I have a question regarding erecting a beam where a partition wall had previously been torn down. This was done by the previous owner, I might add. As a result, the joists on the second floor are spanning about 22 feet and the ceiling is starting to sag. I initially had entertained the idea of putting up the beam, with help, but after doing a bit of reading I’m uncertain. I had intended to erect the 8 ft beam on top of posts that would be located on the interior of the walls as opposed to within the walls themselves. The home is old and I suspect it was built with balloon framing. My concern is regarding the posts and where they should be located. As I understand it, they should be on top of the main floor ceiling joists or at least on blocking between 2 neighbouring joists. Can you shed some light on this situation or should I consult a contractor to do the work?
Removal of walls in homes can have very detrimental effects if they are done incorrectly by amateur carpenters or homeowners. You are observing one of these effects in the sagging ceiling. You are absolutely right in your attempt to correct this situation, before serious structural damage occurs. I would strongly recommend installing a temporary support beam to prevent further damage to the ceiling and floor joists until proper repairs can be made.
The size of the beam and positioning of the support posts or columns has a lot to do with the nature and location of the removed wall. If the wall removed was a load-bearing wall, which is generally located above the main beam below the main floor joists, the support columns should also be located directly above the beam. These posts don’t have to sit directly over the floor joists below, but they will require solid blocking between the floorboards and the main beam, to transfer the load directly to the beam. The beam may also require reinforcement in this area, if the new posts are mid-span between the support teleposts or wood columns for the beam. If the removed wall was load bearing you had better install something immediately, even if it is a temporary fix, to prevent a collapse of the floor system above this area.
If the missing wall was only a partition wall, as you suggest, it may not be fully supporting the upper floor joists, but may still have provided some support for the joists above. Shorter joists or upper walls may have had been overlapping framing sitting on top of this area, which is causing the sag in the ceiling. It is less likely that the interior walls are balloon framed, as this is mainly found on exterior walls, but there is still that possibility. If the second scenario, of the wall being a partition only, is the case in your home, a smaller beam may be required and the placement of the posts less critical because they will be carrying a much smaller load. For that situation, placing the support columns directly over a double joist, that is properly supported, may be sufficient.
From the description you have provided, it appears that the previous homeowner may have dangerously removed a load-bearing wall that supported the overlapping ends of the floor joists above. The sagging you describe leads me to this conclusion, as it is unusual to see 22 foot long continuous floor joists, even in older homes. The thoughtless actions of the previous weekend warrior may have caused a potential major life-safety hazard within your home. If too large a load is placed above this area, the entire ceiling could collapse, injuring yourself or anyone on the floor above.
The point you raise in your question is an excellent one about contacting a professional for this type of work. All you have to do to answer that for yourself is to look at the current state of affairs in your home. Anytime a major structural renovation like this is attempted, professionals should be involved in the entire process and the proper building permits should be obtained. The permit will have to be accompanied by an architectural drawing or sketch and may require an engineer’s stamp, if the wall is load bearing. Obviously, this was not done in your home, so the onus is on you to complete the process.
The first professional to consult is a licensed structural engineer, for a site visit, to assess the situation and provide you with the correct sizing of the beam and support columns and other details for the proper repairs. Once this is obtained, you can then decide if you feel competent in installing the beam as designed by the engineer. You may find that a competent general contractor may be a better choice for this extremely important, but not tremendously difficult installation. To limit your cost, you could attempt the drywall sheathing, taping and painting of the finished area yourself.