Crappy Subfloor Installed in Cabin - Suggestions?

Well, I had a local handyman build an addition onto a small cabin I own. (I didn't do it myself because it's an hour away near the lake and I simply didn't have time.) Well, it appears the guy used the cheapest subfloor he could. It doesn't interlock and there appears to be some dipping in the floor in between the joists, which causes to curl very slightly where the edges meet. Guess that's what I get for not specifying materials and going with a cheap price.

I told the guy I would finish out the interior and only notice the condition of the floor when I started to do so. The 10 by 20 addition is being divided into two rooms - a bathroom and a bedroom. Here are my questions:

- In the bathroom area I already have the shower installed. Should I install something like a hardie board on top of the existing subfloor? If I do go with a Hardie board, is 1/4" board enough or should I go with a 1/2" board? I am planning on install vinyl stick on tiles which can be grouted. I don't want to go with a ceramic tile floor due to the cold nature of the tile and the fact this is an elevated cabin on 6 by 6 treated posts. The bathroom is smallish - only 7 by 6 floor space with the shower installed - and I have yet to install the toilet and sink, so I'm open to anything.
- In the bedroom, I was planning on installing industrial carpet with a pad. I think this will work good enough so the floor is not noticeable, but didn't know if I should consider reinforcing the existing floor first. If I do need to reinforce, would installing luan (or lauan) boards over the entire bedroom to help it out, or should the carpet pad help hide any subfloor issues?

I appreciate any comments or suggestions. Thanks.

You didn't say how thick the subfloor is. If it is 5/8 you can fix the seams by hilding a 2x4 block under the seam while a second person drives screws from above, with a little glue on the block first it is better than tongue and groove.
If the plywwod is thinner than 5/8 then you may want to add another layer.
If floor joists are at more than 16" on center the numbers change.
If you are adding to the subfloor because it isn't thick enough to call it a subfloor then you do glue and screw it to make one thicker subfloor.

IMO sounds like its less then 5/8" or it's not 16" oc. You need 3/4" of ply at bare min for bathroom. You will have to add 1/2" or 5/8" over, then 1/4" cbu board in unmodified thinset bed, galvanized screws.

Cbu doesn't hold strength value at all for subfloor for tile.

If you add 2nd layer of ply run it perpendicular from joists, both layers should run same way.

Don't add 1/4" plywood it will pucker when you screw it down.

Yeah, I'm finding out I'm sort of screwed here. The OSB installed on the subfloor is not going to cut it. Either they didn't crown the floor joists when they were installed or the floor is just that bad because where two boards meet up on a joist, there is a noticeable rise / ridge there. There are no markings on the OSB, except that the ends are spray painted green. My guess is that this stuff was meant for side walls or roofing and not flooring.

There are products that look like osb but they are for the flloor, they are tongue and groove at the joint on the sides and should be marked somewhere with this side down and the thickness.
Regular osb is marked on the shiny side and it will have a thickness marked there as well.
http://www.hubergreen.com/main.aspx?pagename=advantechflooring

If this is just 7/16 osb, it will want to be removed as any moisture just makes this stuff thicker and is not good for any part of the floor.
I found this link to show how the blocking has to be done to support the sides and the ends of the sheets. Notice at the area under his door he has blocking every six inces to support the ends of the sheet. His fifth picture.http://thehouseisgoingtobegreat.blogspot.ca/2012/10/laundry-beginnings.html

Well, I needed to do something, so I belt sanded the seams which were raised to level them down, then painted them with some old exterior paint in an effort to keep them from absorbing more moisture. I was considering removing and replacing, but I already had the shower installed and an interior non weight bearing wall before looking at the floor closely.

I do have access to part of the structure from underneath and will go with the blocking to help provide additional structural support. Just hate it when you pay someone to do work for you and they buy and use cheap materials.

While not ideal, hope this will last a little while. This was an addition onto an existing cabin at a camping community, so while it didn't need to be perfect, I expected it to be better than the end result.

You probably already know this, but you're gonna keep having problems with this floor. I've found through experience, it's always easier in the long run to just redo it right. It may take more time and money in the short run, but in the long run you'll be thankful.

I'm betting that this is probably 7/16 roofing or your joist are too far apart/not level or the sheets are not oriented the right way. Or, all the above!

Kevin: pull the shower and the wall and remove this stuff, really this is a big deal.

Ok, I know you are right. Do I need to pull up the old floor or can I put new subfloor on top of the existing? Reason I ask is that the addition was stick built, so the external walls sit on top of the existing decking, so I can't pull up all the flooring, it would need to be cut out.

Generally you would cut 1 1/2" from the wall and replace it with matching thickness but in your case I would cut it right next to the wall with a saws-all and then add the blocking like in the link I gave you in post #6, the end wall is only sitting on one joist so only cut out a few feet at a time and add the blocks as you go so the wall dosn't sag.

Have we ever figured out how thick the OSB is or what the floor joists are on center?

Was the sub floor nailed or screwed down and how close is the pattern? Glue?

What did he use for a foundation?

Being it is a cabin and from what the OP described as what he wanted to do for final floor finish I don’t think I would take it up. Working from below doing the blocking isn’t that easy depending on how much room is below. Knowing the span and center distance and joists size will let you know if you have enough support and the problems are just with the OSB. If the structure below is ok and it has enough screws in it I would add another layer after taking the shower up. I would overlap the seams and glue and screw it down.

If the structure of the joists and spacing are not strong enough maybe you can add a beam or more points for it to rest on from below.

I will need to take a better look at everything the next time I'm at the cabin, but know in the original quote the guy stated he would be using 3/4" OSB. From what I've seen, It is not tongue and groove from what I can tell and doesn't have any markings or stamps on it, only green paint on the sides. (What does the green mean anyway? Was it just the manufacturers attempt to seal the edges to prevent the OSB from sucking up moisture?)

If I get out to the cabin this weekend I'll grab some photos. Here's the underside of the cabin, but it doesn't help much. There's limited space underneath and this photo was to see how the pex got attached to the existing supply line. This is a seasonal cabin and the other end of it connects to a water shutoff.

On the bottom side you will find a block of printing that will tell you what it is and how thick it is. OSB always has painted edges, blue, green, or red. The maker uses the colour to tell at a glance how thick it is but all the makers don't use the same colour code, so that won't help you. The lines on the other side are to mark out 16" or 24" on center and we mostly see that on 7/16 roofing material.
Flooring that looks like OSB and plywood has tongue and groove on the long sides and is marked this side down so you don't screw it up.
Your guy also but it down in the same direction as the floor joists which is also a big no no.
There are rules and tricks to putting a floor down so when your ready for that, we can help.

Apologize for the delayed response, but the wife has had a lot of doctor appointments lately, so the projects have had to wait.

Good news is I was able to get some photos of the stamp on the bottom of the subfloor and got the following: It is 23"/32" category 24" span rating single floor exposure 1. It is SFI rated. The floor joists are spaces 16" apart, so that's good.

Bad news is that the subfloor is installed wrong. It is installed parallel with the floor joists, not as it should be. That is why the floor feels like it is sticking up on the beams where they meet.

Here's a (bad) photo of the stamp on the underside of the floor. Don't know if you can make it out, but it might help.

Well that is good news, I think. A few things I can see from your photos, the butt joints in this floor need solid blocking under them to make a solid joint between sheets, the tongue and groove would usually do that job. Any span longer than seven feet should have had bridging to stop the joists from warping and twisting, 2x4 blocking between the joists near the bottom of the joists can be added. Not sure why they used treated lumber for joists but the newer treatment will eat steel so the hangers and hanger nails should be hot dipped galvinized you should be able to find information on the hangers. If they are not galvinized, checking them for rust from time to time would be a good idea.
It might be a good idea to contact Adventech's support for suggestions on what best to do with the floor it self.
http://www.huberwood.com/contact-us

Ok, so I will add 2 by 4 bridging in between the floor joists to keep them from twisting and I will add support underneath the floor joints where there is no support. Other than power sanding the top side of the joints to level them (and guess I'll seal where I sanded with paint just for good measure), I should be good to go?

Appreciate the guidance. With the wife having a lot of hospital visits lately, I haven't had much time to work on all of my projects.

As an added bonus, when I was looking underneath to look at bridging options, found this photo. Apparently since they installed the flooring wrong it didn't reach the next joist, so they had to rig it and used scrap pieces of wood to do so. Tisk, tisk.