Floor Insulation

Mod: Insulated Floor – Part Three

RV insulation is a pivotal improvement to your cargo van, that impacts how you will use the vehicle. Type and amount of insulation is chosen based on location, vehicle type and size and material cost. But remember, with temperature control, insulation plays a partial role and at least as much attention must be given to ventilation and humidity control.



Project Insulated Floor Content

Tie Downs & Wheel Wells
Paper Plywood Templates
Floor Insulation
Fasten Insulation With Glue
Spray Foam Application
Plywood Installation
Hardware & Soft-Ware

What You’ll Learn:

  • Choosing the right type of insulation.
  • Choosing the right amount of insulation.
  • How to cut Poly-Iso foam boards.

What You’ll Use:

  • Carpenter’s Square.
  • Utility Knife.
  • Tape Measure.
  • Marker.

What You’ll Need:

  • 2 Sheets of Poly-Iso – ½” x 4′ x 8′ each (actual use: 37 SF).

Approximate Duration For This Project: 5 hrs.


Many decisions that follow are based on my 2016 Ford Transit LWB (Long Wheel Base) and Medium Roof. Keep that in mind, when applying this information to your specific vehicle model.

The general amount of insulation is greatly influenced by the location(s) where the RV has its primary use. If you live in one of the northern or plain states or Canada and you’ll use your van mainly on ski trips or other winter outings, insulation (and heating) play a bigger role. Thicker insulation materials, air barriers and window protection are needed to keep your house on wheels livable.

I live in Florida and plan to use the van primarily in warmer climates, such as the South West. The trips I’ll make, will include all the states and Canada, but mostly during summer. I’ll be following the sun, meaning that when temperatures go down, it’s time to pack up and move further south.

In my years of experience, I know that you cannot avoid colder temperatures or even freezing entirely, so a good heater is at the top of my list, but in general my focus is more on ventilation, while moderate insulation should suffice.

That said, my number one issue, that directly relates to the amount of insulation, is the interior height of the van. Most private and commercial upfitters choose a high roof vehicle for their conversion project. In most cases, they have room to spare to implement all their ideas. My medium roof Transit has more limitations. I’m of medium size and can walk straight up in the empty van without any difficulty. That changes after applying a floor and ceiling to the interior.

With a ½” sub-floor on top of the floor ribs, there’s less than an inch left for a ceiling and a finish floor. That leaves enough space for insulation between the ceilings bows, but almost none at floor level. Thankfully, in my opinion, insulating the floor is less important than shielding the roof of the van from the sun’s rays. I decided to fill the spaces between the floor ribs with foam board and use a spray foam for the remaining cavities between the ribs and the plywood sheets above it.

floor insulation rvThe type of material I choose, was Poly-Iso (Polyisocyanurate). It has the highest R-value per inch of any rigid foam board insulation and is locally available at very reasonable prices. Don’t use ordinary polystyrene, that has a much lower insulation value. An aerogel may offer the best in thermal performance, but is exorbitantly expensive. Than there is the popularity of Reflectix, a material that on its own, has little or no R-value and where long term performance may be uncertain.

The height of the floor ribs is slightly more than a 1/2 inch and I needed about 37 sf (3.3 lbs); that meant two 4′ x 8′ sheets with lots left, that I can use later in the walls and ceiling.

Before you start working on the insulation and/or sub-floor, you should consider, whether any electrical cables or plumbing lines should be installed prior to laying the floor. In general, that’s not advised as these features can never be accessed at a later time, without major modifications.

The actual work is quite simple and uncomplicated. Cutting with a sharp utility knife and a carpenter’s square is easy. The Ford Transit however, has a lot of grooves to fill, with many different lengths and widths and it took me the better part of the day, to get all the pieces together.

Cutting Poly-Iso

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

  • Mark and cut the individual panels.
  • Set the blade to slightly less than the thickness of the material.
  • Score the surface with the blade at a 10 degree angle.
  • Then make a cut at a 75 degree angle.
  • Score the back to release the individual panel.

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A job well-suited for even the most inexperienced DIY-er, but it will take multiple hours to complete.

The materials for this part of the project, where acquired locally and the total cost was about $15.00.

Other projects of this Van Conversion:

I’m just a DIY’er with a lot of common sense, but with some of the projects, I use some tools and materials, that require you to really know, what you’re doing. Always read the manual and consult an expert if you’re in doubt.

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  1. The R-Matte Plus-3 1/2 in. x 4 ft. x 8 ft. is not anymore available at the local stores (Home Depot, Lowe’s). Could you recommend something else to use for floor insulation on my 2018 Ford Transit Cargo Van (pretty similar with yours)?
    Thank you!

    1. Hi Patica,
      It’s difficult to know what stores carry nationwide, but locally (Central Florida) Home Depot has “GAF 0.5 in. x 4 ft. x 8 ft. EnergyGuard PolyIsocyanurate Insulation Sheathing”. That my differ from your store, but the crucial search term is ‘PolyIsocyanurate’ or ‘PolyIso’.
      If neither can be found, try to find a material with similar R-values or look at a local (family-owned) building material store.
      If that doesn’t work out, Thinsulate is an automotive insulation material, that is well-suited, but is somewhat expensive. You can buy it on eBay. eBay-Thinsulate
      Let me know if it works out. Take care.

      Van Williams

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