How to get good new home/ADU construction specifications?

Question

Hi BP community,

So my friend is spinning their wheels a bit. They are planning to put a detached ADU (accessory dwelling unit) on the property containing their SFH (single family home) in southern California.  They already have architectural plans.

They are now writing detailed specifications to ensure they get what they want but also help any potential contractor bid correctly and reference the specifications in a SOW and/or contract.

They've been scouring various resources to help them.  It's easy enough to write specs for cosmetic materials (e.g., "The toilet shall be make / model # XYZ123 and be white in color"). But looking at some example specifications on the Internet for things like the foundation, they found clauses like this which seem important but which seem like they require a decent level of expertise (e.g., it would help you are a general contractor which my friend is not):

Joist framing. Joists framing into the side of a wood girder shall be supported by approved
framing anchors or on ledger strips not less than nominal 2" x 2" (51 mm x 51 mm).
(Section XYZ13.ABC IRC)

1) So the question is - what have you done to get the right level of detail in your specifications, especially for an ADU, which is a smaller building than a single family home but would probably require the same level of detail to be constructed and bid on correctly? Have you hired outside help? Since they're based in CA, it seems like you'd want to take extra care to ensure your building matches the appropriate state and local codes.

2) Also, is the level of detail in the "joist framing" example is too much for a specification intended to get an accurate bid from potential contractors and serve as a line item in a SOW contract?

Sebastian Marroquin · Answer

Great advice on here:

I would say: your friend would only have to understand the building code and specifications of framing or foundation for example- if he will be the GC (general contractor) and will hire subs for the full job...

or if he plans on learning every detail to then be a consultant on other future projects.

Think about this almost as a "cooking recipe"

If you needed a specific cake baked and you purchased a recipe for it (i.e. the approved building plans): then you would interview 3 different chefs that would have a license and therefore have the "know how" and experience to make it and they would have to understand every item to bid on it. For example: you or your friend as the client - would not have to understand items like: nutmeg... or baking powder and how much of it to buy... but the chef would have to understand it, know how to use it and estimate how much the "cake" would need.

So, the contractors would have to understand all the building material needed for the ADU, timing, building codes, depth of foundation, beams and brackets to use... etc. and where they would need detail would be: on the finish work: i.e. tile, window type, flooring, cabinets (type, texture, color) etc, anything that would be considered aesthetic (as one tile could be $2 per sq ft and another would be $10 dollars per sq ft) and even choosing one or the other would entail more labor work or less and hence the labor costs could change with every decision made.

You could get a 3rd party company to give you : material costs estimation also :) and then you could be bidding just on the labor work and timing!

Let me know if you have other questions or concerns. Sebastian

Sue Hough · Answer

@Bruce P.. There is no need for you to specify every building code detail, as it is accepted and understood practice to include the term “Code compliant” or “build to code” on your SOW.  If your contractor is not familiar with the term, that is the best litmus test to find a different contractor, whether it be an electrician, plumber, carpenter or any other.  Seasoned contractors have a full working knowledge and understand which building codes are applicable (or it is their responsibility to clarify which codes apply) and fully understand it is expected to build everything in compliance, you do not need to spell it out.

There are always instances which I am unfamiliar with a certain code (as all contractors) and how it applies. Recently we were framing a new home and I was unclear as to the specific spacing which was required for “hurricane clips” on the framing.  It was my responsibility to find the correct code and be in compliance.  Do not rely on architects, as many of them do not know the small detailed codes. It is not their responsibility to spell out every code, or your blueprints would be 1000’s of pages :).

Good luck!

Bruce P. · Answer

Thank you @Sebastian Marroquin

Bruce P. · Answer

Thank you @Matt Lewis @Sue Hough @Whitney Hill (and @Colin L. for the link) - makes perfect sense!

Whitney Hill · Answer

To echo @Sue Hough, the contractor will provide an important perspective on building to code. They will also help ensure you can build the project on budget, which is why we like to get involved during the design phase if possible to work hand in hand with the architect to make adjustments as needed before finalizing construction drawings.

In this case since you already have plans... sending them out to bid with 2-3 contractors should turn up fairly comparable quotes, so pay attention to how they each handle processes, what systems are in place etc... that will heavily impact timeline and adherence to budget.

For reference, figure on $275-325/sqft for all-in ADU project costs…so an 500 sqft 1BR standalone ADU would typically cost around $160K.

Pre-construction costs: $10K for design, construction drawings, title 24 energy report & electrical layout, permit processing. $5K or so for permits, assume 10X the sqft of ADU (500 sqft = $5K fees).

Construction costs: $250/sqft + $10K sitework (e.g. preparing the building pad, connecting utilities, plus a small amount of landscape and concrete work)

Matt Lewis · Answer

@Bruce P. - Hey Bruce!

I’m a Designer and GC in Seattle. Sounds like your friend needs an Architect. They usually go into specific detail about every element of the physical construction. Your friend can work with them to spec finishes to make sure everyone is on the same page throughout the build.

That being said I’ve had Architects mess things up and Subs mess things despite everything looking as if it’s laid out ahead of time. Communication with each Sub is key!

How to get good new home/ADU construction specifications?

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