Can shipping containers make good ADUs? Experts say probably not

[che...@smartergrowth.net]

Can shipping containers make good ADUs? Experts say probably not

Can shipping containers be converted into good little urban dwellings? Shipping containers have sometimes been touted as the miracle structure that could offer a cheap way to create an ADU. Asking various people with shipping container, prefab and modular construction experience, I learned that shipping containers are not considered the best approach for creating a permanent living unit in a city. Among prefab/modular options, shipping containers seem to rank at the bottom in most cases. Below are the many reasons why.

Here’s what Zach Gasper said. He’s Director of Design with GreenSpur, a design/build firm working in the DC area (their work includes ADUs, and ADUs that can be built in their warehouse):

We’ve done our fair share of shipping container conceptual designs and seem to come to the same conclusions on all of them - they are a great way to provide low cost, temporary shelter/space (great for a temporary office, outdoor bar, merchandise stand, etc), but as soon as you start retrofitting them to be habitable spaces/residences (and adhere to building code) they lose their inherent value. The biggest problem we’ve come across is insulating the containers.  Standard size containers are 8’ exterior dimensions, and code minimum for exterior walls is r-20. So by the time you pad in the walls to accommodate this you are really left with a small space. Probably OK for an at home office, but not for bedrooms/kitchens/full dwelling unit. Also, the shipping container gets part of its structural integrity from the corrugated wall panels.  So as soon as you start cutting into those panels you need to reinforce them in some way which means more money.

Another experienced architect working for a modular home producer offered a similar perspective. He said:

While I understand the initial appeal of the shipping container house, I am not a fan. They don't provide any compelling advantages over other off-site construction (modular or panelized). Here are some quick thoughts:

1. Structure: Shipping containers are very strong at the corners. Otherwise; the tops are weak and typically need more structure to support loads. The metal walls are integral to the structure so if you cut much of any opening for windows/doors you need to add new structural reinforcement.

2. Size Limitations: The containers are fairly small before you insulate.

3. Aesthetics: While I love a rough-n-tumble, industrial aesthetic, the shipping container has a particular look that I do find appealing like some agricultural or industrial buildings.

4. Insulation: The box needs insulation. If you wrap the outside with insulation, you prevent the metal of the shipping container to the interior. If you insulate on the inside, you make an already small space that much smaller.

5. Containers Past Use: What was in the container? Was it noxious or toxic?

6. Best Use: Most of the containers used for buildings are fairly new (so they look nice). This means they are being pulled out of circulation as shipping container long before their useful life is over.

Containers have one big advantage in that there is a global network of intermodal transportation for shipping the units. If I had a project where there was a lack of local skilled labor, a site with extreme conditions, or a need for temporary emergency shelter, then I would consider using them. Otherwise, there are better options.

I asked another colleague, Patrick McAnaney, who is now working in affordable housing development. He worked with shipping containers in the past when he managed the launch of the Las Vegas Downtown Container Park. View the Las Vegas project here: https://lasvegassun.com/news/2013/nov/25/joe-downtown-container-park-opens-another-draw-eas/. He said: “I'm pretty skeptical on using the shipping containers for permanent structures based on my experience in Vegas. They are great for temporary pop-ups or even as a fun draw for retail or other commercial uses, but once you want to use them as a permanent structure the costs to add insulation, HVAC, plumbing, electrical and all the other basic systems makes them very noncompetitive from a price standpoint."

I also asked an ADU/real estate financing expert, who followed up on Patrick’s comments:

I agree with Patrick. I considered containers homes at one point but there were some major issues. Like Patrick pointed out, it costs a lot of make sure those homes are actually livable. The second is appraisals. Appraisers are going to want to see comparable home sales to create a valuation. With no nearby comparables appraisers will make the smart call and simply decline the appraisal. Third is coding and financing. For [Fannie] financing, [Fannie] at least will want a local certificate of occupancy. If a home does not have that, it cannot ultimately finance it. I like container homes as a marketing gimmick, but ultimately it's not going to be what will create a tremendous amount of new homes in the country. Not like ADUs.

The only possible exception is container homes built to be an ADU in someone's backyard. But even then I'm struggling to see what benefit a container home has over a standard modular home. I have a lot of doubt about shipping container ADUs being a good source of investments. The cost to maintain, install, service, etc is so new that I haven't seen much information out there. Given all the unknowns and risks I would not personally use them as an investment.

A manufactured home (MH) is significantly better as its building code has been refined over the years. These homes are high quality and they're safe. MH can get to as low as 320 sq feet legally, but most people see 400 square feet as the cut off. MH can easily last over 30 years. It's all about general proper maintenance. I've seen homes over 50 years old that I would have guessed were 15.

I'm curious why so much emphasis on container homes when MH and even just stick build ADUs have a lot more advantages. I would even say Tiny Homes are a safer bet than container ship ADUs.

To get more (skeptical) perspective on the issue, check out these articles.

San Francisco architect: http://markasaurus.com/2015/09/01/whats-wrong-with-shipping-container-housing-everything/

Northwest builder: https://hammerandhand.com/field-notes/outside-box-shipping-containers-make-sense/

-- post by Cheryl Cort, Coalition for Smarter Growth, che...@smartergrowth.net

[Ileana Schinder]

Hi group,

As architect here let me share my 2 cents on innovative construction products, shipping containers being on of them. Any time you are offered a prefab structure think of it as a SYSTEM. Why a system? 

Any residential structure, any building for that matter, is a combination of the following SYSTEMS:

• STRUCTURE (foundations, load bearing walls, posts, beams, roof, etc)
• WEATHER PROTECTION (insulation, shading)
• WATER PROTECTION (underlayments of roof, walls, siding, etc)
• INFRASTRUCTURE (water, electricity, waste, HVAC, etc) and last but not least... 
• FENESTRATION (doors, windows, etc)
• INTERIORS (equipment, cabinetry, finishes, fixtures, etc) 

Those systems need to be connected to a grid. The most obvious ones are water and electricity, but what about transport for materials? 

Each of the systems listed above has a cost associated with:

• MATERIALS (per square foot, per linear foot, per item)
• INSTALLATION (per hour of specialized or non specialized worker)
• MAINTENANCE/REPAIR AND... (how soon, how often and how much will cost to repair when thing break)
• TRANSPORTATION (how far, how difficult to install, how risky to move, etc)

Most of the prefab systems I've seen to address ADUs ONLY count for the material cost and forget the price of transport and installation (how much does a crane cost per hour in DC? and insurance? A LOT). 

I hope this email helps people understand that the cost of construction is the combination of SYSTEMS plus METHOD OF CONSTRUCTION. I understand how giddy we can all get with the next construction innovation (3D printed concrete houses?! omg....) but when you look at the cost per square foot, how does it compare with traditional construction? How many systems does this new products are including their houses? Are they providing the same size and quality of space? 

Feel free to reach out if you need help to compare construction systems or products.

Cheers

ile

PS: stay warm people.  

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Ileana Schinder, Architect

AIA, LEED AP BD+C

Certified Passive House Consultant

i...@ileanaschinder.com
202-431-6760

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