Assessing Site Conditions & Utilities for Your ADU

When your accessory dwelling unit is complete, what guests and visitors will see is the new exteriors and interiors of the ADU space. But before your ADU project breaks ground, your existing property conditions and utilities can often be far more important for your project.

Let’s take a closer look at some of the key site-specific considerations for your ADU project.

When construction begins on an ADU, the builders will have to dig down before they can build up. As a result, the existing conditions of your backyard are important to know for your project.

You may run into questions around one or more of the following areas when considering your ADU project. The Cottage team is happy to help discuss your options and walk you through the feasibility for your ADU project based on your specific site. Some pre-existing site conditions can make your project more expensive due to the construction site work needed—others can make your project infeasible from the beginning.

Here is a quick summary of the core site condition questions that we like to ask about:

Access to your future ADU construction site is an important factor to consider for your build. The easier it is for your builder to bring in larger pieces of equipment and materials such as a dirt excavator or wooden roof beams, the smoother your construction will be.

Your ADU builder will be looking for wide and straight access to the build site wherever possible. Wider driveways are typically the easiest, while side yard access is also common.

Don’t have access to your backyard or garage that sounds this simple? The Cottage team can help you discuss your options, as the builders certainly can and will work in tighter spaces—this may just require more manual labor by hand for your project.

Poor drainage is a key consideration for your ADU, as standing water and/or flooding concerns can cause significant damage to your ADU and also your main home.

Think back to the last heavy rain—did it cause rainwater to pool or flood a certain part of your backyard? This is good to know ahead of time to ensure that the foundation and location for your ADU takes this into account. For most projects, this means smart placement of the ADU and a thorough site grading plan before construction. However, for some more severe drainage issues, this may mean a special type of foundation for your ADU or a professional drainage plan may be required.

For garage conversions, rotting or moldy wooden framing close to the foundation is a telltale sign of drainage issues on the property. Flagging this early to the Cottage team or contractor is important to ensure that the team properly plans for these concerns.

Heritage trees are important to our neighborhoods and environment, whether in a public park or in your private backyard. Many cities have regulations restricting the cutting down or aggressive pruning of certain size or species of tree in your backyard—and these rules can apply for your ADU construction project.

For example, most Northern California cities protect native redwood trees, restricting homeowners from cutting them down or building an ADU within a certain distance of the tree trunk. Other cities require a licensed arborist’s report to verify the tree’s species and condition, and provide a tree protection plan for your ADU construction.

Have a large or known protected tree in your backyard? Let your ADU team know early on in the process to design accordingly. Cottage can help you design your custom ADU in a way that fits perfectly with your existing foliage or structures. Check out this great example here of an ADU built in the shade of redwoods.

How much slope there is at your intended ADU project can significantly impact your budget. Leveling the future ADU site can require additional grading and/or soil compaction work up front as well as the potential for additional foundational support to prevent future drainage and lateral movement of your ADU unit.

These costs can range significantly depending on the significance of the slope and your overall site conditions. Make sure to let your ADU team know about the amount of slope in your backyard space if it involves your intended ADU location.

Related to slope, your property may already have retaining walls to hold soil and ground in place in situations where there are elevation changes in your backyard.

Optimally, your ADU location will be far enough away from any existing retaining walls to not involve them. If your intended ADU location overlaps with an existing retaining wall, be sure to note that down—retaining walls can be costly to remove and relocate, so it’s important to know that potential cost upfront.

Unlike other site conditions that can be handled with smart construction techniques and/or additional project budget, existing power lines can be an immovable blocker for your project if you don’t plan around them.

Most times, overhead power lines indicates that the local power company has easement access to the power lines and equipment (such as utility poles) that are on or span your property. In most cases, you are unable to build any habitable structure—including an ADU—within the designated property easement area. Typically, these easements stretch either 5 or 10 feet from either side of the power lines.

Luckily, most power lines span the very rear of the property or between properties, thus limiting their impact. However, definitely check your title report and other property deed records to see the extent of any easement on the property. One other easement to look out for—sewer easements may be hard to notice, but they can be up to 20 feet in width.

Just as building a new pool requires a municipal permit, building an ADU on top of a former pool requires additional permitting documentation. Infilling a former pool space requires significant soil compaction and/or the full demolition of the pool so that the foundation will be able to permanently support the ADU built on top.

Note that some pool-related contractors that may be unaware of your intention to build an ADU on the property may quote you for only demolishing the top half of the pool, rather than the entire pool demolition so that it’s ready for ADU construction.

If you’re building near your ADU, keep in mind that almost every city has a limit to how close you can build to the pool itself. This minimum distance to build from the pool can vary by municipality, so make sure to flag this question when discussing your ADU project.

For garage conversion ADUs, the conditions of the existing structure are important for your project feasibility and build. Here’s a few key elements to consider:

When was the structure built? What kind of shape is it in? Common issues Cottage has seen with garages include leaning walls, sinking roofs, drainage issues, and cracked foundations. If your garage has any of these things, you should definitely note it to the ADU expert, designer, or contractor you are working with.

For earthquake prone areas like California, it’s common to see cracks in the concrete slab foundation of your garage. While this does not necessarily mean that your garage’s foundation needs to be re-poured, larger cracks can indicate structural issues with the garage. In some cases, this may mean the garage will need to be torn down before a new ADU unit is built.

These are the concrete ledges that sit on top of the concrete foundation of your garage, and the wall framing sits on top of these ledges. The footings should be in good condition in order to be re-used for your ADU. Don’t see a footing or the framing is built directly on top of the concrete floor foundation? This likely indicates that the structure will need to be rebuilt.

Proper wood framing can last longer than a century and forms the backbone of most homes and garages. However, overexposure to weather conditions such as rain can lead to rotting wood framing that will need to be replaced or demolished entirely. Termite and other animal damage can also reduce the longevity of your garage space. Take a look at the condition of your wood framing to see if you see any signs of wear and tear beyond the norm.

Is the roof in good condition, or is it caving in? Over time, garage roofs can suffer from the same weather damage as your main home. But unlike your main home, garage roofs can often go unnoticed or ignored for years.

Your utilities are the veins and arteries of both your existing house and your future ADU. City planning offices will be checking to see that utilities can support the new ADU space.

Here’s what they’ll be looking for:

No matter which utility under consideration, the further the utilities are from your ADU, the longer the trenching distance and materials required to hook up your ADU to electricity, plumbing, and gas.

In addition, where you have to trench can make a difference; trenching through 50 feet of solid concrete requires significantly more labor and cost than trenching through that same 50 feet but through soft garden dirt. Lastly, if your plumbing has to travel against gravity, that may require additional trenching work or a sewer ejector pump to force the plumbing to travel against gravity and exit to the street.

The new lights and appliances in your ADU require additional power that your existing home may or may not be able to provide. Most ADUs require that the main home’s electrical panel be at least 200 amps. If you’ve updated your existing electrical panel in the past decade, you may already have at least this much power already ready to go for your ADU.

However, many older homes have 150 amp or even 100 amp panels that will require a panel upgrade. This cost can vary depending on the municipality—check with your ADU team if you know what your existing meter capacity is.

For rental ADU units and ADUs on multifamily properties, many property owners opt for a more expensive dual gang or separate utility panel for the ADU in order to measure the energy usage separate from the existing home. This can be useful to track usage of different tenants separated by unit.

However, these separate panels and the electrical wiring hook-ups required to be installed by a contractor and the local utility company (such as PG&E in the San Francisco Bay Area and the LA DWP in Los Angeles) can add thousands if not tens of thousands of dollars to your budget and can delay your project for months. If this is a consideration for your ADU, don’t delay in flagging it to your ADU builder.

Your water meter measures the volume of water flow into your existing home and eventually, your ADU. The biggest concern at the initial pre-construction stage is understanding whether the existing width of your water piping can handle the additional flow of your ADU’s water usage.

While it’s possible to split your water meter between the existing home and the new ADU, this can be costly. Check with your ADU builder to see whether the benefits outweigh the costs of having a separate water meter installed for your ADU.

As many cities move towards all-electric ADUs, the gas meter is becoming less and less important for many ADU projects. However, in cities such as Los Angeles where ADUs can still have gas appliances installed, your ADU builder will have to dig trenches and lay additional gas lines to support those appliances, which can add to the labor and material costs.

Flagging what kind of appliances and whether gas is a must-have for your ADU project will help you arrive at the most accurate ADU estimate.

It can be easy to overlook, but the existing conditions of your backyard space or garage tend to be the most important factors for the relative ease or difficulty of your project. Cottage has worked with homeowners across the spectrum of property and utility conditions, and can help you decide the best way forward for your ADU project.