We designed a holistically sustainable compact home in a remote location by finding creative solutions to unique challenges.  Our small treated floor area resulted in a high form factor of 5.0, whereas the sweet spot for certification of a Passive House is a form factor of 3.0 or less.  We were not only trying to certify a small home, but the site was shaded from noon onwards, year-round, due to the surrounding forest and mountains.  The primary views are to the East. So, not a lot of potential for solar heat gain.  Thanks to our dedicated team and motivated clients, Kōshōshiki Passive House on Stilts was able to meet the PHI Low Energy Building Standard.   

The decision to build a prefabricated house on stilts was driven by several ecologically inspired reasons:

• Reduce the use of concrete and foundations to reduce embodied carbon / CO2 emissions.
• Eliminate the need for rigid foam insulation entirely, as the wood frame floor is insulated with cellulose and rock-wool.  Rigid insulation is derived from fossil fuels and it is not biodegradable.  
• Prefab: for this remote location, being able to prefabricate the whole house (walls, floors, roofs) means that the panels will show up on site and can be tilted up in a couple of days, taking us from a site with a few steel posts to a site with a weather-tight and insulated building shell almost instantaneously. 
• Minimal site disruption of the topsoil and ground water.  Groundwater run-off and erosion are limited by leaving most of the site permeable to on-site infiltration. 
• Continuity of flora and fauna – bears and deer have access to river without it feeling like a human space, which was important to us in such a delicate eco-system near the stream.
• Cantilevered deck off of the living room provides a secure outdoor space for our owners, to blur inside and out.  The bears stay on the ground where they are happy, and our clients can enjoy their deck space and leave their doors wide open, without fear of unwanted visitors. 
• Creates a covered outdoor living space below the house, to enjoy a rainy day or to escape the sun.  It could also double as a carport, and is a great place for storing a canoe and other outdoor equipment.
• Improved solar access and views by raising the house above grade.  Solar access was limited by surrounding trees and mountains, raising the house by one storey improved our solar heat gain noticeably.  
• Healthy air.  By lifting the house out of contact with ground we have also lifted it above potential sources of radon and other soil gases
• Pests will find it much harder to get into this house than your typical home.  
• Affordability. Although the steel posts are not cheap, neither are building basements with concrete, foam, and excavation.  In a remote location where trades and materials have to travel to a distance to site, creating a structural steel grid on which to sit the prefabricated house cut down travel and construction time.  It also aligned well with the challenges of building on an uneven and remote terrain.  

Kōshōshiki is certifying under Passive House International’s Low Energy Building Standard, due to its relaxed targets specifically created for projects like ours with limited access to the sun or with smaller footprints.  The heating demand limit is 30kWh/m2a, which is still admirable if you were to compare it to the Vancouver high-performance building code which sees projects in the range of 90 – 120kWh/m2a.

Our assemblies have extremely high insulating properties in order to overcome our lack of solar access.  We undertook the exploration as to “what it would take”, and were surprised at how thick the assemblies needed to be.  We were also surprised to find that this added insulation didn’t add too much to the overall construction cost, so our clients were motivated to pursue certification.  It should be noted that our annual consumption of energy for heating is much lower than our other Passive House projects because of the small footprint.  Our final assemblies:

• Roof: R130 effective (started R52)
• Walls: R83 effective (started R49)
• Floor: R97 effective (started R52)

Every square inch of Kōshōshiki Passive House on Stilts is considered and brings meaning and beauty to the experience of this cabin in the woods.

#ONESEEDstilthouse 

Architecture: ONE SEED Architecture + Interiors

Interiors: ONE SEED Architecture + Interiors

CPHD: Sara Malekpour E3 Eco Group

Structural: Twin Peaks Engineering

Prefab: TAG Panels