The three hidden conditions in pre-1965 homes that blow up ADU budgets

Most San Fernando Valley tract homes went up in the 1950s and 1960s, and the ADU budget stories that go sideways usually trace back to three parts of those homes that nobody looked at before construction started.

First, the sewer lateral. The original clay line from the house to the street is often near the end of its life, and an ADU adds real load to it. A camera inspection costs a few hundred dollars and tells you the truth before you commit. Finding out after the trench is open is how a five-figure surprise lands mid-project.

Second, the electrical panel. Many mid-century homes still run 100 amp service, and an ADU usually needs more capacity. Ask every bidder to price the panel upgrade scenario up front. A bid that is silent on the panel is not a lower price, it is a deferred change order.

Third, the garage foundation, if you are converting. That slab was poured seventy years ago to hold a car, not a dwelling with plumbing, insulation, and drywall. When the walls open and the footings are not what a dwelling requires, the plan changes and the permit follows it. Budget as if some structural work is likely and be pleasantly surprised if it is not.

None of this is a reason not to build. It is the reason experienced builders carry a 10 to 20 percent reserve on top of the base budget, and why the ADU Budget Builder on this site bakes that reserve into every estimate. Check your home's age and lot details from county records with the free property check, then build the budget with the reserve included.