subfloor repair and toilet flange question

As a newcomer to the website, all advice will be gratefully received!

I've run into an issue during what was meant to be a 'simple' upstairs bathroom update - subfloor damage around toilet due to water leaking for some time.

- how do I deal with installing new plywood when I only have access to a joist to the front of the flange and one to the side (i.e. 2 joists at 90 degrees to each other with the flange in the corner - hopefully I'm making sense) - the joist at the back of the flange is actually behind the wall in the adjacent room and would be a nightmare to get at! Is it sufficient just to use the available joists and 6" planks (or similar) spanning old and new plywood attached with screws and construction adhesive on all other sides?

Or does anyone have any better suggestions within the capability of a DIYer?

- next concern is the flange (which was the reason for the leak in the first place). It's a 4" abs flange, which I want to replace and raise so that it'll be level with the new tiled floor. The existing flange is glued directly into an elbow joint. Is there anyway to get it out without damaging the joint?

How about cutting off the top lip of the old flange and gluing in a replacement made to slide into the old one? Is this considered a 'professional' repair, and code acceptable?

Should the new flange sit on top of the tiles, or is it ok to sit it on the cement board and tile around it? I'm asking because it's easier to screw it into the cement board than tile.

Best Regards

Paul

As far as the subfloor, you have to do what you have to do. Sometimes it is easier to take up a bigger piece of existing floor. A larger piece of plywood will tend to be more stable. I have supported new plywood piece by sistering joists, using joist hangers to add cross-joists, and if necessary using a 2X6 on the flat between two joists. This is sometimes necessary as in your case adjacent to the wall where there is nothing else to support the subfloor. I support this with Simpson corner angles brackets under. Also select a really good piece of dry 2 by with minimal crown. If any crown noticeable, put the crown side DOWN. You can fill this with floor patch. You can not smooth out an upraise crown.

There are drill bits to auger out a fitting. They are very expensive. You might get a plumber to do it. But, since you have a lot of access, you can try to make vertical slices in the fitting with a saw blade held in hand, then try to pop out the pieces. This will usually work with ABS (black) but not PVC ( white )

The new flange should sit flat on top of finished floor. If you set if flush with tile, you will need to use an extension flange to bring the height up. This is done all the time in remodels where changing the flange is impractical.

If there is one thing that makes home repairs and remodeling different from new construction, it's the need to find unconventional ways to do things. As Jimbo pointed out, ya gotta do what ya gotta do! You just have to keep in mind structural strength, code requirements, and final appearance. The latter is only important where it will show. In your problem area, I'd likely consider the options mentioned by Jimbo. You will have an easier time with structural strength by spreading the weight over several joints. I also have found that deck screws are much easier to use than nails when working in tight places like between joists, etc., especially since almost always the old wood is very hard, and it's difficult to drive nails into it even in open areas with room to swing a hammer. It's also far easier to remove and reposition a piece if you goof up. (Not that I've ever had that experience)

follow up question

Thanks a lot for the help. Since my subfloor is only 5/8" plywood, how about I repair the rotted section as discussed and further strengthen the whole thing by putting down another layer of 1/2" ply and 1/4" cement board on top of that for the tile? Originally I was planning 1/2" cement board directly on the subfloor. It starts getting a little high, but maybe I can accept that.

Best Regards

Paul

You could do that, but I don't think you really need to do that. In older homes subfloors are 3/4" shiplap lumber and 5/8" plywood is stronger than that. I infer from what you write that you have removed the entire old floor down to the subfloor, and if that's true, you need to bring the entire floor up to the level of the adjoining floor so you don't have one higher that the other. I'd determine how much total must be added to the top of the subfloor. If the tile is 1/4" and the cement board is 1/4", subtract !/2" from the total to know how much more needs to be added. Assuming (dangerous to do this, I know) the old floor you took out was 3/4", then you would need another 1/4" to reach even. I may have assumed too many things, but I think you should be able to get the gist of what I'm driving at.

Before you put down tile thatmight fail, check how sturdy your floor is. The information needed to check this is: the depth of the floor joists, the spacing of the floor joists, and the length of the unsupported joists (NOT the size of the room usually, unless all sides sit on the foundation or a supporting wall). It also depends on the kind of tile; real stone requires at least 2x the floor structure needed for vs ceramic stiffness in order to ensure a reliable install.

If you are hard up on height differences, an antifracture membrane can be used instead of cbu - they are typically about 1/8" thick vs the minimum cbu of 1/4". One brand is Ditra. You can check that out on www.schluter.com

5/8" plywood is usually the minimum and more is definately desirable if possible to produce a stiff floor BETWEEN the joists. You need to meet the L/360 req both along the joists (joist structure) and between them (subfloor).

I,m afraid you,re over your head

find an experiancer carpenter ,remove all substrate to joists,add blocking

do it right!