Mandatory Housing Affordability (MHA)

MHA Zoning and Development Examples

Illustrations of example buildings in various zones under new MHA development standards and affordable housing requirements were presented to the Housing Affordability and Livability Agenda (HALA) Focus Groups in September and October 2016:

Summary of MHA Zones

A summary of the MHA zoning changes is given in the table below. MHA Zone differences are shown in crimson.

Existing Zone:
MHA Zone:

RSL
LR1
MHA LR1
LR2
MHA LR2
LR3
MHA LR3
MR
MHA MR
NC-30
MHA NC-40
NC-40
MHA NC-55
NC-65
MHA NC-75
NC-85
MHA NC-95
MHA Zoning Allowed UC & UV citywide citywide citywide citywide citywide citywide citywide citywide
Height Limit
(feet)

30

30

30

30

40

40

50

60 base
75 bonus
75
80 addition
30

40

40

55

65

75

85

95
100 NC-100

Floor Area Ratio

0.75

1.2

1.2
1.3 (townhouses)

1.3

1.4

2.0

2.2

3.2 base
4.25 bonus
4.5
2.5

3.0

3.25

3.75

4.75

5.5

4.5 single use
6.0 mixed use
5.0 single use
6.25 mixed use
Max Density
(units/SF)

1:2000
1:2000
N/A
N/A
N/A
N/A
N/A

Notes:
MHA Zone differences are shown in crimson.
UC & UV = Urban Centers and Urban Villages.
Parking Required: 1 space per unit; none required in UC & UV.

MHA Performance and Payment Requirements

The MHA proposal creates three tiers of MHA requirements for multifamily residential and commercial development based on location in a Low, Medium or High Area and whether proposed zoning increases moves a zone from one category to another. The MHA performance requirement is a percent of units that must be set aside as affordable housing, or alternatively, a payment contributed to the Seattle Office of Housing.

Proposed Requirements for Residential and High-rise Commercial

Scale of Upzone Low (%) Low ($) Medium (%) Medium ($) High (%) High ($)
Standard M suffix 5% $7.00 6% $13.25 7% $20.75
Zones with M1 suffix 8% $11.25 9% $20.00 10% $29.75
Zones with M2 suffix 9% $12.50 10% $22.25 11% $32.75

Proposed Requirements for non-high-rise Commercial (up to 95 feet)

Scale of Upzone Low (%) Low ($) Medium (%) Medium ($) High (%) High ($)
Standard M suffix 5% $5.00 5% $7.00 5% $8.00
Zones with M1 suffix 8% $8.00 8% $11.25 8% $12.75
Zones with M2 suffix 9% $9.00 9% $12.50 9% $14.50

Notes:
Fractional housing units are rounded up to the next whole unit. The developer may pay for the fraction to round down instead.
Cost is dollars per square foot ($/SF) based on the Gross Floor Area, which is the product of the Lot Area multiplied by the maximum Floor Area Ratio (FAR).

MHA Upzoning Categories

Category 1 Single Family (SF), Residential Small Lot (RSL)
Category 2 Lowrise 1 (LR1), Lowrise 2 (LR2)
Category 3 Lowrise 3 (LR3), Neighborhood Commercial 55 (NC-55)
Category 4 Midrise (MR), Neighborhood Commercial 75 (NC-75)
Category 5+ Zones with heights greater than 85 feet.

Notes:
The City is not clear on which category includes Neighborhood Commercial 40 (NC-40), and which category includes Neighborhood Commercial 95 (NC-95).

If a rezone results in no change in category, the zone would receive a standard M suffix.
If a rezone resulted in a zone changing to the next highest category, then the zone would receive a M1 suffix.
If the rezone resulted in a zone changing by two categories or more, the zone would receive a M2 suffix.

Map of MHA Performance Areas

The proposed map shows where the MHA High, Medium, and Low performance requirements apply.
Map of MHA Performance Areas

Examples of MHA Development

A summary of the MHA development examples is given in the tables below. MHA Zone differences are shown in crimson.

Existing Zone:
MHA Zone:

RSL
LR1
MHA LR1
LR2
MHA LR2
LR3
MHA LR3
MR
MHA MR
NC-30
MHA NC-40
NC-40
MHA NC-55
NC-65
MHA NC-75
NC-85
MHA NC-95
Example: Cottages Small Site Small Site Small Site Small+Depth Small Site Small Site Small Site 5 Over 3
Lot Size (SF) 10000 5000 10000 5000 10000 12000 15000 12000 28750
Floor Area Ratio
0.75
1.2
1.2
1.3
1.4
2.0
2.2
4.25
4.5
2.5
3.0
3.25
3.75
4.75
5.5
6.0
6.25
Total Floor Area
(SF)

7500
4800
4800
10400
11200
8000
8800
34000
36000
20800
25600
32200
38200
37600
44800
121324
127052
Average unit size
(SF)

1500
2400
480
650
650
800
650
514
514
711
711
796
796
575
575
790
790
Total units
5
2
10
16
17
10
14
72
76
29
36
40
48
65
78
153
161
MHA units factor 500% 500% 106% 140% 106% 124% 120% 120% 105%
Parking spaces 3* 0 8 5 0 0 underground underground underground
Parking ratio
(spaces/unit)

0.60
0.00
0.00
0.50
0.47
0.50
0.36
0.00
0.00
0.00
0.00
unknown
unknown
unknown
unknown
unknown
unknown
Existing Zone:
MHA Zone:

RSL
LR1
MHA LR1
LR2
MHA LR2
LR3
MHA LR3
MR
MHA MR
NC-30
MHA NC-40
NC-40
MHA NC-55
NC-65
MHA NC-75
NC-85
MHA NC-95
Example: Townhouses Large Site Large Site Large Site Small+Height Large Site Large Site Large Site 9 Story
Lot Size (SF) 6000 10000 15000 15000 10000 16000 18000 46000 28750
Floor Area Ratio
0.75
1.2
1.2
1.3
1.4
2.0
2.2
4.25
4.5
2.5
3.0
3.25
3.75
4.75
5.5
6.0
6.25
Total Floor Area
(SF)

4500
9600
9600
15600
16800
24000
26400
34000
36000
27520
33920
38000
45200
142800
170400
124348
129996
Average unit size
(SF)

1500
1900
700
650
650
650
650
563
563
827
827
707
707
710
710
774
774
Total units
3
5
14
24
26
48
51
64
68
33
41
54
64
201
240
161
168
MHA units factor 300% 280% 108% 106% 106% 124% 119% 119% 104%
Parking spaces 3* 11* 16 12 0 underground underground underground underground
Parking ratio
(spaces/unit)

1.00
2.20
0.79
0.67
0.62
0.25
0.24
0.00
0.00
unknown
unknown
unknown
unknown
unknown
unknown
unknown
unknown
Existing Zone:
MHA Zone:

RSL
LR1
MHA LR1
LR2
MHA LR2
LR3
MHA LR3
MR
MHA MR
NC-30
MHA NC-40
NC-40
MHA NC-55
NC-65
MHA NC-75
NC-85
MHA NC-95
Example: Stacked Rowhouses Townhouses Rowhouses Large Site NC-100
Lot Size (SF) 6000 5000 10000 5000 20000 28750
Floor Area Ratio
0.75
1.2
1.3
1.2
1.3
2.0
2.2
4.25
4.5
6.0
6.25
Total Floor Area
(SF)

4500
6000
6000
8000
8800
68000
72000
123872
129647
Average unit size
(SF)

1500
1500
1300
1500
1625
800
650
605
605
759
759
Total units
3
4
5
8
8
10
14
112
119
163
171
MHA units factor 300% 125% 100% 140% 106% 105%
Parking spaces 0 3 6 0 underground underground
Parking ratio
(spaces/unit)

0.00
0.75
0.60
0.75
0.75
0.00
0.00
unknown
unknown
unknown
unknown

Notes:
MHA Zone differences are shown in crimson.
MHA units factor = Number of units with MHA zoning / number of units with existing zoning.
* Parking greater than required.

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