As mentioned, local codes state that the ceiling has to be a minimum of 7 feet above the floor (or 84 inches) in at least 50% of each habitable room. My basement ceilings are only 81 inches tall from floor to the bottom of the joists (Meaning that if I were to drywall along the joists, my ceiling would be 3 inches too short of the requirement). But, the joists are 2X8s. My question is, can I leave my ceilings open (rather than drywall them) to workaround this? If I simply paint the joists and leave them open, will this legally give me an extra 8 inches of space, making them 89 inches tall? Granted, the joists would still be there, but more than 50% of the room would be high enough. It seems like a simple solution, and I'm wondering if it's too good to be true. I'd appreciate anybody's advice!
The guide to the 2021 IRC code regarding the ceiling height for the basement is provided below:
According to the IRC (International Residential Code), that basement ceiling height requirements for any habitable basement space, laundry rooms, toilet rooms, bathrooms, or corridors must meet a minimum standard height of 7 feet 0 inches in new buildings. This includes finished basement ceilings and unfinished basement ceilings.
The distance is measured from the finished floor to the lowest point of obstruction, whether an enclosed duct or installed drop ceiling in the habitable room or finished basement. Therefore, any obstructions like girders, ducts, beams, plumbing, or electrical components must be calculated into the equation and meet the 7 feet rule.
Notable exceptions are rooms with sloped ceilings where at minimum 50% of the space must be at the height of 7 feet, and the remaining space must reach a height of 5 feet and not lower.
Basement spaces in existing homes must have a minimum ceiling height of 6 feet 4 inches and include allowances for girders, ducts, beams, plumbing, or other architectural obstructions.
Bathrooms within existing old construction homes must meet the 6 feet 4 inches standing height requirement for flush toilets, bidets, and sinks. A showerhead must also meet the 6 feet 4 inches height above a 30 inch X 30-inch space and function as designated.
However, sloped ceilings and soffits are allowed as long as they do not interfere with plumbing fixtures.
For your case, you need to figure out whether your house is considered a "new construction", or an "existing construction".
If it is the former, I don't see you having an easy way out without consulting with an engineer. If it is the latter, it seems you are fine with the addition of a ceiling that is kept within the allowance (6'4"). However, as IRC code changes ever so frequently, it really depends on your ADJ to make the call. Below is the 2015 IRC for your info,
R305.1 Minimum height.
Habitable space, hallways and portions of basements containing these spaces shall have a ceiling height of not less than 7 feet (2134 mm). Bathrooms, toilet rooms and laundry rooms shall have a ceiling height of not less than 6 feet 8 inches (2032 mm).
For rooms with sloped ceilings, the required floor area of the room shall have a ceiling height of not less than 5 feet (1524 mm) and not less than 50 percent of the required floor area shall have a ceiling height of not less than 7 feet (2134 mm).
The ceiling height above bathroom and toilet room fixtures shall be such that the fixture is capable of being used for its intended purpose. A shower or tub equipped with a showerhead shall have a ceiling height of not less than 6 feet 8 inches (2032 mm) above an area of not less than 30 inches (762 mm) by 30 inches (762 mm) at the showerhead.
3. Beams, girders, ducts or other obstructions in basements containing habitable space shall be permitted to project to within 6 feet 4 inches (1931 mm) of the finished floor.
Portions of basements that do not contain habitable space or hallways shall have a ceiling height of not less than 6 feet 8 inches (2032 mm).
Exception: At beams, girders, ducts or other obstructions, the ceiling height shall be not less than 6 feet 4 inches (1931 mm) from the finished floor.
The Code requires a minimum ceiling height of 7’-0” for habitable spaces, unless 1) it’s a slopped ceiling, 2) basement remodel, 3) bathroom or shower. (See R305.1)
Slopped ceilings shall have at least 50% with at least 7’ and slope down to no more than 5’.
Basements can have 6’-8” ceilings in non-habitable spaces. (Habitable spaces are for living, sleeping, eating or cooking. Non-habitable spaces are bathrooms, closets, halls, storage or utility spaces.)
Not more than 75% of a sloped ceiling in a bathroom can be less than 7’ if a space in front of toilet, sink, shower is 6’-4” high.
The Code also states that “Beams and girders spaced not less than 4’ on center may project not more than 6” below the required ceiling height.” (See R305.1;exception 1)
So, you could remodel the ceiling/flooring above to install beams every 4’ and remove the joists in the habitable space only.
However, that’s a lot of work and I think I would discuss this requirement with the Local Building Official. I’d explain that some areas (bathrooms, etc.) will be higher than the minimum in exchange for the 7’ requirement for habitable space. (Show the areas in % )
If this is for your private residence and not for a rental, I think I’d just go ahead and use the space as is and as needed. If there are no structural changes or adding bedrooms, you don’t need a Building Permit and I’d ignore the local Building Official. (You can either ask permission or ask for forgiveness. I raised 2 teenagers so I know how to whine and get my way. But remember, insurance adjusters may exclude any claim from this area for future claims.)