Ooh That Smell!

With apologies to Lynyrd Skynyrd

Frame-off Renovation

There’s a foul smell in your vintage trailer and that’s not the worst of it. What’s hidden inside the floor and walls could be a significant risk to your health and your investment. But fear not, we take the trash out of the trailer so it doesn’t stink. Hofmann Architecture restores and protects the foundation of your investment from the ground up. This blog explains the basics of our frame-off renovation process.

In the vehicle restoration industry a frame-off (aka a shell-off for trailers) is a process where the chassis* is separated from the body or shell. A frame-off is performed to sustain the useful life of your mobile space for another 30, 40, even 50 years. Hofmann Architecture specializes in completely custom frame-off mobile renovations to remove any causes of nasty smells and ensure maximum longevity for all trailers.

Monocoque (no, it’s not eyewear)

Here’s some knowledge that is sure to impress your friends. Metal trailers, such as Airstreams, are built with a monocoque** shell design that was inspired by the aircraft industry during World War II. The aerodynamic shape and method of construction of an Airstream is very similar to an airplane.

What’s a monocoque? A monocoque shell is when the body and chassis form a single unit, with the shell carrying the majority of the weight and stress.

Structurally speaking, Airstream trailers are designed like a home, with the walls being bolted to the foundation. Wood framed homes are protected from falling apart due to an earthquake by bolting the walls to the foundation. Unlike a traditional home or other square box trailers, Airstreams are not built with wood framed walls.

Airstream walls are built with lightweight aluminum frames. In Airstreams, the aluminum C-channels at the base of the walls connect the walls to the floor, much like a traditional home. The steel chassis, plywood subfloor, and the body all work together to provide overall strength. When one of these three systems fails, such as the chassis or sub-floor, the entire trailer is weakened, and the trailer’s longevity is dramatically reduced.

Benefits of a Frame-off Renovation

“Why would a trailer stink?“ you ask. Good question.

A vintage trailer stinks because it’s old. Over time, water infiltration creates rot and mold = stink.

A frame-off renovation insures that the foundation (aka the chassis) is clean, is treated for rust resistance, and structurally reconditioned to be solid and straight.

Virtually every vintage chassis we’ve encountered since 2010, and we’ve seen hundreds, has been a hotel for rats, mice, raccoons, possums, snakes, or all of the above. These critters have made your chassis their permanent home before you rescued it. We’re assuming you intended to only rescue the vintage trailer, and not a bunch of varmints, so we kick them out.

In addition to becoming an animal habitat, after years of rainwater or high humidity, a vintage trailer’s steel chassis can rust and the wood subfloor can rot. Telltale signs of water damage are soft, spongy floors and musty smells. Resulting moisture can promote mold, particularly under the bathroom shower, bathtub and toilet. It’s no wonder these airtight, enclosed spaces begin to gather unpleasant odors and stink.The health risks of molds are well documented, and should be taken seriously.

In addition, frame-off renovations arrests further degradation of the foundation of the mobile space. In Airstreams and many of their aluminum-built cousins – such as a Bowlus, Curtis Wright, Avion, or Spartan – the chassis, axle(s) and hitch are the only components that will rust because they’re made from steel. When the chassis is separated from the subfloor and the body, the chassis can be properly inspected, straightened, refinished, and any structural members replaced, as needed.

A full frame-off restoration it is not intended for owners with a limited budget due to the time, cost and expertise required. The price tag for a properly done, full frame-off restoration ranges from $20,000 to $30,000.However, a full frame-off renovation will greatly increase the life expectancy of your vintage trailer.

Ask any professional renovator and they’ll tell you: A full frame-off renovation is the right way to restore a vehicle. A full renovation process addresses all the structural and stinky issues.

Steps to a Frame-off Renovation

Hofmann Architecture’s basic steps to a complete frame-off renovation are described here. (Caution! This list is for general information purposes, only. A frame-off process should only be attempted by experienced professionals with proper equipment and using best safety practices.):

1. Demo the interior. All cabinets, fixtures, systems, and flooring are removed. The trailer is secured and proper personal protective gear is worn throughout the process.
2. Remove interior skins, electrical systems and insulation from the walls
3. Remove exterior trim pieces.
4. Separate the interior C-channels at the base of the walls from the subfloor by grinding off the bolts, or separate them with a pry bar. Chances are they’re not going to unscrew because they’ve rusted.
5. Remove ceiling vents, skylights, and air conditioners.
6. Position the body with a lifting system.
7. Remove the exterior rivets that connect the body with the belly pan, but do not remove the rivets that connect the exterior skins to the C-channel.
8. Lift the body off the chassis.
9. Pull the chassis out and lower the body onto 4×4 pressure treated stickers
10. Create a template of the existing subfloor for the new subfloor because the dimensions of the body are unique for each unit.
11. Remove the subfloor from the chassis. The fasteners will either be Phillips deck screws or flathead bolts. Unscrew the Phillips or pry bar off the flatheads and grind off the heads below the metal cross members.
12. Remove ducting, grey and black water tanks, gas piping, electrical wiring, and brake lines. Clean the belly pan of organic material, vermin treasures, insulation, dirt, and animal waste. Be sure to wear an approved mask for this step.
13. Remove the underbelly skins. Be sure to SAVE the quarter panel corners of the belly pan. These are often dented, but can be straightened.
14. Replace the axles, brakes, and suspension.
15. Sandblast the entire chassis.
16. Carefully inspect and repair any chassis issues.
17. Remove and SAVE the bumper.
18. Spray entire chassis with a rust converter then paint the chassis with a rust inhibitor base paint.
19. Re-assembly starts with reinstalling new waste and fresh water tanks, then new water lines, electrical wiring, and any heating systems.
20. Lay new subfloor using the template, attach with self-tapping 3/16” Tec screws.
21. Replace any rusted or damaged C-channel pieces.
22. Remount the body back onto the chassis.
23. Secure the body with self-tapping 3/16” Tec screws around the edge of the chassis.

Voilà! A fresher-smelling and longer-lasting Airstream.

* A chassis is the skeleton framework of a vehicle that hold the body in place.

** Monocoque is derived from Greek, mono = one, and French, coque = shell. So, monocoque construction is where the structural load of an object is supported by a single interconnected external material. In the case of an Airstream, it’s the curved shape of the skin, rather than the internal structure, such as a stick-framed home. A good example of a monocoque design in nature is an egg. When an eggshell is complete it is very strong compared to its weight. However, when one part is weakened, or removed, it collapses easily. A poor example of monocoque construction is an automobile because it uses a series of tubes and bulkheads to provide support while the external body adds little strength or support.