Refs: IMC 306.3-306.4.1; NFPA 70.
Plain English:
306.3 Appliances in attics: Provide an access opening >= 20x30 in and large enough to remove the largest appliance. Passageway to the unit is >= 30 in high x 22 in wide and <= 20 ft long, with continuous solid flooring >= 24 in wide. At the unit, provide a level 30x30 in service space.
Exceptions: No passage/service space if service/removal is through the opening; or if passage is unobstructed and >= 6 ft high x 22 in wide, max length is 50 ft.
306.3.1 Electrical (attic): Provide a luminaire switched at the access opening and a receptacle at or near the unit, per NFPA 70.
306.4 Appliances under floors (crawlspaces): Provide an access opening >= 22x30 in; passageway >= 30 in high x 22 in wide and <= 20 ft to the unit; 30x30 in service space at the unit. Where the passage or service space is > 12 in below adjacent grade, line the walls with concrete/masonry extending >= 4 in above grade with adequate lateral capacity. Opening must allow removal of the largest appliance.
Exceptions: No passage where service space exists at the opening and unit can be serviced/removed through it; or if passage is unobstructed and >= 6 ft high x 22 in wide, length is unlimited.
306.4.1 Electrical (crawlspace): Luminaire with switch at the access and a receptacle at/near the unit, per NFPA 70.
On Plans: Why It Matters
Missing opening size, 24 in flooring, 30x30 at the unit, or light/receptacle = fast inspection holds and rework. These are straightforward, measurable clearances-show them once and pass once.
🧾 Where To Show It (sheet map)
M-001: Post attic/crawl rules: opening sizes, 30x22 passage limits (20 ft / 50 ft high-clear), 24 in flooring, 30x30 at unit, crawl lining trigger, NFPA 70 light + receptacle.
M-101+ (Plans): Dimension openings, passage HxWxL, flooring, and 30x30; trace removal path.
M-501/502 (Details): Hatch/catwalk, 24 in flooring, service platform, crawl lining section, light/receptacle locations.
M-601 (Schedules/Notes): Opening (in); Passage (HxWxL); Flooring (in); 30x30 (Y/N); Crawl Lined (Y/N/NA); Light (Y/N); Recpt (Y/N); Removal Path (Y/N).
Code Path: Access Panel and Attic Equipment Documentation
Show the access panel or hatch location on the reflected ceiling plan for any equipment installed above an inaccessible ceiling - size it to allow equipment removal.
For attic equipment: show the working platform, lighting fixture, and electrical outlet on the attic equipment plan per IMC 306.3.
Access panel and hatch dimensions must be shown on the plan - minimum 20x30 in for general access, larger if equipment requires it for removal.
Check: Attic and Ceiling Access Verification
Confirm every above-ceiling AHU, fan-coil, or in-line fan has an access panel shown on the reflected ceiling plan at the unit and at every access point in the duct run.
For attic equipment: confirm working platform, light, and electrical outlet are shown - these are code requirements, not options.
Verify the access panel is large enough to allow replacement of the largest serviceable component (typically the coil or heat exchanger).
Review Risk:
Attic equipment without working space, lighting, or electrical outlets is a chronic problem on residential projects - these requirements are frequently added at inspection, requiring field changes.
Access panels not shown on the reflected ceiling plan are a common plan review comment - reviewers specifically check that every above-ceiling unit has an accessible service point.
Underfloor equipment without the applicable opening, passageway, service-space, lining, removal-path, and exception checks can require field correction.
Field Tip:
Declare your route: 20 ft standard or 50 ft high-clear-note it on plans.
Size for the largest unit: confirm it fits through the opening and along the passage/turns.
Build the catwalk: continuous 24 in flooring to the unit; mark the 30x30 at the service side.
Crawl trenches: if deeper than 12 in below grade, install concrete/masonry lining to 4 in above grade.
Power & light: place the switch at the access and the receptacle at/near the unit (NEC/NFPA 70).
Masterbuild QA Lens
Attic and crawlspace access openings are required to be large enough to remove the largest appliance - and most plan sets show only a generic access hatch with no dimension check. Confirm the opening is >=20x30 in, the passageway is >=30 in clear width and 30 in headroom, and that the electrical luminaire and receptacle requirements are noted on the electrical plans. Coordinate with the MEP coordinator before submittal.
Drawing / Submittal Check
For IMC 306 access and service space (Part 2 - access panels, attic and crawl space equipment): equipment installed above an inaccessible ceiling or in an attic must be accessible. Show the access panel or access hatch location on the reflected ceiling plan, sized to allow equipment removal. For attic installations, show the required working platform, lighting, and outlet. Equipment installed in unconditioned spaces without a lighting and electrical outlet shown will get a comment.
Common Review Risk
Attic and crawl space equipment without working space, lighting, or electrical outlets is a chronic problem on residential projects where these requirements are added late or forgotten. An inspector who finds a furnace in an attic without a light or an outlet will write a deficiency. Confirm the attic mechanical requirements (working platform, light, outlet, switch at access point) are on the permit drawings - they are quick to add and slow to fix after installation.
When To Escalate
Escalate when a required access panel conflicts with architectural finishes, rated assemblies, security, tenant operations, or lease boundaries. Coordinate an approved location and responsibility before permit issue and construction.