ADU Construction Costs

12 Replies

I'm looking at a property with a detached garage (550 sq ft) built in the 50s and am researching the costs of

  1. converting the garage into an ADU, or
  2. adding an ADU on top of the garage

The property is in Tigard and has a SFR on it. Adding an ADU on top would allow me to keep the garage (which is valuable to most people), but I'm guessing is significantly more expensive than just converting the garage.

Does anyone here have experience building ADUs and have an idea of how much I could expect to pay? My research so far has shown a really wide range of costs.

Portland's own Kol Peterson just wrote the book on this:  

https://accessorydwellingstrategies.com/backdoorre...

In fact, there is a book launch party this Tuesday. 

He also maintains a very informative website: http://accessorydwellings.org

If you attend the book launch (Google the book title on eventbrite), you'll be able to ask Kol about your specific situation. 

Updated almost 2 years ago

Edited to mention, you may want to get a contractor out to take a look at that garage, see if it's just on a slab or if it has a foundation. If it's just a slab, you likely won't get a permit to convert it to living space. Even if it has a foundation, you'll need a registered architect/engineer to verify that the foundation is strong enough to add a second story. Typically building foundations are sized according to the dead and live loads that are anticipated in that specific structure for its intended use. Many detached garages were built without foundations.

Jacob, 

I recently worked with a client and he bought a property on SE 84th and lafayette that had an 800 sq ft detached garage. Cost him around 35k total, All permitting done with the city/ connect the sewer line from the main to the ADU/ and all electrical done. These were the biggest expenses for him. Let me know if you have any questions or would like to see the excel sheet for all the costs associated with the conversion.

Chase

@Raul Lopez

Seems impossible to convert 800 sq foot garage to legitimate adu for 35k Way too cheap I converted a 960 sq foot space into very nice 2 bed/2 bath house but cost 160-170k. Maybe I got ripped off apparently! Haha. At least it rents for $2,800 monthly

@Chris Miller What area are you located in? And wow. That's a lot more than I anticipated. I do have a contractor buddy that said he did a similar space more like 500 sq ft for about $60k very bare bones but still aesthetically pleasing. I'm looking at doing some of the work on my own really simple stuff to save.

In my area I don't think I could rent it our for more than $1700. I'm in North Long Beach but what do I know. Not much really lol That's why I'm here.

Hey Raul. That adu prop I did is in east side circle area. I didn't do any work myself as I'm busy enough with work, little kiddos and surfing! But in the end very happy with the outcome and look forward to doing many more ADU's with the new laws!

Originally posted by @Raul Joey Lopez :

@Chris Miller What area are you located in? And wow. That's a lot more than I anticipated. I do have a contractor buddy that said he did a similar space more like 500 sq ft for about $60k very bare bones but still aesthetically pleasing. I'm looking at doing some of the work on my own really simple stuff to save.

In my area I don't think I could rent it our for more than $1700. I'm in North Long Beach but what do I know. Not much really lol That's why I'm here.

Raul a gentleman here from Santa Maria converted his garage for $37k doing some of the work himself. A neighbor by me (near Cal State Long Beach) spent $54k, and he added on 200 sf to his garage. Another neighbor built one from the ground up for $180k. It's all over the place.

On 1/1/20 the BS Long Beach development impact fees charged, roughly $5k for an ADU under 750sf, go away but solar power is required for around the same amount after tax credit.

We are lucky not to be serviced by the LADWP because if your power lines are over or close to the structure you are out of luck.SCE has no problem for now at least. My thought would be to get going with the permit as soon as possible after the first of 2020 before any new costly plans are put in place.

 

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