I’ll start this thread with several posts describing strategy planning and my current thinking on how to proceed. I value your input on anything. Please feel free to comment on any post or all of them. I’m breaking it up into smaller “chunks” to make it easier to quote or address comments to a specific thing.
I’ve been researching posts on this forum to develop a strategy to repair the sagging roof on my 1987 Bigfoot
fifth wheel. This is the trailer previously owned by “Maureen M” and Chris, and then by “Linda Clary”. I recently had a small fire in the trailer (don’t ask, don’t tell, but totally my fault). I have to do some reconstruction and this is a good time to fix the roof. I’ll share the reconstruction in a separate thread.
The Problem. The curb side of the roof is sagging several inches, the sag extending out to just past the midline. The main symptoms are water pooling next to the A/C and an upper cabinet door that hits the ceiling panel when I open it.
The Roof Construction. Here’s a photo I stole from a post by Chris (Maureen M) showing a cross section of the laminated roof. As you can see the top is a thin layer of fiberglass. Once inch of blue foam is glued to the fiberglass with a pink glue. Then a layer of Luan is glued to the foam. The luan is inner surface of the ceiling. My thanks to Chris for such a great photo!
The Method. I plan to bend laminate wood (thin wood strips glued together in a curve) right into the ceiling against the fiberglass. Bend laminated wood is very strong because multiple pieces of wood glued together are far stronger than a single piece of wood the same overall size. Thin strips of wood can be formed to fit the curve and the grain will go from end to end. This should be a permanent solution to the problem. If anything, it may be overkill!
The Glue. Online research indicates that the right glue is critical for maximum strength and durability. Normal “white” wood glue makes a very strong joint, but is subject to “glue creep” especially when hot. I found that the water activated version of Gorilla Glue should work fine if I don’t use too much glue or moisture. This glue foams a bit, which can help fill small gaps and increase the strength. Too much foaming can create gaps (reducing strength) if the foam can’t squeeze out. This glue should give me enough open time to get all the strips in place before it starts to set.
The Best Way to Glue. Research shows that I don’t want wet wood, just a bit of moisture. Some say if you’re in a humid place, letting the strips sit overnight should do the job. I’ll do some testing to find the method for me.
a. Test with just very thin glue and ambient humidity (in Houston)
b. Test with a light
misting, waiting several hours before gluing
c. Other ideas?
The Wood. I chose Douglas Fir because it’s strong, relatively hard, strong, and can be gotten in high quality boards at a reasonable price. I couldn’t find what I wanted at a big box store, so I visited a Real Lumberyard. I found two 10’ 2x4s with flat grain along the wide side of the board and close, straight, edge grain on the narrow side. I will rip the 2x4s into 1/8" to 1/4" strips (1.5" wide, 0.125-0.25” thick, 10’ long). This gives an ample number of strips with straight grain running from end to end. I need strips thin enough to flex easily into the needed curve. Research shows that the optimal thickness is the maximum thickness with the needed flexibility. More strips are marginally stronger than fewer strips, but is more work. The final thickness of the glued up support should be a bit less than 1" thick so it doesn’t protrude beyond the surface of the luan covering of the laminated roof panel. 4-6 strips should do the job and will be very strong.
Supporting the new “beam”. I struggled with the best way to support the glued up support member. I’m planning to run the strips between the fiberglass and the top front of the cabinet out to the outer wall and curve it down the side wall the back floor of the upper cabinet (where the cabinet is screwed to the wall). The top of the cabinet will support the beam about a foot from the side wall; the bottom of the cabinet will give extra support to the end of the beam; support from the side wall will help keep the beam from flexing.
Question: Should I cut a channel in the outer wall panel to accommodate the beam or run the beam down the surface of wall? A channel allows the beam to mold against the fiberglass curve as it transitions from roof to wall. But, this is harder to do and will take more time. I can run the strips down the surface of the wall leaving the wall panel intact. This is easier and might support the beam end better. I’ll probably cut a bit of an arc from plywood to go between the strips on the outside corner. This will enable a wider radius bend at the corner.
Unless I hear a compelling reason otherwise, I’ll bring the strips down the surface of the wall.