Floor Slopes

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  #1  
Old 05-31-06, 10:38 AM
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Floor Slopes

I'm in the process of purchasing a 1954 home that has 2 additions. The first was a bedroom (12x16) and the second was an attached bath (9x14). These were added sequencially on the north end of the building.

The bedroom addition has about a 1-1/2 to 2" slope downward from south to north (12' dimension) and the bathroom floor is level, flush with the north edge of the bedroom floor.

The entire house has a crawl space with conventional stem wall type foundations which show no cracks. I'm guessing that the bedroom addition was built level to start with but that the footings for this room were not well founded in firm soil originally. I would like to jack this up and insert an additional plate or grout between the concrete stem wall and the wood stud buildup so as to level the additions to the original house. I understand that this should be done slowly to prevent cracking of drywall or plaster, but I need to know what sort of jacks to use and what the time frame would be.

I plan on putting in 3 beams to jack against the joists adjacent to the foundation walls with a jack at about 2 feet from the end of the bearing walls. I estimate that the maximum load on a jack would not exceed 7000 lbs.

How much vertical lift can be done at one time? What about if each jack was raised just about 1/4" at a time and then do it all again until the total of 1-1/2 to 2" was reached?

Thanks, Joe
 

Last edited by Joe.Carrick; 05-31-06 at 12:49 PM.
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  #2  
Old 06-01-06, 12:34 PM
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Joe:

Did this kind of thing last summer, but I was not trying to raise any sills, just leveling joist sag. Got impatient and caused a couple of plaster cracks trying to push up an area too fast. About 1/8"/day is recommended, and you may still have some damage.

If you are using hydraulic (bottle) jacks, don't leave the weight on them indefinitely while you gradually raise the floor over a period of days/weeks. Use them to lift but use cribbing (temporary supports) to hold the weight in between lifting sessions. I used concrete pads 18" x18' x2", with concrete blocks and wood shims to support the lift beam.

Use 1/4" thick steel pads between the jack and the lumber beam(s) that you use to lift the joists. Otherwise the concentration of force will crush the wood fibers.

The sills may be affixed to the stemwalls with fasteners of some type, if so you will have to locate them and release trhem somehow so the sill can move upward.

Check the condition of the sills carefully. Lifting it the way you plan, you are relying on the nails that fasten the joists to the sill to hold up the entire weight of that end of the addition, including the roof, as you lift it off the stemwall. Any rot or termite damage that might have weakened this area could lead to trouble.

In fact, I don't think I would attempt to do this in this fashion. I would
1) Remove enough siding at the bottom of the addition wall to expose the sill.
2) Use HEAVY GUAGE bolts to fasten large wood blocks [12x12s] to the sill.
3) Raise the addition by jacking under the wood blocks.

Good luck.
 
  #3  
Old 06-01-06, 12:54 PM
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Since the exterior siding is plywood and goes down below the sill plate, I plan on removing it from the floor line down in order to get at the foundation bolts which will need to be released so that the sill plate can move upward. That will also allow me to simply shim under the sill plates as I jack the floor upward. I will be able to place the bottle jacks with the beams above them (naturally with steel plates for bearing against the jacks) and a cripple wall on top of the beams up to the floor joists.

Shimming under the plates will relieve the load on the bottle jacks, so it should be pretty stable and safe during the raising process. I plan on using 1/4" x 3-1/2" masonite shim strips. I'll need a lot of them, but probably not more than I can cut from a couple of 4'x8' sheets.

The only problem might be resecuring the foundation bolts afterwards if they are not long enough. In that case I'll need to use allthread extensions.

I don't think I need to worry too much about cracking, since there's no stucco and only the bathroom is drywall. The interior of the bedroom is wood paneling and the entire exterior is 5/8" plysawn with 1x2 plant-ons to make the house look like board and batt siding.
 
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