Height to width ratio for sound structure?

[Jim Timber]

I'm in the design phase of what will be a utility shed on the main floor, and a bunk house/ lounge on the second story.

I'm thinking 16' wide would be nice, but only want to make it 20' long. I want a full 8-9' ceiling on the ground level, and at least a 7' ceiling upstairs. I'll probably be using dimensional lumber for the structure, so I need to build with that availability/cost in mind.

The questions I have are how tall can you go before wind becomes an issue (we are in tornado country), and if you had a shed roof (slanted) would it be less desirable than a typical gable roof? Prevailing winds are from the NW, and the peak would be aimed South, so it should deflect some, but it's also a larger surface to push against.

I'd like to eventually have a deck for the second floor, so that could be incorporated to help keep it from being too skinny.


The foundation will be concrete pads. It'll have a full ground floor for structure.

 

[ace10]

...
The foundation will be concrete pads. It'll have a full ground floor for structure.

What exactly do you mean by concrete pads as a foundation?

 

[Jim Timber]

The set in place blocks. Not a drilled/poured foundation.

 

[Shenandoah]

Jim,

Building codes will most likely not allow for those 'pads'. They certainly don't in my area for any structure where the roof edge is 10 feet or more off the ground. That includes the gable ends. Any two story building will exceed those limits.

Additionally, you want to have the structure firmly anchored to the ground as much as possible without allowing for wind to get under the structure and lift it in high winds. I know it will be heavy, so is a fully loaded Boeing 747, lol.

I would strongly suggest a trip to your local building authority to get some real answers and parameters for what they will allow you to build. You'll most likely need a building permit for a structure that size. We need one for anything over 180 square feet around here, as an example, unless it's a farm outbuilding. And many times they dictate the HOW to build for certain elements of the structure.

 

[Jim Timber]

Well, it is a farm outbuilding, and a permit will have to be pulled for the size. The only height restriction is that it can't be over 34' mid span without a variance.

I'm trying to avoid needing equipment, as there's no access. I'll use a generator to run my air compressor, and haul everything in via atv trailer.

 

[BHD]

If one does a story and a half type build you do not increase the height that much, over a single story building, this is one I spotted and considered, I wanted a little cabin,





the original barn was,

Ashokan Barn Plan
I felt that not filling in the back corner would be a waste, and I for the cabin Idea wanted a sleeping loft that would be nicer,

 

[ishiboo]

I'm in the design phase of what will be a utility shed on the main floor, and a bunk house/ lounge on the second story.

I'm thinking 16' wide would be nice, but only want to make it 20' long. I want a full 8-9' ceiling on the ground level, and at least a 7' ceiling upstairs. I'll probably be using dimensional lumber for the structure, so I need to build with that availability/cost in mind.

The questions I have are how tall can you go before wind becomes an issue (we are in tornado country), and if you had a shed roof (slanted) would it be less desirable than a typical gable roof? Prevailing winds are from the NW, and the peak would be aimed South, so it should deflect some, but it's also a larger surface to push against.

I'd like to eventually have a deck for the second floor, so that could be incorporated to help keep it from being too skinny.


The foundation will be concrete pads. It'll have a full ground floor for structure.

You can go to 2-3 stories with conventional building methods with no issue.

But you're in tornado country and worried about wind. No matter how small of a building you build, it's waiting to be picked up/moved when built just sitting on concrete pads. I'd never build anything that substantial simply sitting on pads.

Given the remoteness, I would recommend building it using a post frame method with posts set into concrete, then stud/side conventionally with OSB or wood paneling thus making shear walls. This will be a very strong structure that is also economical. It will be easier to get bagged concrete out there, and all you need is a post hole digger for the holes.

 

[hddnis]

What about a pole building?

I don't know if code allows them in your area, but they are fairly common here and many are a garage on the bottom and living quarters on top.



Mr. HE

 

[Jim Timber]

This will be insulated, and covered in hardy boards. I'll run heat of some form in the winter.

Pole construction isn't a bad idea, but poles that long get expensive, and it would require a much more substantial main floor to keep from heaving in the middle where the joists weren't supported with footers. We have 5' frost depth. I mainly wanted it free floating to constrain costs/labor. I could anchor it down like mobile homes do. Maybe I need to get my buddy's Alaskan mill for a week and make some pole and beam wood when it comes time to putting this up. I know my 71cc Jonny isn't ideal for milling.

Loft for sleeping isn't what I want. I want a loft for occupying at walking around not hunched over height. It will serve as a living room (why I called it a lounge). I'm 6', and I have friends and family who are 6'4+. 7' minimum upstairs at full width, no less. I also despise dormers with a passion, and barn roofs make me vomit.

 

[ace10]

You can stick build on a wood pier foundation. Strength of traditional residential construction without the need for yards and yards of concrete.

Under no circumstances would I occupy a structure that relies solely on gravity to hold it in place.

 

[kraftykeltic]

put in piers for a foundation, should have no problem with them getting to 5 foot and would save a lot of concrete and insure that the building stays level. could also use them to tie the building down. 16 feet wide means that you will be using engineered lumber for floors for a 16 foot span, or you will be putting in center piers for the building.

 

[Jim Timber]

You don't think I could anchor it sufficiently with cables?

Mobile homes get ripped to shreds from their 2x2 construction, not lifted up and flung. I'll be doing 2x6 on 16" walls.

 

[ace10]

In 2008, we had a small microburst in my area. It picked up my (brand new, not even registered) 24' enclosed car trailer then rolled it out into my field. Like someone tossing dice at a craps table. Wind is a scary force.

 

[Jim Timber]

put in piers for a foundation, should have no problem with them getting to 5 foot and would save a lot of concrete and insure that the building stays level. could also use them to tie the building down. 16 feet wide means that you will be using engineered lumber for floors for a 16 foot span, or you will be putting in center piers for the building.

I can get 16' 2x10's here which is sufficient for a 40# live load on the second story.

I fully intend on having multiple pads under the main floor to support a lighter framing.

 

[Jim Timber]

In 2008, we had a small microburst in my area. It picked up my (brand new, not even registered) 24' enclosed car trailer then rolled it out into my field. Like someone tossing dice at a craps table. Wind is a scary force.

Did you have it anchored to the earth?

 

[ace10]

Did you have it anchored to the earth?

Of course not. It's a trailer.


I'm going to step away from this thread. It would appear that you are set on going down a path that is fundamentally not something I would do or would advise someone to do. At the end of day, this is a twenty five foot tall building... nothing to mess around with.

Stick with time-tested construction techniques.

Best of luck to you.

$0.02

 

[Jim Timber]

Which is precisely why I'm concerned with height to width ratios.

 

[BHD]

I also despise dormers with a passion, and barn roofs make me vomit.

can you be a little more clear on how much you do not like dormers and barn type roofs,

 

[Jim Timber]

: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.

 

[BHD]

about the only way you will have a "tornado proof" is to dig down and put in a full concrete foundation and run rebar up and pour a concrete reinforced wall that is solid and with rebar in it both directions at least 2 foot on center and better at 12" spacing ,and it should run continuous from footer to roof deck, and pour a structural reinforced concrete roof deck, and that does not mean a tornado will not damage the building but that it will still be most likely standing after the storm,

and the shape of it can help as well, such as pyramid or domed shaped, (and I do not care if they do make you vomit)
http://www.deltechomes.com/assets/Image/Hurricane 2013/Anatomy-Hurricane-Resistant-Home_all-in-1.pdf
Tornado-Resistent Concrete Houses

In a Nutshell | Hurricane and Tornado-Resistant Concrete Houses

unless one uses a special shape that will not let the wind get to it, pyramid or dome shape, and going to have a conventional building and a two story building at that, you will need a foundation to work like an anchor, and then build a building that is structural to the point that it can with stand the wind pressures, and wood is not strong enough in most instances, and just building out of concrete or concrete block is not enough either with properly sized and placed steel reinforcements and building it in a way it is all tied together so it reacts as a single unit, that is one of the problems of modern wood building you build a floor, then walls then a floor and walls and then a roof, and besides a few nails holding things together It a group of components that are not working as one, (why modern building codes require all the metal clips and some times tie bolt from foundation to roof, to try to make them work as one,

but on wind if the wind speed is doubled the force of it is cubed.

WIND POWER RIDDLE
Riddle: A hurricane strikes a city on the Gulf coast with a maximum sustained wind of 100 miles per hour. The city rebuilds from this hurricane. There is another hurricane heading toward the same area of the Gulf coast. A weathercaster mentions that this next hurricane will have the wind power to do twice as much damage as the previous hurricane. Under this condition what would be the expected maximum sustained wind from the next hurricane?

Answer to Riddle: There is not a linear relationship between wind speed and the damage that is produced. For example, a 150 mph wind would not do twice as much damage as a 75 mph but rather it would produce many times over the damage of the 75 mph wind. The relationship between wind power and damage is going to depends on factors such as building design, wind gusts, wind duration, wind direction change and the amount of buildings per unit area. When considering wind power alone there is a cubic relationship between wind speed and the power produced by the wind. For example, suppose the wind speed is 15 mph and produces 3,375 units of power (15^3). If the wind speed is doubled to 30 mph then the power produced by the wind would be 27,000 units (30^3). As the wind speed increases the power produced increases at a rapid rate.

Assuming the cubic relationship mirrors reality which is does not for all wind speeds and situations, if the wind is 100 mph the damage produced will be 1,000,000 units of damage (100^3). If the units of damage are double to 2,000,000 then the wind speed that produced this damaged can be found by taking the cube root of 2,000,000 which has a value of 126 mph. Thus, the damage produced increases significantly as the wind speed increases, especially as it increases above hurricane force. The 126 mph wind does twice the damage as the 100 mph although the increase in wind speed is about a fourth greater. Damage increases at an exponential rate as wind speed increases in a hurricane.

a simple blocks for footers will not hold your building if the winds get strong, all most regardless of construction type or height, (the height will increase the wind load)