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BACK TO BASICS – CHAPTER 5 GENERAL BUILDING HEIGHTS AND AREAS

Presented at UMass, October 2013

Christopher R. Laux, A.I.A. Architect/Building Official/Consultant

Contact Information

Christopher R. Laux, A.I.A.

PO Box 636

Woodbury, CT 06798-0636

(203) 263-5787

codeguy@charter.net

Applicability of discussion

This discussion is based on the provisions of Chapter 5 of the 2012 International Building Code (IBC) No State amendments included in

discussion

This discussion is conceptual and general by nature. Time allotted does not allow for in-depth analysis of salient points.

Disclaimer

This discussion does not pretend to include all items the code user needs to be aware of. Purchasing, opening and frequent, careful reading of the code is essential to understand its many intricacies.

The handout does not take the place of owning or reading the code.

501 - General

Applies to heights and areas of new buildings and additions to existing buildings (no existing building plus additions can exceed requirements)

You must also evaluate change of occ.

New 2012: new and existing buildings must have approved address identification in plainly visible location

503 – General Limitations

Heights and areas of buildings shall not exceed Table 503 except as modified herein…..so Table 503 is only a starting point!

Buildings separated by fire walls are separate buildings

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Table 503 Table 503

This is the starting point in determining the actual allowable height and area of a building given its occupancy and construction type.

Can also be used to determine minimum construction type when height and area are known

General limitations

503.1.1: limited application for exemption from T. 503: applies to buildings housing special industrial processes that require large areas and unusual heights to accommodate craneways or special machinery or equipment. Examples include rolling mills, structural metal fabrication; foundries & power production.

General limitations

503.1.2: when multiple buildings on the same lot could be combined into a single building that complies with T. 503, you need not establish fire separation distances between them

Most restrictive construction type and occupancy regulates

Code provisions that are applicable to aggregate building apply to separate buildings

Example 1 Example 2

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General limitations

503.1.3: Type 1 buildings permitted to be of unlimited height or area by Table 503 based on construction classification do not have to comply with other unlimited area building requirements.

Building height

504.1 exception to height limits: 1 story aircraft hangars; aircraft paint hangars; and aircraft manufacturing buildings not limited in height if sprinklered and surrounded by yards or public ways not less in width than 1 ½ times the building height.

Building height

504.2: sprinklered buildings receive a one story, 20 foot height increase over T. 503 limits

Group R with NFPA 13R systems limited to 60 feet and 4 stories

No increase for Group I-2 in IIB, III, IV or V buildings

No increase for H-1, H-2, H-3 or H-5 occ.

Building height – roof structures

504.3: unoccupied towers, spires, steeples and other roof structures shall be of same materials as building (unless permitted by 1509.2.5)

Unlimited in height if noncombustible

Max. 20’ above allowable building height if combustible

See Chapter 15 for additional requirements

Mezzanines & Equipment Platforms

Mezzanine is portion of story below

Does not contribute to building area

Not considered a story

Does contribute to fire area

Clear height above and below 7’ minimum

Mezzanine & Equipment Platform Area Limitations

Mezzanine limited to 1/3 area of room with which it shares a common atmosphere

Enclosed spaces in room below can’t be used in calculation

Multiple mezzanines in story; same 1/3

When mezzanine and equipment platform, limit is 2/3

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Mezzanine example: Mezzanine & Equipment Platform Area Limitations

Exceptions:

Aggregate area for mezzanines in Construction Type I or Type II special industrial occupancies = 2/3

New 2012: mezzanines in Type I or Type II building with sprinklers and emergency voice/alarm communication system = 1/2

Mezzanines

505.2.3: mezzanine must be open and unobstructed to room below except for 42” walls, columns and posts (no glass)

Exceptions:

10 or fewer occupants

2 or more MOE; 1 of which is exit

10% of mezzanine may be enclosed

Group F control mezzanines may be glazed

New 2012: Other than H or I: 2 story sprinklered buildings: mezzanine not required to be open

Building area increases

Frontage: 1% additional area for each 1% frontage above 25%

If = [F/P - .25] W/30

If = area increase for frontage

F = building perimeter with 20’ min. width

P = entire building perimeter

W = width of public space (20’ min., 30’ max.)

Frontage example: Example:

100’ x 50’ building with 250’ (83%) OP, 100’ of which is only 25’ wide:

If = [250/300 - .25] 28/30 = .544 = 54.4%

Allowable area (w/o sprinklers) = 1.544 x Table 503

Note: W= 100x25 + 150x30 / 250 = 28

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Sprinkler area increase

Only applies to NFPA 13 systems, not 13R or 13D

Not permitted in buildings with Group H-1 occupancy (entire building); buildings or portions of buildings with Group H-2 or H-3 occupancies (other portions can take increase); buildings where the sprinkler system was substituted for fire-resistance rated construction (see T. 601, note d)

Sprinkler area increase

200 % increase for multi-story buildings

300% increase for single story buildings

Permitted in addition to height increases for sprinklers and area increases for frontage

Only stories above grade count in this evaluation; not basements

Example One:

Group A-1 (theatre); 1 story, Type VB construction, 54.4% If, fully sprinklered. How big can it be?

Tabular area = 100% =1.00

OP = 54.4% = .544

Sprinklers = 300% = 3.00

Total = 454.4% = 4.544

5,500 s.f. x 4.544 = 24,992 allowable

Example two: Find the required construction type for a 30,000 s.f. per floor two story Group B, fully sprinklered with 100% OP (min 30’ wide):

Tabular = 100% = 1.00

If = 75% = .75

Sprinkler = 200% = 2.00

Total = 375% = 3.75

Equivalent area = 30,000/3.75 = 8,000

Per Table 503, any construction classification works, including VB

Maximum building area

506.4 - Multi story, single occupancy:

Determine allowable area per floor; for 2 story, multiple by 2; for 3 or more stories multiply by 3

No single story shall exceed the allowable area per story

A single basement that does not exceed the allowable area per floor does not count toward maximum area of the building

506.4 Example

Group B; Type IIA; fully sprinklered; 75% OP increase; 6 stories; basement:

37,500 x 3.75 = 140,625 per floor

140,625 x 3 = 421,875 total building

Distribute among 6 stories however you want but no story can be over 140,625

Single basement doesn’t count but can’t be over 140,625

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Maximum building area

506.5 - Mixed occupancy:

1 story: see 508.1 (more on that later)

More than 1 story: each story shall comply with 508.1; more than 3 stories – total building area shall be such that sum of ratios of the actual area of each story divided by the allowable area of such stories shall not exceed 3.

Again, a single basement doesn’t count

506.5 example:

Unlimited area buildings

New 2012: 507.1 clarifies that unlimited area buildings can have accessory occupancies in them.

Yards: measured perpendicular from exterior wall to nearest lot line or face of opposing building on same lot

Public way: measure entire width (road, highway, railroad, etc.)

Unlimited area buildings 507.2: Non-sprinklered 1 story: F-2 or S-2 surrounded by 60’ yard/public way

507.3: Sprinklered 1 story: B, F, M, or S any const. type; or A-4 other than Type V surrounded by 60’ yard or public way

Type I or II with rack storage and no public access have no height limit

Sprinklers not req. over participant sport area with direct exits and alarm system (not considered fully sprinklered bldg.)

Mixed occupancy unlimited area w/ Groups A-1 and A-2 (507.3.1)

Other than Type V construction; sprinklered, 1 story; B, F, M or S occ.

A-1 and A-2 must be separated from other occupancies per T 508.4 with no reduction for sprinklers = 1 hour F-2 or S-2; 2 hours B, F-1, M, or S-1

A-1 or A-2 areas cannot exceed T. 503 w/ If & sprinkler increases

Exits from A-1 or A-2 must discharge directly to exterior

Unlimited area buildings

507.4: Two story B, F, M or S:

Must be sprinklered

Must be surrounded by min. 60’ yard or public way

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Compliant? Unlimited area buildings

507.5: Reduced open space – open space can be reduced to 40’ when all of the following:

Reduced width for not more than 75% of the perimeter of the building

Exterior walls facing reduced width: 3 hour

Opening protectives facing reduced width must be 3 hour

Applies only to 507.2; 507.3; 507.4; 507.6 & 507.11 (not to A-3 Type III or IV, E, H or Aircraft paint hangar)

Unlimited area 1 story Type II, Group A-3 (507.6)

Allows place of religious worship, community hall, dance hall, exhibition hall, gymnasium, lecture hall, indoor swimming pool or tennis court

No stage; platform OK

Must be sprinklered

Minimum 60’ yards or public way

New 2012: Unlimited area 1 story Type III & IV, Group A-3 (507.7)

Same requirements as 507.6 plus:

Assembly floor must be at or within 21” of street or grade level and all exits must have compliant ramps

Means no mezzanines allowed

Group H occupancies in unlimited area buildings

See 507.8 for Group H occupancies in unlimited area buildings

See 507.9 for unlimited area aircraft paint hangars

Unlimited area buildings

507.10: Group E, 1 story of Type II, IIIA or IV construction:

2 MOE each classroom; one exit direct to outside

Must be sprinklered

Must have 60’ yards or public ways

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Unlimited area buildings

507.11: Motion picture theatres

Must be Type II construction

Must be located on first story above grade

Must be sprinklered

Must be surrounded by minimum 60’ yards or public ways

507.12: covered malls & anchor buildings complying with 402 shall not be limited in area

Mixed Occupancies

New 2012: moved from Chapter 3 to Chapter 5, Section 508

Three ways to handle:

Accessory occupancies

Non-separated

Separated

Can be all 3 in same building

Can also use fire walls – separate bldgs.

Mixed occupancy exceptions

Special provisions of 510

H-1, H-2 & H-3 required to be in separate buildings by T. 415.5.2

Live/work units complying with 419 are not separate occupancies

Incidental uses

Accessory occupancies

Must be ancillary to main occupancy

Limited to 10% of story

Cannot exceed tabular area T. 503 (no increases)

Retain occupancy classification

Building height & area based on main occupancy

Accessory occupancy cannot exceed tabular height T. 503 (no increases)

Accessory occupancies

No separation required between main and accessory occupancies

Exceptions:

H-2, H-3, H-4, H-5 must be separated

I-1, R-1, R-2 & R-3 DU & SU separations required (generally 1 hour but exceptions for ½ hour floor/ceiling in sprinklered IIB, IIIB & VB – see 420, 708 & 711)

Nonseparated occupancies

Still individually classified

Code requirements apply per occupancy

Most restrictive provisions of Chapter 9 apply to entire nonseparated area

When in high-rise, most restrictive provisions of 403 apply to entire building

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Nonseparated occupancies

Allowable height and area based on most restrictive occupancy

No separations required except:

H-2, H-3, H-4, H-5 must be separated

I-1, R-1, R-2 & R-3 DU & SU separations required (generally 1 hour but exceptions for ½ hour floor/ceiling in sprinklered IIB, IIIB & VB – see 420, 708 & 711)

Separated occupancies

Each occupancy individually classified

Code requirements apply to each separated space

Separations must be fire barriers (707) or horizontal assemblies (717) or both

All fire areas have 6 sides – like a box

Separation ratings per T. 508.4

Table 508.4 Allowable area and height

In each story the sum of the ratios of actual area divided by allowable area shall not exceed one.

Each separated occupancy’s height within the building shall comply with Section 503.1

Exception: special provisions of 510

Sum of ratios example Incidental Uses - 509

Ancillary functions that pose a greater risk – limited to those in T. 509

Incidental uses in DU need not comply

Option not available for storage rooms

Incidental use areas included in main occupancy

Limited to 10% of story

Separation/protection = T. 509 & 509.4

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Table 509 Special provisions - 510

510.2: permits a 3 hour horizontal separation to create two buildings stacked on top of each other. Lots of conditions, among them: Lower building Type IA, sprinklered, one story

max.

Special rules for openings through horizontal separation

Occupancies above & below limited

Height in feet from grade plane

Special provisions - 510

510.3: permits 1 story S-2 enclosed parking garage below S-2 open parking garage of a different construction type

See code for specific requirements

510.4, 510.7 & 510.8 (new): provide special exceptions for parking structures beneath or above other occupancies that are less restrictive than T. 503

See code for specific requirements

Special provisions - 510

New 2012: 510.9 - allows multiple buildings above the horizontal assemblies prescribed in Sections 510.2, 510.3 or 510.8

The End

Questions????

Thanks for trying to stay awake!