Spray foam insulation (SPF), is still relatively new to the insulation industry; at least in terms of its use in stationary structures. After initial success in vehicles and airplanes during the 1940’s, SPF began appearing in newly constructed homes of the 1970’s – but only when specially requested. Now as we find ourselves in the second decade of the 21st century, SPF is being installed in residential and commercial buildings with more frequency. Part of the motivation comes from federal and state initiatives aimed at reducing the cost of the nation’s energy consumption, and sometimes residents choose SPF because they have seen the raised R-values and lowered utilities bills in published articles and research. With all that taken into account, it seems quite clear the future of SPF is looking bright.

Then in 2002 the US Department of Energy created the Solar Decathlon. This international competition was designed to challenge up to twenty collegiate teams “to design, build and operate the most attractive, effective and energy efficient solar powered house.” Aside from those initial demands, the winner must also blend affordability, market appeal and a profound level of success in the design – all with an eye to the most efficient energy production. There are ten contests within the decathlon, each earning a maximum of 100 points. They are defined as architecture, market appeal, engineering, communications, affordability, comfort zone, hot water, appliances, home entertainment, and energy balance.

Judges are looking for excellence in each category, but the overall goal is to produce a house that can be appealing to the buyer, wholly powered via solar energy and be completely comfortable. In 2011 the winner of the Solar Decathlon was the University of Maryland with their ‘WaterShed’ house. The students reported their design was inspired by the Chesapeake Bay ecosystem. They illustrated their inspiration by managing water in four categories: potable water (drinking), rainwater, greywater (wastewater that does not contain biosolids) and blackwater (contains biosolids).

Each category is dealt with in a specified way and used to the maximum of its potential, unlike processes in most homes. Potable water is used only for consumption in WaterShed, while mainstream methods use potable water for irrigation and toilets. The difference in Watershed is 50% less potable water is consumed each day. Rainwater is used for irrigation and toilets, greywater is filtered and also used for irrigation, blackwater contains biosolids and therefore requires treatment before releasing to the environment. The significant use of rainwater in WaterShed’s use as a functional home means its collection has to be more efficient than just a rain barrel, without compromising the building envelope.

The University of Maryland Solar Decathlon team knew they had a challenge front of them: engineer a home that was ultra-energy efficient, but keep it warm and dry while maintaining affordability. Ultimately, their answer was a full integration of all systems. The building envelope was built multi-layered, each layer protecting against energy loss and negative infiltration of air or water. The team used a soy-based open cell SPF in the exterior walls, but closed cell SPF in the roof and floor. For the outer walls, the SPF was covered with wall sheathing, a liquid applied membrane, and then two inch thick polystyrene rigid insulation for extra protection against “thermal bridging”. Over top of the polystyrene are “thermo-treated wood” siding panels which purposely shed rainwater into collection apparatus’ via vent strips. Due to the special venting strips in the wood siding, an additional layer of ‘furring’ was needed to create a ventilated cavity.

The WaterShed home is anything but standard. The design is extremely interesting from various points of view, and does present some very intriguing ideas for home design and efficiency. However it is important to view the project for what it is, an experiment. For example, the addition of polystyrene panels to the building envelope while SPF was already in place is overkill. One must ask why an additional layer of SPF was not applied instead of the polystyrene. Nevertheless, for the standard residential building, open or closed cell SPF (whether it is soy based or polyurethane based) will do the job just as efficiently without those polystyrene panels. Which means if the future of the typical family home lies along the lines of the WaterShed, then we can happily report that SPF has a bright and useful future!