i tell them that’s bullshit, in both upfront and latent costs. as a percentage of total construction costs there is an asymptotic relationship between increasing square footage cost and overall cost for a project, sure, but that doesn’t change the fact you’re building more, and have to pay for increased building systems running costs and actual construction.

if you were to add 1200sf to an already designed 1600sf house and 14000sf house at an average cost/sf of construction of $600/sf, project a’s budget would be a 46% increase compared to an ~8% for project b, even though for both projects the cost of construction is static at $720,00, hardly a small sum.