Hi, A friend is seriously considering building a detached 600 square foot ADU in their backyard in Southern California (specifically the Westlake/Moorpark area in Ventura county). It will have separate metering (electrical, gas, water, etc.) with a private fence to make it "feel" like a private studio. What is a reasonable contractor estimate for building an ADU including materials and labor? (let's not worry about permits since those are city specific). If it makes the estimate easier, let's say they are not using "top-end" materials (e.g., super fancy granite counter tops) but "solid" (mid-level in price/quality) that give the ADU a modern look and feel and a foundation of materials that would last a fairly long time without being refurbished. She is getting quotes with a fairly wide range, from $140K all the way up to $190K. Thanks in advance!

My friend did his permitted detached existing garage for about 30k. Rents $1800. He did some of the work or lets say GC on the job. No seperate utilities and no central hvac. I like the on wheels idea though to add another one.

Those quotes sound pretty typical: $200-350/ft depending on finishes. If you’re able to GC the job, you can likely bring it down to around $100-125/ft or a tad bit above that. I’m currently researching options as well, since we can now build ADUs on multi family in Oakland. I have a good network of subs so I think I’ll be able to build a 600 sq ft unit at around $100K including permits, utilities, plans. We shall see.

@Matthew Forrest pre-fab house costs very rarely include foundation, site prep, and utilities in the advertised costs, which puts prefab above stick built in terms of cost. (If pre-fab were cheaper all buildings would be built that way)

That's it Matt. I would have put more windows in personally. There are a couple of folks here who have also done garage conversions for around 80k sf. One posted pictures that showed a clean and attractive interior, nothing fancy but nothing to be ashamed of, and perfect for a rental unit. Just like Matt's friend's. Living next to a huge college (CSULB) I anticipate renting to college students when I do rent. As such my plan is to keep it simple, leaving the interior as open and as well sun-lighted as possible, as a studio. I'll pretty up the shower walls and the counter tops and install nice flooring but every thing else will be basic; everything with a focus on durability and ease of cleaning. I'll top it off with a tankless water heater and a mini ductless unit and sub-meter the electricity but prob not the water. Thankfully the $5k developer impact fees are history which will keep my fees around only a few thousand. My architect went downtown yesterday to submit the plans, hoping for an over the counter approval, but was told no more OTC approvals for ADU's; and that it will take 4-6 weeks. I hope the city doesn't come up with any new change$ in the meantime.

I agree with @Hai G.'s estimate. That being said there is definitely decreasing cost per square foot as you go larger. Since the fixed cost is so high (permits, Gas, etc) it often makes sense to build more house. Also take a look at prefab house. Many of them look even better than stick builds and come in at a lower price point.

Once comment: assuming you’ll have decent quality tenants, I wouldn’t be a cheap ass on the finishing materials, as that is the end result that tenants see and use. Usually the difference between the cheapest ass stuff and slightly better are minor- maybe $4-8k difference for a unit you’ll spend $150-200k to build. Don’t over spend on custom materials and installs, but be smart about finishes. Make sure your GC has a clue, and ask to see pics of finished projects.

Account Closed Tiny Homes on Wheels are an excellent option! They are not required to be on a pier foundation in Fresno, but they could be placed on one if you wish. I used to think they were the same as campers until I really looked at them. Being made of regular and many times upgraded housing materials instead of that lighter fiberboard stuff, energy efficient windows, and even wood studs gives you more of solid feel. Many homes already have RV hookups that will fit a THOW, and they can be purchased for as little as 25-35K complete. Plus, if the state decides in 5 years to take away the non occupancy rule, your THOW ADU is easily relocated to another place to rent out there.

What is a reasonable estimate for constructing an ADU in LA?

Matt R.

Sherman Oaks, CA · Member since 2013 · 3k+ posts · 2k+ votes

6y

I think you could get $1000-$2000 a month all day for this in LA areas. Cost 16k includes trailer. Then factor for the rest.

$16,000

Adorable brand new custom built 8’x16’ tiny house studio, on new Ronco deck over flat bed trailer. Has registration and license. Daybed that folds out into a king bed ~ Full bath with full size shower and toilet ~ High Quality siding and trim ~ Fully insulated ~ Bruce hardwood floors ~ Oakridge roof shingles ~ Prewired ~ Pre Plumbed

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Karen MargraveBusiness Member

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Realtor, General Contractor, and Developer · Redding, CA · Member since 2009 · 7k+ posts · 4k+ votes

6y

@Arnold Baghom finishes matter and affect rental amount. As to "affordable" that's relative to the city and neighborhood where it's being built. As to finishes, the ADU should be if the same style and quality of the main house, and offered in the neighborhood. You want to increase value, not tank a neighborhoods appraisals.

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Karen MargraveBusiness Member

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Realtor, General Contractor, and Developer · Redding, CA · Member since 2009 · 7k+ posts · 4k+ votes

6y

This is my ADU conversion. It's located in Redding, CA. It's on a 20 acre parcel. This is 2500 sq. ft. but only 1/1. The main house is 4600 sq. ft. 4/4. The ADU was originally permitted in 2005 as a gameroom/shop. to the left side and down stairs is the living room, kitchen and bathroom. Upstairs are 2 rooms. No bathrooms upstairs. I've fought for 2 years with County on this as they wanted 10k in impact fees. FINALLY with the new laws they understand they can't do that.

I have the option of permitting as an ADU, or declare it as a 2nd home on property (as zoning permits it) then building another building that's an ADU. The problems with this is the new laws governing septics would probably mean one of the above grade septics that can cost up to 30k.

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Liam B.

Investor · Los Angeles, CA · Member since 2018 · 43 posts · 20 votes

6y

@Karen Margrave How are appraisals for ADU's? What % increase in value have you seen it give the home?

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Karen MargraveBusiness Member

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Realtor, General Contractor, and Developer · Redding, CA · Member since 2009 · 7k+ posts · 4k+ votes

6y

Mine isn't a typical ADU, and I haven't had it reappraised. It will be interesting to see what ADUs are going to add to value though.

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Karen MargraveBusiness Member

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Realtor, General Contractor, and Developer · Redding, CA · Member since 2009 · 7k+ posts · 4k+ votes

6y

Reasonable and Construction Costs in CA NEVER go hand in hand. I was looking at a production builders site that does work in various western states. In CA they charge $100k more for the same identical plan. It's out of control.

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Bruce P.

OP

Rental Property Investor · Los Angeles, CA · Member since 2017 · 154 posts · 24 votes

6y

Thank you @Will Barnard - it does include separate meters and lines but not permits - my friend already had architectural plans and will have to spend $10K to $15K separately for city permits (Moorpark / Westlake area was very restrictive before the California state law regarding ADUs and nuissance fees was passed).

Thank you @Karen Margrave - it is a 600 sq foot detached unit. Most of the bids were not very specific in the type of finish materials they would use (I assume finish materials mean the "cosmetic" stuff the ADU renter would see visually such as tiles and flooring). So I have a bunch of questions I need to get answered regarding the bids.

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Karen MargraveBusiness Member

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Realtor, General Contractor, and Developer · Redding, CA · Member since 2009 · 7k+ posts · 4k+ votes

6y

@Bruce P. When you're comparing bids you want to always make sure you are comparing apples to apples as far as quality of materials, etc. If one person is bidding formica and the other granite, if one is bidding under counter sinks the other set in, one a tankless water heater the other a standard, one laminate the other engineered wood, one a 30 year roof another tile, it makes a big difference on what you get in the final product, and what the appraisal comes in at.

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Bruce P.

OP

Rental Property Investor · Los Angeles, CA · Member since 2017 · 154 posts · 24 votes

6y

@Karen Margrave - I've noticed contractors tend to give these rough estimates. Is it fine to ask them to specifically itemize the type of materials they will be using for each line item? (e.g., please specify what type of door, what type of roof, what type of pipes, etc.) I've had one contractor want to charge me $300 for more specifics. I realize it's somewhat of a risk for them to spend time specifically enumerating material types as I may not end up picking them. On the other hand I would think an experienced contractor would have a fairly good idea of the range of materials available off the top of their head and that would make sense to use based on the project SOW for a small dwelling like an ADU. But this is also my first time through this process so I'd appreciate anyone correcting any mistaken assumptions I have.

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Karen MargraveBusiness Member

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Realtor, General Contractor, and Developer · Redding, CA · Member since 2009 · 7k+ posts · 4k+ votes

6y

They don't need to get too deep into the weeds, but you do want to know the main materials. If you have a specific budget you have to fit in, you need to let the contractor know what that is, and then find out what they can offer for that price, or if it's possible. If you are wanting it to match the house and want it to have specific finishes, then the contractor needs to know what specifically you want bid.

If you already have the plans, etc. it should indicate what is called for on things like siding, etc., type of roof material, etc. When asking for bids make sure you tell them what you want used in bid (granite or tile countertops, flooring - vinyl, carpet, laminate, etc., wood cabinets or composite, etc.) On a small building like that it's not that hard to figure it all out.

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What is a reasonable estimate for constructing an ADU in LA?

What is a reasonable estimate for constructing an ADU in LA?

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