Subfloor repair for mobile home addition

[yuchia31]

Hi,

The subfloor closer to the wall in my mobile home addition has water damage.

Top view.jpg

Here is the close up of the damage.

Top view close up.jpg

I would like to get it replaced. The subfloor is 1 1/8 plywood. I think it is tongue and groove.

The subfloor is supported by three beams underneath.

beams.jpg

I think it is different than the mobile home itself (beam + joist). I am trying to figure how to cut off the damaged subfloor. If I only cut off where it was damaged, then the new subfloor is only supported by one beam, which does not seem to be enough. I can add joist using joist hanger but the joist is perpendicular to the beam, which means there is a gap between the old and new floor and there is nothing underneath the gap. The youtube video I watched always have wood underneath where the subfloor panels join together.

Another idea is to cut to the center of the center beam so both the old and replaced subfloor has one full beam and one half beam underneath them. Is it better?

Thanks,
Joseph

[Greg]

The best way is to cut the damage out & replace it.
It looks to me like someone was smart enough to use 4x6 for the joists so you can simply make a shallow down the center of the joist on that side of the repair. You may get lucky and be able to either jack up the other side from under or use a pry bar. Adding cross joists like you said is always an option and you can never have too much support.

Greg

[yakima4$]

I would go with three joist with hangers.
Good support and never need to worry.
I would worry about how the water got in and what is growing in the wall.

[yuchia31]

Greg, did you suggest to only cut to the middle of the beam that is closest to the wall?

Yakima4$, I think the problem was due to our lack of cleaning of the gutter near the top of the wall so the water leaked out. Did you suggest to cut to the middle of the center beam so both old and new subfloor sharing 1+1/2 beam?

Today I spent the morning to rip the remaining old artificial grass off in my addition. (I don't like artificial grass in my addition) Then I realized how the walls are hold in place. The wall actually screws down to the subfloor.

Door.jpg

So I can't completely remove the subfloor without unscrew these bolts that screw into the subfloor. However, I can not access them because they are covered by the frame of the wall.

frame.jpg

Here is the outside of the wall.

outside.jpg

The frames are hold by rivets.

Does anyone know how to temporarily remove the wall panel so I can unscrew the bolts that screw into the subfloor? I think I need to first remove the wall panel so I can unscrew the bolts. Then cut the damaged subfloor off and install the new one. Screw down the wall to the subfloor. Finally put the panel back.

Any suggestion or reference? I tried to find out how this kind of frame is connected but I wasn't able to find any useful information.

What is the reasonable price to replace the damaged subfloor? I'm here in central coast of California.

Thanks and happy Thanksgiving,

Joseph

[yakima4$]

Don't cut the beam. Hang off both beams with your hangers (perpendicular). Then install you other 2X parallel with the existing joist and directly under your seam.

[Greg]

You can do a 1 1/8" deep cut down the center of the second joist (don't cut through the joist) and cut as close to the outside wall as possible. It will be a major pain since you can't get up tight to the wall. Sister a second joist to the one closest to the wall so you have a support for the new subfloor.

Greg

[HouseMedic]

Along the wall is there another joist there or is the wall just screwed down to the plywood? If their is a joist there I would just cut out the bad plywood right along the wall and then sister another joist onto the joist under the wall, then use joist hangers to run joist the other direction at the new seems of the floor.

Ron

[yuchia31]

Unfortunately, there is no joist along the wall. The wall is screwed down to the plywood. Some part of the plywood is totally rotten all the way to the wall. Should I also cut of the bolts that screw the wall to the plywood so my new subfloor can go under the wall?

Thanks,
Joseph

[Greg]

That is why I said the wall side is a major pain. If you can unscrew the wall from the floor it will make things a LOT easier. All you would need to do is lift the wall a few inches and work a 4' section at a time. I'm not saying it's easy, but it is easier than doing a main floor inside your home.

Greg

[yuchia31]

I'm not sure how to remove the frame temporarily to unscrew the bolt. I think this is currently the biggest challenge for this job...

Thank Greg for your clarification.
Joseph

[yuchia31]

Had two contractors come and they both suggested to put new (5/8 or 3/4) plywood on top of the old subfloor. It becomes very difficult to temporarily hold the wall and install new subfloor.

What kind of screws or nails are used for this job? What is the typical spacing between screws or nail? (6" at the edges and 8" in the field?) Does it need construction adhesive?

Does the old subfloor need any cleaning/sanding/special treatment? It is fairly rough and uneven. I am thinking to send with maybe 80 grit sand paper to get rid some of old debris.

Really hope that I can get this done before the Xmas...

Thanks, Joseph

[Greg]

It wouldn't hurt to scuff up the old floor first, you could add some adhesive between the two layers I would use galvanized deck screws 8" +/- should be fine.

Greg

[ponch37300]

I have mixed feelings on using construction adhesive between two layers like this. The problem is if you use adhesive you really want an even layer over the whole floor. Which is next to impossible to do with construction adhesive. So you end up with high spots where the adhesive is and air gaps where there is no adhesive.

Now, if your floor is already in rough shape with high and low spots you may never notice this. What is your finished floor going to be?

[yuchia31]

After many hours researching online, I think I will go with screws only (without construction adhesive). I have read the same thing as Ponch37300 described. Another benefit with screws is that you can readily remove the plywood if there is something wrong in the subfloor in the future.

The finished floor is going to be vinyl plank (TrafficMASTER Allure from HD). I actually bought some 5/8 ACX plywood sheets so I don't have to spend hours to sand the plywood.

I was debating between the laminate and vinly plank. I decided to go with vinyl mainly because of its thickness. With the new 5/8 plywood and foam underlayment and the thick 7~8 mm laminate, it will just be too thick. Using vinly I am only adding about 3/4 inch.

[HouseMedic]

After many hours researching online, I think I will go with screws only (without construction adhesive). I have read the same thing as Ponch37300 described. Another benefit with screws is that you can readily remove the plywood if there is something wrong in the subfloor in the future.

The finished floor is going to be vinyl plank (TrafficMASTER Allure from HD). I actually bought some 5/8 ACX plywood sheets so I don't have to spend hours to sand the plywood.

I was debating between the laminate and vinly plank. I decided to go with vinyl mainly because of its thickness. With the new 5/8 plywood and foam underlayment and the thick 7~8 mm laminate, it will just be too thick. Using vinly I am only adding about 3/4 inch.

I would just make sure to use tongue and groove plywood if there are going to be any joints. Most of the vinyl flooring that I have installed will show just about any imperfection of the sub-floor. As long as it is smooth you will be fine but the joints will expand and contract.

Ron