When it comes to building an ADU, there are a few different construction options: stick-built and prefab ADUs are the two most common. The term ‘stick-built’ refers to the traditional method of construction; building the entire structure on site from the foundation to the roof. In this case, the ‘sticks’ refer to the pieces of lumber used to frame the ADU structure. Learn about ADU meaning here.
Recently, there has been a new industry trend developing which allows the majority of an ADU to be built in a factory. These types of ADUs may go by a few different names including manufactured, modular, panelized, factory-built, or most commonly ‘prefab ADU’ (pre-fabricated). There are pros and cons to both methods, and it’s worth understanding them in detail before selecting which is right for your situation.
Here at GreatBuildz, we speak with clients every day who are considering building an ADU on their property. GreatBuildz is a free service that connects homeowners with reliable, pre-screened ADU contractors, then provides ongoing project support to ensure a stress-free experience.
Is prefab or stick-built cheaper?
Because the cost of building an ADU is substantial, most people want to know which type of ADU is cheaper. In order to answer that question accurately, a homeowner must be willing to compare the various options in an ‘apples to apples’ way. To get a price on an onsite constructed or stick-built ADU, a homeowner would have to get one or more estimates from an ADU contractor or general contractor.
For a new ADU in Los Angeles or Southern California, you can expect to spend $250-350/sf on average (the bigger the ADU, the lower per square foot). The total costs include developing plans, permit costs, digging and pouring a foundation, all utility hook-ups, and of course, the construction of the ADU home itself.
Costs aren’t quite as straightforward for a manufactured or prefab ADU. Most factory-built ADU companies will quote you a price on one of their specific units. They can probably tell you exactly what you get inside the ADU, including various finishes & materials. Having this cost number is a good start and can often be lower than the cost of a site-built ADU.
However, there are a few major things that may or may not be included in this price. Sales tax and options/upgrades may be extra. The cost of shipping or hauling the unit from the factory to your home might be an extra cost; as is the cost of craning the unit from the street to your backyard if necessary.
Also, many prefab units will require you to hire a local builder to install a foundation for the unit to sit on. You’ll also need this contractor to run all your utility lines to your new ADU, which typically include sewage, water, electrical, and gas. The foundation & utilities are often not included in the factory-built ADU price and can easily cost an extra $30,000 to $50,000 extra. So, please make sure you include all the pertinent costs of a prefab ADU in your analysis so you aren’t surprised later by the extra costs.
Are prefab ADUs faster to build?
A stick-built ADU will have to proceed in a linear schedule, meaning you start by creating plans, then submitting them to the city for plancheck and permits, and finally construction. The construction portion of the project will require between 3-6 months depending on the size and complexity of your ADU. And bad weather could cause delays with site-built ADUs.
A prefab ADU timeline can be condensed somewhat because the unit is being built in a factory. That process might take 1-3 months, and you can simultaneously be doing the site work at your home in preparation for the ADU to arrive…foundation, utilities, etc. It might take up to a week or two for delivery. Finally, the installation of the ADU onto the site depends on which specific prefab ADU option you choose. You can expect start to finish construction to take roughly 2-4 weeks, however some companies may be able to install in just one week!
What are the risks of going the prefab route?
Stick-built ADUs are being constructed the same way your house was built and based on today’s building code. It’s relatively clear what you’re getting when you build in the traditional way. Lenders are comfortable with the building method and should have no issue providing financing. And appraisers will have no issue evaluating this structure when it’s time to sell or refinance. Finally, once a plan is permitted through the city of Los Angeles or other jurisdiction, you can be confident it was designed to withstand weather and hazards like earthquakes.
Prefab ADUs may still be a bit riskier in this regard. Until they gain more acceptance, there could be issues with financing or appraisal. Since every prefab manufacturer is different, it’s hard to fully understand their construction methods and how they vary from each other. Certainly, if an ADU manufacturer has received approvals for their models by your local state or jurisdiction, they would seem to be designed to withstand local conditions. It’s important to make sure that your ADU company has installed more than a few ADU’s in your area because they have to be inspected by the city during construction and you don’t want to be the ‘guinea pig’ if issues arise.
Additionally, before making the commitment to purchase a pre-fab or factory built ADU, check on insurance. First of all, check with your own home insurance agent to determine if they’ll be willing to issue you long-term homeowners insuance on your proposed pre-fab structure; and inquire about the costs. Also, make sure to get specific documentation about both the insurance and warantee that the pre-fab ADU company offers. You want to make sure you’re covered if there is an accident during installation or if you have issue with the home in the first year or more.
Related: How to Properly Legalize an Unpermitted Los Angeles Garage Conversion/ADU
Are modular ADUs more convenient?
Modular ADUs can be convenient because the amount of on-site construction is reduced, but there are a few scenarios that could make this method a hassle or totally infeasible. If the prefab ADU you’re considering doesn’t meet city requirements like height, setbacks, etc, then that may be a non-starter. Also, if these ADU plans haven’t been approved in your jurisdiction, the plan approval process might be lengthy and not worth the wait.
Additionally, the following location/geographic constraints might prevent you from installing a prefab ADU unit on your property: trees or utility lines in the way, hilly or narrow streets that make delivery impossible, or a site location that’s too far to reach with a crane. Prefab units are much better options for large, flat properties with plenty of room for delivery and assembly, while stick-built ADUs can accommodate a wider variety of property types.
Are prefab ADUs more customizable?
Most prefab ADU companies have several models to choose from depending on your desired size and bedroom/bathroom count. However, because they are modular and built in a factory, many of these units have minimal ability to be customized (except maybe the finishes inside the ADU). This is the opposite of standard stick-built construction where you get to design the plan/layout of your ADU to your exact specifications and needs. With a traditional ADU, you can design it in a style to match your home, customize the size of windows, the roofing material, the size of the kitchen/bath, location of patio doors, patio covers, etc.
Recently, many California jurisdictions have been requiring solar systems on all new buildings, so you should check to see if that’s required so you can ensure a prefab ADU can accommodate that. Another concern for some people is that factory-built ADUs are really difficult to modify, renovated, or expand in the future, which isn’t an issue with stick-built construction.
Related: If you’re considering converting existing space (like a garage), you’ll likely be using a traditional construction method.
Are prefab ADUs more valuable?
Foretelling the future is impossible, so it’s hard to know whether prefab ADUs will be more or less valuable over time. An ADU’s value over time will likely depend on its quality and durability. With stick-built ADUs, there is some level of confidence that they will appreciate over time just like any other single-family home. With prefab ADUs, their long-term value will depend on the quality of construction.
Some people believe prefab ADUs will have a very high level of quality because they are built in the controlled and precise environment of a factory. However, in the past, manufactured homes have generally had a bad reputation and were associated with mobile homes which never had the same value as standard construction homes. We just won’t know for some time whether the materials and construction methods of prefab ADUs will withstand the test of time.
Related: Top 50 Frequently Asked ADU Questions in Los Angeles
When it comes to finding the best ADU contractor in Ventura, Los Angeles, Orange County, or San Diego – GreatBuildz is simplifying the contractor search. GreatBuildz is a free service that personally connects homeowners with reliable, thoroughly screened general contractors and provides project support from start to finish.
Call now (818.317.3567) to chat with a real person about your next renovation project or visit our website for more information: www.greatbuildz.com
