Efficient by what metric? By energy usage, sure, but the one metric that seems to override all others in the US is capex, not opex considerations (which over the long haul can overshadow initial capex acquisition costs).<p>The rule of thumb I&#x27;ve heard about construction is stick-built SFR is considered relatively baseline cost. Multi-Family Residential (MFR) with a few stories that requires some more robust structural elements is about 2X SFR per square foot. Mid- to high-rises are about 2X MFR (4X SFR) and up per square foot.<p>Economically living in high-rises is a non-starter in most of the US for many working-class and middle-class families, and you won&#x27;t see Krugman&#x27;s touted beneficial effects unless that middle of the population bell curve is in high-rises. I advocate dense urban development, but I have yet to figure out how it can be economically implemented without compromising quality of life, especially with the multi-decade long asset inflation we&#x27;re experiencing in real estate that is ongoing.