We are looking into continuing work on our story duplex basement. Our basement in most areas is anywhere from 6.1 to 6.5 feet. I am looking to gain an additional 2 inches of head room. Right now the cost of lowering the floor would not net a vailable return. However…
The basement is approx. 1200 sq/ft. The floor joists are 2×10, (16" OS) (true cut) and do not run longer than 11 feet. This is an older construction, at the moment there are no hangars attaching the joists to the 2 main cross beams. My idea is to sister 2×8 beams to the existing 2×10 and trim down the 2x10s to 8 inches and use a 4×8 or 4×6 joist hangers. Additionally all the beams are notched at either end, but the notch doesn't serve a purpose.
The tables indicate that a 2×8 with my current span is feasible. I have just not found many references to this type of job. We want to keep an open ceiling concept in the basement, so any head room gained is worth it and I would assume, in theory, be shoring up the floor with the sistering of the joists, addition of hangers and would add blocking (since there is none). Does this make sense?
Best Answer
The Code requires a minimum ceiling height of 7’-0” for habitable spaces, unless 1) it’s a slopped ceiling, 2) beams in ceilings 3) basement remodel, 4) bathroom or shower.
1) Slopped ceilings shall have at least 50% with at least 7’ height and slope down to no more than 5’.
2) Beams in ceilings spaces not less than 4’ on center, can drop down 6” below the 7’ ceiling.
3) Basements can have 6’-8” ceilings in non-habitable spaces.
4) 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.
Yes your 2x8’s at 16” on center spanning your maximum length of 11’ will be strong enough and comply with the structural code requirement of providing a minimum of 40 lbs. per square foot. (Sistering a joist to the original joists may be overkill.)
However, you have other issues regarding ceiling heights, exits, etc.