Repairing Sagging Roof on a 1987 Bigfoot Fifth Wheel - Fiberglass RV

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Old 04-09-2016, 03:06 PM   #1
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Name: Rich
Trailer: 1987 Bigfoot Fifth Wheel
Posts: 47
Repairing Sagging Roof on a 1987 Bigfoot Fifth Wheel


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.

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Old 04-09-2016, 03:07 PM   #2
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Name: Rich
Trailer: 1987 Bigfoot Fifth Wheel
Posts: 47

Raise the Roof. Cut several sections of 2x6 to support the roof, attach each to the end of a 2x4 stud with a plywood triangle to keep the 2x6 at right angles to the 2x4. I want a wide lifting area.

Remove the screws that hold the cabinets to the roof so I can get between the cabinet and the roof. Note: the cabinets support the roof not the other way around. Removing these screws while I work should not cause any problems.

SLOWLY raise the roof, spreading the force as widely as possible (multiple jacks and supports). My helper slowly raises the jacks while I watch the roof from a ladder on the outside. I’ll stop him when the roof looks properly crowned. We must not raise it too much (less is more)

Once the roof looks good, we’ll set enough interior supports to keep it from moving. My challenge will be to support the roof completely without blocking access to the seams between the roof panels.

Prepare Area. I plan do the rear seam first, because it sags less than the middle seam. The rear seam is very close to the back cabinets so it has good support just a few inches away. I’ll do most of my learning on the seam with the least amount of sag, and then apply it to the seam with the greatest sagging. The seam over the door and the one in the “loft” are fine.

Remove the strip that covers the seam between ceiling panels

Use a sharp utility knife to cut the luan ceiling panel parallel to and about 2” from the seam (cut on the side away from the back cabinets).

Carefully remove the luan from the cut area, and dig out the blue foam. The layer of fiberglass is thin and may be delicate. I’m thinking that a steel brush might be a good way to remove the foam. Any suggestions?

I plan to leave the pink glue used to laminate the fiberglass, foam, and luan. Any thoughts about this?

Once this channel is cleaned out, we’ll make a pattern of the curve out of corrugated cardboard. I’ll cut the curve from ¾” plywood. Normally you bend laminate against a form with clamps, in this case, I will glue up the strips in place against the roof. I plan to compress the glued up strips with wedges between the plywood curve and the strips while the glue sets.

Prepare the Wood. Rip the 2x4s into strips on a table saw with a high quality blade. After cutting the first strip, verify that it is fit for purpose: the flat sides are very smooth and ready for gluing and the strip is flexible enough to mold to the curve of the roof. If needed I’ll adjust the thickness and rip the rest of the strips.

Rough fit the strips against the plywood determining the best length (cut them a bit long and adjust length later). Mark the strips with “top – glue” on one side and “bottom – mist” on the other. If needed, number the strips.

Mount the plywood below 2-3” below the open channel.

If possible, I’ll dry fit all the strips against the roof, adjusting each for the correct length, numbering them if they are not all the same length. If fitting can be done ahead of gluing it greatly reduces the need for “open time” with the glue.

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Old 04-09-2016, 03:08 PM   #3
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Name: Rich
Trailer: 1987 Bigfoot Fifth Wheel
Posts: 47

Lay the strips on a clean floor with the “bottom – mist” side up. Prepare as needed using the best method determined in glue testing.

Lay the first strip in next to the fiberglass and loosely prop in place.

Question: Should I glue the first strip to the fiberglass or leave it clean? Or should I put a layer of vinyl or felt between the first strip and the fiberglass to prevent abrasion to the fiberglass?

a. If needed, dry fit the second strip, adjust length if needed.
b. Apply a THIN layer of Gorilla Glue to the “top – glue” side of the second strip, scraping most of it off.
c. Lay in the second strip of wood with the “top – glue” side against the previous strip. The moisture in the previous strip will begin activating the glue, so work quickly from here on out.

Repeat a, b, & c until the “beam” is just below the level of the luan roof panel

Add one or two more strips without glue so the surface is above the level of the luan

Use curved wedges to press the glued strips together as tight as possible. Even pressure along the full surface is better than strong pressure in a few spots.

Do not disturb for at least 24 hours.

Remove the wedges and extra strips. Cover the opening with a 3-4” strip of luan and finish to match the rest of the ceiling.

Repeat with the next seam.

What are your thoughts?
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Old 04-24-2016, 03:49 PM   #4
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Name: Rich
Trailer: 1987 Bigfoot Fifth Wheel
Posts: 47
Off to a SLOW start

Now that you read my plans, I’ll share what is actually transpiring.

Despite my hopes, when we opened up the firt strip on the ceiling, we found a lot more stuff than expected. I hoped only to find a layer of luan, a one ince layer of foam and then the fiberglass roof. Not so!

Instead I found multiple pieces of 3/4" pine of varies widths. Some appear to serve as a backing to tack the edges of the luan. Other pieces go a different direction, perhaps providing support in a fore and aft direction. And there are channels with wires in them.

Here are some photos…

1. Able TALL assistant cutting the luan in preparation of removing it and exposing the foam. The luan has been removed on the left side and yet to come off on the right side

2. A closer photo of the section where the luan has been removed. This section is just forward of the edge of the laun. In other words, we’re removing about 2” from the edge of the luan. For the most part, anything pick is wood, the foam is mostly blue and you can see wires near the left end of the cut.

3. Close up of the middle section. We dug out part of the blue foam to expose the fiberglass.

[I cannot remember how i inserted a photo into the middle of a post]
Attached Thumbnails
IMG_5052.JPG   IMG_5050.jpg  

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Old 04-24-2016, 04:06 PM   #5
Rich Ess's Avatar
Name: Rich
Trailer: 1987 Bigfoot Fifth Wheel
Posts: 47
Plan of Action (Rev 1)


1. My original plan of cutting channels through to the fiberglass is not practical because I’d have to cut and remove multiple pieces of wood, which I do not want to do. The ceiling height on my fifth wheel is more than ample. I must stand on a foot stool to work on the ceiling. My TALL is assistant is probably 6’ 2” tall and he must reach up to work on the ceiling. In other words, surface mounted support does not pose a bump hazard.

2. Surface mounted supports must penetrate the top of the cabinets in order to reach the sidewall. This does not pose a problem except for the one cabinet with sideways opening doors. (Most of the doors open up.) I may have to cut off the top of one the sideways opening door, at least until I can make one to fit.

3. Examining the outside of the trailer show that I do need support running from front to back as well as from side to side.

4. The ridge of the fifth wheel is in good shape, so I don’t need to provide support more than about 6-8 inches forward the middle seam in the paneling. I imagine that this would not be true of a pull behind Bigfoot of a similar vintage.

How to proceed?

I considered using 3/4" square aluminum tubing doubled up. In other words, two tubes running together from side wall to side wall, bent to fit the roof curve. I’d braise the tubes together every six inches to act more like a single beam. I could connect the back ribs with the front ribs with tubes running fore and aft, braised to the ribs. This would be fairly elegant, but I wasn’t sure they would support the weight of someone on the roof. I do want to be able to maintenance by carefully getting on the roof. Plus the number of tubes I’d need would not be cheap. Steel would be cheaper, but steel braises at a higher temperature and rusts.

I ended up at a modified version of my original solution: use bend laminated wood cross ribs with solid ribs running fore and aft. Or I can glue up the fore and aft ribs, alternating where they pass the cross ribs. This would be cheap, not too heavy, and pretty strong. I think glued up wood supports would flex when stressed. Yes, they will break if there is too much weight on top, but I don’t plan to have that much weight on the roof.

Stay tuned…
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bend lamination, bigfoot, roof repair, sagging roof

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