Building a camper van floor: construction and materials

A typical camper van floor consists of these layers from bottom to top:

1. The metal van floor is the original floor of your van. Clean it thoroughly and treat any rust spots with rust converter and primer.
2. Sound deadening (optional): a layer of bitumen or butyl rubber (e.g. Silent Coat, Noico) on the bare metal reduces vibrations and road noise. 2-3 mm thick, 1-2 kg per m².
3. Insulation: XPS boards (20-30 mm) are most suitable for floor insulation. XPS is compression-resistant, moisture-proof and doesn't absorb water. Lay the boards over the ribs so any water underneath can drain away.
4. The structural board is 9-12 mm plywood as a base for your furniture and floor covering. Poplar plywood is the lightest (~400 kg/m³).
5. The finish layer is vinyl, PVC click flooring or rubber flooring. Choose something waterproof, wear-resistant and easy to clean.

Total build-up height: 35-50 mm. Factor this into your standing height!

For floor insulation, XPS (extruded polystyrene, e.g. Jackodur, Styrodur) is by far the best material:

• Compression-resistant: XPS can handle 20-70 tonnes/m² without collapsing. You can place heavy furniture and batteries on it.
• Moisture-proof: XPS doesn't absorb water (closed cell structure). Crucial for a floor where moisture can come from below.
• Good insulation value: thermal conductivity (λ) 0.029-0.036 W/mK. 30 mm XPS gives R 0.86.
• Easy to cut with a utility knife or fine-toothed saw.

Armaflex is less suitable for floors because it's not compression-resistant. Use Armaflex for walls and ceiling, XPS for the floor.

Lay XPS boards loosely (not glued) over the ribs of the van floor. Fill gaps with PU foam. This way, condensation that gets under the insulation can drain through the original drain holes in the van floor.

On top of the insulation you lay a structural board as a stable base:

Poplar plywood is the lightest option (~400 kg/m³). 12 mm thick is sufficient as a base. A sheet of 250×122 cm weighs ~15 kg. Ideal when weight is an issue.

Birch plywood is stronger and harder than poplar (~680 kg/m³), but also heavier. 9 mm birch is comparable in strength to 12 mm poplar. More popular with professional converters.

Moisture resistant? Choose plywood with WBP glue (Water and Boil Proof). Standard interior plywood can swell with moisture.

Fix the structural board with stainless steel screws through the insulation into the ribs of the van floor, or use construction adhesive. Pre-drill with a thin bit to prevent splitting.

Tip: mark the position of the ribs on the structural board before screwing. This way you know exactly where you're screwing into solid metal.

1. No rust treatment: if you don't treat the metal floor before insulating, rust develops invisibly underneath. Use rust converter on rust spots and apply a coat of primer.
2. Blocking drain holes: the original van floor has drain holes for water. Do NOT seal these. Water that gets under the insulation (condensation, leaks) needs to be able to drain.
3. Armaflex on the floor: Armaflex is not compression-resistant and gets squashed by furniture and your own weight. Use XPS for the floor.
4. Structural board too thin: 6 mm plywood flexes under heavy loads. Use at least 9 mm (birch) or 12 mm (poplar).
5. Forgetting standing height: 40-50 mm floor build-up costs standing height. Measure your standing height after both floor and ceiling finishing. In an H2 van (1.90 m interior) after floor (45 mm) and ceiling (25 mm insulation + 6 mm board) you'll have about 1.82 m left.

Cost: budget €200-€300 for a complete camper van floor (sound deadening + XPS + plywood + vinyl). Time investment: approximately 15 working hours.

A bare steel floor with a board on top has a thermal resistance of about R 0.21. That is almost nothing, and it is why your feet stay cold while the heater runs flat out.

What happens with insulation, worked out with the insulation calculator:

• 20 mm XPS: R 0.80, almost four times better than bare
• 30 mm XPS: R 1.09
• 40 mm XPS: R 1.39
• 20 mm PIR: R 1.08, the same as 30 mm of XPS

That last line is worth gold in a floor. PIR insulates better per centimetre, and in a floor you pay for every centimetre in standing height. If you are just short of standing upright in an H2, PIR wins you a centimetre back without giving up insulation.

The first two centimetres do by far the most work: R 0.21 to R 0.80 is a leap, R 1.09 to R 1.39 barely registers. Above 40 mm it rarely pays off in a floor, unless you spend winters in the mountains.

Almost every panel van has a profiled floor pan. Those ribs are there for stiffness, but they make insulating harder.

There are two common approaches. You fill the troughs with strips of insulation cut to size, giving you a flat base for a continuous layer on top. Or you lay battens lengthways on the ribs and insulate between them.

The first insulates better, because no air layer is left connected to the outside air. The second is quicker and gives you something to fix the board to.

What you do not want either way: leaving the troughs open. Condensation collects there, and since it is the lowest point of the van, it stays. Rust nearly always starts there.

Leave the original drain holes in the floor pan clear, or close them deliberately with a permanently flexible sealant. Half-closed is the worst of both.

Every screw through the floor pan is a hole in your rust protection and a thermal bridge in one. Yet your floor has to stay put, because a loose floor creaks and shifts.

Most self-builders bond the insulation to the degreased pan with construction adhesive and float the plywood board on top. The weight of the furniture holds it in place, and the furniture itself is fixed to the walls or to the original mounting points in the floor.

If you do have to go through the pan, use the existing load-floor fixing holes. Those are treated at the factory. Drill a new hole and you treat it on both sides and use a bolt with a rubber seal.

Do not forget that your floor can move a few millimetres with temperature. Leave a gap of 5 to 10 mm along the walls and finish it with a skirting.

The top layer takes everything: wet boots, sand, a spilled pan and furniture sliding about.

What works well in a camper:

• Sheet vinyl, because without seams no water gets underneath
• Marmoleum, a little heavier but remarkably hard-wearing
• Click flooring with a plastic core, which does not swell with moisture

What disappoints more often: laminate with a fibreboard core. One tipped bucket and the joints swell, and they never go back down.

Leave the top layer loose at the edges under the skirting, especially with click flooring. A floor that bulges in summer because it is trapped against the wall is one of the most annoying things to fix afterwards.

Count on a total floor build-up of 4 to 6 cm: insulation, plywood and top layer together. That measurement comes straight off your standing height, so take it into account if you are still weighing up an H2 against an H3.