FLEXHOUSE is North River’s own line of net zero energy homes that find a sweet spot between flexibility, emotional aliveness, affordability, low/no maintenance, and high function living for a range of budgets and sizes. They all incorporate a few simple design principles that we have found over the decades of our work to provide the most sustainable house that we know how to build.

It is a starting point and every client modifies them to their own design and site to some degree. It involves five simple design concepts that aim to maximize the longevity, flexibility, and affordability of living design. Hint: just start with choosing a ‘simple shape’, though, and you’re well on your way.


flexhouse 1

1,000 sf 1 bedroom, 1 full bath

The smallest version of the series is perfect for a
weekend cabin or an Airbnb rental.

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flexhouse 2

1,200 sf 2 bedrooms with sleeping loft, 1 full bath

Compact and bold, with room to grow.

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flexhouse 3

2,200 sf 3 bedrooms with sleeping loft 3 full baths

Smaller in footprint than FLEXHOUSE IV, without sacrificing drama and high ceilings.

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flexhouse 4

1800 sf 2 bedroom 1.5 bath but adaptable to 3,200 sf 5 bedroom 3.5 baths in same envelope.

Our prototype house demonstrates all of the design features of the FLEXHOUSE concept of adaptability, affordability, low no energy or maintenance costs including transportation.

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custom flexhouses

40% of our projects are custom designs, essentially starting from scratch while using the flexhouse system as a starting point in order to benefit from the same efficiencies and templates of design detailing. Ask us about how making it your own house can work within the flexhouse system as all the projects on our website have done.


In 2024 north river is launching a partnership with BIOBUILDS, a European-based pre-fab builder of completed passive house homes. This would be the first such undertaking in North America, where panelized passive house components are currently available at very high quality, but not yet at a savings to project costs. Our hope is to see 35% reduction in construction costs and time of our flexhouse models, starting with ADU’s and with our flexhouse I and II models. Stay tuned, and inquire if such a model interests you to hear more about!


As part of our initial 2024 launch of our upcoming U.S. partnership with BIOBUILDS, modular passive house builders in Europe, we will be offering a flexhouse ADU design for the first time. We expect to test the limits of providing least-cost net zero / passive house living using north river’s time-tested flexhouse system. Please inquire if this might be of interest to you.


Shellhouse is our new version of the flexhouse system that is designed to lower the cost of a completed flexhouse while providing a way for clients to fit out the remaining interiors over time, as they are able, with minimal additional expense. The shellhouse concept provides a kitchen, a full bedroom suite, and a fully accessible loft within a completed house shell, with all wiring, windows, finishes and structural components completed, and ready for building out over time. The shellhouse is most advantageous for the Flexhouse III and IV models, but can also work for the flexhouse II, and the savings upon initial investment can approach 30%. Ask us about whether this might be a good fit for you.


Most of our projects come with additional structures as part of the master plan, and we like to design, and often build them as part of the first phase, where budget allows. These typically include garages, studios, guesthouses, and garden sheds. In all cases, we like to link them in materials, concept, and site layout with the main house. Each of these are considered add-ons to the base price in our whole project budget process from the very beginning of the work together.

For more information about the design ideas, range of plans, and costs for FLEXHOUSE models, contact us at info@nriverarchitecture.com.