While there is no intent to claim; an engineering or architectural “stamp of approval” or such. YOU WILL MAKE YOUR OWN DECISION/ I accept no responsibility whatsoever.
There are things to consider when raising a building that use to stand 10 feet off the ground/ to over eighteen feet off the ground. You need room for 3: 6 foot bales/ at 25 feet across you also need to stagger the bale line/ and for considerably more room you do need to tip them over onto forklift tines. Because you can’t sit them against the walls/ they weigh too much.
For your consideration: the basic wind load in 64 mph constant wind is about 20 lbs per sq foot. While that might not sound like much; you have a 75 foot long building that you expect to raise at least 18 feet high. If we add 2 foot to that for safety, due to wind pressure on your roof: we then call it 20 feet tall for simple math; in the purposes of this. A 75ft building with one side facing the wind times 20 feet tall=1500 sq feet of barrier to the wind. By simple math 1500 sq feet times 20 lbs per sq ft of wind pressure =30,000 lbs of pressure pushing on that side.
What becomes critical is: that the wind must push up or go around the building; which causes density to increase. Air weighs 14.5 lbs per cubic ft, denser is heavier. But the big reality is IF THE BUILDING MOVES; even a little, that weight transfers; “like a crowbar” at your attachment to the base. Which is now being pushed at the top with a “twenty foot of height to one a one foot of space” at the bottom; just for simple. IF the building itself is that size. So now that 30,000 lbs against the side of this building; height divided in half to average the actual top push, as a crowbar effect; begins to equal: times roughly 2 times more pressure at the upper and lower joints= primary, is now at the upper joint which keeps the building from falling down. A functioning pressure of roughly 30,000 lbs over the wall surface; without gusts/ pushes entirely against the lower seam where concrete wall meets wood wall. But at the joints, where collapse occurs; the pressure multiplies and must fight against it all so we multiply by roughly two. If there is any movement in any location on the building; a joint will fail, causing more to fail/ and roof weight begins to add in. A ten percent lean adds ten percent more vertical weight the structure must hold up.
So now we look at the joint structure which holds the horizontal roof to the vertical wall: because how long that is and how stable that is determines if the building will stand. If you have 10 supports per side/ you have two sides holding the building against the wind or twenty supports; if only two more on the ends that equals 24 supports in all; and what is left of the sides; beyond the opening; must have x bracing. A critical pressure of 60,000 lbs at the roof/ wall joint divided by 24 = 2,500 lbs per joint. A car sitting on that joint. IF the building moves at all/ half of that if it does not.
If you bring the building back down to ten feet the pressure is less than half of that. But that makes your joint from concrete wall to wood wall very important. So putting concrete blocks under that portion of the building to raise it to your height of 18+ feet gives you a building that has withstood the test of time at a lower level; basically the same. But will not survive at the new height: if the blocks fail/ or the building can be pushed at that concrete to wood horizontal joint. Putting it on concrete blocks means while the building itself can be all right; so long as nothing moves. The 6 foot tall or more blocks x 75 feet long; must withstand the forces of not moving against the wind; along the entire wall. Or the building falls down. And your weight on top of that wall will vary tremendously due to a variety of factors. A relatively light 10,000 building will have weight gaps at that seam; making it much easier to push there. With minimum corners and open doors: the wind goes through those doors to push upon the opposing second wall; adding to the stress of weight; but not increasing the joint stresses greatly. This pressure also works to raise the roof; but generally not greatly until you get tall. Lifting it, even a little less weight on your concrete blocks allows for any imperfection to let the wall move. Your 75 ft concrete walls/ or short corners are not likely to stand, particularly in gusting wind; it it moves at all, concerns begin at 55 mph, with gusts; it is possible things could go wrong. Or more directly you don’t have concrete walls anchored into the floor, which is a must with the anchor itself extending down into the ground in more concrete than a simple floor would have. Which means, without that; you don’t have your wooden plate on which your wood walls will stand on top of that concrete tied down either. Thirty thousand pounds of sideways force, over 75 feet=400 lbs per horizontal foot. Ten thousand lbs on top, reduces that force to sliding 130 lbs per foot/ divided by two walls: which makes it 65 lbs per foot of friction. If the pressure is the same all the way down the wall. But that is for each foot over 75 feet, and you have walls that are going to be ‘up and down” (heavier here/ lighter there); and the wind, particularly as gusts; can get stronger than 64 mph. Got six horizontal feet between your wooden plate and concrete wall; with no real weight= 2400 lbs of push, in that area; ANY MOVEMENT IS BAD; but the wood plate is involved and resisting movement. UNFORTUNATELY, even a little movement in the plate results in a crowbar effect on the wall/ roof joints. Tying down block would include steel rods and solid sections in the wall; which come up from beneath the floor to the top of the blocks; and are then bolted to your seam section. Or blocks can be turn out as perpendicular supports for concrete blocking to create tee shapes in the wall for support, with anchors built in. The simplest way to resolve that would be to use the large concrete 2x2x4 blocks which weight 2500 lbs each 4 per side; with cabling going through the side wall up to both levels of the roof trussing so as to tie it all together. On the back side of the side walls; to anchor it down. While that will raise and fall due to freezing/ so will everything else so it should not be a big problem; or dig them down into the dirt. As to your roof/ wall joints: simple angle bracing adds a lot of strength, and takes only a little room; at worst one bale less on top per six feet. But at the building has survived the wind this long once your lower walls are stable, and the building itself cannot be moved or pushed off that lower wall; you might get by without the added strength. I would sacrifice a little space for security; as is the money spent will not be lost. But I prefer strength to being wrong. Jim Osterbur