The answer to this question depends on a few different factors, including the size and location of your tiny house. In general, you will need resource consent if your tiny house is:
Located on land zoned for residential use
Connected to utilities such as water and sewerage
Built on a foundation or wheels
If your tiny house meets all of the above criteria, you will most likely need to apply for resource consent from your local council such as Seattle city council. The process and fees for this can vary depending on your location, so it’s best to check with your council in advance.