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Irregular Site Line Offsets


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#1 Jim Crook

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Posted 19 January 2015 - 10:38 AM

On a Site Plan what is the proper way to offset an irregular shaped lot line ( i.e. water frontage )  to establish the setback line ?  

In my experience you can't really just offset the frontage line in it's entirety due to it's irregular shape you actually end up with 

different setbacks at various points along the line.  In other words due to the irregular shape not all parts of the line are being moved

back at an equivalent 90 degree angle.  Alternatively if you try to offset individual parts of the line at 90 degrees you change the shape

of the line. So how is it typically done ?

 

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#2 Martin Livingston

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Posted 19 January 2015 - 04:47 PM

The offset line shape can change dramatically because it is measured at 90 degrees along all points of the original line. convex arcs get smaller and concave arcs get larger. Angled lines will intersect at different points on other angled lines. The only line that will remain the same shape is a straight line.

 

If you copy the original boundary line and paste it at the required setback it would be the same shape but would not represent the actual setback requirements.

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#3 Chris Stewart

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Posted 19 January 2015 - 07:29 PM

I do not know what is typical,

As far as I know you just move every line and arc back the required amount. 

 

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#4 Keith Almond

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Posted 20 January 2015 - 07:17 AM

That's the way I understand it Chris, but problems can occur when side yard setbacks are different from rear or front yard setbacks. I would advise you to check with the municipality what they would accept.


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#5 Gary Hood

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Posted 20 January 2015 - 10:53 AM

Do you not have a survey to go with? That would be the first thing the AHJ would be asking for around here. The survey would show the property lines, plus the setback lines. Also, if it was a watercourse the property was fronting, it would show that (special) setback (differant from a regular setback).



#6 Jim Crook

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Posted 20 January 2015 - 01:04 PM

I have attached an example of what I'm talking about.

 

As Mike said you can't just take the front property line ( shoreline ) and block copy it back the setback distance you want

because that won't really give you the actual setback to the strucutures that you want due to the various angles involved.

 

Trying to offset a polygon or even individual lines at 90 degrees each works great in a large lot but in narrower lots the

setback lines can actually leapfrog past each other to the opposite side and/or when you fillet lines the resulting setback 

is not really the shape of the frontage line at all.

 

In one case I just block copied the frontage back 20 meters to see how it would relate to the buildings and in another

case I copied each line back 20 meters at a 90 degree angle for each and try to fillet together what makes sense.  Many

of the lines that copy too far to the other side become totally redundant and just get erased.

 

I just wondered if there was some logical way to deal with developing the setback line without copying all the individual

lines and filleting as best you can ?

 

2015-01-20_14-02-53.jpg  



#7 Chris Stewart

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Posted 21 January 2015 - 07:15 PM

Nope -just like in the example I showed and you just mentioned some lines become irrelevant and you can not just block copy. 

 

It is not necessary to fillet the best you can, there will always be only one correct line. 

 

The center point of radius will always remain the same and lines are always moved back on a perpendicular axis.

 

If for example a 20' setback is called for, than no point on the setback line will be closer than 20' to any point on the lot line.  

 

Maybe someday there will be an auto-setback button. 

 

My guess is that you are having problems with the radius lines.

 

I find it helpful to use arcs and or circles and lines to find the intersection where the setback radius meets the setback straight line  

 

Maybe someone else has found a better method,

 

Clip_13.jpg


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#8 Thomas Parker

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Posted 23 January 2015 - 11:09 AM

I gave up trying to outguess each municipality plan review process and interpretations - I usually figure anything out of the ordinary (especially lake front) is best to run a preliminary site sketch through the plan review process prior to finalizing plans. Seems to be lots of 'gray areas' in interpretations, around here anyways!!!! HA HA :blink:


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#9 Chris Stewart

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Posted 23 January 2015 - 01:06 PM

I suppose it would be much easier to deal with property lines if they behaved like any other type of line or arc. 


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