How best to calculate perpindicular boundary line in terrace

[macadonald]

Hi guys,

Had an interesting couple of nights marking out the walls for our rear extension. May seem like a silly question to those experienced in it, but I'll ask anyway.

We are end of terrace. I used string down the external alley wall from front of house extending beyond the back. In theory this is straight forward and a straight t line. The other side that is shared with the neighbours is the challenge. I built a little tool with parallel pieces of wood to match the inside party wall wit the outside boundary. At first, I did my best to measure the width of the back of the house and then I measured the same width from the extended string. Was a little surprised as it appears the neighbours patio may very slightly come across our boundary at an angle.

To confirm, I tried to build a large right angle and this seems to have confirmed what I thought. How would the professionals out there mark out a perfectly square rear extension?

Thanks[/b]

 

[nickjb]

The boundary might not exactly line up with the building. The plans probably won't help as the line will be way to thick for this level of detail. Ours are all slightly skewed. It might be down to evening out the garden widths rather than the end of terraces being bigger, it might just be lazy laying out when they were built. It means my new extension is slightly nearer the fence at the back edge.

I used a big 3-4-5 triangle, a large off-cut of plywood and lots of corner to corner meauring to lay mine out (Very much not a pro, though)

 

[^woody^]

You would either mark out 90° off the original house via 3,4,5, or extend a the flank elevation and go parallel off that, or mark out parallel off the main house and then go back square to the house, and do some diagonal checks too