You nailed it with the “hidden surprises.” I once opened up a backyard for a guest house and found an old septic tank no one knew about—talk about a plot twist. Permits are their own flavor of headache, but yeah, once you’re knee-deep in mud trying to explain to your plumber why there’s a 1950s Buick bumper under the lawn, it’s a whole new ballgame. Still, nothing beats that feeling when you finally get to hand over the keys and see someone’s face light up. Worth every gray hair... mostly.
Hidden stuff in the ground is no joke—last year I budgeted for a simple 400 sq ft ADU and ended up sinking an extra $18k just dealing with “mystery” utilities and a concrete slab nobody had on the plans. Permits are their own beast, but it’s the unknowns that really torch your contingency fund.
- My rule: build in at least 20% over your initial estimate for surprises. If you don’t use it, great. But you probably will.
- Don’t underestimate permit timelines either. City said 8 weeks, took 5 months. That’s holding costs and lost rent.
- On the flip side, I’ve had projects where everything went smooth...but honestly, that’s been rare.
I get the satisfaction part—it’s huge seeing someone move in. But those gray hairs are well-earned. If you’re thinking about cost, just remember it’s not just materials and labor; it’s chasing down old paperwork, unexpected demo, and sometimes explaining to a city inspector why there’s rebar from 1962 under your lawn.
I get where you’re coming from, but I don’t know if the 20% rule always fits. On my last backyard build, I padded the budget by 10% and still had a bit left over—even after a surprise sewer tie-in. Maybe it’s luck, or maybe it’s just obsessively checking old site maps before breaking ground. Not saying the unknowns aren’t real (they definitely are), but sometimes a little extra research saves a lot of cash. Permit delays though...those are brutal no matter what.
I’m with you on the permit delays—those can eat up weeks, no matter how well you prep. On my garage conversion, I only padded the budget by 12% and it worked out fine, but I probably spent double the time researching utilities and city records. Found an old water line that saved me a headache later. Sometimes all that digging (the paperwork kind) actually pays off more than just throwing extra money at the problem. But yeah, there’s always something you can’t plan for...
That’s the thing—no matter how much you budget, there’s always some curveball. On my last ADU build, I thought I had the utilities mapped out, but the city had zero records on an old sewer tie-in. Ended up spending a week with a shovel and a lot of cursing. Honestly, I’d rather over-research than overpay. Still, even with all the prep, I always tack on at least 15% to the budget just for the “unknowns.” It’s never as simple as it looks on paper.
