Asked AI: What is the fallacy of relying on sales price per square foot in valuing residential real estate of very large houses, such as 5,000 square feet and up?
Relying on sales price per square foot as the primary method to value very large residential homes (such as those 5,000 square feet and up) is fundamentally flawed due to several key reasons:
1. Diminishing Marginal Value of Additional Space
As homes get larger, the price per square foot typically decreases. This is because adding more square footage does not proportionally increase the total value. The additional space is often less valuable on a per-foot basis, particularly since the core functional areas (kitchen, bathrooms, living spaces) dictate most of a home’s utility and value, while “extra” bonus rooms or oversized spaces contribute less to overall market appeal.
2. Economies of Scale and Fixed Costs
Larger homes benefit from economies of scale in construction: fixed costs like land acquisition, permitting, and foundational work are spread over more square footage, lowering the average building cost per square foot. However, buyers do not necessarily attribute the same per-foot value to every square foot, especially when the home exceeds what is typical or practical for the area.
3. Land Value Disparity
Land value is essentially fixed, regardless of house size: a bigger house on the same lot dilutes the influence of land cost per square foot. A small house and a large house with identical lots will both reflect the same land value, but the per-square-foot price of the larger home will appear significantly lower, giving a misleading impression of lower quality or desirability when in fact it is just a mathematical artifact.
4. Non-Linear Pricing
Price per square foot is not a linear metric—meaning a 2,500sqft home might sell for $400/sqft, but a 5,000sqft home nearby with similar style and finishes will likely sell for much less than $400/sqft, even after accounting for differences in quality or upgrades. This non-linear relationship is a well-documented phenomenon in residential real estate markets.
5. Quality, Layout, and Usability
The price per square foot fails to account for critical qualitative factors such as layout efficiency, ceiling height, views, architectural appeal, and the proportion of “expensive” areas (like kitchens and bathrooms) relative to the whole. In very large homes, additional square footage may end up being comprised of lower-value space like extra corridors, oversized secondary bedrooms, or bonus rooms, none of which command a high per-square-foot price in the eyes of buyers.
6. Market Appeal and Buyer Pool
Larger homes appeal to a smaller buyer pool due to higher total cost. The law of supply and demand suggests that reducing the number of potential buyers means sellers must price large homes more competitively, further depressing the per-square-foot figure versus more moderately sized properties.
7. Appraisal and Transaction Errors
If you use average neighborhood price per square foot to estimate the value of a particularly large home, you are likely to overestimate its value—sometimes dramatically. Appraisers typically apply much lower adjustments for square footage when comparing larger homes to their smaller peers because the market does not reward bulk space at a constant premium.
Conclusion
Using sales price per square foot as a simplistic value shortcut fails to recognize the nuances of how value is attributed in residential real estate, particularly with very large properties. Accurate valuation requires considering size in conjunction with quality, amenities, layout, land value, location, and current market conditions, ideally by comparing to similar-sized homes rather than just applying a straight multipler.
....................
I think they taught us this in Appraising 101.