Common Issues with Accessory Dwelling Units: How to Avoid Them

At a Glance: Avoid ADU pitfalls: zoning/permits, setbacks/parking, utility connections, design integration, neighbor concerns—plan early with pros for value-adding backyard homes.

Introduction

Accessory dwelling units (ADUs) have become increasingly popular as homeowners seek to maximize their property value and create additional living spaces. Whether you’re planning to build a backyard cottage, convert a garage, or add an in-law suite, being aware of common pitfalls can save you time, money, and headaches. This guide will walk you through the most frequent issues encountered with ADUs and provide practical solutions to avoid them.

Zoning and Permit Challenges

One of the most significant hurdles in ADU development is navigating local planning and zoning laws and obtaining necessary permits through the building department. More often than not it is the planning and zoning side of things that ends up being the primary culprit resulting in the failure of an ADU project to take off. This is because many homeowners discover, sometimes too late, that their plans conflict with local regulations. The vast majority of difficulties revolve around complying with zoning concerns such as lot coverage restrictions, setback requirements that limit buildable area, height restrictions when compared to the existing primary residence, parking requirements, and historic district regulations, which can add a whole additional layer of complexity.

But sometimes it’s as simple as an issue with the property itself, specifically that the site and its zoning district simply does not allow for ADUs in the first place. To combat this, the state of Colorado recently passed an extremely important addition to its legislation. House Bill 24-1152 significantly impacts the development and proliferation of Accessory Dwelling Units across the state. This bill was signed into law in 2024 and aims to streamline and promote the construction of ADUs by easing certain zoning restrictions and offering incentives for homeowners.

For example, here are two Key Provisions of House Bill 24-1152:

1. Zoning Flexibility: The new law mandates that local governments revise zoning codes to permit the construction of ADUs in residential zones where single-family homes are allowed. This change removes previous barriers that restricted ADU development in many neighborhoods.
2. Streamlined Permitting Process: The bill requires municipalities to simplify and expedite the permitting process for ADUs. By reducing bureaucratic hurdles, the law aims to make it easier and faster for homeowners to get approval for their ADU projects.

However, even with this bill’s passing earlier this year, the legislation has a ticking clock for initiation, meaning building jurisdictions still have until June 2025 before the bill must be fully implemented. Because of this, many homeowner’s ADU dreams may have to go unrealized until then.

How do you combat this so that your project moves as smoothly through the zoning process as possible, or at least uncovers major conflicts before too much money is invested? First thing’s first, before even beginning any design work, research local zoning laws thoroughly to see if your zoning district currently allows for ADUs or if you will need to wait until that 2025 date. It is also highly recommended that you consult with a local architect that is familiar with ADU regulations as this kind of familiarity brings a plethora of nuanced information to the table. One of the first things your architect will likely recommend is that you schedule a pre-application meeting with your jurisdiction’s planning department. This meeting is a great way to get one-on-one assistance with a planner that will do preliminary research on your specific property and relay any potential project blockers, or worse, project killers.

Design and Layout Mistakes

ADUs are definitely an example of “compact” architecture as they typically range anywhere from 150 square feet up to about 800 square feet. Designing smaller can be an extremely fun and exciting exercise that allows one to see firsthand just how small of a space can be laid out to be properly lived in and provide all of the basic needs for a specific homeowner.

Compact architecture can also lead to poor design choices, resulting in uncomfortable living spaces and reduced property value. You do not want your project to suffer from inadequate planning in the early stages, and so once more, consulting an architect will help negate those design issues. An architect will be able to take your ideas and make them a reality with special consideration to many aspects that may otherwise go overlooked.

When space is limited it is critical that basic design concepts be considered such as  privacy, sufficient natural light and ventilation, flow between spaces, maximizing storage needs, mechanical equipment and much more. On these specific subjects your architect may recommend solutions such as proper orientation of the ADU entrance, clerestory windows or skylights, an open kitchen/living/dining space, built-in storage, compact laundry spaces, and even unique thoughts of where to locate your water heater, such as in the attic or in a cabinet above the toilet. And if your ADU is going to be attached to an existing structure, it also needs to be properly integrated from construction, insulation, structural, and utilities standpoints.

Infrastructure and Utilities

Connecting an ADU to existing utilities often presents unexpected challenges and costs. Similar to the discussion revolving around zoning, each permitting jurisdiction has unique requirements. Another unique jurisdiction, for example, is Wheat Ridge as their Sanitation District actually requires that the sewer for a detached ADU be connected directly to the city’s sewer line, rather than to the home’s existing sewer line.

Some more common utility-related issues include:

• Inadequate electrical service capacity
• Sewer line complications
• Water pressure problems
• HVAC sizing difficulties

In order to negate these it’s important to make sure that you have as much information regarding your utilities as possible, and as soon as possible. For example, when requesting a survey it is extremely helpful to make sure that the existing site utilities are documented. Also, check your electrical panel to verify what size it is, as this could result in the need  to increase your home’s electrical service size, or the need for an entirely separate service that is tied to the ADU only. To hark back to the zoning conversation once more, some jurisdictions will not allow you to have a separate service for your ADU, or if they do, they may require that your ADU has a separate address.

On the subject of heating and cooling, ductless mini splits are most often the way to go as they are compact units that can mount to the exterior wall of the ADU, and they do not require ductwork that is part of conventional forced air systems. If adding onto an existing home and wanting to use the existing home’s furnace and ductwork, then consulting a mechanical subcontractor prior to permitting is going to be necessary so that they can document the existing duct system and design a revised duct layout for the entire project scope.

Budget Management

Finally, in addition to zoning regulations, the next largest ADU project killer is cost overruns. This is fairly common in ADU projects, often due to inadequate planning, thereby resulting in unexpected issues. One of the most important financial concepts to understand is that ADUs do not have the “economy of scale” factor going for them. While a typical 2,500 square foot home can be built for approximately $300/SF, a significantly smaller ADU is likely to fall anywhere in the $400/SF – $800/SF range. This is because even though the project itself is smaller, there is more material waste, less bulk purchases, and the same number of subcontractors involved as a larger project would have.

As discussed earlier in this blog, proper project planning and obtaining the maximum information as soon as possible will help mitigate unknown or unexpected costs when construction does finally come around. Surprises when it comes to utility upgrades or separate sewer connections are not fun to encounter, especially when they are not factored into your budget.  On a similar note, your architect will recommend obtaining a survey as well as a soils report at the project onset so that any new foundations are designed properly for the site’s soils conditions the first time. Discovering poor soils during excavation not only leads to structural re-design fees, but can also lead to more costly foundation solutions. Finally, it’s also highly recommended that you talk with your contractor about an open-book policy, in which all expenses are outwardly presented and nothing is hidden.

Conclusion

When done right, building an ADU can be a fun and exciting process, as well as a rewarding investment. Success depends on thorough planning, attention to detail, and awareness of potential pitfalls. By addressing these common issues early in the planning process, you can create a valuable addition to your property that will provide returns for years to come.

Remember that every jurisdiction and property is unique, so consult with local professionals familiar with ADU projects in your area. The extra time and money spent on proper planning and design will pay dividends in reduced issues during both permitting and construction. If you’re looking to design and build an ADU of your own then get in touch with us today!