If the one-time purchase comes with maintenance costs, though, you have to add 25x the annual maintenance costs to your stache. E.g. a one-time cost of $15k to finish a basement might cause you to need $2k per year for increased property taxes, insurance, repairs, repainting, etc. So you'd need not only the $15k but also an additional $50k (at 4% WR) in the stache to support it.