Curved roof load calculations

Agreed, our affordable housing crisis in America has roots as a social, political and economic issue as well. I believe architects thinking “outside-the-box” could improve the situation, however they can not solve this large problem alone. The residential home building industry here is largely what we term “stick built” focused: bring large piles of standard dimension material (mostly wood products) to the job site then cut each one, attach to other members … repeat 10,000 times.

Only a tiny minority of residential homes use prefab or modular construction methods and those few are more expensive per square foot (or psm) than stick-built homes. In the past 15 years in America, dozens of modular residential startup companies funded by venture capital have gone bankrupt, Glide Homes started by well intentioned architect Michelle Kaufman being only the most famous of the medium sized firms and Katerra which produced large multi-family apartment complexes, funded with $3-billion of Softbank and other VC firms capital went bankrupt with 4,000 employees unpaid. More startups keep trying but much of the VC money has dried up. These modular/prefab companies failed for reasons I think are quite logical, having mis-understood both the residential market and more critically: assembly line production as it relates to residential housing modules, which are nothing at all like automobiles …etc.

For a powerful concept such as prefab construction to succeed in the American residential market the approach must be re-evaluated and re-engineered from first principles. Glide Homes built their large but road transportable home modules in a warehouse (they mis-identified as an assembly line - which it was not) using “stick-built” construction methods - wrong choice from the beginning in my opinion. They promised customization for clients that totally broke the fake assembly line almost immediately. They burned thru $350-million in VC money which for a time gave them the luxury of ignoring critical problems with their business and design models. The result was bankruptcy as it was for Katerra on an even larger scale.

I am trying to learn from these recent lessons and from the 100-year history of prefab architecture and am self funded for now thru the design and construction of several prototypes. It is a very difficult and daunting problem … time will tell.


You might explore the use of concrete for your curved/arched shaped elements as I have. Curved concrete as architect/engineer Pier Nervi demonstrated decades ago can be a very beautiful and efficient structural solution, though it is quite uncommon to apply this solution to residential scale building projects. I developed residential designs that employed parabolically curved concrete arches then evaluated them using SkyCiv FEA. More steel rebar (stirrups) must be included in the curved arches because they also act as beams to resolve wind loads which require shear transfer. Gravity snow loads were easily resolved, however max wind sideloads required more detailing as did a cost-effective waterproof and insulated outer skin that meshed with the curved arch skeleton. These issues all seemed solvable, but the design was getting more complex and elaborate so I temporarily set aside the curved concrete arches design to give me time to re-evaluate if this design direction was still promising in light of alternatives.

One of the alternatives I am considering recently is folded plate roofs, which are efficient for many types of loads. Since they consist of mostly straight members, I have found they are less expensive to apply a waterproof and thermal barrier skin onto. Folded plates handle both gravity, wind loads, and seismic loads well (if certain details are applied).

Aesthetically, arches are not in the same category as folded plates, however they allow interesting openings for light at their peaked ends and are in my opinion inherently more pleasing than simple flat roofs… YMMV.

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I though Blu Homes was developed out of Glide Homes. It’s still around.

The lineage of modular residential construction companies is confusing. My understanding is: Blu Homes purchased the assets of Glide Homes when Glide went bankrupt.

When Blu Homes, like Glide Homes a VC fueled Northern CA based company, started they quickly ramped up to a 300+ person workforce and purchased (or leased ?) a big vacant manufacturing facility with the help of Bay Area politicians and investors. Blu Homes management was top heavy in young rich tech entreprenours who were not experienced in either residential construction or physical manufacturing of any type. They argued among themselves, changed strategy multiple times and in the process alienated their production line workforce. Then threw most of their remaining VC capital into sales/marketing not manufacturing development. This began a slow downward spiral. National sales were halted and retrenched to Northern CA only. Workforce declined to approx 35 employees according to Open Door.

Honestly, I haven’t followed Blu Homes for a few years and do not know if they have recovered, which would be a positive development. Wish them well, but in my opinion their business model is not well thought thru and fragile just like Glide Homes… hope I am wrong for the sake of the employees.