When planning an accessory dwelling unit (ADU), it’s important to know where the ADU will fit and how big it can be… but that is just the beginning. There are a host of factors to consider when determining the best location for your ADU that will provide an optimal outcome & value. Does the ADU fit within required setbacks? How will the ADU be accessed? Are there views or environmental factors to consider? Is there a more favorable area to build due to slope, vegetation or utilities?
Sometimes the worst information is the best information.
Why is the worst info sometimes the best? You want to know about these potential cost pitfalls before you invest heavily in a project. It’s important to know about the all-in costs to make an educated decision when you compare ADU bids.
You can easily know the vertical building cost for your granny flat upfront. Since the structure and foundation are new, we can accurately estimate the materials and labor needed for the guest house. However, sitework costs can vary significantly for two homeowners building the same ADU plan, potentially by tens of thousands of dollars. We aim to identify any applicable costs for your project as early as possible. Sitework is often the least predictable expense in an accessory dwelling unit project unless thorough planning is done upfront. Fortunately, at SnapADU, we focus on details to eliminate surprises.
Based on our extensive experience building on ADUs, we know that $25K will cover sitework for a flat lot, provided we can perform tie-ins all within the bounds of your property. Our standard design/build process is to first perform a robust assessment of all utilities on site (prior to even starting floor plans) to determine, size, location and serviceability. With that info, we are able to provide firm pricing for site work so you have that information available very early in your project.
Read on to understand the most common additional costs and whether they will likely apply to your property. Below are 10 sneaky costs to watch out for when building your ADU in San Diego.
1. SEWAGE & LONG UTILITY RUNS: What is the type, location and distance of utilities?
Learn more about water, sewer, and gas connections for your ADU.
2. SLOPE: How much of a slope will need to be flattened for the ADU?
Our example costs for ADU sitework apply to mostly flat lots. If your property has a steep slope, terracing, or a hillside, creating a buildable pad for the casita can be more costly. For very sloped lots, grading and retaining wall costs can exceed $20-30K, including both the work and the grading plan. These costs depend heavily on your property’s specifics.
As a rule of thumb, check the “building corner differential” for your ADU. This measures the maximum elevation difference across the corners and indicates the type of grading and foundation needed.
- More than 1′ and up to 2′ differential: Deepened Footings – $4500 price (this is also triggered when ADU within 10′ of a slope or structure)
- More than 2′ and up to 4′ differential:
- Grading (when space permits) – ranging between $10-20K
- Raised Foundation (when space constrained) – ranging between $10-20K
- Beyond a 4′ differential: Custom design best suited for site constraints may involve a combination of methods, price varies
3. SOILS EXPORT & GRADING: For grade changes, how much will be required to get to a buildable pad?
Unless your lot is very flat, you’ll need grading work to prepare for an ADU. If we can’t keep the soil on-site, we’ll need to export it. In space-constrained lots, budget for soil export. Grading and soil export costs depend on property specifics and typically range from $5-10K. For more details, read about grading plans and soil reports for ADUs.
4. SURVEY: Is your lot challenging with unclear boundaries?
5. SOILS REPORT: Do you need a soils report?
Chula Vista, Poway, Encinitas and Vista always require a soils report, while Carlsbad and San Marcos require soils reports for units of 500 sqft or more. Declining a soils report means that no soils compaction testing will be performed by a Geotechnical Engineer, and the ADU will be built to the most stringent UBC design standards & thresholds. A soils report typically costs $3K and can be obtained as part of the ADU build process with SnapADU. Over excavation required by the city due to soils conditions can add another $4-5K. Read more about when you may need a soils report for your ADU.
6. SUFFICIENT ACCESS: How much space is available for bringing in construction equipment?
We will need to access the ADU location with construction equipment and materials. If there is not sufficient access, we will likely need to do some of the digging by hand and/or crane materials onto the site. If there is less than eight feet of clear vertical access (e.g. eaves could restrict the clearance) to the back yard or if the surrounding soil cannot support heavy equipment, this will typically increase cost by about $5-8K.
7. STRUCTURES & SURROUNDINGS: What accessory buildings and landscaping are in or near the desired building area?
You may have existing sheds, large trees, retaining walls, or hardscape in the area where you want to build the ADU. We will need to plan for relocation or removal accordingly, the cost of which will be highly dependent on the site specifics. For instance, removal of a large tree can be $2-4K.
8. SEPARATE ELECTRIC PANEL: Do you have a separate meter for the ADU?
When you add an ADU, you will need to add a separate electric meter for the ADU at a cost of $10,500 (this is something that was not historically enforced, but SDGE now requires ALL new construction ADUs to have a separate meter). There are additional factors that may require more work on your electrical service and you can read more about electric panels and service upgrades for ADUs.
9. SOLAR: Is there solar power on the primary dwelling?
Most additions and new buildings in California are now required to meet net-zero electricity guidelines. Particularly for larger units and/or in hotter climate zones, this means your ADU plan must include a solar energy system with capacity to generate enough electricity to offset the ADU’s electrical usage. You can meet this requirement by adding more capacity to an existing system or adding a new system for the ADU. A solar panel system for an ADU typically costs between $12-18K installed, though each city has their own requirements and your ADU size will also impact the size of system needed. Also note that you can take advantage of a 30% federal tax credit on the cost of the solar system in the year it goes into service, so you will get back thousands at tax time. Read more about solar on ADUs.
10. SPRINKLERS: Are there sprinklers in the main house?
ADU regulations require that, if the main home has sprinklers, any ADU built on the property must also have a fire sprinkler system. This is usually the case in high fire zones. If you go >1200 sqft – which you can in Poway – you will also need fire sprinklers. A sprinkler system design & installation in an ADU costs $5-10K depending on the size of the dwelling unit. Another factor here is that adding a sprinkler system will increase the water line size requirements, which can add significant expense. Read more about fire ratings & sprinkler systems.
Other watch-outs that can result in additional costs
Property Specific
- Easements. If you have an easement on your property, you will need to request a title report to verify the location of the easement. Read more about easements.
- Illegal construction. If your property has existing structures that are unpermitted, you may need to bring them into compliance with current building codes.
- HOAs. In areas where an HOA is in place, they may require some upgrades in the exterior of the ADU, such as a tile roof or custom trim work. Read more about HOA requirements.
- Swimming pool. If you have a swimming pool on your property, you will need to secure it in order to get occupancy for your ADU.
Special Zones
- Coastal zone. Properties in the coastal zone will usually require minor use permits. Read more about the coastal zone.
- High fire overlay zone. These areas may require additional construction requirements such as boxed in eaves and fire-rated windows. Read more about fire requirements.
- Special Vegetation. Environmentally sensitive lands will have special requirements for building. The level of classification, for instance Potential Sensitive Vegetation (PSV) vs. Sensitive Vegetation (SV), will determine what is possible. Check your status on ZAPP.
- Historic Review. Properties designated historic, or even properties over a certain age, may trigger additional reviews. Read more about historic reviews.
Special City Requirements
- In-person submission. Certain jurisdictions require in-person submission of plans, which means more printing and labor costs as we must produce paper plans and physically take them into the city. Check your city specifics on our service area page.
- Storm water management. Some cities, like Vista and Encinitas, require site drainage and storm water mitigation for ADUs. Finish grading work may be required to create a bio-swale, drainage basin (bioretention basin) or other contouring work to handle on-site storm water, which will cost around $5-10K in most cases. Read more about stormwater management for ADUs.
- Street tree requirements. The City of San Diego requires inclusion of street or interior trees when there are three or more dwellings on the premises. Typically you must have 1 canopy tree for every 5,000 sqft of lot space, plus 1 tree for every 30′ of street frontage, excluding curb cuts. If your existing trees are not sufficient to meet requirements, this can add a cost of $1,500-$2,500 per tree that must be added.
- Existing floor plan measurements. Poway requires a floor plan of the existing home, while some HOAs and Coastal processes may as well. This costs around $750 to produce.
- Metering. Some cities, like Oceanside, require a private water meter, which will run about $1,500. More about water connections & meters for ADUs.
Financing
- Construction loan coordination. If you are obtaining a construction loan, there will be significantly more required paperwork and inspections. SnapADU handles the processing of loan documents during design and coordinating with the lender inspections and draws during construction, which adds about $3,000 in cost. Read more about ADU financing.
So what’s next?
Whew. It’s a lot to consider, and we haven’t even covered how the design features of a custom ADU will affect the build cost. The type of siding, roofing, windows, floor plan layout, and finish materials will of course impact your price as well. Our standard designs are designed to keep these build costs predictable. If you do choose to go semi-custom, we will ensure you have a clear picture of cost every step of the way.
Do you know the approximate cost to add a separate meter for electric and water to an adult in LA? Does a separate address need to be created before this can be done?
While we’re not familiar with the details of LA (we specialize in San Diego), it’s like the costs are comparable to what we list in our blog:
The separate electrical meter for a new accessory dwelling unit will typically cost around $12,000. More on electric panels and upgrades.
As for ADU connection to water service, the water line that services the ADU will always be connected to the private water service line between the water meter and the water regulator before the service enters the primary residence. This ensures that the ADU water service is not affected by the regulator that throttles pressure to the primary residence. A secondary water regulator will be installed on the water service line before it enters the ADU.
Water service can be metered privately by means of a metering device that is located on the ADU. Upon request, SnapADU will provide the preparation to accept a metering device which can be connected to WiFi and monitored remotely on your smartphone or computer. We recommend this product as a WiFi enabled water meter.
Separate addresses are typically required for ADUs, and utilities reference these addresses as part of their process.