Cutting new subfloor today

[gYpsydreamin]

I'm planning to cut the wood for my new subfloor today but I want to make sure what I'm doing isn't a terrible idea. I've only cut out about a foot of my old subfloor, in the very rear. Is it okay to replace such a small amount back there? Should I cut further back past a crossmember?

[rugjenkins]

Sure. If that is the extent of the rot. Many have patched and spliced. Put a few overlapping pieces on the bottom from the old to new after you attach it to the frame. Some will disagree but structurally it will be fine.

[sgschwend]

I agree, get the new ply into the channel and then when you splice just glue and screw together.

[brokeboater]

I'm no expert and I've seen commentary by some I respect that say the method weakens the structure, but I did pretty much what you are doing. I cut mine back maybe 18/24" and then another 8" for a splice. I made a cardboard template to make sure my repair piece would fully insert into the channel. I epoxied the whole thing, drove it fully into the channel and replaced all the bolts connecting the shell to the trailer. I screwed in 6" plywood supports under each side of the remaining opening then inserted my two piece 8" splice, driving both sections fully into the channel also. Seems pretty rock solid to me but if the back end of my trailer falls off on the road somewhere I'll post pictures, if I can ever figure out how to post pictures on here.

[Minno]

The only issue with putting a gusset underneath the seam is if that's where the waste tanks go. You'll lose 3/4" of space for the tanks because of the gusset. If the tanks don't go there, then no issues provided the remaining piece of plywood is still sound. Use good exterior wood glue, epoxy, or gorilla glue (or similar).

[oldmanvader]

I have done both, generally I try to find a crossmember wherever possible. In all my floor replacement I always resin coat at least the edge, about 3 or 4 inches in, especially at the back. In my 73 I coated the whole rear bath floor (top only) in resin to limit any future water intrusion. I Used marine grade plywood as well. The rears of vintage airstreams are particularly vulnerable in rear bath models. Good luck, you will appreciate the work once it is all done!

[Siegmann]

I'm not familiar with your floor plan, but if that seam is in an exposed area where you will walk, you might feel it flex if it doesn't have a gusset or lie on a cross-member.

[Tbeck11931]

I went to a cross member for structural integrity.

[gYpsydreamin]

So if you went to a cross member, did you have the two ends (the old but good floor and the new piece of floor) meet and share one crossmember together?

[sandgrubber]

I presume you've looked underneath and made sure that the next cross member is ok. I was going to do something like you're doing and oops! Looks like the cross member has succumbed to moisture.

[MarkR]

Just to be clear, the gusset plate should be continuous from outside edge to outside edge (except at the main frame rails). It should be 6" wide min. (3" overlap (or "underlap") per side). I'd use 3/4 CDX (or better) Plywood. Glue and Screw w/ "deck screws" (or some other "substantial" wood screw) at something like 3" on center staggering back and forth (side to side) on each side of the lap. It'll end up being stronger than an un-interrupted piece (in my opinion anyway . . . your mileage may vary)

[Tbeck11931]

Originally Posted by gYpsydreamin

So if you went to a cross member, did you have the two ends (the old but good floor and the new piece of floor) meet and share one crossmember together?

I ran my skill saw with the depth set where it cut 90% through the old subfloor and then made my cut halfway over the support beam.
Make sure the saw blade cannot come in contact with the support beam and there are no screws or bolts in your path.
That way my new floor overlapped the support beam and the adjacent old floor is still supported by the beam.
I found pressure treated plywood at my local lumber yard. (Not easy to locate).
After I cut my new piece I painted the outside edge and all cut locations with kilz paint for added protection.
Maybe over kill but that's the aircraft mechanic in me. Lol

[gYpsydreamin]

Tbeck, so you did indeed have two ends of wood both meeting and sharing the support of one crossmember. Did you secure either piece of wood to that cross member? Seems difficult to do since the cross members aren't but so thick.

[Tbeck11931]

Yes
If the crossmember is 2" wide you cut the old floor out 1" over the crossbeam.
When a carpenter installs new roof decking he always puts the edge of the OSB or plywood halfway over a ceiling joist or rafter.
Just adds strength to your new floor.

[71tradewind]

That kind of repair is fine, just make sure you use marine grade or normal plywood.Pressure treated lumber should never come in contact with aluminum, because it eats aluminum.