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enter image description hereWe 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 2x10, (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 2x8 beams to the existing 2x10 and trim down the 2x10s to 8 inches and use a 4x8 or 4x6 joist hangers. Additionally all the beams are notched at either end, but the notch doesn't serve a purpose.

The tables indicate that a 2x8 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?

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  • Hello, and welcome to Home Improvement. Do you mean that your basement headroom is between 61" and 65"? Adding a picture or two to your question would help. And, you should probably take our tour so you'll know how best to participate here. – Daniel Griscom Nov 30 '19 at 14:06
  • Sorry that was an error on my part it is feet and not inches. – Jonathan Jacobs Nov 30 '19 at 21:09
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    Thanks; a picture or two would also help one of our pros better understand your situation. – Daniel Griscom Nov 30 '19 at 21:24
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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.

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  • The basement is up to code (montreal) with regards to window egress and exits, 2 total. The basement will not be "habitable" area. It will serve primarily as a TV room/play room for the kids, a small workshop for me and a secondary bathroom/powder room. I understand that sistering would be overkill (based on the tables), but is it safe to trim the joists without some added support? – Jonathan Jacobs Dec 1 '19 at 17:54
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    @JonathanJacobs The Code defines Habitable space as “living, eating, sleeping or cooking”. Are you sure it’s not habitable space? – Lee Sam Dec 1 '19 at 18:26
  • @JonathanJacobs Yes, you can trim your 2x10’s down to 2x8’s without consequences, provided 1) no notched occur in the remaining “2x8” after your cutting, 2) no knotholes (2” and larger) occur in the edge of the joist after the trimming – Lee Sam Dec 1 '19 at 18:32

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