Square footage adjustment

[alebrewer]

I use this free online tool for GLA adjustments and Time adjustments: https://the-adjustments-app.streamlit.app/GLA
It calculates the GLA adjustment using group data, regression, sensitivity, and ppsf.

Cool app, but I think it's only performing a single variable regression for GLA PPF, which - if that's the case - would tend to overstate the adjustment factor. My sensitivity analysis generally returns a factor of ~ $60-$80/foot for the market transactions I'm modeling, but this app suggested $140-$150. It's even more interesting when running the market conditions app. I'm in a pretty stable market, but this is what the model returned for market adjustments:

 

[weird_limbs]

Cool app, but I think it's only performing a single variable regression for GLA PPF, which - if that's the case - would tend to overstate the adjustment factor. My sensitivity analysis generally returns a factor of ~ $60-$80/foot for the market transactions I'm modeling, but this app suggested $140-$150. It's even more interesting when running the market conditions app. I'm in a pretty stable market, but this is what the model returned for market adjustments:

View attachment 91003

Interesting. Maybe the Linear (Year-over-Year) Market Conditions Adjustments Model works better for your market. The Non-Linear model needs a lot of data points.

 

[Terrel L. Shields]

Terrel's attachment might be similar; I didn't open it.

I think the one I attached was originally put on the site by @Metamorphic back years and years ago. Maybe he will chime in and take credit for it. My own is a two stage sensitive where I 'do' both effective age and SF.

 

[alebrewer]

I think the one I attached was originally put on the site by @Metamorphic back years and years ago. Maybe he will chime in and take credit for it. My own is a two stage sensitive where I 'do' both effective age and SF.

the model you uploaded is MUCH closer to what I get from my efforts, although it doesn't appear that it isolates the 'adjusted values' after all other adjustments have been applied - which would indicate there is potentially some cross contamination WRT site size differences, age differences, etc.... but - it models the data pretty well.

 

[David S]

I use this free online tool for GLA adjustments and Time adjustments: https://the-adjustments-app.streamlit.app/GLA
It calculates the GLA adjustment using group data, regression, sensitivity, and ppsf.

Thanks! I tried that link, it is said at least 30 sales? Are these 30 sales have to be comps? Or can I use 1004MC data set? Actually these data set also related to the comps, probably relax parameter a little bit and extend to one year period. Thanks!

 

[Terrel L. Shields]

Are these 30 sales have to be comps?

Sensitivity would require only your 3 comps.

 

[David S]

I have a property that I have no matched pair sales for square footage and had ran across a simple percentage formula but I cannot find it and was wondering if anyone could provide.

For my limited 100+ appraisals so far ( not including training period), I feel in my local market, GLA grid adjustment is about 20%~30% of GLA's $ / sq ft (meaning sold price / GLA sq ft or called dollars per square foot) and lot grid adjustment is about 10%~20% of site $ / lot sq ft (meaning from cost approach, you have the site value, right? then divide by lot size). This may not be correct but just the actual result from my accumulation.
In this forums, many senior appraisers must did 1000+ appraisals . They should have more experience to share.

 

[David S]

Correct. Remember - your goal is to reach an adjusted range of $0. In reality that is not possible (think of residuals in regression analysis), but that is nonetheless the goal. So, then, if all your other adjustments are correct, the GLA adjustment factor that minimizes the range will be the correct factor.

Great! That's what I am doing now. Will that lead "hit number" issue because you "try" to narrow the adjustment range?

 

[David S]

I use this free online tool for GLA adjustments and Time adjustments: https://the-adjustments-app.streamlit.app/GLA
It calculates the GLA adjustment using group data, regression, sensitivity, and ppsf.

I use 1004MC cvs file try again. It is said file format is incorrect. Can you share one of that cvs sample file so we can know what is column 1, column 2, column 3, etc.? Thanks!

 

[weird_limbs]

I use 1004MC cvs file try again. It is said file format is incorrect. Can you share one of that cvs sample file so we can know what is column 1, column 2, column 3, etc.? Thanks!

The app has an "Example" button that you can click to download a csv file with sales data.