Hands-on Hexacube Review

The Two HexacubesWhat 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.
Addressable Issues:
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.

Fundamental Flaws:
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.


  1. Lost Chief

    Seems like the main problem is the stove. With a proper small stove and some tinkering it should work for minimal short term housing.

    If you made each one 8×16 you would have room for the stove/wood and everything else. You probably want to put some sort of adjustable intake in one of the walls so when the fire is starting or running you can let air in to keep the smoke from filling the room.

    I used a wood stove to heat the farm house i was in the winter before last. I have a small portable wood stoce now thats super light and works great. I used it in my large chicken coop 2 winters ago. Maybe the guys there could weld you up a simple square box stove with a door on the front with a vent? I got my stove at a yard sale. Its packed deep in my stuff because im moving or i would post a pic. Do you have a pic of the stove in the cube?

    Oh and spray foam works great for seals and is easily trimmed. Makes tight seals in large gaps. I have owned 8 or 9 RVs and always have to seal them up. Im actually sitting using my laptop in MY rv right now :+)

  2. Mark

    Wow, you just made me go hug my woodstove! It is our main source of heat (we also have a non-functional infrared gas stove for emergencies). It’s a non-catalytic stove designed for a 2000 sq ft space. We bought it at Home Depot about 5 years ago for $600.

    The specific woodstove we have is pictured here:–catId_1002164__locale_en__productId_3851355.html
    We heat a 1000 sq ft space with it. It can just about burn a load of wood through the night (23:00-06:00) unattended.

    Introductory design info on non-catalytic stoves is here:

    Looks like this would be a good early project for the XYZ table!

  3. NegligibleK

    I agree with Mathew on the flat roof and the stove.

    I’ll build a pocket rocket stove to cook and heat with next time I come.

    I’ll also see if we can get some single seam metal roofing to save the two flat roofed cubes.

    No, Matthew, you weren’t the only one. I slept in the Hexacube in below freezing weather. I didn’t even use a sleeping bag either. I suspect Molly also slept in the Hexacube once but I’ll have to ask her.

  4. Mathew

    When did you sleep in it? before or after I sealed it up?

  5. Mathew

    you could also try building a real small house, with amenities and everything

  6. Jeremy

    I’ve been living in the other hexacube for the past couple weeks. I’ve sealed it up pretty well with insulation and caulking, so it’s not too bad. It usually doesn’t have much solar gain, but it’s still better than the cordwood, if only because it’s more airtight. Orin is planning on making a heat exchanger for it. I raised the entire back end of the hexacubes so that the roof should direct the rainwater away from the stove pipe, and caulked the stovepipe, so the rain shouldn’t fill the stove anymore. Also the second cube is watertight after I added caulk along the outside edges. We’re planning on painting the roof’s with exterior primer, which should help protect the wood better than the driveway sealer stuff.

    Ultimately we’re going to have to go underground.

  7. Sekenre

    If you want to make a heater from CEBs I would suggest following this mud-brick oven guide.

    The Masonry Heater Association of America seem like a nice bunch of guys who share lots of detailed photographs from their annual meetings, lots of good stuff on building with materials like cob, firebrick, soapstone etc.

  8. Mathew

    so you propped up the back of the roof? that’s great! I’m still worried about the material, no matter what it is sealed with. NegligibleK’s suggestion of single seam metal sounds better to me.
    Glad to see someone is working on heat exchangers, that’s totally the way to go.
    These two can be improved, I just don’t think the design is mature until it actually works as a solar cubicle- that was the original design rationale and it hasn’t been met.

  9. Lost Chief

    That tiny house website gave me some great ideas. Thanks for sharing.

  10. Jeremy

    Mathew, you can work on the “solar” cubicle design if you like, but we’re pushing ahead on getting CEB done so we can focus on better designs for the future, rather than the temporary housing designs of this past year. The last frost is coming in a few days so cold wet weather shouldn’t affect living in the temporary housing again until the end of the year, when we hope to have earth sheltered buildings by then.

  11. Mathew

    I’m just evaluating the project based on design criteria you guys laid out. No, I wouldn’t bother to revise this design, but no one else should be building them either.
    This is the OSE product development cycle in action. Accuracy and realism, not boosterism is the name of the game.

  12. Ama

    FACINATING, thanks for all the new data as to what happened with the Cube after we left!
    see new pics from NC of solar gain buildings and we are curreently living in a sheet metal building: a school bus! its damn cold for 20 minutes till the woodstove gets kickin it! we need one of those $600. models I think – thankee kind sirs for all the shared data, ewtc.

    Digging in,
    Much Love to FactorE Farm!
    Great luck Overseas at the conference!!

  13. Proockbuicirm

    Neat website,, Hope to definitely come back again soon!

  14. Ron Garrett

    Did you give any thought to building an A-frame with the panels.