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Thread: Arched Roof Trusses for Underground Shelter

  1. #1
    Sustainable Member 9anda1f's Avatar
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    Arched Roof Trusses for Underground Shelter

    Hi All,

    In keeping with the "How" theme of this forum I thought I'd post the sequence of steps it took to rebuild the arched roof trusses and roof of an underground shelter/root cellar that was on my place when I got it. These trusses are quite unique, simple, and effective and I have never seen anything like them before. You'll see the load they easily carry and by following along with the rebuild you can see how to construct these roof trusses for yourself. I think they'd be especially good for an underground shelter that was away from any road/driveway because the components could be packed it and assembled without heavy machinery.

    Anyhow, there was dirt falling in from the roof inside the shelter when I purchased and a flashlight examination showed much rot and decay in the ceiling. This cellar is where the well pressure tank resides and also an irrigation pump plumbed to the immediately adjacent in-ground 3000 gallon cistern. Not wanting it to weather another winter, I began excavation:

    That dirt's about 30" thick on top


    Roof exposed. It consisted of two layers of planks and a thin layer of roofing felt (or what was left of it). I don't know how long this had been there, but judging by the condition of the outside of the concrete blocks and the adjacent building, I'd say at least 50 years!


    Some of the deterioration where dirt was falling inside


    After removing the planks, the trusses were exposed. They weren't in very good shape either

  2. #2
    Sustainable Pioneer ♥RĎRMR♥'s Avatar
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    Yeah that roof sure did look like it had been around a while......

  3. #3
    Sustainable Member 9anda1f's Avatar
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    I'd hoped to only replace half of the trusses, but they were all rotted to some degree so I bit the bullet and began to rebuild each of them. Each truss looks like this:

    The truss works by translating downward pressure on the arch into tension on the steel joist. The joist naturally resists this and creates a stressed member that can hold significant weight. I haven't taken time to do any calculations, but the finished product holds the weight of 30" of dirt with ease!

    I bought spruce planks at 1" x 4" x 12' so I could cut them to length for the 10' spans. But they were too stiff to merely bend into shape and I realized that they needed to be steamed. So I threw together a steaming tube from a 12' x 4" ABS pipe and cap ends with some valves for pressure relief/control and steam input. Connected it all to an old pressure cooker on a propane stove and, voila! Down and dirty steamer.


    I also needed to use an original truss as a form/pattern to get the correct arch.


    Two boards at a time would fit into the steamer and it took about an hour before they were "done". When they came out, the planks were hot and wet and flexible. They each went onto the forming jig to be marked, then were cut to length and c-clamped into place. Once all four planks were in place I could drill holes to match the steel and bolt the truss together.

  4. #4
    Sustainable Member 9anda1f's Avatar
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    Some detail shots of the metal joist ends showing how the ends are welded to the rebar:


  5. #5
    Sustainable Member 9anda1f's Avatar
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    Once the trusses were complete, they were positioned on the cellar walls


    Blocking and a fascia board keep everything aligned

  6. #6
    Sustainable Member 9anda1f's Avatar
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    Three layers of 3/16" plywood were screwed down to the joists making sure that no seams were in the same place


    Two heavy layers of roofer's felt and an overlapped layer of rolled asphalt roofing were next



    Then two layers of 6 mil plastic sheet that extended well beyond and below the wood portion of the roof were layed out. The air vent chimney was reused from the original installation.

  7. #7
    Sustainable Member 9anda1f's Avatar
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    Covered it all with about 30" of dirt, lightly packed (it has settled some since)



    The building adjacent to the cellar houses an in-ground 3000 gallon cistern, which connects to the irrigation pump in the cellar. Installed a new metal roof and gutters, pressure washed and applied some paint, then plumbed the gutters into the cistern via a homemade sand filter


    Finished pressure washing and painting the exposed blocks of the cellar

  8. #8
    Sustainable Member 9anda1f's Avatar
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    This cellar makes an excellent storage place for root vegetables and long-term storage for dried/freeze-dried emergency food supplies. It is dry, the temperature remains between 45F and 60F when outside temps are -15F up to 105F. I think it will also make a great fall-out shelter after I build in some living arrangements. It would be quite easy to make one, especially for places further "out there" and wouldn't need any heavy equipment as would necessary to bury a container or pour large concrete walls. It doesn't need any huge structural timbers for the roof and the arched shape helps with strength and to make it shed water. Multiple layers of covering make sure it's dry inside. Even if you don't have a welder, you could contract with one to make the joists for minimal funds.

    Anyhow, I really liked this old farmer's design (wish I could have met the guy who designed/built this) and have been looking for an opportunity to share the idea with others. There you go! If you have any questions, feel free to ask!

  9. #9
    Sustainable Stowaway northern farmer's Avatar
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    I am in awe. Amazing job. Ever thought about moving north o' the border?
    This is my life, and it's fine, it's where I spend the vast majority of my time. It's not perfect, but it's mine.
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  10. #10
    Sustainable Member DirtyHowi's Avatar
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    dude, you rock...that is some damn fine craftmanship
    Travelling to the 18th Century So, ponder away, ask questions, fume, vent, cuss, kick the dirt, ball your fists and cry out loud, then get back to work. This is the road your on and it aint gonna walk itself ~BGF

  11. #11
    Sustainable Member Arabi's Avatar
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    Fantastic job! Thank you for sharing that, it's a gem.

  12. #12
    Sustainable Pioneer ♥RĎRMR♥'s Avatar
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    Amazing...... what a job it was... and what a great result...

    I am impressed you steamed the wood yourself... i would love to know more about that! The design is elegantly simple..very nicely done indeed!

  13. #13
    Sustainable Pioneer BrightStarChalice's Avatar
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    Well, I got to see some of this in person, but I think you must have painted it since I was there. Looks very spiffy! Excellent work!
    "If I ever go looking for my heart's desire, I won't look any further than my own backyard." Dorothy

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    Sustainable Regular DonnerPartyofAte's Avatar
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    Blows my mind, yes, blows my mind the things creative people can do.
    I am in awe.
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  15. #15
    Sustainable Member toby the lesser's Avatar
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    I was lucky enough to see it in person and it really is a beautiful design. Thanks for the pictorial step by step.

    I would be happy to volunteer if you need help with any other projects.

  16. #16
    Sustainable Member weaver's Avatar
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    I would highly recommend that you put this into a PDF file and send it off to Backwoods Home, Countryside or even Mother Earth News magazine!! They love articles written by regular people and your photos of the process and progression are fabulous. Excellent work and I'm sure the original designer would be so pleased to see that you repaired, rather than replaced, his work.

    At the very least, might you consider putting this into a PDF for those of us on the forum to add to our "homestead ideas" notebook? You're an inspiration!
    looking for a great handwoven item for someone special? http://www.etsy.com/shop/PermaWeaver

  17. #17
    Sustainable Mascot SubAliasTen's Avatar
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    Awesome 9anda1f. Thanks for sharing.. Loved the steamer rig.

  18. #18
    Sustainable Member BigGreenFrog's Avatar
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    My grandparents had an almost identical cellar at our old home in Oklahoma. It was originally built in 1928 and we rebuilt it in 1977. When he ripped out the old roof trusses he built a form, laid rebar and replaced the entire roof with a single pour of concrete. We borrowed a mixer and spent an entire day mixing, pouring and troweling the concrete. After it cured the dirt was put back on top and it is still in use today, sadly by another family as we moved out of the old homestead in 1984. The recession in 1980-82 financially did my grandfather in. We were lucky enough to own some land on the edge of town and moved to it. Still gardened and had a shop but the farm was gone. Sucked then and still does...


    By the way, wicked awesome job!!
    Last edited by BigGreenFrog; 10-31-2010 at 10:16 PM.

  19. #19
    Sustainable Member weaver's Avatar
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    BUMP - just wanted to bring this incredible thread back to the surface for people to take a second look at. I wanted to get a copy of that truss metal welded-thingy to save on my computer.

    Incidentally, how's it holding up? Any updates?
    Last edited by weaver; 01-06-2011 at 10:57 PM. Reason: typo
    looking for a great handwoven item for someone special? http://www.etsy.com/shop/PermaWeaver

  20. #20
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    That's a VERY good way to set up for a POURED CONCRETE ROOF also...
    Some rebar on top of the plastic, some sides formed off to form a 'Cap' for the top of the cellar, and pour/form a concreate cap for the top...

    30" of dirt on top would keep it from thermal shocking so it wouldn't crack to pieces in the winter cold and summer heat, and you probably wouldn't have to change it again in the next couple of hundred years!

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