Pre-design ADU plans

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Pre-design ADU plans

Brandon Carlson
Real Estate Consultant · Glendora, CA · Member since 2019 · 314 posts · 95 votes

Hi BP,

For over a year now I have been thinking of building an ADU. With that said, what's your experience been like when obtaining architect plans/designs? I live in Los Angeles County, specifically the San Gabriel Valley.

I've called around and received quotes ranging from $4500 - $7000 for a 2 bedroom 1 bath ADU at 749 sqft. The services include the following:

Architectural Design: Creating a new design that fits your scope and complies with city requirements, and providing necessary drawings and details

Structural Design: Designing the structure to support the new ADU and items and providing necessary drawings, details, and calculations

Title 24: Requirement for new living space to analyze energy efficiency and utility effectiveness with new square footage. 

I discovered ADU Building Plans.com and they have pre-designed plans for $50. If I go this route, would I have to sub out the structural design and title 24 part? How much architectural work is actually needed for an ADU? I am trying to justify the cost. I plan on project managing this job and using subs for framing, foundation, etc. to help control costs.

And what are development impact fees and the cost?  I hear they don't apply for units under 750 sqft.

Thank you for any input or advice. My goal for next year, is to complete this project. 

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Whitney Hill
Contractor · San Diego, CA · Member since 2016 · 88 posts · 100 votes
6y

Hi @Brandon Carlson, just chiming in on the total cost. For a 750 sqft 2BR/2BA, all-in costs are going to be more like $210K if you go with a contractor. If you sub it out yourself, would imagine saving ~$40K. Either way, I don't think that budget is realistic unfortunately.  Here's a breakdown of costs:

1) Design & Engineering: $6,000-10,000. Full set of construction drawings along with a site plan (even if you use a standard plan, it has to be situated & adapted to your property specifics). Design also includes Title 24 (required by CA), structural engineering, building code review with the city, permit processing, and a final estimate with a fixed guaranteed max cost for construction.

2) Permits & Fees: $6,000-8,000. A good rule of thumb is $10-12/sqft in fees. While ADUs are now exempt from many fees, there are still several to consider. There are no impact fees for ADUs under 750 sqft. School fees are also still due, as well as sewer connection fees. 

  • Sewer: Connection fees are usually $2-4K, with recurring fees thereafter of about $1K/year. Note that a new septic system is likely required for an ADU if your property is on septic.
  • School: Usually $4/sqft, so $2-5K

3) Site Work: $10,000. This number will of course be highly dependent on your specific property conditions. For a level lot, expect the sitework and foundation to cost $10K. If you need to start moving dirt and putting in retaining walls, sitework costs can quickly escalate.

4) Vertical Building Construction: $187,500. With a 750 sqft unit, cost is about $250/sqft.

5) Solar: $7,500. All standalone ADUs are required to have solar in place, with basic systems costing $7,500. Silver lining here is that you'll save on utility costs :)

6) Other Costs: TBD. While typically not required, you may have additional costs come up if you require additional structural engineering, civil engineering, or soils engineering.

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  • Jim Weller
    Member since 2020 · 8 posts · 3 votes
    6y

    @Brandon Carlson I've also priced out building my own ADU but the cost (not too mention hassle and work) didn't pencil out vs. buying a prefab ADU which I am looking at now. Guess it depends if you're a DYI guy or not. Jim.

    1Reply
  • Dan H.Pro Member
    Investor · Poway, CA · Member since 2015 · 7k+ posts · 8k+ votes
    6y

    Some cities have plans available for free.  If you are going with a generic, not site specific plan, I would consider looking at the free options prior to paying for something similar.

    Leucadia in my market is a city with free plans.  I do not know if they are free to use in another city or if you can only get them if you are building in Leucadia.  I have seen the photos of the exterior and they have a few different looks and each look then has different size/configurations available.  So you pick the look you like, then you pick the size/configuration.

    Good luck

    1Reply
  • Matthew Forrest
    Rental Property Investor · Torrance, CA · Member since 2016 · 263 posts · 132 votes
    6y

    @Brandon Carlson I don't have any experience with pre-approved ADU plans, but getting the plans approved were definitely the most difficult part of my project. Im not 100% sure if that was because I had a bad architect, but avoiding the back and forth with the city was definitely worth more than
    $4500 - $7000. From what I understand I feel like you get more than the plans, you also get the architects relationship with the city planning office as well as experience on how to get things through as quickly as possible.

    As a side note, what's stopping you from getting started on the projects? I sounds like you're pretty committed to doing it so every day you wait is a day your forgoing rental income that you'll never get back. Unless your cash is currently deployed elsewhere, the opportunity cost of not doing it is huge!

    0Reply
  • Whitney Hill
    Contractor · San Diego, CA · Member since 2016 · 88 posts · 100 votes
    6y

    Another important consideration here is build cost. Most pre-designed plans put out by cities (and probably those on ADU Building Plans) have not been evaluated by a builder or value-engineered. For instance, most aren't designed with truss roof systems (much more efficient to build). The few thousand you may save could quickly evaporate.

    Also, the vast majority of standard plans require at least some amendments… e.g. a door or window needs to be moved due to site layout or constraints. So you’ll likely still need to pay for plans to be drawn up.

    1Reply
  • Brandon Carlson
    OP
    Real Estate Consultant · Glendora, CA · Member since 2019 · 314 posts · 95 votes
    6y

    Thank you all for your input!.

    @Matthew Forrest to answer your question, it's more of figuring out cost of the project. Ideally, if I can keep it between $85k - $95k all in I can move forward. 

    0Reply
  • Whitney Hill
    Contractor · San Diego, CA · Member since 2016 · 88 posts · 100 votes
    6y

    Hi @Brandon Carlson, just chiming in on the total cost. For a 750 sqft 2BR/2BA, all-in costs are going to be more like $210K if you go with a contractor. If you sub it out yourself, would imagine saving ~$40K. Either way, I don't think that budget is realistic unfortunately.  Here's a breakdown of costs:

    1) Design & Engineering: $6,000-10,000. Full set of construction drawings along with a site plan (even if you use a standard plan, it has to be situated & adapted to your property specifics). Design also includes Title 24 (required by CA), structural engineering, building code review with the city, permit processing, and a final estimate with a fixed guaranteed max cost for construction.

    2) Permits & Fees: $6,000-8,000. A good rule of thumb is $10-12/sqft in fees. While ADUs are now exempt from many fees, there are still several to consider. There are no impact fees for ADUs under 750 sqft. School fees are also still due, as well as sewer connection fees. 

    • Sewer: Connection fees are usually $2-4K, with recurring fees thereafter of about $1K/year. Note that a new septic system is likely required for an ADU if your property is on septic.
    • School: Usually $4/sqft, so $2-5K

    3) Site Work: $10,000. This number will of course be highly dependent on your specific property conditions. For a level lot, expect the sitework and foundation to cost $10K. If you need to start moving dirt and putting in retaining walls, sitework costs can quickly escalate.

    4) Vertical Building Construction: $187,500. With a 750 sqft unit, cost is about $250/sqft.

    5) Solar: $7,500. All standalone ADUs are required to have solar in place, with basic systems costing $7,500. Silver lining here is that you'll save on utility costs :)

    6) Other Costs: TBD. While typically not required, you may have additional costs come up if you require additional structural engineering, civil engineering, or soils engineering.

    8Reply
  • Brandon Carlson
    OP
    Real Estate Consultant · Glendora, CA · Member since 2019 · 314 posts · 95 votes
    6y

    @Whitney Hill Thank you for your breakdown. You are right, I may have to up my budget to complete this project. The design & engineering seems right, I gather a few quotes that we're in that price range. The city that I live in has their own water & power, and after reviewing permit cost, it falls in that price range. The construction cost seems a bit high, but I am not a contractor, to my understanding lumber is pretty pricing right now... not sure if that has anything to do with the tariffs. 

    Best,

    0Reply
  • Whitney Hill
    Contractor · San Diego, CA · Member since 2016 · 88 posts · 100 votes
    6y

    @Brandon Carlson Yes, the price / sqft is considerably higher for ADUs vs a home, since you're still incurring many of the same big ticket items like a kitchen and bath.... yet that expense is spread over a smaller area, driving up the cost / sqft vs a larger home. Same goes for permits, plans etc as it applies to the "all-in" cost / sqft.

    0Reply
  • Will BarnardPro Member
    Moderator
    Developer · Santa Clarita, CA · Member since 2008 · 15k+ posts · 10k+ votes
    6y

    Depending on site conditions and your finishes, I think $210k for 750sf ADU is on the high side for contractors. I am building an 800sf ADU in North Los Angeles for $150k all in (including all soft and hard costs) with higher end finishes.

    As others have stated, buying or getting free existing plans will likely require edits and likely do not come with structural plans or Title 24 and LID. Plus you need to know how to get through the plan check process which is no easy task for an inexperienced party, these city people will eat you alive. There is extreme value in paying an experienced expediter to get you through those hurdles!

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    4Reply
  • Jonathan Taylor
    Lender · Los Angeles, CA · Member since 2017 · 916 posts · 647 votes
    6y

    @Brandon Carlson Im currently converting an existing ADU so not the same but similar. Costs for my project are below:

    Architect and plans: $7500 (I'd pay more for the help and guidance he has given me, worth every penny)

    Permits, printing, and a permitting consultant (yes, he was needed): $2500

    Quotes for a build out $115 sq/ft for existing 300 sq/ft building: $34,500

    All in $44,500. 

    ADUs are a case by case basis and I would not trust a cookie cutter sheet from a company because I am educating myself on the building codes and they are tricky. As I am learning through my first reno and now this project, it depends on who from the city is looking at your plans. My plans have been stuck in the city for almost 8 months. Some plans get approved in 3. Who knows?

    1Reply
  • Brandon Carlson
    OP
    Real Estate Consultant · Glendora, CA · Member since 2019 · 314 posts · 95 votes
    6y

    @Jonathan Taylor congrats on beginning your ADU project!

    Thank you for the break down, to your point I'm realizing the architect/plans are a necessity, especially if they provide guidance with city ordinance. 

    Your quote on the build out is a great deal! 

    Will you be renting out the unit? if so, what kind of rents can you get. 

    Best,

    0Reply
  • Whitney Hill
    Contractor · San Diego, CA · Member since 2016 · 88 posts · 100 votes
    6y

    Another cross-reference on build cost, since we're seeing numbers all over the map in this thread... Maxable is a well-known aggregator of information in the ADU space and puts costs at $250/sqft for construction + $50/sqft for soft costs.  For reference, our margins as a GC are 15-20%... so if you manage it all yourself (and can keep things running as quickly as a good GC will), you could get closer to $200/sqft all-in.

    2Reply
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