What follows is my personal experience and my evaluation of the design, if you want a quick read jump ahead to the evaluation at the end. According to Marcin and Jeremy I’m the only person to have slept in the Hexacube in below freezing conditions.
I arrived at Factor E farm late in the evening on 3/10/09 after a two-hop flight from New York City. Jeremy picked me up from the airport, and when I arrived Marcin had cooked a delicious dinner of rice and beans. After a bite to eat and a small chat Jeremy showed me to the Hexacube to turn in for the night. The temperature was already well below freezing and the clear skies suggested bitter cold ahead. According to the weather report the night got down to 11 degrees Fahrenheit. After a long day of travel I was looking forward to settling into an insulated structure.
The ill-fitted door took a crowbar to open and could not be closed after me, leaving a large crack around all sides of the frame, up to 1/2″ wide at its worst. Inside was an army cot, a top-loading army stove surrounded with CEB bricks for thermal mass, and a pile of pine lathing strips and small kindling to burn. Jeremy asked me if I could start a fire myself (yes), gave me a few tips about the Army stove, and wished me goodnight.
The stove had a small puddle of water below the fire grate, suggesting that the chimney needed a better top. But the skies were clear so I noted it as another bit of maintenance to do in the morning, along with planing the door into shape. With a fire going and a winter sleeping bag I figured I’d be fine.
Starting a fire proved difficult. The Army stove is a poor design- every time the top is opened it belches smoke into the room, so there is no safe way to build a fire with the Hexacube’s door closed. With the door open the wind is constantly opening and shutting the stove’s hinged vent (why not a rotary vent like every other wood stove in the world?), and the gusts put out my first teepee of kindling. I managed to get a small fire burning with the lathing strips I could break down and fit in the stove, shut the Hexacube’s door, closed the stove’s vent, balanced a CEB brick on it’s top, and snuggled into the sleeping bag in cotton long underwear and a wool hat.
I woke up 2 hours later, shivering horribly. The fire had gone out and no trace of its heat persisted beyond a smoky pine scent. I dared not leave my sleeping bag for fear of the cold, but managed to snag a wool sweater and my sleeping mat. Contorting myself around the cot so as not to lose any precious heat, I managed to spread my sleeping mat out below me for extra insulation and get a sweater on. I then tucked myself entirely within the bag in fetal position, and warmed up enough to go to sleep.
Although I had planned to spend all my 5 days at Factor E documenting the project and building a shower, I realized that the Hexacube needed a significant overhaul if it would ever support humans in cold weather. My morning inspection revealed several design and construction problems; some I was able to address that day, while others are fundamental design issues. I spent the day inspecting and sealing the Hexacube and preparing firewood for the night.
My strategy for the second night was to get a big pile of hardwood coals burning an hour and a half before turning in. I prepared a good base of small pine kindling, and Marcin cut some walnut logs for me, which I split down into 1″ thick 4″x 8″ pieces so they’d burn hot and nearly smokeless. But the stove leaked out the top, and I couldn’t prevent the room from filling with smoke no matter how I layed the fire. Defeated, I slept in the cordwood hut.
Over the next several days I popped into the Hexacube to check if it was getting any solar gain, but it was not noticeably warmer than outside. The R13 insulation might have kept me warm with only my body heat but I never tried it out.
1) The six panels do not meet flush to each other, creating gaps along all twelve edges. This can be easily solved by laying strips of carpet down along the edges before attaching the panels together. I retrospectively addressed this issue by caulking as much as I could (the cold made caulking tough).
2) The door does not fit flush into its frame, which is to be expected of rough construction. A little more planing, and then added a carpet-coated jam to the hinge side. it aught to have a carpet coating around all the edges.
3)The chimney pipe leaks and is not double-walled where it passes through the ceiling (an important fire protection measure). I didn’t address the seal because I think it needs the top section replaced, and it doesn’t leak that badly.
4) The army stove is horrible to use, grossly inefficient with wood, difficult to control, a health hazard, and it occupies too much floor space. It should be replaced or removed, it’s worse than useless.
1) The roof is an insulated flat panel of chip board coated in driveway sealer. Chip board delaminates and warps quickly when exposed to water. I think that no matter how much sealer is put on this surface, it will pool water, warp, and leak. A flat roof is definitely not climatically appropriate, and it is already pooling water Adding an angled roof will eliminate all the construction efficiencies of building a cube, and Marcin’s plan of stacking Hexacubes like a ziggurat would exacerbate pooling and warping.
2) There is no effective solar gain on the structure. The black outer surfaces are in a windy area and on the wrong side of thick R13 insulation, so there is no heat transmissance and what is collected is lost to convection. Even after sealing the inside of the Hexacube it never warmed up noticeably during the day.
3) There is no enclosed entry way and the space is too small to add one, so much of the heat is lost out the door every time it is opened.
I’ve made an 11′ x 7′ room function comfortably as live/work space before, and I think 7’7″ x 7’7″ could work with some collapsible furniture, but not when a stove is added. Currently it is only big enough to be a bedroom. Combined with the fundamental design flaw of a flat roof, lack of solar gain, and un-enclosed entryway, I doubt the Hexacube will ever be low maintanence or cheap to heat.
Conclusion: If you need a four season structure, follow Vinay’s guidelines in the Hexacube comments and insulate a Hexayurt, the Hexacube is not a mature design.