concrete floor in crawl space.

by Kris
(Warren - MI.)

Q. The tips of a couple of joists under the main floor have rotted off, due to moisture, causing the floor to sag a bit in a small area.
I'd like to use a couple of jack posts in the crawlspace underneath to prop up the sagging joists tips, but I don't know if my concrete crawlspace floor is strong enough to support those 36 in. jack posts. I wish to confirm that it's only a 70 yr old ranch style, single level house, and those joists do not appear to be load-bearing.

Can I just set up the jack posts directly on the crawlspace concrete floor,possibly using a slightly larger metal footplate, or do I need to provide additional concrete footing reinforcements?
Please advise. Grateful thanks.
K.

A. Tap the concrete with a hammer, if it sounds hollow underneath then a larger footplate under the jack will be required to distribute the weight of the joist and flooring.

If the concrete does not sound hollow then the metal footplate you have should work just fine.