ADU Erosion Control

A vital part of any building site plan, including an ADU, is erosion control and stormwater management. Its lack can lead to serious issues such as water pollution, soil erosion, and, of course, flooding. In some areas of California, you can’t get a building permit for an ADU construction if your project plan doesn’t include anti-erosion measures.

In our article, we’ll look at the main dangers of erosion for accessory dwelling units, the construction characteristics of stormwater management systems, and what to do if erosion has already affected your property.

Stormwater Management 101

Rainwater is one of the biggest causes of flooding, erosion, and pollution. It can do irreparable damage to buildings and driveways. Almost every major city requires homeowners to manage rainwater runoff with the help of so-called “bioretention basins” — special systems that collect water. They resemble ditches or pools whose size depends on the impervious surface area. Water accumulates in them and gradually seeps into the ground.

Erosion Effect on ADUs

The main goal of an erosion control system is to drive clean water away from the house area. It helps the property owner reduce the damage caused by rainfall, such as ground destabilization or sediment discharging.

High-quality stormwater management can help keep sediments in place and prevent them from sliding downhill. Thus, it improves property conditions, removes the necessity of additional costly cleanups, and helps save the local underwater ecosystem.

Also, erosion, humidity, and sediment discharging often lead to postponing the construction process. Because of this, materials stay in stockpiles, and decay because of the wet weather. Thanks to stormwater management, you’ll be able to prevent all this.

For the successful completion of your ADU anti-erosion system, you’ll need to ensure that it fits all the local sediment control regulations. The best option is to hire qualified ADU professionals who will do a top-notch job in complete accordance with all the requirements.

Factors That Influence Erosion

The erosion process depends on many factors.

Let’s name the most important of them:

• The slope. If it’s large and steep, the erosion effects will be more profound;
• The disturbance characteristics — its length, strength, and nature;
• The type of soil. Soils with higher clay percentages can bring more harm to the environment. If the soil has lots of sand, it may increase traffic risks and cause drainage issues;
• The climate in the area. Frequent rains and strong winds can increase erosion. So, if your property is located in a humid or windy climate, you’ll need to take this factor into consideration, too;
• The property size and landscape. A stormwater management system is easier to install on larger property lots. The presence of a slope heading down to the road, on the other hand, makes it way more difficult. Big village lots with plenty of greenery often don’t need any special control measures.

Ways to Prevent Erosion

It’s always better to prevent a problem than to fix it. So, when planning an accessory dwelling unit project, you’ll need to pay close attention to the stormwater management system. It will help you increase the safety of the house and the environment. During the system installation, you should avoid cutting plants as much as possible. Try to cut them only in the places that you’re going to use for ADU construction work. Plants’ roots prevent erosion very efficiently, so the more vegetation you have on your lot, the better.

If you strongly want to remove plants, at least delay it till the beginning of the unit construction process itself. Also, pause all building activities involving ground disturbance during rainy weather.

Erosion Control is Vital for ADUs

Often, people think that stormwater management is something unimportant for ADUs because of their small size. But if there’s a pool, a driveway or other waterproof surfaces near the unit, it’s completely necessary to install a rainwater management system. Without it, water can cause lots of damage to your property. So, we strongly encourage you to include an anti-erosion system in your ADU site plan.

ADU Erosion Control Defined

Usually, erosion control of ADUs consists of gutters. Stormwater accumulates in them and flows into a basin. From it, the water seeps into the ground. Such a system needs constant maintenance. Regularly make sure that nothing obstructs the water flow and that the basin’s condition is good.

ADU Erosion Control Costs

An average stormwater management system suitable for ADUs, be it a drainage basin, a bioswale, or any other one, costs approximately $5 to $10. Lots of factors determine its exact price – construction characteristics, quality, the ADU project type (attached, detached, etc.), and others. If the density of buildings in the neighborhood is high (for example, in a city), there’s an increased risk that the water can run off to the neighbors’ lots, which will result in lawsuits. So, a high-quality erosion control system, although more expensive, is completely worth its price since it can prevent even bigger expenses.

Erosion in Progress: The Way Out

Some homeowners noticed the erosion after the ADU was completed. If it has happened to you, you can solve this problem with the help of so-called “micro piles.” To make them, you’ll need to drill holes in the ground, put pipes into them, and fill them with grout. The diameter of the hole can range from 2 to 8 inches. The bigger the damage and the lot itself are, the wider the micropiles should be.

Other foundation repair methods for ADUs include:

1. Tieback anchors;
2. Slope stabilization;
3. Slab leveling;
4. And so on.

Usually, specialists combine those methods with micropiles, thus increasing their effectiveness.

But if the issue is really grave, you’ll probably have to remove a part of the ADU and create a completely new foundation. This procedure is long and costly, so it’s only a last-resort measure. You shouldn’t do it without consulting with a specialist.

However, even if there’s erosion in the foundation of your ADU, it doesn’t mean that this building is beyond saving. You can seal all the cracks and install anti-erosion barriers – for example, liners or pavers. After that, address this subject in a consultation with support specialists and ask them which repair method is the best for avoiding the further damage.

Frequently Asked Questions — FAQ

Do I need a building permit for an ADU in California?

Yes. The eligibility for an accessory dwelling unit in California depends on having a building permit. Permitting is necessary even for garage and basement conversion ADUs. To obtain this permit and thus get eligibility, you’ll need to comply with all local ADU regulations and safety rules. You’ll have to take this into consideration during the ADU planning process.

What is the size limit for an ADU in California?

It depends on the accessory dwelling unit type. Attached ADUs can be up to 850 sq. ft, detached ADUs — 1,000 sq. ft, junior ADUs (sometimes referred to as guest houses) — 500 sq. ft. The height of an ADU should not exceed 16 ft. If your ADU project exceeds those limits, you won’t be able to get a permit. Submitting all these limitations is necessary for permitting the project. There are also other factors that determine the size limit – for example, the property’s square footage — the bigger it is, the larger the building can accommodate.

How close to the property line can you build an ADU?

You can construct an accessory dwelling unit with 4-ft side and rear setbacks. If you don’t have these setbacks in your project plan, you won’t be able to get a permitting document.

How much does an ADU cost in Sacramento?

The prices of ADUs vary depending on their type, size, materials, location (for example, whether the building is located in a village or a city), and many other factors. Attached and converted ADUs are usually cheaper than detached ones. Typically, an ADU in California costs from $200,000 to $400,000. However, there can also be cheaper or more expensive accessory dwelling units.