Making posts square

[Craig Farrall]

Hey - I feel that this may be a simple question, but I am struggling to get my head around it to achieve it.

Basically I am building a pergola that is going the whole width of my garden, from fence to fence (roughly around 11m in total size). I therefore have numerous posts dotted around to give the pergola the support it needs. I am struggling to work out how to make the four corners square though?

Obviously there are numerous methods, including the 345 method which makes sense (looking at the diagram here - https://westerninterlock.com/how-to-square-a-corner-3-4-5-method/) - but this assumes that there is space around the corner to add the posts to create this - which I don't have, with the posts being next to the fence panels - how can I get around this to create squared corners?

The posts in the middle are fine as when I have the four corner posts completed and squared, I will run a string line and use that to line up the rest.

Appreciate any help you can give me!

 

[Notch7]

Use Pythagoras to work out the diagonals - there are plenty of online calculators for right angled triangles, there's even an android app: triangle solver.

 

[Craig Farrall]

Thanks for your comment - how would you do this based on the fact the posts diagonally will be roughly 11m apart? Would you add one post in first (brace it, not concrete it yet) and then do the diagonal of that next? How would you then tackle the other two corners? Sorry for the many questions, struggling to work out how best to do this.

 

[Harry Bloomfield]

No, you add two posts where you want them, then use Pythagoras to work out where the remaining two need to go, by measurement from the first two. Instead of setting the first two posts, you could use two bricks stood on end, with two more bricks for your other two posts.

 

[Notch7]

Thanks for your comment - how would you do this based on the fact the posts diagonally will be roughly 11m apart? Would you add one post in first (brace it, not concrete it yet) and then do the diagonal of that next? How would you then tackle the other two corners? Sorry for the many questions, struggling to work out how best to do this.

It can be confusing I know -you have nowhere to start!

basically you use the triangulation method
You could use some non stretchable string.

this is what I would do:

1) get your distance between the posts -ie width of garden.
2) put in a marker post on the first side, then use 3 4 5 to get a marker post on the other side of the garden (which will make them 90 deg to the fence)

3) mark the distance down the garden, the length you want your structure -and put in a string line parallel to the first pair of posts
4) calculate the diagonals and then take a string line from the first corner and where it crosses your parallel string line is your post position
5) repeat for other diagonal
6) check the distance between post 4 and post 5 and tweak accordingly

 

[lostinthelight]

If you dont have an exact starting point it may be worth looking on GE to see if you can establish if the two fences are running anywhere near parallel or which way they are splaying ,have you started digging yet?

 

[scbk]

Measure the diagonals, corner to corner. If both measurements are the same, then the whole thing is square.

 

[Craig Farrall]

Thanks for everyones responses, I have tried to follow up with each below:

No, you add two posts where you want them, then use Pythagoras to work out where the remaining two need to go, by measurement from the first two. Instead of setting the first two posts, you could use two bricks stood on end, with two more bricks for your other two posts.

This sounds like a good idea with the bricks. For the first two posts that you mentioned - does it matter which those are? Should those be diagonal or does it not matter?

2) put in a marker post on the first side, then use 3 4 5 to get a marker post on the other side of the garden (which will make them 90 deg to the fence)

I have already dug the four holes in each of the corners, so I can't really add a marker in for this and I have no space around it, as the whole goes up to the fence panels - any suggestions?

If you dont have an exact starting point it may be worth looking on GE to see if you can establish if the two fences are running anywhere near parallel or which way they are splaying ,have you started digging yet?

Sorry for the dumb question, but what is GE? The back fences that this will be running across is far from straight so definitely wouldn't use that as any sort of guide. Yes, I've already dug the four corner holes - so I am just trying to position everything now, to make it all squared.

 

[lostinthelight]

Google earth