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papakevin 06-27-2013 01:19 PM

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.

nealtw 06-27-2013 01:45 PM

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.

isola96 07-05-2013 07:41 PM

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.

papakevin 07-07-2013 07:36 AM

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.

nealtw 07-07-2013 10:51 AM

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.

nealtw 07-07-2013 01:52 PM

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.

papakevin 07-14-2013 07:47 AM

1 Attachment(s)
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.

BigDon 07-14-2013 08:21 AM

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!

nealtw 07-14-2013 11:15 PM

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

papakevin 07-15-2013 05:07 PM

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.

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