How to Calculate Site Adjustment

[DaveH]

I use to do estimates for lineal footage when I was a civil engineer, I came up with about $1,000 per lineal foot of roadway for improvements. It still is the case in our area, so you can get a rough idea of the costs of improvements.

 

[Rice Brewer]

You should be looking at the marginal value of land. If a 10,000 SF has a market value of $20,000 but an otherwise similar 18,000 SF lot has a market value of $25,000, the the marginal value of the difference in only $5,000. Remember the general rule that as the size of a parcel increases the value of each unit (SF, FF, LF, etc...) generally decreases. To be sure, there are exceptions like the last 5 acres of vacant land on a commercially developed street with a high traffic count. However, it generally holds true in residential appraising.

 

[DMZwerg]

$$/SF is one consideration. Have you consider $$/Front Foot?

I use to do estimates for lineal footage when I was a civil engineer, I came up with about $1,000 per lineal foot of roadway for improvements. It still is the case in our area, so you can get a rough idea of the costs of improvements.

Then there can also be additional frontage and other adjustments as well.

Shape can be a major factor, especially if it narrows as it goes back, widens as it goes back, or has more frontage than depth. Part of the reason is setbacks and what they leave in regards to buildable area. Often times front yard setbacks may be as large as 60-70 feet and thus a property that is a wedge is generally worth more if wider to the rear (like in a cul-du-sac) than if wider to the front as prospective buyers may well consider how much they have to pay for road maintenance compared to the buildable area (and for the same size lot the wide frontage wedge would likely have significantly less buildable area). Similarly a very wide but shallow lot (say twice as much frontage as depth) will have much less buildable area and yet suffer twice as much in road improvement costs. Corner lots are generally addressed as having one street side as a declared "side lot" and thus not suffer as much from loss of buildable area.

Another factor can be water frontage, but again there are often setback requirements that can greatly squeeze a property's buildable area, as well as erosion concerns (particularly on large lakes or oceans) and again lot shape and setbacks can be major concerns.

Therefore even though increased frontage can increase value sometimes you can actually discern DECREASED net affect if the lot shape is problematic (wrong type of wedge or insufficient depth).

Then there is view, but that is a whole 'nother kettle of fish I will leave to others to explain ... same with slope & such. :new_multi:


Just figured I put in two cents about lot shape & view so the OP has more ideas on what all can affect $/sf of lot size.

 

[Michigan CG]

You should be looking at the marginal value of land. If a 10,000 SF has a market value of $20,000 but an otherwise similar 18,000 SF lot has a market value of $25,000, the the marginal value of the difference in only $5,000. Remember the general rule that as the size of a parcel increases the value of each unit (SF, FF, LF, etc...) generally decreases. To be sure, there are exceptions like the last 5 acres of vacant land on a commercially developed street with a high traffic count. However, it generally holds true in residential appraising.

Rice has it 99% correct. The correct term is Marginal Utility. Utility is the satisfaction of a need. Additional land may provide additional utility. If there is a set back requirement of all improvements of 20 feet a 60' wide lot may not allow for a third parking space; an 80' wide lot would.

The additional land may provide additional utility but it is typical in residential properties for the additional land to be worth less than the minimal land required to provide minimal utility.