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2018 National Home Improvement Estimator, All Rights Reserved Page 55

If only the joist end is decayed, brush wood preservative on the affected area. Then jack the existing
joist up to the correct level and nail a short length of new material to the side of the existing joist. See
Figure 4-3

Some sag is normal in permanently-loaded wood beams. It’s not a structural problem unless the walls
above are obviously distorted. Deflection that doesn’t exceed 3/8” in 10’ is generally acceptable for
structural purposes.

Sagging floor joists aren’t serious unless the foundation system has settled unevenly, causing
excessive deflection in the floor. Look for deflection caused by poor support of heavy partition walls or by
joist sections cut away by a plumbing, HVAC or electrical crew. If the floor appears to be reasonably
level, joist sag is probably acceptable. Otherwise, jack the floor back to a level position and double the
joists or add a floor beam supported at each end by concrete piers.

You can reinforce a sagging floor beam with jack posts. See Figures 4-4 and 4-5. Jack posts used to
stiffen a springy floor can set directly on concrete. Where a jack post has to carry a heavy load, install a
steel plate to distribute the load over a larger area of floor slab. Jack posts aren’t made for heavy
jacking. If heavy jacking is required, use cribbing and an automotive bottle jack to lift the load. Then slip
the jack post into place.

If the floor bounces under foot traffic, check to be sure joist bridges are installed between joists every 8'.
If you see adequate bridging, consider adding extra joists alongside every second joist in the affected
area. Be sure to place new joists with the crown up. It’s more work, but you could also add a
supplemental beam at mid-span under the joists. Support the beam on both ends by installing concrete
piers or posts. Sagging or bouncy floors may also indicate one or more broken floor joists. Inspect the
area around the furnace – furnace heat may have caused excessive drying and cracking of floor joists.