Framing and Sub-Flooring - Adding a main beam support in crawl space

I have rented out an old farmhouse built in the early 40's for about 20 years. It has had a noticeable floor sag from the outside walls to the middle of the house since I have owned it. However, while in the crawl space recently I noticed that a concrete block pillar supporting the center beam near one end had toppled. The main beam is 8"x9" and is sitting on the edge of the home's fieldstone footing. I would like to 1) stabilize the situation by pouring a new footing in the crawl space 2) supporting the beam with one of those steel posts with the threaded plate ends and 3) eventually raise the beam a bit to remove some of the sag from the house.

The crawl space is about four feet deep where I would like to add the support (about three feet from the end of the beam). The soil is mainly sand. Was told to remove loose sand to undisturbed ground then pour a two foot square by 6 inch thick concrete slab with rebar in a tic-tac-toe-like pattern centered in the footing. I think the steel post at the local Menards was called a mobile home jack and was about two feet tall, so would need to block up the footing or find a taller post.

Does this sound like a reasonable plan? Is it something a fairly handy guy with little concrete experience can pull off? A solid footing is key to the whole plan so any suggestions/tips regarding size and strength are welcome.

Welcome to the forums! You have the right scenario going, with the exception of the steel post. They aren't code compliant in most areas. If in your area they are accepted, then OK. With 4' of space, I would, after the footing is poured and cured, use 12" concrete block as high as you can. Jack the house slowly to the point of levelness+, and add either additional block or dimension lumber and hardwood shims to tighten it up.
You shouldn't have much problem pulling this off as it is definitely a DIY project. Keep us posted.

Where did you come up with footing 6" deep? That may work for a 1 story, if your soil conditions are not expansive, shifting (sandy), or compressible, then you need a soil test by an engineer.
You may need to go 12-18" deep in undisturbed soil, 7" thick for a two story, 8" for a three.
I would at least run this by your local building department for approval or all your work may be in vain. You may have poor soil conditions there as I doubt it was built that way.......
Be safe, Gary

Thanks for the replies. The footing suggestion was made by an employee at a local building supply store. I have done some internet research and as GBR correctly pointed out the site's soil conditions are a major factor in footing design. The home sits on glacial till (mostly sand with some gravel and rocks) so it is not the most solid ground. The house foundation is fieldstone/concrete and has held up very well over time. There is no reason I couldn't dig 15" into undisturbed earth make a 2 foot square hole and fill that with baseballish size cobbles and concrete, then maybe do an 18" square by 7" thick poured footing and block it up from there. Would rather err on the over side on this project...

I did examine the toppled pier and it was essentially just 2 stacked concrete blocks sitting on a concrete pad about the size of a basketball, clearly inadequate for the main beam of 30' x 24' house. Will be working on the house today (multiple projects going on) and take another look at the situation. Any further suggestions appreciated.

Spoke with a couple knowledgeable people about this project today and am ready to begin. One person had experience doing similar work and offered to loan me his house jack (which I graciously accepted). The other was a concrete sales rep at the local supply yard who offered some really good advice. First, am going with a 24" square by 8" thick pad. The rebar will be 22", set 4" down (midway in the pad), 4 pieces wired together like the number key symbol on a keypad. On top of the pad will be 8" concrete block 2 side by side for each tier (a 16" square 8" tall) as needed. Putting plastic down under concrete so sand will not suck the water out. No fieldstone in the mix. Blocks can go on pad next day but then allow several days for the pad and mortar to firm before setting weight of house on the pier. Since this is being done in a crawlspace, main priority is on solid rather than pretty.

A few more good tips were to take a chalk line, draw it as tight as possible across opposite sides of the house at floor level above where the support will be and perpendicular to the beam. Measure the difference between floor and the line and that will be how much the beam will need to come up to make the floor level. Since the block tiers are 8" thick it should be possible to figure downward in 8" increments where the top of the finished pad should be. Err on the side of being a bit low and the difference can always be shimmed. Very slick! When jacking up the house (to be done slowly), take it a tad high to allow room for the top tier of blocks to slip in under the beam. There is something called a pole barn pad that can be used to temporarily base the house jack while raising the house and curing the pier. The jack needs a solid footing as well.

Since the carpet in the room above the pier has been removed for replacement, I will cut an opening in the plywood between joists and mix the concrete above and pour or lower it down into the crawl space. That alone will save a bunch of extra hauling and crawling (will be hard on back and knees regardless). Anyway, that's the plan. Going to get started today and work over the weekend. Will post some results next week.

When I have to crawl in my crawl space, I wear my son's old roller-blade palm protectors with the metal inside the cloth half glove. Knee pads and elbow pads, what a difference!
Check this deck site for your footing and post sizes, then add to it. You can caculate it out if you know the spans of floor joists and roof support bearings if present. http://www.awc.org/Publications/DCA/DCA6/DCA6.pdf http://www.ideas-for-deck-designs.com/deck_post_size.html
Mind you, these are for decks not center bearing floor loads.
Be safe, Gary