These discussion items address Denver ADU design topics, but many of these are applicable to Colorado construction in general. These are presented as discussion and opinions of The ADU Lab. Contact us or consult with your contractor for your specific situation.
How Much Does a detached ADU Cost?
This is every homeowner's first question. From our experience in the local Denver market, and using approximate construction costs that we have seen in 2023 and 2024, the starting cost for an ADU is on the order of $300,000. There are many ancillary expenses in addition to the actual construction, such as design fees, permit fees, site improvements, etc. We can coordinate with you or your contractor during design to maintain cost-efficiency of your project, but that baseline construction cost is difficult to shift in Denver, so this hopefully gives you a rough order of magnitude for a typical ADU budget.
Do I really need to get a soils report?
Jamie's Discussion:
In Denver: Yes. The building department is very clear that for new detached construction with habitable space, a soils report is required. You can try to get by with building a "shed" which is a non-habitable space and falls under less rigorous requirements, but then you'd also have to get by without plumbing or air conditioning for the space; plus the Denver building department has been closely scrutinizing "shed" permits which look suspiciously like living spaces.
In other jurisdictions: Maybe. For a quick discussion on other jurisdictions outside of Denver, such as Centennial or Cherry Hills Village or Aurora or wherever have it, it depends on your local building department. Some building officials are starting to follow the example of Denver. However, we are currently seeing that they are most often not required for ADU's outside of Denver. Without a soils report, the accepted practice is to match the type of foundation construction of the main house. In the front range, that would be either spread footings or drilled piers. If your main house is on drilled piers (drilled piers = higher construction cost), then any structural engineer will require a soils report prior to designing an ADU foundation. Helical piers are another consideration but in the interests of not getting bogged down I'm not going to discuss them here. We have worked in multiple building departments across Colorado, so feel free to reach out if you would like to discuss your jurisdiction in particular.
Follow-up: Can The ADU Lab provide my soils report? No, we cannot because we are not geotechnical (soils) engineers. You will need to contact a geotechnical engineering company for a soils report. We can help direct you towards local geotechnical engineering firms.
Why do I need an architect / architectural drawings?
An architect helps understand the specific planning parameters and considerations unique to your site and project vision. An architect can help generate different options and pose multiple designs that might meet your project vision in different ways, based on adapting pre-set plans or starting from scratch (depending on your vision and budget) to find the best solution tailored to your project needs. If you go with a pre-set plan, the architect will help adapt that plan to your site and ensure it complies with your location's zoning and building codes.
Why do I need structural drawings for an ADU? Are these the same as architectural drawings?
Jamie's Discussion:
Structural drawings are separate drawings from the architectural plans. They contain information about the foundations and framing (things that are hidden by architectural elements). They need to be coordinated with the architectural drawings so that they work together, but they are typically provided by different entities, plus structural drawings need to be stamped by a licensed engineer.
Can The ADU Lab provide site plans?
The architect provides a site plan as a required drawing in the permit submittal package. This is a detailed plan that shows everything from the location of the new building in relationship to zoning parameters, existing trees/infrastructure, and the existing home to spot elevations and new utilities (lines and locations) on the property, which will be reviewed in detail during permitting by the City of Denver's various departments. This is a custom drawing that is unique to your site and zoning, and will be required for permitting through the City of Denver.
Can I build an ADU on top of my existing detached garage?
Jamie's Discussion:
This is a very common question because it seems completely logical to save cost by using the existing framing and foundations that are already in place. Unfortunately, most existing garage foundations are not suitable to be re-used for a second floor ADU. The foundations for most contemporary garages don't even have foundations or footings in the conventional sense--it's just a thickened slab edge under the whole perimeter. While appropriate for a garage, that style of foundation is not deep enough and does not provide enough support to meet current building codes for a second floor addition. Of the approximately 20 times I've been called to assess whether an existing garage can support a second floor, only once have I seen a garage with an appropriate foundation that would work. So let's call that a 5% chance your existing garage can support an ADU.
Why is it important that my architect and/or engineer are familiar with the Denver Building department?
Jamie's Discussion
The Denver Building department's permit review process is notoriously difficult and time consuming. But that fact is only known to contractors, architects, engineers, and any homeowner who has tried to get a building permit. Possibly this has happened to you and that is why you are looking at this page. Avoiding extra cost and delays related to the Denver permit process is why it is critical in Denver to use an architect and/or engineer who has experience with the local building department.
I'm a contractor and I need architectural and/or structural drawings. Can you provide those?
Absolutely! We typically work with either contractors or homeowners, so if you have an ADU project and need either architectural drawings or structural drawings for permit, then please reach out. If you just want an idea of our typical design fees, we can provide a preliminary fee schedule upon request.
What's the difference between using The ADU Lab and using an all-in-one ADU contractor?
Jamie and Beth's combined experience in structural and architectural design provides a studied, thoughtful approach to ADU design and planning that considers your unique site, context, and program. Having completed the permitting process through the City of Denver many times for ADU's, they are well versed in the unique requirements of this housing type and would be happy to work with you to deliver a successful project that you can then bring to a contractor. Another advantage of working separately with a structural engineer and architect is that once the design is complete, you can have several GC's bid on the project, hopefully creating the best fit for you from a working-relationship standpoint, while also providing you with a competitive price point.