Installing roof racks: Properly sealing the threaded points on the roof
Denis KhristolyubovWhen installing a roof rack (e.g., on a VW T6 / T6.1, but also on other vehicles), people usually think about load capacity, crossbars, accessories, and appearance. However, what often determines long-term reliability is a small detail: the sealing of the threaded fastenings on the vehicle roof.
Because it is precisely at these points that water can enter the body – not just anywhere, but through the threaded points where the roof rack is bolted. And this happens more often than many people think.
What are "threaded points" on the roof – and why are they critical?
Threaded points (e.g., threaded inserts, rivet nuts, factory-fitted threaded receptacles) are the fastening points where the feet/adapters/brackets of the roof rack are attached.
These areas are continuously exposed to stresses:
Rain, snow, condensation
Splash water from the road
Car wash / high-pressure cleaning
Important: A thread is structurally not automatically watertight just because the screw is tight.
How water gets into the vehicle through threaded fastenings
Even with a correctly tightened screw, microscopic gaps remain. Water often finds its way precisely there:
1) Capillary action in the thread
A thread acts like a fine channel. Water can "wick" its way inwards along the thread turns – especially with prolonged moisture and temperature changes.
2) Under the screw head / washer / contact surface
If the contact surface does not seal properly (e.g., due to minimal unevenness, settling, slipping), water flows under the contact surface – and eventually ends up at the thread again.
3) At the base of the threaded insert
Depending on the roof construction, water, once it reaches the threaded area, can get into cavities/layers – often initially unnoticed.
Rule of thumb: Water doesn't need a visible gap – a micro-gap is enough.
What can happen if it "only leaks a little bit" through the thread?
A thread leak is insidious because it is often gradual. Typical consequences:
Corrosion around the threaded point (and later poor grip)
Damp insulation → odor, mold
Water migrates into components/plug connections → electrical risks
Stains on the headliner, deformations, complex drying
Important: The problem often only becomes apparent weeks later, when moisture is already "working" inside.
Why this quickly becomes a big problem with Multivans
With some simple interior fittings, access to areas under the headliner is relatively straightforward.
With a VW Multivan (and generally vehicles with complex technology under the headliner), a leak at a single threaded point can mean:
more dismantling (headliner/trim),
more troubleshooting,
more time for drying and reassembly.
In short: What is still manageable with a "simpler" version quickly becomes a real headache with the Multivan.
Airholder Recommendation: Always seal threaded points
When installing a roof rack (e.g., Airholder on VW T6/T6.1), we strongly recommend:
✅ Every threaded fastening on the roof must be sealed – not just "around the outside", but in such a way that water cannot find a path along the thread.
This always includes two levels:
Sealing of the thread path (so that water does not migrate along the thread turns)
Sealing of the contact surface (so that water does not even reach the threaded point)
Important: Sealing only works on a clean, dry, degreased surface. Otherwise, the material will come off later – and leakage is pre-programmed.
Sealing at a Glance: Mistakes vs. The Right Solution
| Common Mistake | Consequence | Done Correctly |
|---|---|---|
| "Tightened = sealed" | Water still travels along the thread | Seal thread path and contact surface separately |
| Only sealed on top/outside | Capillary action draws water inwards | Apply sealant into the thread |
| Installed on a dirty surface | Seal detaches, leakage pre-programmed | Prepare surface clean, dry, and degreased |
| Unsuitable sealant | Material ages and detaches | Use permanently elastic, suitable sealant |
Typical mistakes we see again and again
"Tightened = sealed" (unfortunately, no)
Only seal on top, thread path remains open
Install dry and "lubricate" externally later
Unsuitable sealants that detach over time
Important: Subsequent "external sealing" rarely solves the root cause if water is already migrating through the thread.
Install roof racks cleanly – with the right system
A tight, well-thought-out fastening starts with the system: Airholder is a modular roof rack with clean, defined fastening points – e.g., for VW T6/T6.1 and other vehicles. Discover the Airholder system and find the right configuration for your vehicle.
