since this got resurrected I might as well follow on. A friend of mine who owned a tile business was going to *try* and tile over his kitchen, laundry, and entry area with big tiles, on a 50's house with 2x6 T&G on 60" centers!
He thought 5/8" subfloor overlay and 1/4" concrete board would stiffen it up sufficiently. Read this as : Cheap bastige. This floor was drumming badly with my 265 pounds, and he is heavier. he would have been cracking tiles, let alone joints.
I gave him the good buddy deal, as I have a pile of 4x6 salvaged from a job, and half the pier blocks. He offered his son to help and he was great. I prepped the wood at my house Sunday, we did about 2/3rds of it Monday and finished it by noon yesterday.
All in all, we were under the house less than 8 hours.
In that time we crawled in 24 pier blocks, 73' of beam, fixed some sad plumbing, and split that 60" span. The existing beams are 6x10s on poured piers. This left about 56" clear between them and I split that where I could. Sometimes plumbing would push me one way or another.
Ideally I would have used 4x8, but I had the 6's and we piered it every 42" or so. Results were dramatic.
What I found under there was not good, one of the center beams was split longitudinally between piers, so I brought in more bases and shored that up.
The house design was atrocious, and I just want to remind people to invest in at least one home inspection prior to purchase. I would have rejected it immediately myself.
Issues:
Hand cut rafters with too long a span. Roof had slight bows everywhere and significant droopage over the garage.
The center wall that supported the rafters was *not* over a beam below! It was about 10" off to one side, bearing on the 2x6 decking alone. WTF!
Many years of atrocious wiring. Completely illegal stuff that could be seen in the attic space above by a competent inspector.