CSI MasterFormat organizes construction specifications into 50 divisions. Knowing the division structure saves hours hunting for requirements on every project.

What MasterFormat Is and Why It Matters

CSI MasterFormat is a standardized classification system published by the Construction Specifications Institute (CSI). It organizes construction specifications, costs, and schedule items into a consistent taxonomy. Every specification book, bid estimate, and construction schedule uses MasterFormat.

Why it matters:

Finding specs quickly. Instead of flipping through 200 pages, you know that concrete is in 03 30 00 and roofing is in 07 20 00. Direct navigation.
Consistency across projects. Every project organizes plumbing the same way (Division 22). Subs and suppliers expect it.
Estimating and scheduling. Bid breakdowns, cost databases, and scheduling software all use MasterFormat numbers as the common language.
Submittal logs and RFIs. You reference specs by division number: "See Division 03 for concrete curing requirements."

The Division Structure

MasterFormat is organized into groups. The current version (2020) has 50 divisions in these groups:

Divisions 00–04: Procurement, Conditions, and Foundation

00: Procurement (bidding, contracts)
01: General Requirements (insurance, safety, permits, submittals)
02: Existing Conditions (demolition, site utilities)
03: Concrete
04: Masonry

Divisions 05–09: Structural and Finish Systems

05: Metals (structural steel, miscellaneous metals)
06: Wood and Plastics
07: Thermal and Moisture Protection (roofing, insulation, waterproofing)
08: Openings (doors, windows, glass, hardware)
09: Finishes (drywall, paint, flooring, tile)

Divisions 10–19: Interior Systems and Equipment

10: Specialties (signage, flagpoles, operable partitions)
11: Equipment (kitchen, medical, industrial)
12: Furnishings (casework, millwork, seating)
13: Special Construction (clean rooms, pools, saunas)
14: Conveying Systems (elevators, escalators)
15–19: Reserved for future use

Divisions 20–28: Facility Services (MEP + Other)

20: Reserved
21: Fire Suppression (sprinklers)
22: Plumbing
23: HVAC (heating, cooling, ventilation)
24: Reserved
25: Integrated Automation (building controls, BMS)
26: Electrical
27: Communications (telecom, data, cabling)
28: Electronic Safety and Security (fire alarms, security systems)

Divisions 30–35: Exterior Work and Site

30: Reserved
31: Earthwork (excavation, fills, grading)
32: Exterior Improvements (paving, landscape)
33: Utilities (water, sewer, natural gas lines)
34: Transportation (roads, parking, runways)
35: Waterway and Marine (docks, marinas)

Divisions 40–48: Process Equipment and Manufacturing

40: Process Integration
41–48: Industry-specific equipment (manufacturing, treatment plants, industrial)

Key Divisions Every GC and PM Must Know

On most commercial and residential projects, these divisions drive the work and budget:

Division 01: General Requirements

This is the most important division. It covers project-wide requirements: permits, insurance, safety, mobilization, site management, environmental compliance, submittals, RFIs, testing, warranty, project closeout. Always read Division 01 first. It sets the tone for the entire project and conditions everything that follows.

Division 03: Concrete

Covers ready-mix concrete, reinforcing steel, formwork, finishing, and curing. Includes foundation concrete, slabs, structural frames. Typical specs: concrete strength (4000 PSI), air entrainment, slump, reinforcing bar placement, slab finishing (broom finish, polished, etc.), curing duration. Cross-reference with structural drawings for size and location of concrete elements.

Division 04: Masonry

Brick, block, stone, and mortar. Specifies material quality, mortar strength, and workmanship. Common specs: "8" running bond CMU, 3000 PSI strength," or "4" face brick, Type S mortar." Includes grout, insulation, and any special finishes (paint, sealant).

Division 05: Metals

Structural steel, miscellaneous steel (plates, channels, angles), and ornamental metals. Specifies steel grades (typically ASTM A36 or A500), connection methods (bolts, welds), and coatings (paint, hot dip galvanizing). Shop drawings required for all structural steel connections.

Division 07: Thermal and Moisture Protection

The most critical and litigated division. Covers roofing (bituminous, membrane, metal), insulation, waterproofing, vapor barriers, flashing, sealants, and air barriers. Specs typically reference roofing manufacturer specs and require specific warranty periods (10–20 years for built-up roofing). This division prevents water from destroying your building—read it carefully.

Division 08: Openings

Doors, windows, glass, and hardware. Specifies performance ratings (fire rating, sound transmission, security), materials (aluminum, wood, steel frames), glazing type (tempered, laminated), and locking hardware. Cross-reference with architectural drawings for locations, sizes, and special requirements (ADA accessibility, emergency egress).

Division 09: Finishes

Interior and exterior finishes: gypsum board, paint, coatings, tile, flooring (wood, vinyl, carpet), suspended ceilings. Specs include surface preparation (prime coats, underlayment), paint types (latex, acrylic, epoxy), tile adhesives and grout, and finishing tolerances. Samples required for all color and finish selections.

Division 22: Plumbing

Water supply, drainage, venting, and plumbing fixtures. Specifies pipe material (copper, PVC, PEX), fixture type and quality (level of trim), pressure ratings, and code compliance. Includes water heaters, backflow preventers, and specialty systems (reclaimed water, snow melt). Cross-reference with MEP drawings for routing, sizing, and connections.

Division 23: HVAC

Heating, cooling, ventilation, and controls. Specifies equipment capacity (tons of cooling, thousands of BTU), duct material and insulation, outdoor air requirements, and control sequences. Complex to coordinate with architectural and electrical. Cross-reference with building code for minimum ventilation rates (CFM per person or per square foot).

Division 26: Electrical

Power, lighting, and controls. Specifies service size and voltage, circuit breaker ratings, cable types, lighting fixtures and ballasts, and emergency backup (generator, UPS). Includes fire alarm and standby power. Key specs: "400-amp service, 208/120V," "LED lighting, 3000K color temperature," "10 kW diesel generator."

Division 31: Earthwork

Excavation, fill, compaction, and grading. Specifies compaction percentage (95% or 98% of max density), lift thickness (typically 6 or 8 inches), and testing requirements. References geotechnical report for soil handling and foundation preparation. Includes erosion control and site restoration.

How to Use Division Numbers to Cross-Reference Specs with Drawings

Specifications and drawings are complementary. Here's how to navigate:

Drawings Show the "What" and "Where"

Structural drawing shows a concrete beam. You see the beam size, reinforcing, and location. To find HOW it should be built, turn to Division 03 (Concrete).

Specifications Show the "How" and "Quality"

Division 03 specifies concrete strength (4000 PSI), air content (6–8%), slump (3–4 inches), curing method (wet for 7 days), and finish. Without the spec, you could build the beam but have no standard for quality.

Cross-Reference by Writing Notes on Drawings

On architectural drawings, you'll see notes like "See Division 01 for warranty requirements" or "Concrete: See Division 03." These are anchors that tie drawings to specs. Follow them.

In Case of Conflict, Division 01 Wins

If a drawing note contradicts the spec, Division 01 (General Requirements) usually has a hierarchy clause: specs prevail over drawings in cases of conflict. Read it to understand the priority order.

The Most Common Mistake: Skipping Division 01

Division 01 is long and dense — 30–50 pages on large projects. GCs and subs often jump straight to their trade division (Division 22 for plumbing, Division 26 for electrical). Big mistake. Division 01 governs everything:

Submittal requirements: Tells you what shop drawings and product data you must submit and when
Safety standards: OSHA requirements, site safety plan, worker qualifications
Site logistics: Parking, material storage, waste management, temporary facilities
Quality assurance: Testing protocols, inspection rights, rejection and correction procedures
Project close-out: Final cleaning, warranty documentation, as-built drawings
Insurance and bonding: Coverage amounts, additional insured requirements

Late submittals, failed inspections, and closeout delays often trace back to requirements missed in Division 01. Read it before bidding or before starting work.

Quick Reference: Finding Specs by Material

Material or System	Division
Concrete foundations, slabs, beams	03
Brick or block walls	04
Structural steel or steel frame	05
Roofing, waterproofing, insulation	07
Doors, windows, glass	08
Drywall, paint, flooring, tile	09
Fire sprinklers	21
Plumbing (pipes, fixtures, drainage)	22
HVAC (heating, cooling, ventilation)	23
Electrical power, lighting	26
Telecom, data cabling	27
Fire alarm, security systems	28
Excavation, grading, fill	31

Related Resources

How to Read Specifications

Learn to navigate and interpret individual specification sections.

Submittal Log Guide

Build a submittal log using CSI divisions as your roadmap.

How to Review Construction Drawings

Cross-reference drawings with specification divisions to catch conflicts.

Drawing Transmittal Guide

Manage specification updates and drawing distribution.

Constructability Reviews

Coordinate specifications with drawings to ensure buildability.

Drawing Version Control

Track which version of specs and drawings are in use on site.

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CSI MasterFormat Specification Divisions Explained