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11 January 2022
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Building an attached ADU in Los Angeles: Basement ADUs Vs Attic ADUs

Accessory dwelling units are increasingly becoming the norm across city suburbs in America. And in Los Angeles, this housing trend has been gathering pace in recent years. Driven by the rising cost of housing, ADUs are becoming both a source of income to homeowners, and an affordable source of housing for Californians seeking more affordable properties.

If you’re considering building an attached ADU in LA, we are here today as design and build experts to help you compare between attic ADUs and Basement ADUs. Which one should you build?


How much does it cost to build an ADU in Los Angeles?

The cost to build an attached ADU in LA is about $250 per square foot. And because both attic ADUs and basement ADUs are attached, the cost here will be almost the same for each. The only difference will be the total square footage of the units.

Looking deeper into the cost, both units would need almost the same degree of work. That includes insulating the floors and walls; laying plumbing, electrical, and gas lines, etc. Sure enough, a basement and an attic will each have some unique additions not found in the other. But overall, the costs should come to about the same estimate.

Time to complete

How long does it take to build an ADU?

On average it takes about 6 to 9 months to complete an accessory dwelling unit project. Here we’re talking of both the design and build aspects of the ADU. And once again, both types of ADUs should take roughly the same timeframe to get done.

The planning process which covers consultations with our ADU design Los Angeles team, site visits, and creating 3D drawings is almost identical in the case of both the basement ADU and the attic ADU. The same goes for the permits process which will take a few weeks.

The construction process itself from ‘breaking ground’ to handover will span about 3 to 5 months for either case when comparing a similar design.


Have you thought about the privacy concerns of constructing an ADU in your Los Angeles lot? It is important to think about your privacy needs, as well as those of the future ADU occupants. And that includes physical, noise, and visual privacy.

So how do the two ADUs compare in this regard?  Have a look at the table below:

ADU TypePhysical privacyNoise concernsVisual privacy
Attic ADUFamily members or guests can use the main door to access their unit.   For rental guests you can install an external entrance to improve privacy for both parties, and for your security.When building the attic ADU, have the attic floor insulated properly to shield noise from the attic travelling down to the main house. And vice versa.An external entrance will keep the ADU occupants from having to use your main door when coming or going.   To maintain your visual privacy while outside, you can install skylight windows that look up instead of down into your front or back yard.
Basement ADUSame as with Attic ADU above.Noise is likely to travel down from the main floor to the basement ADU as opposed to the opposite.   You will need to find a way to insulate your main floor or the basement ceiling properly to keep the ADU noise-free.Similarly, an external entrance will keep the ADU occupants from having to use your main door when coming or going.   Visual privacy with a basement ADU is less of a problem.

Home value

When adding any installation onto your property, you want to evaluate whether that new addition will add or reduce your home value.

Does an ADU add value to your home in California?

In almost all cases, an accessory dwelling unit will increase the value and price of your Los Angeles property.

So now then, how does the value addition compare between a basement ADU and an attic ADU? It will all depend on how well built the units are. The unit with a better floor and build design, as well as finishes, will add more value to the property. After all, both units can be used for similar applications.

Range of applications

What can you do with both ADUs? Which one has more applications than the other?

The good news is that both units can be used for pretty much the same functions as we said earlier.

These functions include:

  • Guest bedroom suite.
  • Bedroom for older kids.
  • Living suite for boomerang adult children.
  • Rental living quarters.

Other non-dwelling functions include:

  • Home office
  • Study room
  • Gym
  • Studio
  • Play room
  • Theater room

Can you rent out an ADU in California?

Yes you can. However, be sure to check with your local council for updated regulations.


Which unit makes a better living space between a basement and an attic?

Now this is an interesting question.

A basement will enjoy cooler temperatures and will be much quieter. You also get lots of vertical space. However, it can be prone to dampness concerns and it might not get enough natural light.

On the other hand, an attic ADU has great views of the outdoors, has access to lots of natural light, and will be warmer all year round. One concern, however, is the vertical space and how the roofing arcs interfere with your living space.


How much space can you get from either a basement ADU or an attic ADU?

Both spaces can offer lots of space, perhaps enough for two ADUs or more depending on the design and build. An attic ADU, for example, might cover the entire floor space of the property. A basement ADU, in turn, might cover a good fraction of that floor space. If the main property has a total floor space of 3,000 square feet, we’re talking anywhere from 1,500 to 3,000 sq. ft. for the ADU.

How many square feet is an ADU?

On average, a one bedroom ADU in Los Angeles will have about 500 to 600 square feet of floor space. Going by the figures we just mentioned earlier, you can see how it is possible to easily have two or more easily.


Is building an ADU worth it? Yes it is. Talk to us for all your ADU design needs in Los Angeles and we’ll build you the ADU of your dreams!

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