Stilts for home needed

[Hawai'i Is Home]

Galvanized steel strapping is one option, sold at HD in 25' rolls.

When you pour your footings, consider adding an ufer ground. Better than copper rods in lava rock.

Mahalo for your suggestions!

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I would use something heavier than the strapping, either a long heavy tie plate (the ones hanging next to the rebar at HD) or some kind of post or column base, viz

https://www.strongtie.com/nonstandoffcol..._base/p/cb

Tie the lower part of the bracket to the rebar.

Some construction of exactly this sort just went up on Kilauea, across from/near the 76 station. Stack of hollow blocks, filled with concrete, big glue-lam beams across the top. The property slopes down, so the stilts put the apartments at eye level with the street.

Consider that large enough beams might require a crane or some kind of rigging.

Mahalo for the help : )

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If you shoot for 9' columns, you could cut the 20' rebar sticks in half, giving you 10' lengths. Then when you pour the footing, and while the concrete is just starting to set up, simply stick the rebar straight down, 1' into the wet concrete, sticking up 9' out of the footings. After the footings set, put the sonotubes over the lengths of rebar. Use a little timber at the top of the sonotubes to hold the vertical rebar in position when you pour in the concrete for the columns. Simple.

Putting a slab on top makes it VERY difficult. This requires massive formwork to hold the slab in place at the top of the columns. This is for professionals only.

It MAY be possible to cast a slab on the ground and lift it into place afterwards, but I don't see the point in going through that. Put a shipping container or a wooden deck on top, much easier.

Thank you, I hope to put a small home with a lanai on top...I appreciate the input : )

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Thank you everyone! Now to figure out just how many pillars would be needed for a 24x24 with a 12x24 covered lanai....

[dobanion]

I plan to do something similar, build 9' columns and then hire a crane to plop a 40' shipping container "home" on top of them. In my case I'll cast steel plates into the tops of the columns, and weld the container to them after it's in place.

[Maggie]

I plan to do something similar, build 9' columns and then hire a crane to plop a 40' shipping container "home" on top of them. In my case I'll cast steel plates into the tops of the columns, and weld the container to them after it's in place.

I considered that but decided to go with wood... the problems with insulating a container were one of the deciding factors for me. I understand that condensation can get in pretty easily. I’ll probably insulate a storage unit for storage but with windows and doors etc, I’m thinking for me, wood. It sounds like you have a great plan for yourself though!

[kalakoa]

Find "Shipping Container Homes" on HGTV, there's only 5 episodes, lots of ideas. The cold-weather build involved framing thin studs inside the container and filling all the gaps with high-density spray foam -- but all the wood was ornamental, not structural.

They did cast steel plates into the concrete so they could weld the containers down.

[Hawai'i Is Home]

Find "Shipping Container Homes" on HGTV, there's only 5 episodes, lots of ideas. The cold-weather build involved framing thin studs inside the container and filling all the gaps with high-density spray foam -- but all the wood was ornamental, not structural.

They did cast steel plates into the concrete so they could weld the containers down.

Thank you, I agree, that's a great show with lots of ideas!

[randomq]

Whatever you build, plan on at least 2ft of roof overhang, and more is better. Also consider going with a high quality white or light colored roof from HPM, with radiant barrier sheathing and 30# felt (or some other advanced water barrier) below the roof. The more the overhangs, the less hot sun will heat up your walls, and the less sideways rain will hit your house or enter windows. (We have a lot of those misty rains that like to drift through your screens.) And going with a white/light roof will reflect most of the solar gain, so your home will stay cooler. And getting nice thick high quality roofing and screws will save you money and/or dangerous roof work down the road, particularly with your home being so high up. The sheathing will keep the noise down when it rains, and prevent condensation from raining inside your house on cold mornings.

[kalakoa]

plan on at least 2ft of roof overhang, and more is better

Friends who went to 3' said it's worth the upgrade: the lanai stay dry.

[MarkP]

The question of truck vs on site comes down to volume (cubic yards) and time (how long do you need to place it). Also, additional consideration, for columns, the wet concrete is gonna need to be lifted to the top of the columns, or pumped.

Take a 10" column, that's 8' high. That's 4.36 cu/ft, or .16 cu/yd of concrete per column. That's not much, at all. You only need to be sure to get each column done, from start to finish, in one go. You don't want to fill it halfway, let the concrete set, then fill it to the top.

I'd suggest buying aggregate (crushed rock and sand) from Puna Rock or Yamada's, and having it delivered on site. Then buy Portland cement from Hilo, and store it on site, OUT OF THE RAIN. Rent a cement mixer. Now mix the aggregate, cement, and water in the mixer, in batches. Take the wet concrete in buckets up a ladder and drop it into the forms. Figure you can lift 50lbs up a ladder per trip, that's about a dozen trips up the ladder per column. Not too bad.

Don't try this approach for big concrete work, it will kill you. But for 600ish pounds of concrete per column, done one at a time, totally doable for a owner builder. I'd guess with two people you could knock out a column per hour without breaking your back.

As for the formwork and rebar and all that, take your time setting all that up, and making sure they are plumb and level. I'd put 4 sticks of gatorbar in each column, spaced equally.

I'm sure some will say just put the columns directly on top of the lava, but then in a big earthquake there's not anything really holding the column to lateral movement. By having footings sunk into holes in the lava, and rebar tying the footings to the columns, it's much more likely to stay put when things start shifting.

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I recently built a small 8' x 8' x 7' high blockhouse out of concrete blocks.  I first poured a slab with steel rebar reinforcement and some #4 copper wire in it for a Ufer ground.  I laid the block on top of the slab with rebar projecting up through the cells.  Some of the vertical rebar was horizontal reinforcement in the slab that I bent vertical.  It was a pain to get it all placed so it came up in the right places.  I decided later to put in more vertical rebar so I drilled the slab in the appropriate places and epoxied in those pieces.  The vertical rebar was not full height to start.  I remember lifting many, many blocks over my head and easing them down into place over the rebar.

I would fill the cells about every 3 courses.  I had a plastic ice scoop that held about a quart of concrete.  Drop a few scoops in then settle the concrete by stabbing into it with a short length of rebar and by banging on the vertical rebar.  I can not imagine carrying 50 lbs up at a time.  I must have climbed that ladder hundreds of times.

You can mechanically join (extend) the rebar if you have the fittings but the most common method is just overlapping by 40 diameters.  I was using 1/2" rebar so that means 20" overlap.  I made sure that there was at least 20" rebar sticking out with 3 or 4 courses to go, built up the last courses without filling them, positioned the wood members along the top, then screwed "candy canes" of rebar to the wood with the appropriate length of rebar hanging down into the middles of the cells and the hooks at the top held in the right place against the wood by the screws, then topped off the cells in the block with concrete.  When the concrete cured I finished off the wood work of the roof, sandwiching the hooked ends of the rebar between two pieces of 2 x 6 lumber with the bolts going through the hooks of rebar.  You could probably lift the whole building by the wood parts of the roof.  Where wood touched concrete I painted the wood with several coats of primer in lieu of the more traditional tar paper barrier.

It was a lot of work but I am very satisfied with the results.  In large part I was following the FEMA plans for a concrete storm shelter.  I would put one of them at each corner of your structure instead of columns.  The engineering of the columns to not collapse in an earthquake is not a trivial task whereas the storm shelters as specified by FEMA are designed to stand up to a house falling on them.  Plus, four storm shelters, amiright?  One at least can be your mechanical room for pumps, etc.  Another for electrical, then two more for unspecified storage.  You will be glad for all of that in a real hurricane or earthquake.

Next time around I will probably do what it takes to build an oversized slab both in thickness and horizontal dimensions and have it poured professionally with a concrete truck. It is really great having a nice flat clean surface to work on. I may be alone in thinking this but having a thick layer of fill under the slab and a good strong slab to tie everything together at ground level would help a lot during an earthquake. In an earthquake the ground is moving. Let it move underneath the structure. If the fill acts like a bond breaker like flowering a cake pan then the house is subjected to less severe shaking.

Anyway I wish I had poured a larger, thicker slab and had someone skilled do it and not tried to mix so many bags of concrete by hand for the single largest continuous pour. Hand mixing was sort of necessary when building the walls due to the slow rate of progress.

[Maggie]

plan on at least 2ft of roof overhang, and more is better

Friends who went to 3' said it's worth the upgrade: the lanai stay dry.

Mahalo! I agree... I was also thinking 3 feet. I had a large lanai on the Windward side of Oahu and the rain still blew in. That was great information you shared and I appreciate it, so much of this will be new to me even though I had a home on Oahu, since each island is different so I really appreciate all the suggestions and insight people are sharing ✿◠‿◠  it’s also really nice when people take the time to explain how and way and where to get the best supplies/deals... mahalo!

[Hawai'i Is Home]

Whatever you build, plan on at least 2ft of roof overhang, and more is better.  Also consider going with a high quality white or light colored roof from HPM, with radiant barrier sheathing and 30# felt (or some other advanced water barrier) below the roof.  The more the overhangs, the less hot sun will heat up your walls, and the less sideways rain will hit your house or enter windows.  (We have a lot of those misty rains that like to drift through your screens.)  And going with a white/light roof will reflect most of the solar gain, so your home will stay cooler.  And getting nice thick high quality roofing and screws will save you money and/or dangerous roof work down the road, particularly with your home being so high up.  The sheathing will keep the noise down when it rains, and prevent condensation from raining inside your house on cold mornings.

Thank you, You really seem to know what you are talking about and I appreciate you sharing information with me : ) I hope to start building this summer but I'm trying to get a good idea of what will need to happen first and this has been a huge help!