Height to width ratio for sound structure?

[Fossil Farm]

:laughing: Just trying to save the effort of people suggesting things I will not consider.

Maybe keeping it movable is too much of a negative in this size building. I had figured several screw in anchors would handle any lift/leverage issues, since tiny houses are roughly the same height/width dimensions only scaled down to a 8' wide package.

Screw in anchors, seriously ??? You say you cannot get equipment to the site, so exactly how will this be accomplished ?? Tornadoes and not a problem. Unless it is an F-0, a direct hit will blow just about anything apart. Straight line winds are your main concern. Our 100+ year old timber frame barn was destroyed by straight line winds before the term became common place. The barn went down, but its location probably saved the house from being destroyed. Winds picked it up and moved it a few feet and dropped it. I am sure the barn weight was many, many tons.

You say you cannot get equipment to the site, but want to make the building mobile ?? Think you need to restart your design and spend a few bucks on a construction engineer if you are serious. In hurricane county, many say that round buildings are the way to go, and in hurricane Sandy, some buildings with piers 20 feet deep or deeper and the first floor above normal storm surge withstood the storm.

 

[Jim Timber]

Earth Anchors Scroll down to underpinning.

I can't get equipment there now. That's not to say it will always remain that way in the future.

 

[hhsco]

getting to sound like it might be easier to just heli-drop a doublewide down there. that or just float a shed and build a treehouse for the lounge!

 

[Jim Timber]

I have a very distinct reason for the design of this building. I may need to make it wider with a lean-to or something on the main floor. Being two story is key to it's functionality. Heat on the ground floor, rises up to the second story. Solid main floor so doors can be sealed against rodents. Second story full height so that windows can be on all sides for hunting. Main floor is where the atv will park - drive up hunting shack with no walking for disabled hunters.

The portability part has to do with how the trees are managed. If the section the shed is in is logged, then it changes the dynamics of the deer movement. Being able to put some wheels under it and towing it around has an appeal, but that means it needs to at least be built in such a way as to be disassembled to trail width.

Cement board siding is chosen for theft deterrence. The building will be far enough away from neighbors to give time to gain entry undetected. So the only option I have is to make it difficult to get in. I would love to get a conex box back there, but it would require a heli-lift: the spot is 1/2 mile from the nearest road in any direction. Right now the widest path to the spot is about 5' (which will change in the future). Accessing it requires crossing a 300' wide section of swamp, which is why I can't just drive a truck up there. The plus side is that no one else can drive a truck up either, and that will limit the tools they're able to carry in to use to break in.

 

[JimRB]

Rodents seem to be able to get in if they want.

The building is going to be heavier than you can tow with a ATV or even a small tractor. Moving the building does not seem likely or at least easy.

A determined thief can be in a building in 10 minutes with modern cordless power tools. Windows break with hammers, security bars get cut with electric cut off tools...

We have a had a few tornadoes blow through the neighborhood. Houses in the path suffer greatly. Those that miss the winds do fine. There are 100 year old house and barns built on field stone stacks still standing, but of course they were never in front of a 100 mph wind.

We see deer on the mountain bike trails that were harvested 3 or 4 years ago. They did not do clear cut but a pretty heavy thinning. Maybe the deer come back after a harvest so moving is not needed.

 

[JimRB]

Part 2. One of my coworkers compound (30 acres and a few houses) was in the path of a tornado a few years ago. Half of her new house was torn down by the winds. We looked at a Google satellite map and you could see the woods torn down for a few miles. If a tornado goes through and it is a good sized one there could be a 1/4 mile swath of destroyed forest. Your hunting lodge could just be some of the debris and part of the new meadow the tornado cut. Worrying about a tornado might be overworrying.

 

[KennyG]

I think the purists are being a little tough on JT. With enough tornado, any structure is at risk and it's not like this is a home. The height to width ratio is not a concern. Sheath it properly and it will not buckle.

If I were doing it, I think I would put in a full perimeter footing with anchor bolts. I don't think drilled in anchors are of any value in this situation. My guess is that building code would endorse this approach for a two story building. Of course, if I were doing it I would go ahead and pour a concrete floor. Over time, the value of having clean concrete and keeping varmints out would make it the better choice.

 

[Jim Timber]

Who said anything about being towed with the atv? I'd tow it with a D6 Cat if I had to. A tractor would likely do it just fine though, the land this is going on has a 20' elevation change over a quarter mile.

This spot is on top of a 30' tall ridge, so it's somewhat protected from straight line winds. It's also got a full stand of mature oak surrounding it.

Deer coming back after logging isn't the concern either - it's what I do with that section of land if I harvest all the trees. Maybe I'll convert it to a pine stand and then there wouldn't be any visibility. Stop trying to decide how I'm going to use my property, it's not working for you. :confused2:


So is there any kind of building guide for multi-story homes? If I say any more, I'm afraid I'll get told what cartridge to hunt with, and what kind of truck I should buy, or maybe that I shouldn't try to bring handicapped friends into the woods, but no one's pointed me towards anything relating to my actual question other than saying they'd do something else. I know about sheer walls, and foundations, and slabs, and anchors, and live loads, dead loads, snow loads, truss design, joist strength, even short wall sections in sheer walls - but what I can't find anywhere is info on height to width ratios, so silly me asked a question about them and every answer has included everything but.

 

[ishiboo]

So is there any kind of building guide for multi-story homes? If I say any more, I'm afraid I'll get told what cartridge to hunt with, and what kind of truck I should buy, or maybe that I shouldn't try to bring handicapped friends into the woods, but no one's pointed me towards anything relating to my actual question other than saying they'd do something else.

Welcome to the wonder of the Internet. By posting a thread, you've opened yourself up to not only answering your original question but everyone's two cents on everything. You've also provided evidence that you're going to be attempting an incorrect method of building it, so of course people are going to be providing their input regarding that despite it not being part of your original question.

Of course there are plenty of construction guides/building codes/etc., most of which would be specific to the type of building you want to build - stick, post, steel, etc., what materials you are using or want to use for sheathing, etc. Again, given your requirements for an "easy" foundation with limited access, I think a post frame building is the way to go.

I know about sheer walls, and foundations, and slabs, and anchors, and live loads, dead loads, snow loads, truss design, joist strength, even short wall sections in sheer walls - but what I can't find anywhere is info on height to width ratios, so silly me asked a question about them and every answer has included everything but.

My concern is that if you "knew about" all of those things in a depth sufficient to complete this project, concrete pads would probably not be something you were discussing - unless they were quite large (i.e., a mono slab would work) A two-story building only 16' wide does have the opportunity to provide leverage when wind loaded on the foundation, and needs to be anchored to a real foundation.

What you're asking for though - a simple "height-width ratio" to answer your question - doesn't exist. The technical name for this is the building's aspect ratio, but it's a rather meaningless factor computed after an architect designs the building, or they design with a specific aspect ratio in mind for a particular efficiency, appearance, etc. Built it correctly with conventional building methods with the dimensions you are speaking of, whether that be stick or post or steel, and you will be fine. A 16-foot wide, 2 story building is not complex. If you can't figure this, it might be time to hire a contractor/architect to design and build this for you... and then you won't have to worry about us getting off track.

 

[hhsco]

.30-06, Chevy, go for it.
jokes
here are some engineers saying they don't have a particular rule of thumb for height/width
Structural engineering other technical topics - Building Height To Width Ratios

I would think that as long as you frame and sheathe it correctly (and don't build it to skyscraper proportions in a swamp) then the height/width wouldn't be all that crucial for just a two story (or story and a half) building. A rectangle is a rectangle. If it isn't secured to a concrete foundation then yeah it will probably get blown away by a tornado no matter what its dimensions- but that would probably happen to most buildings not best described as "bunker-like".

Everybody could probably take a step back from being internet-angry.

(fwiw, I would pour a monoslab!)

 

[TCJatko]

One fundamental requirement to multi-story homes is that they MUST have a proper foundation including footers and frost walls. One cannot construct more than one story on a floating slab. I'd suggest you shelve your plans until you can get proper access to the site.

 

[ishiboo]

One fundamental requirement to multi-story homes is that they MUST have a proper foundation including footers and frost walls. One cannot construct more than one story on a floating slab. I'd suggest you shelve your plans until you can get proper access to the site.

Lots of two story houses are constructed on floating slabs. Not common where I live (we all have basements), but where I work (Las Vegas) has a ton of post-tensioned slab foundations with two/three story homes. There are also 4-5 story buildings on top but I believe many/most may make use of piers under the slab.

I wouldn't hesitate to build the structure the OP is speaking of on a monolithic slab.

 

[Cord]

Believe it or not, but a building designed to code is intended to survive a direct hit from a category 1 tornado. Now, this is a really weak storm, not the monsters we see on TV. Those storms will wipe a foundation clean. "Survive" has to be qualified. This means that the building isn't a total loss. The roof stays on, the walls stay up and the occupants are safe. To achieve this there has to be a tensile load path from the rafter or trusses all the way down to the foundation. The foundation keeps the building from being lifted up.

For your building, if you sheath it with plywood, nail it well and don't have any large openings (like a door) on a corner, then you'll be fine. The plywood will act as a shear panel and keep the building from racking. If at all possible, try to get a full sheet of plywood on each corner.

This is empirical design and I'll take no responsibility for a life safety issues that may crop up.

 

[myjohndeere]

Jim Timber,

If you are still concerned about height to width ratio there is a simple calculation to determine overturning moment. overturning moment is the tendency for a structure to tip over due to wind loads in this case. some things must be know first; dimensions, weight, roof slope or peak height, roof overhangs, peak sustained wind speed for your location(I have charts for this), and terrain such as hilly, flat, wooded, ect.

If the weight of the structure alone cannot resist the overturning then anchors or deeper foundations must be used.

let me know if you are interested and i can help you out. I am a civil/structural engineer working towards professional licensure, my word, advice or calculations are not legally binding.