How are sale values of ADU's?

[Peter Lee]

Anyone have recent experience on how an ADU (accessory dwelling unit) or backhouse is valued these days relative to the main house?

For example, say if you have a house that is 1500sf and it would normally sell for $500/sf, what are people's thoughts if there was an ADU of 750sf built in the back with similar construction type as the main house?

Would future buyers significantly discount the ADU? If so, how much? 10, 20, 30% relative to the cost/sf of the main house?