Help squaring posts for a pole barn

Getting ready to set posts for a small pole barn and I want to make sure I have my dimensions correct when I set my posts so asking for professional help here. It's going to be small to start. 20x20 it will have 3 posts along the outside and 3 more in the inside center total 9 all together. At what measurement should my posts be for it to be square and so that I can run the 2x8x10 around the top. I assume it would need to be less to account for the 1.5" 2x8x10 running around the outside of the posts? Thanks. Any other info appreciated.

Niteblaster - where is your 20x20 dimension?
is that the inside room dimensions or is that outside corner to corner

what size posts, 6x6?

I can sketch something up quick in CAD with whatever dimensions you need

Use Pythagorean Theorem. A2+B2=C2. Your hypotenuse should be 28.1" from outside corner to outside corner if my math is correct.

ol'dad

That answer wasn't in the back of mu math book.

The diagonal to the outside corners of your posts of a 20 x 20 building should be 28,28 ' the the building will be square. Then string a line between the outside posts and set the center ones to the line.

the math for that is a square plus b square is c square......... consequently the root from c gives you the length of that line.


In your case (20X20) + (20X20 = 800 The square root of 800 is 28,28

330 beat me to it

I would consider buying 2x8x20 foot planks for the uper plate. if they are available. Will give your building more stability. old243

20x20 is outside dimension, posts will be 4x6 and 20' planks are not available I don't believe have not gone to order yet going this afternoon if they are I will go with them.

nite - PM sent with email.

20x20 is the same as a 45x45x90 degree triangle. So being a retired design engineer the shortcut is length of the leg times 1.414 (1:1:square root 2) gives you the hypotenuse (28 feet 3.36 inches).

Scuba got it, just a different route.

Ok so I’ll take this question one step further. You measure your hypotenuse and you’re out an inch, so you adjust. Now it throws off the hypotenuse of your other angle. So I know you have to take away or add to the other length I just don’t remember which.

Which is it and what’s the best way to do it?

The T-man mathematicians are just showing off. Just measure diagonally from outside corner to outside corner and then do the other two corners. Adjust until the two measurements are the same.No need for complicated math formulas.

What Lug said...

×2.
I will say though, this site is full of an array of very smart people. A bunch of "mountain men" trappers talking about hypotenuse and A2+B2, whodathunkit!
I love this place!

If you are "out" an inch, you shorten the 'long' side by half an inch. You need one fixed corner point that you never adjust. It is your reference for all other posts

YOu are getting great advice- you can even line out those posts w/ the 2x8s laying on the ground and already have them measured diagonally. It can also be said that if your 2x8s are the right length- a string can be used for your corner checks and you can leave the tape at home.

The hard part with squaring pole buildings is getting them square both at ground level and at the header for your trusses or rafters. Posts tend to bow and twist some.

Once you have it squared at ground level you just need to make sure your posts are plumb and you’re good to go.

There's a reason I never, ever build ANYTHING!

Moosetrot

Setting your initial post and putting cement in the hole and bracing it to the level both ways will work. Then you have a constant control point to work with.

Measuring becomes the normal at the base/top of the new posts to be accurate. Once all post are in, cover around the base where concrete will attach.

Use the base of the poles for your cement floor forms. That will hold it all in well and make it easier to pour now than later with sides on.

If your diagonals are equal, you are square.

There are some of the most skillful artists in building I've ever known , right here.

At 19 feet 9 inches x 19 feet 9 inches you will be 27 feet 11 3/16 inch diagonl .

Making the calculated dimensions just give a starting point. Once you get your anchor point just tweek the other three corner posts to get as close as you can to your calculated dimension. Not rocket science just take your time. You probably won't get it perfect, but it should come out pretty darn close. Building a pole barn for the first time is a lot of work but when done is a thing of beauty. Three years ago my son and I built his 30' x 40'. Biggest hassle was auguring the post holes, lots of good to big rocks, and then jockeying the 8x8x20 posts. those suckers are real heavy.

I wouldn't believe this guy if he said the earth was round !

Thanks for all the help guys next problem is finding treated lumber. Seems to be a shortage around here. I had to order longer lengths and hope they get shipment in tomorrow to finish the rest of my order.

There is a shortage of treated lumber everywhere right now. Been that way for a month or more. I was at my local lumberyard to pick up some 2 x 12 x 8 treated to build a deck steps for a customer. All they had was a handful of 2 x 12 x 10’s. They gave them to me for the 2 x 8 x 12 price.

For large measuring like yours I use the 3/4/5 triangle. A triangle with one leg any unit of 3 with the other leg the same unit of 4 with a Hyp of 5 will have a 90 degree(right angle) between legs. I've laid out large rectangles using long 1x4's or even rope. The woods costs a little but when screwed into magic triangles can be placed at each corner and moved around easier until all squared up. I make 15'x12'x 9'. Haven't yet not found use for the 1x4's reused in the project so no money lost on them.

Cheapo Depot can special order lumber up to 26'.

If it is going to be steel sided, I would make it 21x21

I built mine to those same dimensions and started out with 9 posts, also. I ended up taking the middle post out; just in the way.

Ha! I was leaving an allowance for the width of the steel siding!

ol'dad