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<br />Although there's no single formula to' convert dulna values applied without "round up" to <br />equivalent dulna values applied with "round up," it's quite straightfornrard to find the <br />equivalency for a specific set of lots, such as those in Area 15. <br /> <br />The basic approach. we took was to create a spreadsheet with in.dividuallotareas for the <br />252 lots in Area 15, exc.luding the O'Hare school and Lighthouse Temple lots. We then <br />applied both "no round up" and "round up" formulas with varying dulna.values to this set <br />of lots and c.alculated the total number of dwelling units allowed~ We also tabulated <br />comparisons bet\veen various pairs of "no round up" and "round up" values to determine <br />how many of the 252 lots would allo\\l a different number of d",,relling units under the <br />densities being compared. <br /> <br />The following table sho-w~s the values that produce the closest equivalent results under <br />"no round IIp'' and "round up" calculations.I3 <br /> <br />1983-era R-2 <br />min. lot area per dl\relling <br />NO round u <br />2,650 s.f: <br /> <br />1983-eradu/na <br />NO round up <br /> <br />16.44 <br /> <br />Equivalent du/ns <br />WITH current round <br />u calculation <br />9.7 <br /> <br />Two examples illustrate the results of applying equiv~alent 1983-era and current <br />maximum densities from the table abo\'e. <br /> <br /> 1 983-era 9.7'du/na <br />Lot size 16.44 du./na WITH current <br />Square feet NO round up round up calculation <br /> (acres) Allowable dwelling units Allowable dwelling units <br />7,500 s.f. 2 2 <br />(0. 2066 acre) <br />5,000 s.f. 1 2 <br />(0. 1 148 acre) <br /> <br />First, <;onsider a 7,500 s.f. (0.2066 acre) lot. For tIlis lot size~ as for most of the lots in <br />Area 15, the correspon.dence is exact. <br /> <br />Next, consider a 5,000 s.f. (0.1148 acre) lot. In this case, a density of9.1 dulna under <br />current R-2 calculations will allo\v one more unit than a. 1 983-era density of 16.44 du/na <br />allowed. For this specific lot size, the equiv'alent density' under the current calculation <br />should 'be lower than 9.7 du/lla. There were VCT)l fe\v such cases alTIOng the 252 lots that <br />were analyzed~ <br /> <br />It may, seem surprising that the equivalent dulna value u.nder current R-2 zOlling rules <br />(9.7) is so much lo\ver than thecon<<esponding 'valu.e u.nd.er the rules in effect in the 1983 <br />era (16.44). But this is due to the l11aJor effect that "rounding up" has on allowable <br />density for small- tomediunl-sized lotS.14 <br /> <br />13 The Excel spreadsheets \\'e used are available by request <br />14 The increase in density caused by addin.g the "round up" provision to the code is the major reason the <br />R-2 zone has become in. effect, a high-density zone \vhen a.pplied to neighborhoods \-vith lots in the 5,000 to <br />12,000 square toot range. The aggregate densi.ty allo\ved in Area. 15 under current R.-21D.aximum density <br />linlits is over 31 du/na- ,veIl above the mini nl um defined in the Metro Plan "High Density Residential'') <br /> <br />8 <br />