Building Underground

Written by Andrew Morrison

building underground house

I recently received an email in which a man asked about using bales when building underground, as in an earth-bermed house. He wants to use bales due to their high insulation value, but is concerned about the effects of moisture on the bales. I too would be concerned about the moisture. We are trying to figure out a way to make it work as it would be a great marriage for sure!

I suggested that if he could find a way to use a material that would provide a break between the bales and the backfill, it may be possible. In other words, he would need to place the backfill against a structural element (what is yet to be determined, but perhaps concrete and a plastic waterproof membrane?) that would provide the strength and protection from ground moisture. He could then stack bales (the back side pre dipped in plaster for fire protection) slightly away from that wall so to leave a ventilation channel between the bales and the backfill assembly. That channel may need mechanical help in providing adequate air movement to protect the bales from moisture.

Seems a bit over the top to me, but I would like to see what other options you may have for such a job. I would really like to see this as a possibility in the future. Thanks for any input you are willing to share.

Want to learn more about straw bale houses and how to build one? Want to do so for FREE? Sign up for our totally free 16 Day Straw Bale eCourse! Find out more HERE.

24 Responses

  1. In his book “The New Ecological Home”, Daniel D. Chiras describes the house he built for himself. It is partially earth-sheltered, with an above grade, strawbale facade on the south side covered with a metal sheeted roof and solar panels. On the north side however, it has walls made of rammed earth tires and is below grade, with a green roof. He is apparently very satisfied with the results, although he acknowledges that making walls of rammed earth tires is very time consuming. I love his solution of an earth-sheltered house + green roof on the cold side, with a southern strawbale facade + solar panels on the sunny side. That pretty much perfectly combines the best of both systems in my opinion.

  2. I was thinking of using ferro cement as a break between the straw bales and the backfill. It then could be done very thin and on the cheap. Create some kind of verticle ribs attached to the cement for the bales to rest up against for the air space. If those ribs had holes through them, they could be used to stitch up the bales as they’re laid.

  3. The main reason for an earth berm house is to take advantage of the natural regulating and insulating effects of the ground. Depending on location anything about 5 feet down or more maintains a pretty constant temperature. Therefore lots of insulation isn’t required, and might actually work against you in these locations. Myself, I would skip it, find a nice South facing slope and just use the straw bale at the exposed daylight walls.

  4. very interesting!
    Ive been mooting the idea for a few years for my ‘one day i will build” house. The introduction of green roofs to the mass market has created some pretty exciting membrane solutions that would create a high quality seal but the void gap sounds tricky.

    In my minds eye i had been toying with the idea of using earth ship style tyres and paacked earth to create Retaining walls with indoor/outdoor enclosed terrace below ground, with hay bale on outside facing walls and intensive green roof with membrane. not as “underground” as the picture above but moving towards… And a similarly low impact on the landscape and thermal properties.

  5. What about earthbags wraped in 6 m poly. Then the bales on the inside. Would give you a frame and then you just complete the wall. Finnish by completly covering the structer!

  6. It is my understanding that while earth berming provides a great system for regulating external conditions…as in mitigating the effects of wind and water and seasonal temperature changes, it isnt a great insulator. The ground can leech away heat. In the project I am planning at the moment I will be using passive solar heating as my main heating source. I am concerned that earth berming would reduce the effectiveness of the passive solar heating. I have read that a fair bit of heat can even be lost through the foundation!

  7. Ok then, here’s one for you. I’m about to build this year following the Mike Renolds “Earthship” principals. However, instead of the earthen berm on the north side I plan to build with an adobe interior wall and strawbale exterior wall. Any suggestions on how this might go together and weather there might be moisture issues arise?
    Great blog by the way:)
    Taos, New Mexico

  8. Read the book Serious Straw Bale; filled with good information including some on this very subject. Roy-Brassard home in Quebec will prove of interest.

  9. I am a sprayfoam contractor and I spray the standard concrete walls and even below the slab with 2 lb density CLOSED cell polyurethane foam. It would work great on the straw bales and create a monolithic water/vapor barrier at thicknesses above 2″. It would also give a very high insulation value. I would recommend spraying the foam below the slab and then spraying the foam against the walls and tying into the foam sprayed below the slab giving the full barrier.

  10. A hybrid underground/strawbale house is a beautiful thing…but like any good thing, the better the prep, the better the result.I think the cost/time benefit of bales below grade is not favorable but some things have been done with “vertical crawl space” (a chamber between back wall and hillside)which may work for you…obviously a roof sytem needs to extend back beond the cavity to a retaining wall or “foundation” of some sort.Tire footings with a pier and earthbag infiil might be nice for this “envelope”.

  11. I’ve had a little experience in trying to prevent water from getting at or into structures built partially surrounded by dirt. The problem really is that water doesn’t give up, and what may seem watertight one year may be soggy the next. The absolute best idea seems to be to keep that water running away from your structure, not toward it. You can do more good by careful grading uphill of your building than you can by trying to outsmart the water at your wall or foundation.

    The natural tendency is to select a side hill location so three sides can be against the dirt and one side can be open for access. But water runs down hillsides all the time, and you have to select a patch of ground that is naturally dry. Another approach is to build above ground and then ramp the dirt up around three sides. Still another approach that has worked is to allow not just inches but two to three feet of space between a retaining wall (which could be a dry stone wall) and the wall of the building, with a tile or perforated pipe curtain drain laid at the bottom of the free space. This allows air to circulate and also gives you acces to your building wall for maintenance, and if you have water around you will have maintenance.

    Having the wall exposed to the air in this way does rob you of the insulating properties of dry earth, but the wall will be protected from the wind and any dead air space will give you some insulating effect.

    Finally, I like to have any banked up dirt waterproofed near its top surface, as by a thick poly film covered first with coarse river rock that will stay put and not cut the film, topped with fine gravel or dirt. A dirt bank that will shed water will eventually dry out and remain stable, and will make a good secondary insulator. In any construction that is surrounded by dirt, it will be better insulated after a full year than it is at first, because it takes time to get it really dry.

  12. You might check out the techniques described in “The $50 and Up Underground House Book” by Mike Oehler. They may be most useful for rural areas with less strict building codes, but definitely affordable.

  13. I have got some thoughts about this same idea, I am designing a three side earth sheltered home and want to use straw bales mortared with cob like you would bricks . My design is to dig the space eight to ten feet bigger on the three sides against the hill side and have a trench to put gravel in then drain tubes in a sock covered with more gravel then to build retaining walls up to three feet above grade so earth can be bermed up against the retaining walls on the outside then to put in a rubble filled cinder block foundation inside the retaining walls eight feet to build the straw bale walls on . I also intend to use a cob wall on the south facing side and maybe a small bit of the east side also . then to cover the whole thing with a earthen type roof and to use rubber roofing as my first layer of water protection and to cover the retaining walls with the roof and the rubber roofing plus six or eight feet before I berm up the earth then to insulate and use heavy plastic in three layers like they do on the earth ships then add earth to the roof and seed it . I think you mite be able to enclose the added space to use as storage and even a cellar type room atleast thats my hopes ! if anyone has any thoughts I would like to read them ! Thanks Russell

  14. Hello,
    I am also thinking about an earth-sheltered straw bale house. I still want to design a full straw bale house on the four walls. Here’s my idea: at the north wall (inside the hill) and outside the straw bale wall, what about adding a stainless steel sheet wall (2mm thick, sorry for the metric unit) plus a gravel wall and drain pipes? As everything will be compact, I would not have an air gap, moisture wouldn’t be able to go in. Rain water would be redirected by the gravels and drain pipes and I would still have a benefit of a full straw bale house protected from the wind. Ok, stainless steel in expensive but you should have a low maintenance then. What do you think about it? Thanks. Frédéric.
    Great blog by the way. 😉

  15. Straw bales can get messy and give out gas when mixed with water , even dangerous in a unventilated place underground place,people have died due to poisoness gas released when the cellar got flooded accidentally , underground mixture of cellulose and moisture is a real problem but if good natural ventilation is employed combined do with complete vapor barrier and insulation straw bales can add more to the existing one , rodennts and snakes will clearly love it ,a house dug In a hill with ventillation ducts or structure openings exiting below the house level may allow heavier gases to slowly flow out of the house moisture will like to exit upwards so a vent uptop may help, the ground fluctuates quite a lot due to ever changing moisture and temperature so strctures build underground have a tendency to crack and seep water , organics are a big factor in a such structure

  16. Thanks for the kind feedback. I don’t think its worth it. The main purpose for straw bale walls is to provide excellent insulation value. The earth does that and adding the bales and the assembly you speak of will be a HUGE amount of work, for very little benefit. Stick with traditional, time tested applications for the below grade stuff and use the straw where you gain the benefits of it. Trust me, baling in and of itself is a lot of work, let alone the extra details needed to protect in an underground application.

  17. This is kind of an odd idea, but I wondered what people thought of it. We’re contemplating building an earth sheltered cabin that would be earth covered on the roof and east and west sides, but strawbale and earth plaster on the north and south walls. Someone suggested that instead of hauling in a backhoe, we simply stack strawbales over the entire structure (we have a ready source of them) and cover it with a few inches of topsoil and a planting of native grasses. Then, as the straw broke down, add additional soil as needed. Thoughts?

  18. That can work. I think you are clear on this, but you would not want to bury the straw bale walls that you want to last long-term. In other words, just as the “sacrificial straw” will breakdown, so too would the permanent walls if they are in contact with continual. subterranean conditions.

  19. Hi, Bruce from Saskatchewan Canada here, just a thought but why not use FLAX straw bales, they don’t rot, or give off fumes.

  20. Hi Bruce. I don’t have personal experience with flax bales, but imagine they would be a great option. I do wonder about the oily nature of the bales and if that could be a risk for flame spread. I don’t know how flammable the bales would be. Perhaps there is some testing information available for that…?

  21. Hello All! Awesome discussions. NEED your thoughts and reflections ASAP 🙂

    I am about to build an earth bermed house on our off-grid homestead this year and am too considering the, slightly risk-ay thought of insulating the exterior bermed walls with bales. The idea of the bales is to give ample insulation to prevent the due point from happening on the inside of the EPDM waterproof membrane. They also have great compressive strength when backfilled. Plus low embodied energy and local. We are building with as much material native to our land as possible and sourcing as locally as possible.

    My thought was:

    – Interior vertical log wall with light-clay chinking in-between a post and beam frame on a stone/cement stem wall. (this will be the main sheer strength and thermal mass portion of the envelope)
    – Then a wall of bales wrapped in 6-mil poly (a big bag) bedded ontop of 8″ of compacted drain rock.
    – The above grade portion of the bale wall would transition into “bagless / no poly” as to have the above grade wall be breathable. ( perhaps a detail of the termination of the bag could allow for venting to happen)
    – Then draping the EPDM from the above grade portion of the wall down over the straw bale bag assembly to act as a root barrier and the first line of defence against water.
    – Definitely detailed grading of landscaping and drainage around the structure and uphill.

    Detailing seems to be the key in ensuring this would last.

    Thanks for your ideas.

  22. Hi Kai. I would avoid using bales below grade. I have not seen a successful example of bales below grade. Keep in mind that the earth itself will provide a consistent temperature once below an active frost line. The space between grade and that frost line might need some insulation materials to achieve the goal you’re after, but I would recommend something other than bales to achieve it.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.