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Basement ADU Ideas - Convert Your Basement Into an Apartment

Updated on June 29, 2020
mroconnell profile image

Ryan is the founder of How To ADU, a site that empowers homeowners to build their wealth and their community, to solve the housing crisis.

What is a Basement ADU?

An ADU is an Accessory Dwelling Unit, or a secondary home or apartment that you can build and rent out on your property.

Basement ADUs are a way to convert your basement into an apartment or studio in California, Oregon, Washington and some other states.

Why build a Basement ADU?

Basement ADUs are incredibly affordable...

And you can turn your basement into an apartment!

Basement ADUs Idea #1 - Know the five biggest budget busters ahead of time...

Why Basement ADUs are affordable

Building a basement ADU is often cheaper than building a brand new building (detached ADU) or bumping out part of your house (attached ADU), because you can save money by using existing walls, ceiling and floor...

That said, the strengths of a basement also put a lot of constraints on your design...

It's a real trade off between cost and design freedom. And a smart homeowner will learn as much as possible about how to design a spacious, well-lit apartment within the constraints of their ADU.

Beware of Basement ADU Budget Busters

There are a few red flags that will instantly add thousands of dollars to your budget and it's important to know those ahead of time.

For example, if you don't have enough headroom or if you need to waterproof the flooring, you might need to tear up the floor, excavate and pour a new slab (which can cost $10-20k and really beef up the price tag of your project!)

Scroll down and you can watch a video all about this topic.

The top 5 budget busters for basement ADUs

Basement ADU cost, square footage, and neighborhood - real examples

Square footage
Portland, Oregon
Portland, Oregon
Portland, Oregon
Portland, Oregon

Know of a basement ADU you want to list in this section? Post a link in the comments at the bottom of this article!

Basement ADU Idea #2 - Study Other Basement ADUs

The best way to learn and get even more basement ADU ideas is to study other basement conversion projects. And the Internet is full of them!

A great Portland-based ADU website has written about several people who have converted their basements into dwellings, interviewing professional designers and builders at the same time.

"Explore these posts to learn about the challenges they faced and how they persevered. They provide excellent advice about what they would do differently if they had it to do all over again!"

--Real Examples of Basement ADUs

These articles reveal that there are many types of basement ADU projects, and they can each have a very unique set of opportunities and challenges.

Every Basement ADU is unique

Some basement ADUs are very small limited projects - like converting an already finished living space into a permitted, legal ADU. You might add a kitchenette, file for a permit and be done.

Others are very involved projects that require tearing up the floor, excavating to add headroom, waterproofing and structural renovation for the foundation walls. In plain English, that's a lot of work - and requires a very experienced contractor!

Read about other Basement ADUs to get ideas

The best way to get ideas is to read about other projects.

How do homeowners find creative ways to make a confined basement space feel very large?

How do people approach accessibility requirements?

What do people do when they find something unexpected in the existing structure like a supporting beam that they now have to work around?

Basement ADU Idea #3 - Save money with Vintage or Salvaged Appliances

One of the easiest ways to save hundreds or thousands of dollars is to buy your big ticket fixtures, appliances and amenities second-hand.

Check out places like:

You can find very affordable fixtures, vanities, appliances and more... with a lot of character.

Or you can upgrade your look on a budget

The last bathroom I redid, I got a really nice Mid-Century Modern Desk that had damage on the top, and I converted it into a bathroom vanity for a large vessel sink.

It cost about the same as buying a new vanity/sink at Home Depot, but it looks like a million bucks because the rich teak wood and hand-made furniture adds a lot of warmth to the bathroom.

Use this idea EARLY - before you design you basement ADU

The key is to buy these BEFORE designing your space so that you can build around the specific (and sometimes quirky) dimensions of your vintage bathtub or sink.

If you're already into your project and it's too late to follow this tip, be very careful about picking secondhand objects that will fit into your design...

If you buy a salvaged toilet and haul it home before realizing that it doesn't fit the space between your rough in and the wall, you'll be very frustrated - and you won't have saved any money at all!

Careful measurements and planning are the best way to save money without breaking a sweat.

Basement ADU Idea #4 - Make it feel spacious with light and long uninterrupted lines of sight

By definition, basements are often well-defined and feel a bit cramped. But a good design can alleviate that sense of claustrophobia or eliminate it completely.

There are two things that can make a space feel much bigger than it is: long, uninterrupted lines of sight and lots of light.

Something about an open floor plan with lots of space and air just tricks your brain into thinking you're in a much bigger space. Think about where you'll frequently be seated or standing in the ADU and make sure there are long lines of sight from that position.

Light also helps - dark rooms usually feel more cramped than light, airy rooms.

A lot of ADUs use high ceilings to increase the sense of space, but that's not usually an option in a basement conversion where there is often limited headroom.

Use your basement windows wisely

Well-placed windows help with BOTH light and line of sight.

Even small, high windows can have a big impact. Look into clerestory windows or hopper windows (that open from the top and block dirt and debris from falling in).

If you're sitting at a dining table, and you have a view of a window placed high on your wall, and there is an uninterrupted line of sight to a bright blue sky, that's not going to feel like you're in a basement at all.

On the other hand, check out the picture below where somebody's placed their basement window facing the trash can and a wall of the primary residence.

If you look closely, you can see the shape of the staircase inside by the window. Every time you walk up those stairs, you will see a big wall a foot away from the window. Every time you walk down the stairs, you'll see a trash can. If you open the window, it may even smell like trash.

And for large parts of the day, there is a wall blocking most of the sunlight that could come through that window. Oof.

Think carefully about basement windows

Basement ADU Mistakes - basement window that gets no light, has a blocked line of sight, and is right by the trash
Basement ADU Mistakes - basement window that gets no light, has a blocked line of sight, and is right by the trash | Source

Get started turning your Basement into a second home!

Basement ADU apartments can be one of the most affordable ways for homeowners to build an ADU and start generating passive apartment rental income, under the right conditions.

Or you can move a relative in, and save money for the family.

Basement ADU Ideas

1. Know your budget busters

2. Study real basement ADUs

3. Save money on vintage fixtures

4. Make it feel roomy

5. Learn more before starting

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.


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