Roof panels present challenges, but replacing them is really no different than replacing other exterior panels.

Replacing a roof panel may seem like a real challenge to a young technician presented with a wooden crate and a roof ‘skin’ for a minivan. Other than the size of the panel and the parts which must be removed to gain access to replace the panel, the processes used are the same as those used to replace a door skin or quarter panel. The repair or replace decision follows the same pattern as well. 

MAKING THE CONNECTION

ATTACHMENT METHODS for roof panels vary. They may be held in place with bolts, adhesives, welds or may be weld-bonded in place. A closer look at replacement methods highlights the differences between adhesive bonding, spot welding and plug welding. Bonded panel repair When replacing a bonded roof panel, begin by removing the trim and glass, then start removing any attachment bolts. Removing most of the roof skin by cutting it near the edge may make it easier to remove the adhesive. The removal procedure will depend on rigidity of the adhesives holding the roof in place.  For semi-rigid and more flexible adhesives—When replacing a roof held in place with a semi-rigid or flexible adhesive, it can often be treated like a glass installation.  Cut most of the adhesive off the vehicle, but do not damage the metal underneath if possible.  Any bare metal must be covered with epoxy primer. Prepare the mating surface of the new part according to the adhesive manufacturer’s recommendations.  Keep in mind proper cleaning and remember that whether the E-Coating should be left intact or bare metal should be exposed depends on the formulation of the adhesive. For rigid adhesives—A combination of heat from a heat gun and an air chisel should be used to remove this type of material. The heat will soften the adhesive, making it easier to cut.  Follow the vehicle manufacturer’s recommendations, if any, for specific adhesives for the job at hand. Welded panel repair Replacing welded panels is similar to replacing quarter panels. Common guidelines follow: Drill or grind away the spot welds being careful to do as little damage as possible to the underlying metal. Heat any areas where crossbeams are bonded to the skin and remove the panel. If conventional plug welds are to be used, mark the new panel to punch the 8-mm holes as close to the original spot-weld locations as possible. Vehicle manufacturers suggest spot welds be replaced with the same number of plug welds and in the same locations. Spot-Welded panel repair If a spot welder is being used, a different standard applies: Those manufacturers who approve of spot welding suggest 20 percent to 30 percent more welds be made than the number placed at factory and that these welds be made not in the same spots as the original welds. Epoxy or weld-through primer should be used to coat any bare metal exposed during removal of the original panel. If the panel was originally weld bonded, using adhesive is optional. Any adhesive used to attach cross beams must be replaced when the panel is installed.

1. 20% to 30% more spot welds, placed away from old welds.  2. 8mm holes punched through existing weld sites. Plug welds in same place as previous welds.

Safety First
Safety and structural issues must be first on the list of things to consider when formulating a repair plan for a vehicle with a damaged roof. The roof is an important safety element and its strength must be preserved or restored. In the last decade, vehicle safety was focused on the front of the vehicle. Today, an increasing percentage of fatalities involve side hits or rollovers. This doesn’t necessarily mean that there are more side hits and rollover accidents but rather that the safety designs surrounding frontal hits are working so well that the attention has shifted to other accident scenarios. With this shift in focus comes increased scrutiny of the collision repair industry’s ability to restore all vehicle’s safety features.

So how does the roof contribute to the safety of a vehicle? For starters, it is part of the box that surrounds the passengers. In addition, it holds the vehicle off of passengers should the vehicle roll over and it contributes to the overall stiffness of that box in the case of side impacts. Because of this, the roof must be considered a system that involves the skin, supporting elements attached to the skin, side rails, the A, B, C, etc. pillars holding it up and the non-movable glasses bonded to those pillars. The windshield is the most important part of the fixed glass and is subject to federal standards that involve dropping a large weight on the roof to see if the bonded windshield remains in place. Thus, the windshield glass helps contribute to the overall strength of the roof system. Various tests are being used and standards proposed in the United States and Europe to demonstrate the ability of roofs to withstand rollover accidents, including actually rolling vehicles over several times to see how they perform in simulated ‘real-world’ situations. 

Any accident involving damage to the skin may also involve damage to the supporting structure, which will need to be corrected before the replacement panel can be installed. This means the same litany of considerations must be followed for roof panels as for all other exterior panels. In more severe accidents, such as a rollover, you must first check for hidden damage, confirm or correct all dimensional and structural problems, then replace the panel. Roof side rails and cross beams must be restored if damaged, and the kink vs. bend rule applies to these structural pieces. Frequently, only the roof panel will sustain damage, such as that from a hail storm or falling tree limbs, or the occasional garage door closing on the roof.

Access
To replace the roof panel, full access to the edges of the roof where the panel is welded on or bonded on is necessary. This usually means removing much of the interior trim including the headliner. Care must be exercised, as many new vehicles will have Supplemental Restraint Systems (SRS) that will need to be disarmed before removing them to work on the roof. These must also be properly stored during the repair process. Bonded glass, such as the windshield, may also have to be removed. The headliner must be dropped down to allow easy access to the roof repair. It may be left inside on some vehicles and will have to be removed from others either from the front or rear glass opening after the glass has been removed. Protective covers should be used to maintain the interior of the vehicle during the repair process.

Considering materials
The process of how the engineers decided to attach the roof may be determined by what materials it is made of, thus how the technician will remove and replace it. Steel is by far the most common material in use. Aluminum is gaining market share, but it is still uncommon as exterior panels in virtually all vehicles except high-end luxury models. Composites are used in some applications. Different welding techniques and equipment will be used for steel and aluminum, and material choices will differ for corrosion protection. But the same basic process will be used. 

Attachment Methods
Roof panels are attached around the edge of the roof and may be held in place with bolts, adhesive, welds, or may be weld-bonded in place. There will frequently be cross braces bonded to the skin as well. Adhesives are gaining use as they contribute greatly to the overall performance in terms of quietness, corrosion protection and stiffness. However, most roofs are still spot welded in place. Many panels are weld bonded, a process in which spot welds are made through uncured adhesive. This process is possible in the repair shop if the proper welding equipment is available. So far, the vehicle manufacturers have not required collision repair shops to use weld bonding when replacing exterior panels, although some OEMs are encouraging it. The standard procedure is to replace weld-bonded panels using standard plug welds.

Bonded Panels
Some panels are simply bonded in place using high-performance adhesives. Bolts may be used, mostly to hold the panel in place while the adhesive cures. To replace a bonded roof panel, after trim and glass have been removed, start by removing any attachment bolts. Removing most of the roof skin by cutting it near the edge may make it easier to remove the adhesive. Two types of adhesives will commonly be found. Semi-rigid or flexible adhesives, very much like that used to bond windshields in, is used in some vehicles. This type of adhesive may be cut out using the same techniques a glass technician would use cutting out a glass—powered blades, hand knives and wire. The other type of adhesive is a rigid material. A combination of heat from a heat gun and an air chisel should be used to remove this type of material. The heat will soften the adhesive, making it easier to cut. The replacement process will differ for these two types of adhesive. The flexible urethane should be treated much like a glass installation. Cut most of the adhesive off the vehicle, but do not damage the metal underneath if possible. Any bare metal must be covered with epoxy primer. Prepare the mating surface of the new part according to the adhesive manufacturer’s recommendations. The performance of adhesives is very dependent on surface preparation. Proper cleaning is essential, of course, and whether the E-Coating should be left intact or bare metal should be exposed depends on the formulation of the adhesive. All adhesives start curing once mixed, so dry-fitting the panel and being prepared to move quickly once the adhesive is placed is essential. It is also very important to leave the vehicle stationary while the adhesive cures. Again, refer to the adhesive manufacturer’s recommendations.

Welded Panels
The more common welded panels are replaced much like quarter panels. Drill or grind away the spot welds being careful to do as little damage as possible to the underlying metal. Heat any areas where cross beams are bonded to the skin and remove the panel. If conventional plug welds are to be used, mark the new panel to punch the 8-mm holes as close to the original spot-weld locations as possible. Vehicle manufacturers suggest spot welds be replaced with the same number of plug welds and in the same locations. If a spot welder is to be used, a different standard applies. Those manufacturers who approve of spot welding suggest 20 percent to 30 percent more welds be made than the number placed at factory and that these welds be made not in the same spots as the original welds. Epoxy or weld-through primer should be used to coat any bare metal exposed during removal of the original panel. If the panel was originally weld bonded, using adhesive is optional. Any adhesive used to attach cross beams must be replaced when the panel is installed. 

Corrosion Protection
Welding always destroys some of the protective coatings used to prevent corrosion. These coatings must be restored during the repair process. Usually this will mean using a long wand to place epoxy primer inside the roof side rails where the side of the roof was welded, followed by a moisture barrier coating. The long-term performance of any welded part depends on controlling corrosion.

No Big Deal
While the size of some roof panels may mean getting lots of help to place the panel, the techniques used during replacement are much like those used for any other panel. There are a few extra trim pieces, and the interior must be protected from all those sparks, but when done carefully, roof panels are just another straightforward repair.