Van floor build-up: insulation, plywood, vinyl

The van floor goes in first, and it is almost impossible to redo later: all the furniture stands on it. So the decision about the layers is made once. It has two conflicting requirements: the floor must be warm and rigid, yet thin and light.

The layers from the bottom up

1. Body metal. A corrugated sheet with stiffening ribs.
2. Filling the corrugations (optional). Strips of insulation or battens between the ribs so the next layer sits on a flat plane.
3. Insulation. Rigid board or foam on a roll.
4. Plywood. A structural base of 9–12 mm.
5. Finish. Vinyl roll flooring 2 mm thick.

How much headroom the floor takes

The headroom in an H2 van is about 1.90 m. With the ceiling insulated and the floor in, a person 1.80 m tall only just stands upright. Every centimetre counts here, and the finish is the only layer where 8 mm can be saved without losing performance.

Insulation: what kind and how thick

• XPS (extruded polystyrene). A rigid board that carries load and does not absorb water. The most common choice for a floor.
• Closed-cell foam rubber or polyethylene. Flexible, easy to stick to corrugations and arches, but it compresses under load. Under plywood it is used in a thin layer or between battens.
• Cork. Natural, but heavier and more expensive.

Mineral wool and other fibrous materials are not used on the floor: they take up moisture.

On thickness: heat leaves a van mainly through the walls, windows and roof. The floor accounts for a smaller share of the losses, so 20 mm is considered a sensible compromise. More than 30 mm makes sense for winter trips to the mountains.

Battens or a continuous layer

With battens. Timber battens are glued to the metal, insulation is laid between them, and the plywood is fixed to the battens on top. The plywood gets firm support and reliable fixings. The downside: the battens act as cold bridges and add weight.

Without battens. XPS boards are glued down as a continuous layer and the plywood is glued on top. The build-up is lighter and warmer. There is one requirement: the board must be dense enough not to dent under a point load.

Furniture, and especially seats with belts, is fixed not to the plywood but through the floor to the body, via reinforcement plates. This is a matter of safety and homologation, to be settled with the engineer.

Plywood

• Thickness. 9 mm on continuous rigid support, 12 mm in most cases, 15 mm on widely spaced battens.
• Species. Birch is stronger and heavier; poplar is about a third lighter. The weight comparison is in the article on campervan floor weight.
• Moisture resistance. Use water-resistant plywood. Coat the edges and cut-outs with varnish or sealant.
• Layout. As few sheets as possible. Place the joints across the van and away from the walkway.

Preparing for the covering

Two-millimetre vinyl follows the base. So:

• the joints between sheets are brought level and filled;
• screw heads are countersunk and filled;
• the surface is sanded and dusted off.

Then come cutting and bonding, following the guide to fitting vinyl in a van.

Moisture and condensation

The body metal is cold and condensation forms on it. To stop rust appearing under the floor:

• before starting, clean the body floor, treat any rust and paint over it;
• do not block the factory drain holes in the sills;
• glue the insulation as a continuous layer, with no air pockets where moisture collects;
• seal the perimeter of the finished floor so that spilt water does not get under the plywood.

A continuous covering with no seams acts here as waterproofing from above: whatever is spilt inside stays on the surface.

Underfloor heating

Electric heating mats are rarely fitted in campers: they need a lot of energy. If you do decide to fit them, check the data sheets for the permitted temperature for your covering and adhesive. For PVC flooring the limit usually quoted is 27 °C at the surface.

Mistakes

1. Soft insulation under plywood with no support. The floor springs and the fixings work loose.
2. Plywood with unprotected edges. It takes up water at the first leak.
3. A thick floor in a low van. Lost centimetres cannot be recovered.
4. Rust under the insulation. The metal was not treated before work started.
5. Furniture screwed only to the plywood. In an accident it will tear away together with the sheet.

FAQ

Can I do without insulation in the floor? For summer trips to the coast, yes: plywood and the covering are enough. The floor will be cool, but you keep the headroom.

Do I need a vapour barrier? A separate membrane is not usually laid on the floor. Closed-cell insulation and a continuous PVC covering do not let vapour through anyway.

What do I use to glue insulation to metal? An adhesive or sealant compatible with polystyrene: the solvents in some products attack it.

What is the thinnest floor possible? Thin foam insulation, 9 mm plywood and 2 mm vinyl: about 2 cm.

Read also: which adhesive holds vinyl in a vehicle and why a floor's lifespan depends on the wear layer rather than the thickness.