price for outdoor space

I am reposting what I think was the best explanation on how to value outdoor space, from a very knowledgeable person who doesn't post here any more:
"30yrs_RE_20_in_REO
"There is NO formula for what outdoor space is worth. Let me give you an example to show why:

Take two apartments in the same building, next door to each other. Lets say were were talking about some building on CPW facing the park and we're on the 15th floor. Each terrace is a nice 15 foot by 15 foot setback with full park views. So in each case we have 225 square feet of terrace of the same exact "quality" (in other words, I'm trying to avoid the argument of comparing 225 square feet of outdoor space at the bottom of a light well to 225 square feet of penthouse terrace).

The first terrace is attached to a 500 square foot studio. The second terrace is attached to a 2,000 square foot Classic 6. Without the terrace, let's say the studio is worth ?$750,000? and the Classic 6 is worth ?$3 million?. With the terrace, the studio is worth ?$1.1 million? and the Classic 6 is worth ?$4 million?

Obviously I'm pulling these numbers out of thin air, but I don't think anyone can argue against the logic involved: the exact same terrace attached to 2 different apartments can vary a HUGE amount. The reason is the terrace is something that can never be bought itself: it only acts as an enhancement TO AN APARTMENT. As such, it affects a percentage of the apartment's worth more than it stands alone on it's own $PSF basis."

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David Goldsmith
DG Neary Realty Ltd."

If you want more, you can search outdoor space value in past discussions. There are basically 2 schools of thoughts: 1- outdoor space should be counted at 20 to 50% of the indoor ppsf, depending on access, light and fitness, and 2- outdoor space adds 10-25% to the value of an apartment, depending on access, light and fitness. As long as the ratio of outdoor to indoor square footage, those 2 values should come pretty close. If you have a very small apartment or a really large terrace, simple calculations do not work, especially if the maintenance is outsize for the apartment.
In your specific example, let's say your 2br/2ba is 1,300sf, and recent comps (without outdoor space) are 850K. Let's further posit the terrace is ideal: accessible from the living room and/or dining room, the views and the light are both fantastic and the landscaping is lovely, with water and electricity installed. Under the first formula, you'd be looking at 850/1300=653 psf for indoor space *50%=326*800sf=261K. Under the second formula, 850*25%=212K.

Here are two separate cabanas in Dumbo - both listed for ~$200k, both ~ 550 sq ft, no apartment attached.
http://streeteasy.com/nyc/sale/472093-condo-70-washington-street-dumbo-brooklyn
http://streeteasy.com/nyc/sale/614005-condo-70-washington-street-dumbo-brooklyn

Freebird, they didn't sell. The problem here is that the access is subpar (through public common space, and not on the same level as the apartment), yet were priced at the bullish 50% of indoor square foot. That building sells around 850psf, and the outdoor space is detached, so according to formula #1: 25-35%*850*550=$116,000 to $163,000 would be a ballpark valuation.