the heavy reliance on rule-of-thumb. This study, using the transaction data of condominiums at Taipei City in recent years, estimates the building depreciation revealed by the market. In addition, the potential autocorrelation problems often found in spatial data are corrected through spatial autoregression and spatial error models. A convex path of depreciation is found. The value of a condominium building decreases at a faster rate at the early stage than at the later stage. Besides, there are variations in depreciation rate for condominiums among different neighborhoods. Empirical results suggest that condominiums in a neighborhood with superior amenities depreciate more slowly than those in a neighborhood with inferior amenities. The market-derived depreciation rate is materially higher than the law-specified rate. The tax base for housing tax is consequently over-estimated. For example, the tax base for a condominium of 41 years is over-assessed by 45 percent.