On Wed, 3 Jan 2018 07:23:43 -0800 (PST), Kat McGrath
wrote:

Hey guys,

Ok so I am remodeling my basement which is technically the first floor of a two story home, I took out the ceiling and noted a cracked joist that runs a 20 foot span under my kitchen and dinning room, there is no center support and it is supported at the ends on top of cinder block and set in concrete. The crack is 8 feet from the wall in my laundry room which is under my kitchen and extends approx. 3in from the bottom edge into the beam across a 1 foot span. The beam is a 2x12x20. To repair this I want to sister it and build a frame to support it in the middle which I can accomplish by adding a door way to the laundry room. I want to put king beams on either side approx. 48in apart and have a 3 foot opening into my laundry room. I was going to use 2 stacked 2x4s to make the header. My question, Is this adequate support? What can I do to make this better? I just want to make sure I do this right, Thanks for your help.
Sister the joists full length with 2X12. If you can't get 20 footers,
use 16 footers on both sides, staggered end for end, plus 4 footers to
fill in the length - bolt and glue. The header above the door opening
is stronger with 2X4 lumber set upright, 2 or 3 wide, than on the flat
2 deep. Supporting the beams on the door posts requires a proper
footing under the support posts - do NOT simply plant the posts on the
concrete floor.