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Wayne Perry 10-06-2012 05:17 PM

Balloon Frame House, sagging floors
I'm working on a 100+ yr. old farm house that my daughter and son-in-law just purchased. There are loads of problems, but lots of charm. My problem right now is deciding what to do to even up the floors. It's a balloon framed house. The room floors tend to be high around the outside, but dip as you get to the middle of the house. It's kind of like they are "cupping". If I sister new 2x8s to the existing sagging floor joists, keeping the new lumber level across the room, is that a good approach? I imagine the number of nails needed for each joist would be high...maybe 2 every 10-12 inches?

AndyGump 10-06-2012 06:56 PM

Since it seems you have access the crawl space you might be better off installing piers, posts and beams.
All of which can be designed without the aid of an engineer, any competent designer or experienced general Contractor or carpenter can help you with the prescriptive design on this.


joecaption 10-06-2012 07:08 PM

Andys got the plan.
It's going to do almost no good to just sister the joist. Floors will still be sagging .
Any old house I've ever worked on had to long a span for the size of the joist, not enough piers, plus moisture, fungus and or insect infestation.

Oh what an adventure for them, I sure hope they have deep pockets when dealing with any old house.

Tham 10-06-2012 09:07 PM

Totally agree. Adding more dead weight won't help.


Gary in WA 10-06-2012 10:36 PM

Little reading for you (for the upstairs floors), pp.136-145;


mae-ling 10-07-2012 12:43 AM

GBR - how do you findthis stuff - you a Google Master?

mae-ling 10-07-2012 12:44 AM

Why would sistering joists not help?

joecaption 10-07-2012 07:43 AM

It would stop the bounce and anymore sagging, but would do nothing to get out the sag.
Without a picture were going to have to guess but most old houses I've worked on notched the ends of the joist and just set them on top of the outside beams. The notch can be the cause of a crack in the joist right where the two angles intersect. It also weaken the whole joist.
By adding footings and piers in the middle of the span it would allow you to set a beam that can be lifted with bottle jacks to set the floor level, once it's level piers can be set to hold the beam in place so there is no more sag or bounce at all.
Lifting the middle of the floor should have no effect on the outside walls.

Daniel Holzman 10-07-2012 08:04 AM

The topic of stiffening sagging floors has been discussed repeatedly on this forum over the past few years. It would be worth doing a search to see some of the threads.

Sistering joists with new, straight lumber is certainly one possible way to stiffen a joist, and provide a level surface to attach underlayment to. The technique is pretty simple, you install the new joist level at the elevation you want, which sounds like it will be about 1 inch higher than the existing joist at midspan. The sistered joist needs to be supported on the ends as would any other joist, using either hangers or directly on top of the wall. Then you fasten the new joist to the old joist, and you have effectively a new floor system that has twice the moment of inertia of the existing system, making it stiffer and stronger.

Other techniques have been discussed on this forum, including sistering using plywood, adding steel straps to the existing joists, or adding a flat 2x4 to the bottom of the existing joist making a T beam. All of these techniques increase the strength and stiffness of the existing joist, but the sag remains unless you jack up the floor joists. Jacking has also been discussed many times on this forum.

Jacking carries many perils, including the potential to crack the joist itself or adjacent walls. Wood is an unusual material in that it undergoes two different kinds of deflection under load. The initial deflection when you load wood is called elastic deflection, and this means if you remove the load the wood springs back to original shape. Long term creep is a form of plastic deflection, meaning that the wood takes a permanent deflected shape and will not return to original shape if the load is removed. This is what happens in older houses, and explains why you need to jack the wood back to position. Even after jacking, the wood will eventually return to its permanently deflected shape once the load is reapplied, so jacking is not a permanent solution.

Creep is generally estimated as a fraction of initial deflection. In many cases, long term creep is approximately equal to initial deflection, so a sawn lumber board that deflects half an inch in the middle initially could achieve a final deflected value of approximately 1 inch, of which only the initial 1/2 inch of elastic deflection will be recovered if load is removed. Creep is complicated, and depends on the species of wood, the temperature of the environment, the relative humidity, and what treatments have been applied to the wood.

Some people on this forum have elected to leave the original joists in place, and simply shim the joists to level. This is reasonable if the joists are stiff enough. If the joists are not stiff enough, then an alternative is to stiffen the joists using one of the above mentioned techniques, then shim to level. If you absolutely need to have a level floor, then sistering with a level board is an option, or jacking combined with strengthening the system is required.

mae-ling 10-07-2012 09:53 AM

That's about what I thought. We have sistered and levelled floors/ If you can't get the old ones straight just sister beside and say if you have 2x8 with 1" sag use a 2x10, will lose about 1" max in ceiling height below.

Now if it is in a crawl space or basement that never will be finished the beam is an easier way to go.

Want to add a lot of strength to sistered joists or beams, put a sheet of thin steel in between the plys, doesn't need to be thick just 14 gauge or something. Engineer will tell you exactly what you need.

Wayne Perry 10-07-2012 04:41 PM

This is great info! My original post was a little unclear in that the floors I'm referring to are the 2nd story floors...the first story is not quite so bad. The 2nd story has 2 bedrooms @ 10x15 (The original house is about 20 x 15), so the joists in question are 3x6 (actual) and 16' long 20" OC, with no support anywhere in the wonder they sag. Our thought is to remove the floor and the ceiling beneath (this is a major renovation) and sister a 2x10 to each one. Although we'll lose some height, it should give us a stable level floor on the 2nd story and level ceiling on the first floor. Thoughts?

mae-ling 10-07-2012 06:16 PM

Can your 2x10's sit on the wall at all?
Will you have to notch them at the ends? If so...

Drill hole then cut in order to make the rounded cut.

GBrackins 10-07-2012 08:19 PM

1 Attachment(s)
From the 2009 International Residential Code, Section R502.8

FIGURE R502.8 CUTTING, NOTCHING AND DRILLING R502.8.1 Sawn lumber. Notches in solid lumber joists, rafters and beams shall not exceed one-sixth of the depth of the member, shall not be longer than one-third of the depth of the member and shall not be located in the middle one-third of the span. Notches at the ends of the member shall not exceed one-fourth the depth of the member. The tension side of members 4 inches (102 mm) or greater in nominal thickness shall not be notched except at the ends of the members. The diameter of holes bored or cut into members shall not exceed one-third the depth of the member. Holes shall not be closer than 2 inches (51 mm) to the top or bottom of the member, or to any other hole located in the member. Where the member is also notched, the hole shall not be closer than 2 inches (51 mm) to the notch.

Wayne Perry 10-07-2012 08:31 PM

Great help, mae-ling! Yes, the current joists are notched. I was actually going to try to use joist hangers, but I don't know yet what I would have to attach them to. Chances are that the ledger board the current joists are resting on are not long enough to accommodate the proper size hanger. If they aren't, and I am forced to notch, then your tip is perfect!

Wayne Perry 10-07-2012 08:40 PM

Gary, thanks for the code reminder, although I would have been checking my code book, anyway. As I've grown older and wiser, I honestly look at building codes as a friend. Additionally, 3 of my grandchildren will be growing up in this house, so I'm not looking for shortcuts. Thanks.

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