Post Frame Buildings & the Code Part II

Last week I started discussing understanding the Building Code – and how it applies to post frame buildings.  Go back to Friday if you want to get caught up – this is part II of a two part blog. Again – this will appear “long” – but hard to break it up, and the tables take up quite a bit of room.

The information below is excerpted from the International Building Code (IBC) and based upon information provided by the American Wood Council. It is meant to be a start towards understanding how the Code applies to post frame buildings, but does not necessarily cover every aspect. The Planning, or other similar, Department which governs a particular jurisdiction should always be consulted as the final authority.

Total Building Area Limit

Single Occupancy

A single occupancy pole building with three or more stories above grade has a total building area of the allowable building area per story multiplied by three. Buildings with four or more stories of the same floor area will have smaller maximum areas per floor than a three-story building of the same type of construction and occupancy. For two-story post frame buildings, the total building area is the maximum allowable building area multiplied by two. The maximum area of any story above grade cannot exceed the allowable building area per story. A single basement is not included in total allowable building area.

The actual building area for all stories added together must be less than the total allowable building area.

Mixed Occupancy

Occupancy SignMixed occupancy pole buildings are permitted a total allowable building area calculated under code Section 506.5. But a single-story basement does not need to be included in the total allowable building area, when the basement does not exceed the area permitted for a single story.

More than one occupancy in a single building can be accommodated by using the allowable area of the most restrictive occupancy referred to as “non separated occupancies” in accordance with IBC Section 508.3. Alternatively, the occupancies can be regulated as “separated occupancies” to allow somewhat larger floor areas. This methodology will often mandate separation of the occupancies by fire barriers. The code also accommodates limited area spaces which are accessory to the function of the main occupancy.

Building Area Tables

The tables are organized by sprinkler status and contain the maximum number of stories and maximum allowable area per floor for Type IIIA, IIIB, VA and VB construction. (Note the original tables also have Type IV which is a “heavy timber” building which does not apply to post frame construction.)

Table 1- Group A Nonsprinklered Buildings – Maximum floor area per story.

Group A-1 Nonsprinklered Buildings a,b,c

 

# of stories

% frontage

Maximum floor area per story (sq.ft.)

IIIA

IIIB

VA

VB

1,2 (f)

0-25

14,000

8,500

11,500

5,500

50

17,500

10,620

14,370

6,870

100

24,500

14,870

20,120

9,620

3

0-25

14,000

NP

NP

NP

50

17,500

NP

NP

NP

100

24,500

NP

NP

NP

Groups A-2, A-3, A-4 Nonsprinklered Buildings a,b,c,d

# of stories

% frontage

Maximum floor area per story (sq. ft.)

IIIA

IIIB

VA

VB

1,2f

0-25

14,000

9,500

11,500

6,000

50

17,500

11,870

14,370

7,500

100

24,500

16,620

20,120

10,500

3

0-25

14,000

NP

NP

NP

50

17,500

NP

NP

NP

100

24,500

NP

NP

NP

Group a-5 Nonsprinklered Buildings a,e

# of stories

% frontage

Maximum floor area per story (sq. ft.)

IIIA

IIIB

VA

VB

UL

0-25

UL

UL

UL

UL

50

UL

UL

UL

UL

100

UL

UL

UL

UL

NP = Not Permitted

UL = Unlimited

  1. Frontage based on open space widths of 30 feet of more.
  2. Interpolation permitted.
  3. Sprinklers must be provided for Group A-1, A-3 and A-4 occupancies when the fire area exceeds 12,000 square feet in accordance with Section 903.2.1, or by reason of other specific conditions in that section. In lieu of sprinklers, compartmentalization of the floor area into fire areas not more than 12,000s square feet can be provided with fire-resistance-rated construction in accordance with Chapter 7.
  4. Sprinklers must be provided for Group A-2 occupancies when the fire area exceeds 5,000 square feet in accordance with Section 903.2.1.2, or by reason of other specific conditions in that section. In lieu of sprinklers, compartmentalization of the floor area into fire areas not more than 5,000 square feet can be provided with fire-resistance-rated construction in accordance with Chapter 7.
  5. Sprinklers must be provided for Group A-5 occupancies when the area exceeds 1,000 square feet in accordance with Section 903.2.1.5.
  6. Type VB construction does not permit two stories above grade plane.

Table 2- Group A Sprinklered Buildings – Maximum floor area per story.

Group A-1 Sprinklered Buildings a,b,c

 

# of stories

% frontage

Maximum floor area per story (sq.ft.)

IIIA

IIIB

VA

VB

1

0-25

56,000

34,000

46,000

22,000

50

59,500

36,120

48,870

23,370

100

66,500e

40,370e

54,620

26,120

2,3d

0-25

42,000

25,500

34,500

16,500

50

45,500

27,620

37,370

17,870

100

52,500

31,870

43,120

20,620

 

4

0-25

31,500

NP

NP

NP

50

34,120

NP

NP

NP

100

39,370

NP

NP

NP

Groups A-2, A-3, A-4 Sprinklered Buildings a,b,c,

# of stories

% frontage

Maximum floor area per story (sq. ft.)

IIIA

IIIB

VA

VB

1

0-25

56,000

38,000

46,000

24,000

50

59,500

40,370

48,870

25,500

100

66,500e,f

45,120e,f

54,620

28,500

 

2,3d

0-25

42,000

28,500

34,500

18,000

50

45,500

30,870

37,370

19,500

100

52,500

35,620

43,120

22,500

4

0-25

31,500

NP

NP

NP

50

34,120

NP

NP

NP

100

39,370

NP

NP

NP

Group A-5 Sprinklered Buildings b,c

# of stories

% frontage

Maximum floor area per story (sq. ft.)

IIIA

IIIB

VA

VB

UL

0-25

UL

UL

UL

UL

50

UL

UL

UL

UL

100

UL

UL

UL

UL

NP = Not Permitted

UL = Unlimited

  1. The maximum floor area for four stories above grade plane was determined by dividing the maximum total allowable building area by the number of stories in accordance with Section 506.4. The floor area of each story is assumed to be equal in area to the other stories.
  2. Frontage based on open space widths of 30 feet of more.
  3. Interpolation permitted.
  4. Type VB construction does not permit three stories above grade plane.
  5. Group A-1 and A-2 occupancies may be in unlimited area mixed occupancy buildings of
    Type III construction when meeting the provisions of section 507.3.1.
  6. Group A-4 Buildings may be unlimited in area if the frontage width is at least 60 feet and the building is of Type III construction in accordance with Section 507.3.

Unlimited Area Post Frame Buildings

The following Group A unlimited area buildings with a single story above grade plane are permitted if the building is equipped throughout with an NFPA 13-compliant automatic sprinkler system, surrounded on all sides by public ways or yards not less than 60 feet wide and meets other requirements listed in code Section 507. The open frontage can be reduced in some circumstances.

Unlimited area Group A-4 pole buildings one story above grade plane Type III construction are permitted by Section 507.3. For indoor activities such as tennis, swimming, skating and equestrian venues, the sprinkler system is not required in the participant areas if exit doors lead directly outside from participant areas and a fire alarm system with manual fire alarm boxes is installed as required by IBC Section 907.

Unlimited area Group A-3 buildings, of one story, Type III, used as a place of religious worship, community hall, dance hall, exhibition hall, gymnasium, lecture hall, indoor swimming pool or tennis court are permitted by Section 507.7 provided the building does not have a stage other than a platform, the assembly area is located within 21 inches of street or grade level and all exits are provided with ramps to the street or grade level.

Group A-1 and A-2 occupancies of Type III construction are permitted by Section 507.3.1 in mixed occupancy buildings containing Group B, F, M or S occupancies of unlimited area provided the occupancies are separated from other occupancies as required in Section 508.4.4 with no reduction allowed in the fire-resistance rating of the separation based on the installation of an automatic sprinkler system and all exit doors from Group A-1 and A-2 occupancies must discharge directly to the exterior of the building.

Additionally, for the Group A and mixed occupancy buildings, it is also permissible to have up to 75 percent of the perimeter open space less than 60 feet in width. These must be at least 40 feet provided and the exterior wall and all openings on those portions of the walls will require 3-hour minimum fire-resistance and fire protection ratings.

Allowable Increases with Fire Walls

A fire wall is a fire-resistance-rated wall with protected openings which restricts the spread of fire and extends continuously from the foundation to or through the roof. Fire walls built in compliance with Section 706 create separate buildings for the purpose of area limitations and other code-required features. Fire walls separating Group A occupancies require a 3-hour minimum fire-resistance rating (2-hour minimum for Type V construction). Each portion of a building separated by a fire wall is evaluated individually for allowable heights and areas based on the type of construction. Fire walls in Type V construction may be wood frame; in other construction types they must be of noncombustible materials in accordance with Section 706.3.

I hope this two day expose on the Building code helps to explain what goes into planning your new pole building. Feel free to bombard me with questions on any of the material I have presented yesterday or today  – and I will do my best to explain the sometimes confusing parts of the building Code.  It reminds me of snow skiing at Jackson Hole, WY after a foot of snow has fallen overnight…”deep and steep”!

 

 

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