I have started a bathroom remodel and am planning to tile with porcelain tile. I thought I was prepared by reading the forums, doing my research, buying book, I didn't really understand the whole subfloor thing until I started the project.
I have removed the top 3/4" plywood layer because much of it was water damaged. The remaining subfloor is 5/8" plywood. I have questions about two areas of the subfloor and I have attached pics to help show what I am talking about since my terminology in this area is not very good.
The first issue is in reference to the bathroom entry. It looks like most of the subfloor was not replaced all that long ago (I have been in this house 5 years) with the exception of the area in the entry hall. Although it looks like this area has been water damaged my carpenter friend said I could probably leave it if i was able to sister the joist underneath. The problem is that there is a heating duct sitting right underneath this area, which is probably why this part of the subfloor was not replaced to begin with.
I could sister a 1" x 6" right next to the duct for a ways (I don't think I can do it until the end of the floor because of more heating ducts) but it would literally be right next to the heating duct which felt pretty hot to me last night. So my quandary is how to support that edge of the flooring before replacing the top layer of subflooring, hardibacker and finally tile. (pics attached - Bath-1, Basement-1)
The second issue is probably more common. The subfloor edge along the wall where the vanity and toilet sit is not attached to anything. The wall sits right between 2 joists. Obviously, the subfloor should be attached to something. Do I fix this by putting blocks (what size?) between the joists and then put new blocks perpendicular to the blocks between the joists so that there is a continuous way to attach the subfloor to? Or are there other ways to fix this problem? (Pics attached -Bath-2,Basement-2a, Basement-2b)
I hope I was able to explain myself. Thanks for the help!
You need to make sure that the subfloor is solid. This would require what you are planning on doing, adding some blocking and a nailer where needed. I can't believe that the interior wall was not placed over a floorjoist...poor detail for the framing. Instead of hardibacker I would suggest Ditra. It is much easier to install for a DIY and a much superior product.