Examples of Application

Example 1: Two story home on a 2,400 square foot lot that is 40 feet wide and 60 feet long.  

This example illustrates how, even on the smallest of lots, it is possible to choose MAFR bonus elements so that the lot owner can take advantage of the full bonus amount.  In this case, the standard MAFR of 1,420 s.f.is  increased, by the bonus, to 1,760 s.f.   It is our position that, since the ordinance works on the smallest of lots, it will work well for larger lots, which provide more “maneuvering room”.

Step 1:  Determine the building area as restricted by standard setbacks and allowable lot coverage:  

Current setback requirements for this lot are:
Front: 20 feet
Side: 4 feet   (minimum is 10% of lot width)
Rear: 6 feet   (minimum is 10% of lot depth)
Subtracting the setbacks from the lot dimensions yields a building area 32 feet wide, by 34 feet deep, or 1,088 s.f.   The lot coverage limit of 45% for R1 lots  is more restrictive (allowing 1,080 s.f.), so the 1,080 figure will be used for further calculations.

Step 2:  Choose Bonus MAFR  design features

In order to receive the MAFR bonus for a two story house, the builder must include at least one 3-point MAFR bonus design feature from the “required” category, and may choose any other bonus features, as needed, to obtain a total of six bonus points.  For this example, to accommodate our sample design, we will use the following bonus design features:
2. The second story is set back at least five additional feet on at least one side elevation as measured from the exterior wall of the first story   (3 points)  This is our required feature.
4.  The gross floor area of the second floor is no more than 75 percent of the gross floor area of the first floor of the main dwelling unit structure (not including detached garage or any accessory structures)    (2 points)
12. Second story windows are offset horizontally at least 24 inches, edge to edge, from second story windows of adjacent houses of more than one story.  This element applies only to clear glass windows.  Frosted windows and glass block are exempt.   (1 point)
Another option allowing use of the full bonus is the combination of features 3, 4, and 12.

Step 3: Calculate Bonus MAFR allowable square footage

2,400 s.f. lot:  1600 + 0.4 X (2400 - 2000) = 1600 + 160 = 1760 s.f.

Step 4:  Determine the amount of Bonus MAFR square footage that may be used
  1. Apply feature 2.  Building area for the second story is now 27 feet wide by 34 feet long, totaling  918 s.f.  Building area for the first floor remains the same, at 1,080 s.f.  1080 (first story area) + 918 = 1998, so at this point, there is room to use all of the full Bonus MAFR  square footage of 1760.
  2. Apply feature 4. 75% of 1080 = 810   Bonus MAFR allows 1760 s.f.    1080 + 810 = 1890 s.f.  This feature is more restrictive than feature 2, but there is still room to use the full MAFR with Bonus.
Feature 12 does not reduce building area.

Step 5:  Determine dimensions and layout of the sample structure

  1.  Establish first story dimensions and placement:   
  1.  Establish first story dimensions and area.  To keep the design within the constraints of the 1760 s.f. Bonus MAFR allowable square footage, we choose to begin by reducing the width of the building area for the lower floor.  To accommodate our design, with a hall and stairway to one side of the garage, the first story should be at least 30 feet wide.  So, we choose to make the new dimensions of the first story 30 x 34, giving an area of 1020 s.f..   
  2. Locate the first story within the building area.  We choose to increase the left setback (as viewed from the street) to 6 feet.  (30 + 6 + 4 = 40, which is our lot width.)
 
  1. Establish second story dimensions and placement:
  1. Calculate second story area.  Subtracting the area of the first story from 1760,  1760 – 1020 = 740, the total allowable area for the second floor.    Bonus feature 4 restricts the second story floor area to 75% or less of first floor area.  75% of 1020 is 765, so with a second story area of 740 s.f., we are still in compliance with all bonus feature specifications.
  2. Calculate second story width and length.   Applying the 5 foot side setback specified in design feature 2, we  subtract 5 feet from the width of the first story.  30 – 5 = 25 feet.    We can now determine the depth of the second story.  Where 25 feet is the width, and X represents the new depth of the second story, we have 25X = 740;   X = 29.6,  giving new second story dimensions  of 25 x 29.6.  
  3.  Locate the second story relative to the first.  We choose to use a front setback of 34 – 29.6 = 4.4, and to apply the 5-foot side setback on the left side, as viewed from the street

             
       

First Story                                                                                      Second Story

                                  30 x 34                                                                                            25 x 29.6

   






Front View  -  Showing placement relative to side lot lines



Example 2: Two story home on a 2,400 square foot lot that is 40 feet wide and 60 feet long. 

This example illustrates a situation in which design decisions prevent usage of the full Bonus MAFR amount.  Total square footage for the sample structure is 1,694 s.f.  In this case, the standard MAFR of 1,420 s.f. is increased  by the bonus, giving an additional 274 s.f.

Step 1:  Determine the building area as restricted by standard setbacks and allowable lot coverage: 

Current setback requirements for this lot are:
Front: 20 feet
Side: 4 feet   (minimum is 10% of lot width)
Rear: 6 feet   (minimum is 10% of lot depth)
Subtracting the setbacks from the lot dimensions yields a building area 32 feet wide, by 34 feet deep, or 1,088 s.f.   The lot coverage limit of 45% for R1 lots  is more restrictive (allowing 1,080 s.f.), so the 1,080 figure will be used for further calculations.

Step 2:  Choose Bonus MAFR  design features

In order to receive the MAFR bonus for a two story house, the builder must include at least one 3-point MAFR bonus design feature from the “required” category, and may choose any other bonus features, as needed, to obtain a total of six bonus points.  For this example, to accommodate our sample design, we will use the following bonus design features:
1.      Both side yard setbacks are at least two feet greater than the minimum required. (3 points)  This is the required element.
5.      The second story is set back at least 10 additional feet at the front elevation for at least 75 percent of the width of the second story, as measured from the exterior wall of the first story or the outside edge of supporting posts for a covered front porch. (2 points)
12.     Second story windows are offset horizontally at least 24 inches, edge to edge, from second story windows of adjacent houses of more than one story.  This element applies only to clear glass windows.  Frosted windows and glass block are exempt  (1 point)

Another option allowing use of most of the bonus amount is the combination of features 1, 5, and 12

Step 3: Calculate Bonus MAFR allowable square footage

2,400 s.f. lot:  1600 + 0.4 X (2400 - 2000) = 1600 + 160 = 1760 s.f.

Step 4:  Determine the amount of Bonus MAFR square footage that may be used
  1. Apply feature 1.  Building area for the structure is now 28 feet wide by 34 feet long, totaling  952 s.f.   For both stories, total square footage is now 1,904 s.f.   At this point, there is room to use all of the full Bonus MAFR  square footage of 1760.
  2. Apply feature 5. The second story front setback of 10 feet reduces the upper floor by (28 x .75) x 10 = 21 x 10 = 210.  952 – 210 = 742.  Adding the maximum first and second story building areas, we have  952 + 742 = 1,694.  This is the maximum square footage allowed for this structure.  The full Bonus MAFR amount of 1,760 cannot be used.

Feature 12 does not reduce building area.

Step 5:  Determine dimensions and layout of the sample structure

  1. Establish first story dimensions and placement:  
  1. Establish first story dimensions and area.  We will keep the 28 x 34 dimensions established in step 4.c.
  2. Locate the first story within the building area.  Location is determined by the side setbacks required by bonus feature 1, and standard front and rear setbacks of 20 feet and 6 feet, respectively.
  1. Establish second story dimensions and placement:
  1. Calculate second story area.  The second story area of 742 was established in step 4. a. when feature 5 was applied.
  2. Calculate the second story width and length.  The length of the right side elevation will be 34 feet. The length of the left side elevation will be 24 feet.   The width will be 28 feet.
  3. Locate the second story relative to the first.  We choose to locate second story front setback, specified by bonus feature 5, on the left side, as viewed from the street.


           



Front View  -  Showing placement relative to side lot lines
    
     Entry is on right side elevation