# forgot how to square up a foundation



## burntside bob

I forgot how to square up a foundation and can not find my notes on this topic. Its been a while since I did this. Real busy you know:whistling
the foundation is 24 x 32
a/b is 24
c/d is 24
a/c is 32
b/d is 32
how do I get the a/d and b/c criss cross meassurement to square the foundation?


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## TimelessQuality

Pythagorean Theorem

All the diggers I know use lasers...


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## 480sparky

burntside bob said:


> I forgot how to square up a foundation and can not find my notes on this topic. Its been a while since I did this. Real busy you know:whistling
> the foundation is 24 x 32
> a/b is 24
> c/d is 24
> a/c is 32
> b/d is 32
> how do I get the a/d and b/c criss cross meassurement to square the foundation?


a²+b²=c²

24²+32²=c²

576+1024=1600

Sqr. root of 1600 is 40.



Or, you could just measure all four sides to verify the pairs are equal (a-b and c-d are both 24, b-d and a-c are both 32) then measure both diagonals and see if they (a-d and b-c) are equal.


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## Randy Bush

480sparky said:


> a²+b²=c²
> 
> 24²+32²=c²
> 
> 576+1024=1600
> 
> Sqr. root of 1600 is 40.
> 
> 
> 
> Or, you could just measure all four sides to verify the pairs are equal (a-b and c-d are both 24, b-d and a-c are both 32) then measure both diagonals and see if they (a-d and b-c) are equal.




Right on Sparky, pretty old school , but it works all the time.


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## ApgarNJ

Get a calculator and it will tell you what the diagonal should be when you give a length/width. 
Depends on the size we normally do smaller addition foundations, so the mason squares it up good, but when we build the deck. I use the 3,4,5 or 6,8,10 method of squaring, usually it's attached to a house, so you can't always go off the corner to corner as there aren't 4 perfect corners.


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## GettingBy

480sparky said:


> Or, you could just measure all four sides to verify the pairs are equal (a-b and c-d are both 24, b-d and a-c are both 32) then measure both diagonals and see if they (a-d and b-c) are equal.


Yes. No calculation involved.

If the diagonals are not equal within reasonable tolerance limits for this kind of project then you'd have to measure each angle to find the problem.
For a home-built picture frame, diagonals equal to each other within 1/16" is probably OK so I'd think acceptable tolerances on something this large could be +/- 1" or so. Civil engineers using steel tapes actually correct for tape sag, tape tension, and the effect of ambient temperature on the length of the tape. 

Maybe the building codes or housing inspectors say something about this.


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## woodchuck2

ApgarNJ said:


> Get a calculator and it will tell you what the diagonal should be when you give a length/width.
> Depends on the size we normally do smaller addition foundations, so the mason squares it up good, but when we build the deck. I use the 3,4,5 or 6,8,10 method of squaring, usually it's attached to a house, so you can't always go off the corner to corner as there aren't 4 perfect corners.


X2, quickest and easiest method.


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## Kent Whitten

In the bind, a simple 3/4/5 in multiples will suffice. 

Meaning 

6/8/10
9/12/15

etc. Or in your case 

24/32/40 as sparky states. 

The last number means your diagonals. First two your sides and front/back measurements.


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