Pre-design ADU plans

[Brandon Carlson]

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. 

[Whitney Hill]

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.