Roof sag behind ac

[DanielM]

Newbie to the group. Purchased an otherwise great 2619, but with one problem. Was about to replace roof seal and noticed sag.
I know this topic has been addressed sometime ago, but I haven’t seen or am unable to find the fix for this other than the crazy suggestion to replace. The rest of the roof is in great condition, no leaks. It is the area directly behind ac unit. It has sagged down about an inch from horizontal. The wood that is used to install seal is solid. I’m thinking perhaps aluminum “c” channel bent into arch to match crown of roof with some minor trim mods. Has anyone come up with a solution for this. If not, I’ll be diving in the fall and will post pics of progress. I’m a skilled fabricator so it should be doable. Any thoughts, ideas or suggestions would be greatly appreciated.

[Shane826]

If you find a fix, please share. As of now the only fix is the crazy one you mentioned.

[rich2468]

Daniel,
I haven't done what you're proposing to do- raise the roof crown rear of the air conditioner, but I did build an aluminum box frame for my rear solar array and bent the box frame to be elevated above the crown.

I used rivnuts installed into the aluminum corner trim (at the edge of the roof and side panels) to fasten the aluminum box frame so that my six glass panel solar array "floats" a few inches above the rear shell.

With that experience in mind, I believe you should be able to accomplish what you've proposed, but I'd suggest keeping a few things in mind:
1: How much "lift"/ tension will you need to create to restore the roof crown? I'd try to get some kind of measure of the lift needed.

2: Will the above amount of lift be able to safely be transferred to the aluminum corner trim? You want the weight safely pushing down on the corner trim vs. pushing the walls out.

3. In consideration of the above amount of lift; you may want to consider a ladder type support to spread the lift force across multiple mount points on the front shell...but you also (obviously) need to be conscious of the support frame weight.

I have three aluminum box cross bars supporting about 85 pounds of solar panels; so each box frame bar is supporting approximately 28 pounds (or 14 pounds on each side) and that weight plus the box bars on the aluminum corner trim. These figures are all approximate, as my solar panels are arranged with the front two panels in a landscape orientation and the rear four in a portrait orientation.

The reason for sharing my array weight is to hopefully give you some kind of baseline of the amount of weight you may be able to support with a single c channel bar and help if you decide if you may want to try to spread the load over a couple of c channel bars.

For clarity, my TrailManor is a newer model (2021) and my solar array is mounted at the very rear of the rear shell. I'd consider the very front of the front shell and the very rear of the rear shell to be the most structurally sound parts of a TrailManor's roof due to the two sides being tied together by the front and rear end sections of shell.

Given that your roof AC unit weighs around 100 pounds, it might take 30 to 45 pounds of upward force to correct the sag at the front shell rear crown.



Rich and Lynn
2021 2922KB

[Bill]

Some time ago, one of our long-time members, Bruce Perens, found himself with a roof sag. To restore the roof to its correct profile, he started looking at possible methods, developing plans and designs in the process. Bruce is an avid radio amateur, and at the same time he fixed the sag, he also wanted to add some support for a bunch of ham radio antennas and such. He ended up with an external framework that was quite successful, if my memory serves. You can read some of his "how I did it" posts here - there may be more.

https://www.trailmanorowners.com/for...ad.php?t=19137

Bill

[DanielM]

Thanks to all of the TM folk for your timely reply. The sag is about 3/4” below a straight horizontal line in the 16” or so directly behind AC, so about 2-2 1/2 “ below the crown that’s on the rear roof section. That s nearly a 3” lift. I would be satisfied to get it back to horizontal. The AC unit is mounted within an inch of the front roof rear lip. It’s a big mother. (Kind of a crap design- mine is an 05 by the way) I’m thinking of an external box channel with some crown. As mentioned in a reply, the trick will be transferring load to side wall. Not sure what TM was thinking with wood framing in this area. I was actually thinking of doing side rails in aluminum also and installing as a unit. Not that big an engineering feat. Then we get into seal attachment. I’m thinking a bolt rope/keeder rail, aluminum extrusion that could be riveted to new frame then sewing new seals with bolt rope. Would make easier replacement down the line. As I said earlier, roof works now, so I think I’m just going to enjoy the next five months and fix it in the fall. I’ll post pics and materials when I tackle it.
In the meantime, if someone has an idea or suggestion, I’m listening.

[Bill]

Over the years, the Forum has had a lot of discussions about sagging roofs. Actually, a better term might be "squashed roofs", since they often happen due to snow load. One thing that has always concerned me is that when any arched or peaked roof is squashed to the point of flattening or dishing (sagging), the sidewalls that support it are splayed outward.

Whatever method is used to raise the roof to its original contour must also draw the sidewalls together, and keep them there. Interior cross ties at the top of the walls would do this, but of course the TM has no interior space for cross ties. This suggests that exterior support might be needed. Bruce Perens did this in the thread linked in a previous post.

My concern is that if an aluminum roof-frame member was originally fabricated with an arch, and later was bent in the opposite direction, I am skeptical that it could be simply bent again, back into its original curve, with its original strength. Aluminum doesn't like repeated bends.

I'm not a mechanical engineer, so I'm just noodling here. Gabled house roofs have collar ties to hold the walls together. In the 1800's, massive brick mill buildings in New England had thick iron cross-rods holding the walls together. Ancient stone cathedrals needed flying buttresses to hold the walls together if the wall-to-wall distance was too long for timber cross-ties.

I'm interested in any thoughts, from those whose knowledge is better than mine.

Bill

[DanielM]

I posted on this topic on a new thread with an exoskeleton idea someone had used for a different purpose. To all who check out this post, check out roof sag fix idea on a new thread
Thanks
Dan

[Kentmeyer89]

Wondering how this went. Any luck?

[Bill]

Kent -

You might try a PM to the guys who tried a solution, or an email if they included an address in their profile. They might not come back here to the topic, and so would not see your query.

Bill

[Wavery]

Originally Posted by DanielM

Newbie to the group. Purchased an otherwise great 2619, but with one problem. Was about to replace roof seal and noticed sag.
I know this topic has been addressed sometime ago, but I haven’t seen or am unable to find the fix for this other than the crazy suggestion to replace. The rest of the roof is in great condition, no leaks. It is the area directly behind ac unit. It has sagged down about an inch from horizontal. The wood that is used to install seal is solid. I’m thinking perhaps aluminum “c” channel bent into arch to match crown of roof with some minor trim mods. Has anyone come up with a solution for this. If not, I’ll be diving in the fall and will post pics of progress. I’m a skilled fabricator so it should be doable. Any thoughts, ideas or suggestions would be greatly appreciated.

I think if I ever had that issue:

#1 I'd get rid of the roof A/C. I don't think that the roof will ever be strong enough to carry the A/C again.
#2 I'd cut about 4, 1" thick roof ribs out of 3/4" of 4x8 sheet of marine plywood. The same length as original rear rib.
#3 I'd laminate 2 (or more) set's of 2 pieces of plywood together (with epoxy resin) to form 2, 1 1/2" x 1" thick ribs that are formed in the original arch.
#4 I'd use 1 rib in place of the original (damaged) rear rib.
#5 I'd place the 2nd rib forward of where the A/C was mounted. Maybe even one front of that hole and one rear of that hole.
#6 I'd replace the A/C with a normal RV electric vent.

Just my thought, rather than scrapping the old roof.