Squaring up structures / planning layout ... shortcut?

Discussion in 'Remodel Forum & Blog' started by Lakee911, Aug 6, 2009.

  1. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

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    Hi All,

    Suppose I'm building a simple rectangular structure and I lay out everything with string to establish the sides and elevation. Paralleling the strings is easy, but to square it up, I'd measure the diagonals, right? Well, is there an easier way than to shift, check, shift, check, shift, check to make them equal and thus square?

    So, given a parallelogram with sides equal to X and Y, diagonals equal to D and E and unknown angles, is there a formula I can plug this in to such that I get answer that tells me how much to shift one side such that I get a rectangle with sides equal to X and Y, diagonals equal to D equal to E and 90 degree angles?

    I have strings setup, but even with a helper, I think it's going to be tough to accurately measure the diagonals over and over again. Maybe set up extra batter boards to stretch a tape across?

    Thanks,
    Jason
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    One of the easier ways to create a 90-degree angle is with a triangle whose sides are in the ratio of 3:4:5. It will create a perfect 90-degree angle. You could make it out of anything, 2x4's cardboard, whatever. The longer you make them, the easier it would be to compare to your existing lines. 6'x8'x10' or anything with the 3:4:5 ratio will work.

    If you are going to do this a lot, you can buy lasers that create beams 90-degrees.
  3. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

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    I've never been a big fan of that method ... it's tough to measure the diagonal (hypotenuse) on the edge of a string. If I'm building something and I can hook my tape to something it's much easier.

    I started to try to solve my original problem and it's tough because there are a lot of angles and not to mention that when I shift one side of the parallelogram, it will no longer have the same dimensions...

    Who said garages have to be square? ;)

    Thx
    Jason
  4. hj

    hj Moderator & Master Plumber Staff Member

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    square

    Measure one side and square the dimension, then do the same to the other side. Add the two together, and then take the square root of that number. It will be the EXACT dimension for the diagonal, but in the real world, it may only get you close to square, if your original measurements are off, or the form is not a perfect paralleogram. Therefore, after you adjust the form to that diagonal dimension, you will still want to check the other diagonal and make any slight adjustments.
  5. jimbo

    jimbo Plumber

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    Seems like you are trying to out-think this. Watch a good framing crew in action. They can measure the diagonals, and based on how much the differ, they know which side to smack with the sledge and whether to smack it once or twice. Usually two iterations max and they are done. They will have the wall up before you get your calculator out of the case.

    Small houses and great buildings are done like this every day.

    When you get to skyscrapers, they do use optical measuring equipment, since the tape measure gets funky over 50' or so.
  6. Terry

    Terry Administrator Staff Member

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    I use the 5, 4, 3 method.
    It's been working pretty good for me.
  7. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

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    That's what I need ... optical measurement! It'll be perfect, but then my wall will be out of plumb on one end so when I get up top it'll be caddywompus again. heh.
  8. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

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    Measuring the diagonal wasn't so bad. It only took two tries. My 'eyeball' was only off 3/4"! :)

    So, now my garage is perfectly square (within my tolerance of 1/8"), but it's not square with my house (off by 4" across 22')that is ~36' away or my neighbors garage (off 2 1/2" across 22') that is ~9.5' away. It is square with the old foundation and the lot line....

    Shall I carefully rotate it, or will something like this never be noticed?

    Thx
    Jason
  9. rburt5

    rburt5 Member

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    Do you happen to be an engineer or an accountant? Nobody else would ever expect a garage to be within 1/8" of being square. The plywood that you nail up probably won't even be that square. Or maybe that's why I don't do construction any more :D. To answer your question...4" over that distance probably won't matter.
  10. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

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    Yes, I am an engineer. :) I would expect it!

    This will be the largest free standing structure that I have built. All of my remodeling has been either small additions, new partition walls, etc. I've always fought out of square, not level, and out of plumb conditions before. I have an older home so I usually get two of the three when I'm lucky. So, no harm in trying to keep it as perfectly plump/level/square as possible.

    I'm sure, though, that when I get the walls up it will no longer be square... ;)

    Thx,
    Jason
  11. jimbo

    jimbo Plumber

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    The tolerance on the dimensions of common construction lumber are greater than that! For one thing, most 2X lumber has a bow in it, and may have some twist as well. Thats why the final step in framing is the use of springboards to make the walls as plumb and square as is "reasonalby posible" then the roof and finally siding, tie it all together.

    Knock yourself out.
  12. Terry

    Terry Administrator Staff Member

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    Like Jimbo mentions, 2x6 and 2x4's don't come straight.

    Find the camber, and line it up the same way.
    Same with floor joists. Make sure the arc is on the high side.
    When you add weight, it will flatten out.

    Whatever you do, don't mix it.
  13. Lakee911

    Lakee911 I&C Engineer (mostly WWTP)

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    Thanks for the tips. I've never paid much attention to the 'camber' on the walls. It makes sense though. I typically lay them down, frame them, sheeth them and then stand them up.

    Any tips on putting up trusses by myself. Lift one side, lift the other and then flip it up? Area is not accessible w/ a crane. It would be tough to get to the site and then overhead electric would be in the way.

    Thanks.
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