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Thread: 27 years later....

  1. #1

    Default 27 years later....

    We are finally going to put something up on the parcel of remote land we staked out and purchased over 25 yrs ago. Materials will be dropped on an ocean beach via landing craft from Seward Alaska, and then sling loaded via R44 on to the site.

    Our 1st structure will be a 20' Intershelter dome.

    http://intershelter.com/index.php

    There are multiple reasons why we are choosing this as our 1st structure which I won't go into now but would be glad to discuss on a different thread (pros vs cons) if someone wants to start it up... The biggest challenge will be managing and building the foundation, and being completely inexperienced in this regard, we need help figuring it out!

    It requires a 20' pad or larger hopefully. The weight of the dome is nothing - only 1100 lbs spread out around the circumference...but the dome construction and material itself is state of the art and incredibly strong.

    I'm looking for suggestions on how best to approach this. Our reality is that dealing with a bunch of very large dimensional lumber is just not gonna happen, or if it does it's going to be extremely difficult for us - its Coastal Alaska primary growth - wet forest with giant Sitka Spruce, sloped very uneven ground with lots of rock, etc, so you get the picture.

    It's an absolute jewel of a spot but not a place to just throw down a bunch of 75lb pyramid blocks (I'm hoping this won't be my best option)... The pad needs to be 20 x 20 at an absolute min but it would be nice to overbuild to 24 x 24, as any finished and level space (decking),will be super valuable, and we'll need at least some space to facilitate the assembly of the dome. Again I realize that the span is rather large, but the loading is very small. The goal is to plan a foundation which will cover the span, but be minimal in terms of dimensional lumber size (weight), and which can be applied to the difficult terrain - keeping in mind that everything must be helicoptered onto the spot for big bucks, and managed by two 55 yr olds (who aren't quite as mobile as we used to be)...

    So laying out a nicely engineered grid pattern and sinking piers will be no more than a pipe dream. Realistically, I plan on clearing off the moss/growth/topsoil to expose the rock or gravel, and then work from there with a difficult rocky, sloping surface. So what are the possibilities? Perhaps I could dig down in a few areas enough to get a sono tube or culvert pipe with cement down to help anchor the overall foundation, but most of the points are going to be floating on the surface via some kind of blocking.... obviously, there is no perma frost issue to deal with there, as the Japanese current keeps things fairly mild with the average temps in Jan in the 20s....and LOTS of snow.

    There is no snow load issue with the dome. The goal here really is to build a foundation for a 24 x 24 platform - not for a conventional cabin / building. I want to be safe but realistic on what's really necessary. My very untrained mind is thinking of using treated 4 x 4s which can be accessed underneath and adjusted over time as things move around, and anchored to some kind of pyramid pad. I wouldn't skimp on the floor sheeting, and again, my untrained mind is thinking that the sheeting could go a long way in providing acceptable integrity of the platform, and perhaps make up somewhat for a bit less integrity in the foundation.....

    So I know I'm rambling. I've wrapped my head around everything so far except the foundation structure possibilities. I'd like to build the pad 24 x 24 with 8 rows of 24' - 4x4 (2 12's tied together) at 3' intervals. So 8 - 24' runs of 4x4s on 3' centers is what I will have to prepare for....

    This IS happening this summer one way or the other! I know you can set this dome cockeyed on uneven ground if you have to but I think we can do better! It's not about what would work in my backyard or some place I can drive to - it's about making this work in an extremely remote and very challenging location..... The whole thing is kind of bizarre really, as the dome itself can be put together in a matter of hours for an almost instant super strong and efficient structure which makes perfect sense for the environment, for us, the logistics - everything really, but the foundation to support it presents a much more formidable challenge!

    Any and all ideas / suggestions will be greatly appreciated!

    Thanks

    Jack & Sue

  2. #2
    Supporting Member bullbuster's Avatar
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    Are you taking in a mini excavator or anything? If not, then you are limited as to your options.

    Here is a thought.
    At first glance your probably gonna peel off the moss and any loose material. That will tell you the next step. If it as you describe, you could go to pad and pier. Frame up however many concrete forms to make the pads/piers. Take a construction transit and determine your level. Then when you see how high the lowest one has to come up, you can plan accordingly. With enough pads poured in place, just the weight and friction should never move. Especially if locked into bedrock crevasses. And you could also dowel into the bedrock with a Hilti gun and rebar, then pour over those. If a spot hits gravel, then dig her down for the pad. Then build your deck on the piers.

    Find some young bucks to help! Good luck and have fun.

    I think there is one of those domes laying out on the mudflats by the Big Su. He didn't tie it to his foundation well enough to stop the wind from carrying it off.
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  3. #3

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    Quote Originally Posted by bullbuster View Post
    Are you taking in a mini excavator or anything? If not, then you are limited as to your options.

    Frame up however many concrete forms to make the pads/piers. Take a construction transit and determine your level. Then when you see how high the lowest one has to come up, you can plan accordingly. With enough pads poured in place, just the weight and friction should never move.
    Thanks much for your advice. No mini excavator - remember what we have will be slung in via R44 at 6-700lbs per pop. Just the idea of pouring concrete is not realistic for us - except maybe in a very limited way... say, at the corners...

    Jack

  4. #4
    Member Music Man's Avatar
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    How are you going to access it after it is built?
    When seconds count, the cops are just minutes away.
    '08 24' HCM Granite HD "River Dog"

  5. #5

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    It's about a 20 minute hike from the lake, with about a 400' of elevation gain... There will definitely be trail work to do but very manageable.... Access is via wheel plane to the beach, or float plane access to the lake....

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    Member AKDoug's Avatar
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    Gravel or bedrock below the forest duff? If you don't know that is the first thing to find out before you start. A structure on slopes without a proper foundation will be a ticking time bomb. If you have adequate soil depth, a foundation of treated posts buried in the ground will probably work. Especially on a slope you need to make sure they are sufficiently cross braced. For something as light as that igloo you could probably get away with a 9 post 20x20 system. 9ea 6x6 treated posts whatever length needed for posts, 6ea 6x6x10 treated for beams, 16ea 2x6x12 treated for cross bracing between the posts, 32 ea 2x10x10 treated floor joists (16" o.c.), 4 ea 2x10x10 treated for rim joists on the ends, 4 ea 2x10x10 treated for splicing the floor joists and blocking down the center, 44 ea 2x6x12 and 44 ea 2x6x8 treated decking for the top. Figure 3lbs per board foot for weight on treated lumber.

    Are you up in the Little Johnstone area? I did some survey work on a couple lots out there. Tough terrain.

  7. #7
    Member cdubbin's Avatar
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    Quote Originally Posted by AKDoug View Post
    Gravel or bedrock below the forest duff? If you don't know that is the first thing to find out before you start. A structure on slopes without a proper foundation will be a ticking time bomb. If you have adequate soil depth, a foundation of treated posts buried in the ground will probably work. Especially on a slope you need to make sure they are sufficiently cross braced. For something as light as that igloo you could probably get away with a 9 post 20x20 system. 9ea 6x6 treated posts whatever length needed for posts, 6ea 6x6x10 treated for beams, 16ea 2x6x12 treated for cross bracing between the posts, 32 ea 2x10x10 treated floor joists (16" o.c.), 4 ea 2x10x10 treated for rim joists on the ends, 4 ea 2x10x10 treated for splicing the floor joists and blocking down the center, 44 ea 2x6x12 and 44 ea 2x6x8 treated decking for the top. Figure 3lbs per board foot for weight on treated lumber.

    Are you up in the Little Johnstone area? I did some survey work on a couple lots out there. Tough terrain.
    Ditto, but he should go ahead and pull the trigger on the 24' x 24' deck; flat space is always at a premium, and a 10' span is a tad much for those 6"x6", IMO. That would be 16 posts instead of 9, but that's SNOW country; better to build it beefy.
    "– Gas boats are bad enough, autos are an invention of the devil, and airplanes are worse." ~Allen Hasselborg

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    Quote Originally Posted by AKDoug View Post

    Are you up in the Little Johnstone area? I did some survey work on a couple lots out there. Tough terrain.
    Johnstone was my first thought as well based on the description, perhaps the east side of Day Harbor also, tho' I don't recall any lakes in close proximity. Beautiful country, but the exposure to the Gulf sure presents a number of challenges i.e. precipitation and wind.
    “Life has become immeasurably better since I have been forced to stop taking it seriously.” ― H.S.T.
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  9. #9

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    [QUOTE=akparajack;1086626]Thanks much for your advice. No mini excavator - remember what we have will be slung in via R44 at 6-700lbs per pop. Just the idea of pouring concrete is not realistic for us - except maybe in a very limited way... say, at the corners...

    Jack, Since you will have a generator there on site one way to keep things from sliding on any slope would be to use a elecrtic hammer drill and drill down into the rock where any support goes and then use rebar set in the rock with Epoxy . You could them use pre baged mix to make a leval area for the post supports. You mention 4x4 for your support post, that is much to small and unstable. A 6x6 an mention by doug would be your best choice and he also stated a lot of cross angle braces. You could leave one peice of rebar extending up about 12" and then drill your post the same and that would stablize the base of the post.

  10. #10
    Member Music Man's Avatar
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    In about 10 years you are going to wish you choppered in a 4wheeler! That 20 min walk up hill will get to you, especially carrying supply's for the stay.
    When seconds count, the cops are just minutes away.
    '08 24' HCM Granite HD "River Dog"

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    What about House jacks and cable for cross ties and 2x4 box beams for the foundation?

  12. #12

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    Quote Originally Posted by AKDoug View Post
    Gravel or bedrock below the forest duff? If you don't know that is the first thing to find out before you start. A structure on slopes without a proper foundation will be a ticking time bomb. If you have adequate soil depth, a foundation of treated posts buried in the ground will probably work. Especially on a slope you need to make sure they are sufficiently cross braced. For something as light as that igloo you could probably get away with a 9 post 20x20 system. 9ea 6x6 treated posts whatever length needed for posts, 6ea 6x6x10 treated for beams, 16ea 2x6x12 treated for cross bracing between the posts, 32 ea 2x10x10 treated floor joists (16" o.c.), 4 ea 2x10x10 treated for rim joists on the ends, 4 ea 2x10x10 treated for splicing the floor joists and blocking down the center, 44 ea 2x6x12 and 44 ea 2x6x8 treated decking for the top. Figure 3lbs per board foot for weight on treated lumber.

    Are you up in the Little Johnstone area? I did some survey work on a couple lots out there. Tough terrain.
    Hi, and THANKS so much for the post and offering to help figure this out. At this point there are as many questions as answers. Yes you are correct - it is a Little Johnstone Bay parcel. It was a tough decision at the time, but I elected to stake a parcel that was off the beach and the lake because I wanted to be away from the surf, salt, and corrosion, and have more friendly relief to work with, a spectacular view of the Kenai Fjord, and have the option to run water generation via a pelton wheel. It was very clear that things would be more difficult in the short run, but worth it in the long run...The parcel has all of these qualities so I guess we will see how things go now that we are finally getting back on track.

    We reached the same conclusion after much discussion yesterday that we must get back in and walk the parcel, pick out a site, and poke around before we can make final determination on foundation realities. Our original plan was to just get some very basic small structure going this summer so that we wouldn't have to tent camp in that environment. Scope things out, and then have someone like Friesen's come in in a year or two and build us a proper Chalet style cabin. Then we discovered and researched the Intershelter and decided that if we could make that work it would be so very worth it. Now, the more we think about it, the more the Dome really shows great potential for us... It basically comes down to the foundation and deck/pad for the Dome.

    How big an issue do you think the frost line will be for us? I doubt if it's silty or full of clay, and I'm thinking that there's probably a good chance that it won't be a factor? Regardless - how big of a deal with this potentially be? I mean I think the reality will be that we're not going to be able to sink piers down 4 or more feet. We're just going to have to do what we can.....

    20 x 20 is not gonna be enough, as that is the foot print (in circumference) of the dome. We have to have room to walk around and work, so I'd say that 24 x 24 is the absolute minimum. I'm sure that 6 x 6s are manageable probably up to 12' lengths I would think for 2 people? Would we want to plan to use mostly Simpson hardware and through bolts for post/beam and other attachments?

    What about the option of composite lumber for decking for the top?

    I suppose when we face the realities of the amount of materials we are going to have lifted onto the parcel, adding some premix bags of concrete along with some blocking or pyramid blocks to help strengthen the foundation would be well worth it. I'm expecting that the site we will want to build on will probably not have the best foundation laying scenario - that spot will probably be back in the dark thick woods where we won't want to be - so there will have to be compromise. If I have 12 posts to anchor, then I suppose it's realistic to think that I would have several different challenges in terms of what I'm dealing with, i.e., gravel or bedrock, or deep soil.....

    We are really hoping to be able to work this with the R44 vs. the old Huey from the valley. It's just a one minute flight from the beach where we will be staged to the parcel. He can do around 700lbs per load, and it's hard to say how many loads we could manage in an hour. We pay by the hobbs meter time so "it seems" as if it would be workable and relatively affordable at this point but still much up in the air...

    Thanks again

  13. #13

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    Quote Originally Posted by cdubbin View Post
    Ditto, but he should go ahead and pull the trigger on the 24' x 24' deck; flat space is always at a premium, and a 10' span is a tad much for those 6"x6", IMO. That would be 16 posts instead of 9, but that's SNOW country; better to build it beefy.
    So a grid of 16 posts at 6' intervals. Then the rest of it would go to 12' lengths? The snow will sluff off the dome, but I suppose that it could pile up along the sides and really add up over the winter....
    thanks!

  14. #14

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    Quote Originally Posted by AlaskaHippie View Post
    Johnstone was my first thought as well based on the description, perhaps the east side of Day Harbor also, tho' I don't recall any lakes in close proximity. Beautiful country, but the exposure to the Gulf sure presents a number of challenges i.e. precipitation and wind.
    It certainly is a jewel of a spot, but very remote and full on for gulf storms and weather. Nothing to block the swell - next stop Hawaii from that beach. We did manage to get in there now and again after we staked through the early 90s. I remember how you could make your first trip in there in early summer, and the river would be coming out through the beach in a completely different place than the previous fall. The storms are so strong that they can completely rework the beach and the mouth of the river....

    This is one of the reasons that I staked across the lake and up the hill. It also puts us in the lee of the big South easterly gales that are frequent so hopefully that was a good choice....

  15. #15

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    [QUOTE=Big Bend;1086762]
    Quote Originally Posted by akparajack View Post
    Thanks much for your advice. No mini excavator - remember what we have will be slung in via R44 at 6-700lbs per pop. Just the idea of pouring concrete is not realistic for us - except maybe in a very limited way... say, at the corners...

    Jack, Since you will have a generator there on site one way to keep things from sliding on any slope would be to use a elecrtic hammer drill and drill down into the rock where any support goes and then use rebar set in the rock with Epoxy . You could them use pre baged mix to make a leval area for the post supports. You mention 4x4 for your support post, that is much to small and unstable. A 6x6 an mention by doug would be your best choice and he also stated a lot of cross angle braces. You could leave one peice of rebar extending up about 12" and then drill your post the same and that would stablize the base of the post.
    Thanks much. Are you talking about a more or less standard hammer drill or a larger more industrial drill? I've drilled concrete with a hammer drill but would it generally work in rock like that, especially if the goal is to drill holes big enough for rebar? If the post spot is just rock, then the idea would be to drill and epoxy in some rebar, then use a piece of sonotube, culvert, or just build a rough form around the rebar to hold just enough concrete to make a level surface to help spread out the load under the 6 x 6 - leaving one piece of rebar as you say to connect and stabilize the 6 x 6 post?

    Really appreciate it!
    Jack

  16. #16

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    Quote Originally Posted by Music Man View Post
    In about 10 years you are going to wish you choppered in a 4wheeler! That 20 min walk up hill will get to you, especially carrying supply's for the stay.
    Although I'm hoping that the walk up the hill will help keep us young - what I'm really planning is to have our own R44 and land it right on the parcel

  17. #17

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    Quote Originally Posted by George Riddle View Post
    What about House jacks and cable for cross ties and 2x4 box beams for the foundation?
    Hi George,

    Do you have a link to pics or info where I could understand the concept you are talking about?

  18. #18
    Member cdubbin's Avatar
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    Quote Originally Posted by akparajack View Post
    So a grid of 16 posts at 6' intervals. Then the rest of it would go to 12' lengths? The snow will sluff off the dome, but I suppose that it could pile up along the sides and really add up over the winter....
    thanks!
    8' spacing on those posts, and don't even think about using 4x4s; 6x6 is the absolute minimum. I built a 4'x10' firewood/generator shed on 4x4s, and it was a total failure. Meanwhile, the 16' x 26' two-story cabin I built ten feet away on 6x6s has had no problems. As for that snow load, at my place in Seldovia, 500 ft. elevation, it's not uncommon to get 6-8 FEET of snow over a weekend, and that's with a mountain range to break the back of the storm; I would imagine your spot to be more exposed. I'd build for 200 psf minimum, I was you.
    "– Gas boats are bad enough, autos are an invention of the devil, and airplanes are worse." ~Allen Hasselborg

  19. #19

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    Quote Originally Posted by cdubbin View Post
    8' spacing on those posts, and don't even think about using 4x4s; 6x6 is the absolute minimum. I built a 4'x10' firewood/generator shed on 4x4s, and it was a total failure. Meanwhile, the 16' x 26' two-story cabin I built ten feet away on 6x6s has had no problems. As for that snow load, at my place in Seldovia, 500 ft. elevation, it's not uncommon to get 6-8 FEET of snow over a weekend, and that's with a mountain range to break the back of the storm; I would imagine your spot to be more exposed. I'd build for 200 psf minimum, I was you.
    Ok, I agree, the 4 x 4 idea is history. So a 16 post grid on 8' centers. Would it be possible to cantilever over by 2 feet to gain additional deck space by adjusting beam and floor joist length? That way I could get to 28' with just a 2' cantilever...

  20. #20

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    Ok so the initial thinking to build a more conventional foundation meets logistical reality. The idea of building a 28x28 or 24x24 pad via conventional dimensional pressure treated post and beam is just too much. Using 6x6 for post and beam, 2x10 for joist, blocking, and splicing, and 2x6 for decking figures out to over 11300lbs for 16 post and 6500lbs for a 9 post.

    We need to be in at or under 6000 lbs which includes the 1100 lbs for the dome. I know this is doable but not like this....

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