Floor Joist Repair Question

[Suncrest]

I just bought a big-time fixer upper. I have reviewed the home. It was built in the 1920's. It is rather small 750 square feet. The basement is dug into the ground about four feet. The floor joists are just that joists and not trusses. The joists are either actual 2x4 or 2x6 the real measurement not the modern 1 3/4 and 3 3/4. Anyway..... There is only one main floor and there are two specific areas where the floor has a sag. Not to mention the proverbial creeking as you walk on the ancient floor. My million dollar question is how can I attempt to bring the floor up to "moderate" level. I have considered using cross bracing to help stop the creeking but am not sure yet how to "lift" the floor.

I have considered using 4x4 set on top of concrete piers elevetated to the floor joist and connected at a modified cross-beam section. Other than that I am not to sure. You got any ideas?

[pushkins]

There are a couple of ways to do what you require and it will depend on just how much work you want to get into.
I'll assume (never a good thing) that as the house is small and has a very limited basement that from one side of the basement to the other is about 20'

At 8' intervals you could dig down in the basement floor a hole 36" deep and 16" square, build a 16" x 16" form from 2x4 lumber nail it all together and position it over the new hole at ground level and fill the hole with concrete right up to the top of the 2 x 4 form, trowel it off and let id dry for 7 days.
On this new footing you will get yourself from Lowes or H.Depot a "lally jack" or a house jack post, they are about $20. Following the directions for setting up the jack. Across the top of the jack or jacks depending on how many you are going to need at about 8' intervals you can use a piece of 4x4 this will act as a new "bearer" from jack to jack to jack. Slowly raise the jacks pushing the 4x4 up to the existing floor joists, make sure that all the jacks are raised up until there is just a small amount of pressure on the 4x4 bearer. Using a level determine which jack needs to be raised SLOWLY raise the jacks a small amount each NEVER just crank up one jack alone, when multiple jacks are used and ALWAYS do this process slowly.

You may well find that you cannot get the underside of the existing joists perfectly level, there are many , many factors that can govern this, the idea is to get the floor as level as you can without undue movement on the walls upstairs, unless you want to get into interior wall repair in the future.

[mrcaptainbob]

I had a similar issue. The span was about twenty feet and the center had sagged almost 3". (The place was built c.1860). There was a wall on the first floor that was not a load bearer to the roof, but none the less was 18" to the side of a wall upstairs. Some of the joists were either rotted or had been ant infested in the past. There were a few added columns in the basement supporting 4x4's under many of the joists. I sistered up new 2x8's and raised them as high as possible. There was a limit! Also, as Pushkins says, I went slowly and not too much. This helped a lot, but it was actually meant to solidify the existing situation and prevent anymore sag, while also replacing the missing wood. To level the floor on the top side, in the 1st room, the flooring was all pulled away, so there was easy access to the jists. Using a laser level I found the difference in heights at points spaced 12" along each new joist. Cut spacers and located them accordingly and glued in place. Laid 3/4" ply on that and lasered it again for a check. It's well within 1/16". The adjacent room (other side of that wall) was a bit different in that the subfloor was not taken up. BUt I laserd that, too, for spacers and glued them in place directly over the new joists beneath. Set 3/4" on top of that and now that too is within 1/16". Both floors are rock solid. No flex, no squeeks. Plus, no more basement columns. Monitoring a couple points in the basement has shown there's not been any change to the floor in almost 12 months.