There is a recent posting on this subject, but I don’t want to hijack it, and my problem is somewhat different anyway.

Background:

We purchased a house three years ago. Built in the late 1950’s with post and beams floor supports over a 4’ crawlspace. The beams are 3x10’s at 48” spacing running the long way of the house. The posts are 10x10’s on poured concrete pads. The sub-floor is 2x6 tongue and groove perpendicular to the beams, running the width of the house. The sub-floor extends under the wall between it and the foundation. The next support is then the 3x10 four feet from the wall. There is 4 inches of fiberglass insulation under the sub-floor.

Last fall we noticed that the toilet was starting to rock a little, and at the same time it started to plug up regularly. I knew I would have to replace the wax ring. We did nothing at the time because that’s our only bathroom, it was getting cold and we were going to replace the vinyl floor at the same time, which involved tearing out the sink cabinet also. The toilet sits next to the outside wall, backed to the bathroom partition wall.

Last Friday we noticed water coming out from under the toilet. I gathered the materials, including a new toilet, and Saturday we started tearing it out.

The first thing we found was a VERY soft spot next to the toilet, the cause of the rocking. When we tore up the vinyl, we found ¾” particleboard rotted to wet sawdust in a area of one square foot on one side of the toilet, with wetness going out another two feet from there. We tore most of that out with out hands. Under that we found what WAS the sub-floor. The board next to the closet flange is rotted clear through, the next one outboard from that and the two inboard toward the wall are all rotted halfway through, in an area two feet in diameter centered on the flange. The 3.5” ID, cast iron waste pipe is supported in place by the soil under the crawl space, and was probably holding up both the toilet and it’s occupants. I wish I could post pictures!

What I supposed happened, based on the evidence, is that at some time in the past, the toilet leaked, probably for a long time. To “repair” it someone (whom I would like to meet and choke) took up the floor, (which was probably oak, since that’s what is in the rest of the house), put clear plastic sheeting over the sub-floor, then laid down ¾” particle board over the entire floor, and around, NOT under, the closet flange (I have an extremely negative opinion of people who put particleboard under or around toilets, sinks, water tanks, dishwashers, laundry areas or showers!). They then put vinyl on that and put the toilet back in, sealing it with silicone all around the base (If you don’t see a leak, it isn’t leaking, right?). They did NOTHING about the sub-floor except to put expanding foam in the new hole next to the waste pipe, thus preventing any drainage from a possible leak.

My question: HOW do I repair the sub-floor? I’m not prepared tear into the exterior wall at this time, nor to jack up the walls. I thought of cutting out the rotted area, fabricating a ledge under the remaining 2x6’s and putting new wood on that, but rejected it as not strong enough. I may be wrong, and it’s the easiest way I can think of. My next thought was to put another beam inboard and next to the foundation, brace it with posts and use that and the next beam as supports for new wood (my shop bench was made with the same 2x6 T&G boards and is four feet long). I can use those to replace the rotted boards in either case. Does anybody have a better suggestion? If not, which way should I go?

Please help with advice. My wife wants her toilet back, and I’ve been ‘invited’ to help her put in her new flower garden…ASAP.

 

You can half a** fix this like the last person or do it right.
To do it right all that partical board has to come out, any thing under that will also have to come out that rotted.
Use A Toe Kick saw to cut out around the outside walls, and an Ossilating saw to cut out into the corners, then make a few 1" deep cuts across the floor to make it into sections so your not trying to remove the whole thing at one time.
Once all the subflooring out it will be far easyer to repair the floor joist.
Most of the time while were under there we try and replace any cast iron drains or steel supply line with new PVC drains and Pex supplys because there just going to leak at some point. If there's room to cut off the old cast flange below the floor we at least cut that off, so when replacing the subflooring all we need is a round hole and not have to cut the subfloor section to try and get it to slide under the flange. We install a new flage with a tail piece on it and connect it with a hubless connector.
Once all the repairs are done replace the subflooring with Advantec sub flooring that get adhesive on top of the floor joist. No glue between the layers, and make sure the seams do not line up with the layers below, your trying to attach the second layer in a way that pulls it down between the joist no on top of them. Build the floor up from there with Subfloor rated plywood, the last layer should be sanded A/C plywood (never use louon plywood !!) and all the seams and nail holes get filled with nongypsym floor leveler. Any flaws will show right through the linolium. That last layer needs to be attached every 4" on the outsides and every 6 to 8" in the field.

 

I knew I hadn't explained properly! I have no problem with replacing the sub-floor, but there are no floor joists. Just the foundation and a support beam four feet from that, or in other words, the floor joists consist of large beams at 48" oc. with a 40' span. I need to know the best way to hold the new sub-floor up on one end, where there is no 'joist'.

 

Well, I bit the bullet and started ripping. Ran into three pieces of good luck. One; the rotted floor and waste pipe are two feet inside the exterior access to the crawl space, ergo, no crawling across the house. Two; the foundation is over 8 inches wide, so the sub-floor didn't go under the wall plate, just butted up to it. Three; the footing for the foundation is 6 inches wider than the foundation. All I have to do is put a 4x4 against the floor at the foundation, and run a support 4x4 from the footing to the new beam. A 'Tee'. The new sub-floor will be partially supported by the foundation as well as the new beam. On the other end, I was wrong about the width of the support beam, it's a rough 4x10. Lots of support on that end.

I'm ready to start putting the new sub-floor in now, after cutting for the waste pipe. Thank the Lord I didn't have to manufacture T&G 2x6's! I really need them here due to the waste pipe hole through two boards.

The waste pipe is in good shape, but one of the inlets to it, from the kitchen sink or laundry, I think, has pretty bad scale on it at the junction. I'll have to replace it soon, but it isn't leaking yet. I'll also need to replace the inlet from the city water soon. probably at the same time. It's galvanized steel, and I know the shutoff valve is rusted solid just outside the foundation. Again, all are just inside the access area, which is a 3x4x4 foot, concrete block, covered access.

If I ever build a house, I'm going to build it like this! Solid as a rock, and easy to work on.

 

I've never heard of floor joist or beams as you call them being 4' apart except in some old log cabin lofts. Not sure how those old 1 X's ever supported that floor since 1 X 's laying flat are only good for about a 16" span. Some how your going to have to add some new floor joist set at 16" on center to hold up the new subflooring. 3/4 subfloor can only span 24". And it needs to be supprted at the seams.
PS 4 X 4's have almost no side load strenght. If you were to take a 4 X 4 and just leave it sitting between two concrete blocks it will sag with no weight on it over time.