Thermal Bridging in Campervan Conversions
Even the best-insulated campervan has weak points where heat escapes. These are thermal bridges — areas where the insulation is thinner or where a solid conductive material bypasses the insulation entirely.
Understanding and eliminating thermal bridges is the difference between a van that stays warm and dry through a UK winter and one that drips with condensation every morning.
What Is a Thermal Bridge?
A thermal bridge (also called a cold bridge) is a path of higher thermal conductivity that bypasses the insulation layer. Heat flows through this path more easily, creating a cold spot on the interior surface.
In a campervan, this looks like:
- Condensation on exposed metal ribs
- Frost forming on screw heads in winter
- Cold patches on the ceiling where the roof bars attach
- Damp wallboard at the van's ribs
The Physics
Heat always takes the path of least resistance. Your insulation has a thermal resistance of about R-0.7 per 25mm. The steel or aluminium van body has a thermal resistance of effectively zero — about R-0.0003 per mm.
If just 2% of your wall area is exposed metal (from ribs, screws, or framing), that 2% can account for 30-50% of the heat loss — and it creates condensation on that spot.
Where Thermal Bridges Occur in Vans
1. The Van's Metal Ribs
The van body is built from a metal frame with thin panels welded to it. The space between the ribs is easy to insulate — fill with foam board or wool. The ribs themselves are 15-20mm of solid steel, conducting heat directly from inside to outside.
Fix: Cover the ribs with at least 10mm of closed-cell foam (Armaflex) before fitting your main insulation. This 'thermal break' layer prevents the rib from conducting heat straight through.
2. Screws and Fixings
Every screw that penetrates through to the van's metal body is a tiny thermal bridge. With 50-100 screws in a typical conversion, they add up.
Fix: Use self-tapping screws with bonded washers (EPDM or neoprene) that provide some insulation. Alternatively, apply a dab of silicone sealant around each screw head before covering with wallboard.
3. Window Cutouts
The metal edge around a window opening is a thermal bridge to the outside. In winter, this edge gets cold and causes condensation around the window frame.
Fix:
- Use double-glazed windows (Dometic or Movera) — the frame design includes thermal breaks
- Apply 10mm closed-cell foam tape between the window frame and the van body
- Fit thermal blinds or window covers (Silver Screens or DIY Reflectix panels)
4. Roof Rails and Vent Openings
If you have roof bars, a roof fan, or a solar panel mount, each attachment point creates a thermal bridge through the roof insulation.
Fix:
- Use plastic mounting feet for roof bars where possible
- Apply a 5mm EPDM foam gasket under any roof-mounted equipment
- Fill gaps around roof fan installation with closed-cell foam before sealing with Sikaflex
5. Floor to Wall Joints
The floor-wall junction is a common area where insulation gaps form. Water and cold air pool at floor level.
Fix: Overlap your floor vapour barrier 10cm up the wall and tape it to the wall vapour barrier. Ensure insulation extends to the lowest point of the wall.
6. The Bulkhead (if retained)
If you keep the driver cab bulkhead, the metal behind the cab is a massive thermal bridge to the cold cab area.
Fix: Fit a removable insulated curtain between cab and living area. A 10mm foam-backed curtain with a batten for mounting reduces heat loss through the bulkhead significantly.
How to Detect Thermal Bridges
Thermal imaging camera: The best tool. A Flir One or Hikmicro phone attachment costs £200-300 and shows cold spots instantly. Check your van on a cold day after heating the interior for an hour.
The hand test: On a cold morning, run your hand over the interior walls. Any noticeably cold patches are thermal bridges.
Condensation mapping: After a cold night, check where condensation forms. The pattern reveals your worst bridges.
Solving Thermal Bridges: Practical Steps
Before Insulation
- Rib covers: Cut 10mm Armaflex into strips 40mm wide and glue them over every exposed metal rib using spray adhesive
- Screw isolators: Use plastic spacer washers (nylon or POM) under any screws that attach to the van body
- Cavity fills: Use expanding foam (the low-expansion window and door type, not the high-expansion general purpose) to fill irregular cavities around window frames and door pillars
During Insulation
- Continuous layer: Ensure your insulation is continuous — no gaps. Overlap insulation at corners
- Vapour barrier: Must be continuous. Tape every seam. A gap in the vapour barrier creates a cold spot where moisture accumulates
- Floor insulation: Use a full sheet of 25mm XPS under the floor ply, not strips between the floor ribs
After Building
- Thermal curtains: Heavy curtains at the cab bulkhead and on exterior doors
- Door insulation: Modify the rear barn doors with 10mm Armaflex on the inner panels, covered with fabric-faced plywood
- Draught excluders: A simple foam tube at the bottom of sliding door and rear doors prevents cold air ingress
Real-World Example
In our LWB Transit build, we measured the following improvements from addressing thermal bridges:
| Area | Before Fix | After Fix |
|---|---|---|
| Condensation on ribs | Daily in winter | Never |
| Wall temperature (coldest spot) | 6°C | 13°C |
| Diesel heater run time to maintain 18°C | 14 hours/day | 8 hours/day |
| Interior RH | 72% | 55% |
Conclusion
Thermal bridging is often overlooked by first-time van converters, but it is responsible for most condensation problems in finished builds. The fixes are cheap (Armaflex tape costs £15, a roll of closed-cell foam is £20) but they need to be applied before the insulation and interior boards go in.
Take the time to cover metal ribs, seal gaps, and maintain a continuous vapour barrier. Your warm, dry van will thank you when the temperature drops below freezing.
