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Tiny Homes: How Long Does It Take to Build an ADU?

Are you trying to help your family find affordable accommodation? Are you wanting to move your aging parents closer to home without success?

Perhaps one of your children has recently returned from college and wants their own space.

According to a recent survey, as much as 10% of the US population’s currently feeling the pinch when it comes to finding affordable housing.  

One way to solve all these problems is to build an ADU in your backyard. Does that sound like a great idea to you but you’re wondering how long you’ll have to adjust your living arrangements to cope with all these extra people?

These are the usual timelines for building various types of ADU’s.

What Is an Accessory Dwelling Unit?

You’ll hear different definitions of what an ADU is depending on where you live. Usually, this term refers to any small dwelling that’s separate from the main house on a property. Some of the other terms for an ADU are granny flats, in-law suites, tiny houses, and garden cottages

There are two categories of ADU’s

Detached ADUs 

These small backyard buildings are stand-alone units separate from your main house. They’re ideal for people who want a little more privacy.

These ADUs are a good option if you want to sing with AirBnB to offer accommodation or if you want to rent out your backyard house.

Attached ADUs

Attached ADUs join onto your home at some point. You can turn a basement, garage, or attic into an attached ADU.

Even if they’re not used for accommodation, these rooms count as ADUs whenever they’re amended beyond their original purpose.

Why Do You Want to Build an ADU?

The purpose of your ADU also affects construction time. Some of the main uses for an ADU include:

  • As extra office space
  • For a home gym
  • As an artist’s studio
  • As a guest cottage for visiting family or friends

Naturally, your budget as well as intentions for your ADU will also impact the size and design of your ADU. The more involved and complicated this process is, the longer you’ll take to build your ADU.

Factors Affecting Your Timeline

In an ideal world, we could all go ahead and bang an ADU together out of plywood in one afternoon. Unfortunately, it’s never as simple as that.

These are the steps involved in building an accessory dwelling unit:

  • Arranging the necessary finance for your ADU
  • Working out a design for your dwelling
  • Arranging floor plans for the design
  • Submitting plans for your backyard house
  • Getting approval from your city
  • Hiring an architect and contractor
  • Recording the City’s Covenant Agreement

Any of these factors can hold up your project. Let’s take a more detailed look at some of these and how long you can expect to wait before your ADU’s ready to receive its first occupant. 

Designing Your ADU

There’s nothing to stop you from designing your ADU yourself. If you feel you have the necessary skills and time to design your ADU, you can go ahead.

You can also get a contractor to design your ADU, be sure to write a proviso in your contract with them concerning this.

You will need to get a professional architect to finalize the formal drawings needed to submit your design to your town planner though. You’ll also need to sign a form agreement with your architect before they go ahead.

A professional architect shouldn’t take more than a week to come up with an effective layout for your ADU.

Of course, the time involved will depend on how busy your chosen professionals are.

Compiling the Necessary Construction Documents for City Approval

Municipal regulations govern any construction in your neighborhood. In some areas, it might not be legally possible to build an ADU in your backyard.

Some of the most common regulations are:

  • Restrictions on the number of dwellings allowed on a single lot
  • Distance limitations regarding how close you can build to your boundary
  • Height restrictions on new constructions in your area
  • Size limits on ADU’s in your neighborhood
  • Parking regulations regarding ADUs
  • Environmental by-laws on ADU construction


This post, gives you some more information about the type of restrictions that might apply to your ADU.

There are two stages involved in getting your ADU through the approval process and you’ll need to submit several documents to your local powers that be. These are the stages involved:

1. Apply For Zoning Approval 

In some cities, you may need to achieve zoning approval before applying for a building permit. Others will allow you to apply for both simultaneously.

These are the most common requirements for zoning review:

  • A site plan detailing the outline and dimensions of your property
  • A list of all property owners within 300 ft. of your proposed ADU

Once you’ve got the go-ahead on this aspect, you can proceed with the next step. 

2. Apply for a Building Permit

When applying for a building permit, you’ll need to submit the following:

If you’re using a contractor or architect or contractor to design your ADU, you can get them to complete this process for you. Some cities require additional permits as part of the building permit application.

These include electrical permits and inspections from the state department of labor and industries. You can check where you need to go for these permits with your local building officials

It can take up to four weeks to finalize all this paperwork regardless of the type of ADU you’re building. Then once you’ve submitted it all, you’ll probably wait another two weeks for a result.

Constructing Your ADU

Once you’ve got approval from your city, you can get started building your ADU. The average construction time for different ADU’s are as follows:

  • Junior suite – four to eight weeks
  • Stand-alone ADU – 15 to 24 weeks
  • Garage conversion – eight to sixteen weeks

Bear in mind that factors like the weather, material shortages, and bank holidays can affect construction time. All things considered, it could take as long as 9 months to complete the entire process of building an ADU.

Final Steps in Building Your ADU

When your ADU’s finally built, you’ll still need to go through a few steps before moving in. 

Take time to inspect your new ADU and make a note of any snags in construction. Then go through this ‘punch list’ with your contractor and get them to carry out the necessary changes.

Once you’re satisfied with the result, you should schedule an appointment with your city officials to conduct a final inspection. If they approve your ADU for occupation, you’re good to go.

Recording the City Covenant

The covenant agreement certifies that you’re the owner of the property and that you acknowledge the presence of an ADU on your land. It’s also an agreement to comply with all the city’s requirements concerning occupying your ADU.

This document serves as proof that you own the ADU and can help you if you need to refinance your home. It’s also evidence that you’ve complied with all the legalities when you want to sell your house.

Considering that an ADU can increase your home’s value by as much as 25%, it’s important to keep a copy of this document for future reference. An ADU’s an attractive drawcard for prospective buyers when selling your home.

When you’ve finally completed all the mandatory requirements for ADU construction, you can get down to the fun stuff.

An interior designer can help make your ADU ‘pop’ while DIY interior design saves money and give you a great sense of achievement. 

Other Things That Can Delay the Process of Building an ADU

Most construction projects experience hiccups along the way. Some of these include cutting corners by hiring a cheap, inexperienced contractor or architect.

These people can overlook potential problems during the initial site inspection which will lead to unforeseen delays and expenses. 

If time’s of the essence it’s always better to go with a reputable, well-established professional for every aspect of constructing an ADU. 

More Great Ideas for Saving Time and Money

When you build an ADU, you can enjoy considerable cost-savings when it comes to housing significant others. You can also earn some decent money if you decide to rent it out to a tenant, or travelers visiting your city.

If you’re looking for some more ways to save money and add value to your property, keep browsing our website for inspiration.

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