home remodelling?

Question

i want to sister the joist below me first floor sub floor. the span of the existing joists are around 25 ft. and i want to sister and raise the floor about a 1/4 to a 1/2 inch in the area of sistering. i want to sister the entire span of joist. the old joist run the entire 25 ft across the basement. should i use two 12 ft sisters one on each end with a beam running perpendicular the joist between the sistered joist or just use a sixteen footer on one end and around nine feet on the other to complete the span. the floors have a little sag and im also installing floor tiles in two of the rooms above the joists. anyone have any better ideas or what is the best way to do it?

Answer 1

That half inch you are raising is going to cause so much damage to your house it is rediculous. Doors will stick, walls will all kinds of crack, hope you don't have a chimney. Windows will probably break. All your plumbing will now be stressed. You are in a old house you can't just raise it in a weekend. Well you could. But when done properly it should take about a month or so to raise it that much without destroying everything in the place. never mind the floor tiles get the wall spackle and tape out. Doors really suck to rehang as well.

Answer 2

Either way would help support the floor, but to prevent further sagging add a support post under the joists.

Instead of trying to raise the entire floor in that area use a floor leveling compound before you lay the tile. It may require quite a bit to account for 1/4 to 1/2 an inch, but trying to raise the floor from underneath will crack up your house .

Answer 3

that is a loooooong span for dimensional lumber. engineered wood beams possibly you will have to check with your local lumber yard. Take the floor lay out along so that they know the tributary loads. the sag isn't that great to straighten out in one shot. the windows should have Little or no effect as they aren't in direct line with the shift of the floor. the doors if hung when the house was first built will go back to where they belong and as for the sheet rock unless it is right over the beam things should go very well. for that long a span I would consider a steel beam the cost is a bit more but properly designed it will take less space than the wood. it is easily possible to bury the beam in the floor joists and have a flush ceiling.