Review of Boxabl SIPS Prefab House
The company Boxabl has created a metal SIPs (structurally integrated panel) house that has caught a lot of folks’ attention.
The main reason it has gone so viral is that it promises it all – fast, easy, cheap, resilient, and healthy.
My job as a Building Biologist is to review homes for durability, indoor air quality, and resilience to mold.
It may be cheap and fast, but is this home a durable and healthy home?
First, is it “eco-friendy”
The basic structure of this house is a steel and styrofoam (EPS) structural panel. This is very safe even for those with chemical sensitivities. That part has practically no offgassing and I am a big fan of SIPS.
They also use MgO (magnesium oxide) board on the interior surfaces which is generally a safe option as it has extremely low or no offgassing in my experience.
It’s not clear how that is attached to the walls in this case, it’s likely glued on, which could be a problem for offgassing. (More on the inherent risks of MgO against steel below).
The flooring appears to be glue-down vinyl, though they have described it in different ways. The countertops and tabletop are laminate (which is a melamine plastic glued onto a substrate which is almost always MDF). And the interior cabinetry is conventional (which is typically particleboard and laminate).
These three elements will contribute to offgassing – plasticizers, and glue from the vinyl floor; glues and formaldehyde from particleboard-based cabinets; and glues and formaldehyde from MDF-based laminate countertops.
While this is not high in offgassing per se, at least according to conventional wisdom, it absolutely could be too high in VOCs for those who are sensitive to formaldehyde.
At this time the interior cannot be customized and it includes all the interior finishes other than the bed and sofa. They do plan on offering customizable interiors in the future.
Even though it would be quite easy to choose your own healthy floor and cabinets in theory, it would likely be difficult to remove the already glued-down vinyl.
With just a little more effort and planning, they could reduce offgassing significantly by choosing better cabinets, countertops, and floors.
(Though keep in mind we do not know the exact materials or brands used in the Casita so I am making some very educated guesses based on videos and what is most typical and economical right now).
Is it a durable design?
In general, metal SIPS are very resistant to mold because as long as the wall remains laminated they are immune to condensation problems. Moisture cannot get into any wall cavity to find a cold spot to condensate.
If they are well connected and well sealed then they could also be durable against leaks. The waterproofing will depend on how well the seams are connected. I owned a metal SIPS trailer (Camplite) that was very leaky!
There are a number of concerns I have with this house:
- There is a clear negative lap at the bottom of the first piece. It’s not just an exterior trim detail, it’s integral to the design. It’s risky in my opinion to have a negative lap that is only held together with caulking. I would suggest a liquid membrane or tape + caulk would be better there.
- It’s nice that it unpacks quickly into a full livable house but how are all those seams waterproofed? I do not think we have enough information on that right now.
- Because it’s done almost entirely in a factory we would need to see a detailed factory tour to see if this is a good design. There are so many details I would want to see including how the windows and all seams are waterproofed.
- The house, like all prefabs, needs to be seen in person, especially during installation, to see if there are any areas vulnerable to water. My prefab post goes over the due diligence needed here.
- MgO and steel have not gone well together in the past. In Denmark, massive problems (and lawsuits) resulted when salts naturally leached out of the MgO board and corroded the metal in the buildings. It’s not clear, even in recent tour videos of 2022 if the MgO is placed against the metal or if the SIPs are metal-foam-MgO.
- The bottom of the house is metal presumedly, so that, in my opinion, should definitely not be placed directly on concrete or directly on any type of ground like soil.
- The website says that Boxabl “doesn’t use lumber or sheetrock” and in an email they said, “we do not use wood or materials that can rot or mold”. But in multiple videos, wood appears to be the framing of the edges of the SIPs. Hidden wood in a metal-based house is a problem for hidden mold (potentially) in my books. Even the window rough openings are framed with wood – what happens when a window leaks?
Is this a reliable company?
Still in development?
When I first wrote this we didn’t know if this is a reliable company yet. As I discuss in my general prefab post I never go with the prototype of a prefab. They commonly have problems.
When I first wrote this blog post, the company still needed to raise 10 million dollars to be in full production. As of mid-2022 they do have a factory set up in Nevada and are still expanding into full production.
As of September 2022, no individual customer has yet received a Boxabl, and some put down their deposit almost two years ago. They will not be producing homes for individuals until the second factory is done.
They are a lot more established since I first wrote about them, but I am still wary of all prototype home models.
On the fundraising page, it says “early investors get a discount”. When someone asked what the discount is they responded “It is possible there will be a discount. We haven’t announced it yet.”
In one of the videos, the rep states that you could install this without a foundation or permit. That sounds ill-advised.
It did not sound like the reps actually knew what the floors were made of in early videos.
Elon Musk Involvement
It definitely adds legitimacy that Elon Musk was living in one (and now uses it as a guest house). But it’s unclear whether he is backing the company or not. His area of expertise is not in construction but it would be great if he did lend his mind to making this a better built home than what it looks like. It has great potential to solve the problem of lack of affordable and healthy housing around the world. But in my view, this house has not proven itself yet.
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