Plywood Installation

During this part of the project, I install the plywood sub-floor and seal it to protect it against moisture. As you may notice, I forgot about the staining until after the installation and fastening of the plywood, so only the visible plywood was sealed with Shellac. You may also stain the other side or abstain entirely as sealing is clearly an option.



Inside Height
The basic composition of the sub-floor in an RV or van conversion should consist of a bottom layer of one-half to one inch of Poly-Iso insulation and a top layer made of exterior grade plywood. The standard ¾ inch thick plywood is sufficient to securely hold all cabinetry and appliances. Don’t use MDF or Particle board as these products have weight and/or moisture issues.

For practical reasons, I have to deviate from these standards as a result of the roof height. The medium roof Ford Transit has an interior height of about 69 inches between the top of the floor ribs and the ceiling cross members. Even with my personal average height, there is very little space left for floor or ceiling materials, without sacrificing the ability to stand up straight in the vehicle.


If you have a high roof vehicle all of this does not apply, but I decided to only use Poly-Iso insulation strips in between the floor ribs, with only a half inch thick plywood sheet on top of that. That and taking my shoes off, will hopefully solve this issue.

Weight is another issue that may change your choice of materials. These sheathing materials are heavy and make a big impact on the overall weight allowances of the individual vehicle. Dependent on the tonnage and size of the van, you may decide to use relatively lighter or thinner materials. The half inch (actually 15/32 inch) thick plywood that I use, adds another 73.5 lbs to the conversion.

As a sub-floor, I prefer to install the plywood sideways as the finish flooring will be installed lengthwise on top of that. But the size of the floor will probably dictate, how to lay the plywood most efficiently to save a few bucks in materials. I ended up using three sheets of plywood, with lots of scraps leftover.

Which Parts To Choose

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Comprehensive Material List

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BCX Plywood

Exterior Grade
4′ x 8′

Shellac Flakes

Substitute finishing material

Denatured Alcohol

1 gal

Spar Urethane

Minwax Helmsman
Spar Urethane

Painter’s tape



Paint Brushes

Angle Brushes
Latex/Oil Paints & Stains
Interior & Exterior

Safety Goggles

Clear Lens
Anti Fog

Hearing protection

Padded ear cup
Reduces harmful noise


5 Amp

Circular Saw

14 Amp


1.75 hp
11 amps


2 HP

Step-by-Step Installation

Gather all the tools and materials before proceeding. Regularly fit the materials, to avoid costly mistakes.

  1. Tape the paper template to the plywood.
  2. Mark the cut-out areas.
  3. Cut out the marked areas. Stay within the lines, to slowly ease into the final cut.
  4. Check regularly by fitting the ply sheet.
  5. Mark and cut any additional areas that need to be removed.
  6. While fitting, make sure that a ¼ inch gap exists between plywood and the surrounding areas. Adjust as necessary.
  7. Cut the rear plywood sheets width at the center of the central floor rib plus ¼ inch.
  8. Cut dadoes at the front & back (from the top, ½ inch wide, ¼ inch deep) and left side (from the bottom, ½ inch wide, ¼ inch deep) of the right, rear plywood sheet.
  9. Cut dadoes at the front & back and right side (from the top, ½ inch wide, ¼ inch deep) of the left, rear plywood sheet.
  10. Cut a dado at the back (from the bottom, ½ inch wide, ¼ inch deep) of the front plywood sheet.
  11. Be sure, the dadoes interlock.


  • Paper templates (made earlier in this project)
  • 3 sheets of bcx plywood (exterior grade) – 4′ x 8′ 15/32” each
  • 4 oz of Shellac flakes
  • 32 oz (4 cups) Denatured alcohol
  • Optional:
    • Marine varnish or
    • Polyurethane


  • Table saw
  • Jigsaw
  • Small paint brush
  • Wide paint brush
  • Tape measure
  • Marker
  • Sandpaper
  • Painter’s tape
  • Safety glasses
  • Hearing protection
  • Vacuum
  • Optional:
    • Hand saw
    • Circular saw
    • Router


This part of the project involves heavier materials and heavier tools, yet is still within the grasp of the ordinary DIY’er. The use of the tablesaw can easily be substituted by a circular saw or a router.

The plywood was acquired locally and the Shellac flakes on-line and the total cost was about $76.00.


Shellac is a resin secreted by the female lac bug, on trees in the forests of India and Thailand and used as a brush-on colorant, food glaze and wood finish.

Sealing the plywood floor has the advantage of protecting it against rot and mold. It also makes these materials more difficult to ‘breathe’, where moisture can evaporate and the materials can dry.

So, optionally you can apply some protection to it with a (Marine) varnish or polyurethane. I love to use Shellac. As a hobbyist woodworker, I use Shellac flakes, mostly because I can store it for an extended period, while the canned version has to be used within a few months.

For this application, I use a 1 pound cut (4 oz of flakes with 32 oz/4 cups of Denatured alcohol) and it takes a day for it to be ready to use. Just add the two together and swirl regularly to help to dissolve the flakes. It has an orange/amber tone when dry and it dries quickly; add Denatured alcohol if you need more time.

Clean up is easy: give brush a swirl in Denatured alcohol and let dry. It will dry stiff, but gets back in shape the next time you use Shellac.


  1. Prepare the Shellac solution the day before.
  2. If you paint in the right sequence, clean the plywood and apply the Shellac on both sides and edges, if not:
  3. Vacuum the floor.
  4. Paint the edges.
  5. Paint the surface.

Shellac Flakes: The Shellac Shack


The missing parts of the complete van conversion process are being added regularly to this Build Guide. If you want to suggest a specific build option for this guide, submit a content correction or have a general inquiry, send me an email.

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Disclaimer: Throughout this guide, all guidance, building techniques and other information are based on my own experiences of converting a cargo van into a Tiny House on wheels. This guide is only for informational purposes; always build according to local and national standards. Be aware that such a project is expensive, requires a substantial amount of broad knowledge of building techniques and involves more work hours than you can imagine. Besides of hitting a finger with a hammer, much more serious harm can be done when you work with 12V/120V electrical systems, propane installations, power tools, etc. Tapping into the vehicle’s own systems can also damage its functionality. Get professional help where needed; never take any risk!

1 Cheap alternatives to an expensive woodworking tablesaws can be found here.