We have a larger property and are considering adding a detached accessory dwelling unit to the back of the property for rental income. First, would love to know if anyone else has done this and any advice you'd give, and secondly what you all think about my high level calculations:

- $80k to build (likely thru HELOC/refi) - Is this estimate in the right ballpark for a small studio/loft ADU?

- Rent out for $1200/month - Studios in this area are renting for $1500-1800/month but these are in big complexes with amenities. I'm not sure if we should consider charging more than this average since the ADU location is unique and literally in the middle of a forest? I'm using $1200/month just to be safe.

-Estimated monthly cash flow after mortgage, expenses, etc would be around $600/month

- This is what the property looks like, the ADU would be "in the woods". The site is not easily accessible by machines and is over 100 feet from the primary house. We're hoping to somehow tap into our existing water and electric, but we'd have to add septic or do composting.

Assuming we can get the permits, this seems like a no brainer to me. Does anyone know of any companies that would be experienced to build this type of structure? We were thinking of companies that make cabins since they'd be more familiar with sites that are harder to access.

Thoughts?

Are you inside Seattle city limits?

How big of an ADU are you thinking? Many people under-estimate the cost of building one. There is a lot of work to bring utilities to the back of the property. Appears you may have "critical areas" in the back of your property? In most cases, you would not be able to build anything near a creek, stream, wetland, etc.

If you are able to get it built. Since accessibility is going to be unique, you may consider something like Air BnB as a back up plan, with a lil creative marketing the landscape may sell it self! IMO

The property is not within Seattle limits, and is in unincorporated King County. We were thinking the ADU would be around 200 sqft with a loft. Adrian you are correct that there is a very small creek in the area, about 20-30 feet away from the potential building site. We are trying to figure out what professionals we should engage to help us figure out feasibility?

Thanks for the advice Kenny, we had considered this as well!

I've got no experience in this area...but if it were me, I would start calling electricians and plumbers and asking them if they do that type of work (running utilities across the property), or for a reference of someone they know that does.

It also never hurts to call up (or visit) the permit office or have a chat with the inspector. Lots of useful information can come from that.

Are you on septic?  It sounds like you are which may be your biggest expense since septic systems are sized per number of bathrooms so upgrading that or installing a new one is a major job.

As for cost saving, there are pre-fab cabins/yurts that look really good and fit your "in the woods" feel.  All you need is the slab with electrical and plumbing done and the cabin/yurt arrives for assembly.

Thanks everyone!