Van Build: Floor Insulation

Having stuck our wooden beams down, the next task for our van conversion is to cut our floor insulation to size and stick it down with aluminium tape.

Written By Freedom Strider

On January 25, 2020

We bought 3 PIR Insulation boards, measured and cut them... Although...when it came to putting them in the first time...EVERY SINGLE ONE was slightly too big. 🤯


Measure the squares

Once the beam sealant had dried, we measured the sizes of all the squares we had to fill with insulation.

Safe to say they were not all exact squares/rectangles, I mean they looked square, but the beams were not always at exact right angles to one another which proved to be a slight problem later.

floor beams structure - van conversion


Squeaky Squeaky

We used a 25mm PIR insulation board, as it is rigid, has good thermal properties, and is easy to work with.

We marked out our PIR board, in the most economical way possible, so we don’t waste material.

And then we tried to cut it up with a bread knife and a crafting knife.

We much preferred the crafting knife since it didn’t produce PIR crumbs everywhere, although it did squeak a lot more, so Sam had to run out the room… foam squeaking is his ‘nails on the blackboard’. 😖


The test fit that nearly fit…

Once cut, we test fit all our pieces and none of them quite fit in their holes (blame Sam’s measuring).

Okay, it wasn’t actually Sam’s measuring skills, it was the incompatibility of a sharpie marker line with a crafting knife cutting blade. The sharpie marks were a 2-3mm thick line and the crafting knife blade only cuts a 1mm thick line, if that.

So, as the boards were cut, the cuts were made both on the inside and the outside of the line with no thought about the error.

Hence everything was a few mm out, and then when you add on the fact our squares weren’t entirely square…yeah.

After spending a few hours trimming them down, they all fit in their respective holes. 🛠️

floor insulation - van conversion
floor insulation - van conversion


For carving the PIR board to go around the wheel arches, we used the original van floor as a template for the arc we needed to cut, and this worked very well at producing an accurate arc.

floor insulation - van conversion


Make the blue beams shiny

Having made the insulation fit, we taped over the blue beams with 100mm aluminium foil tape. This is to ensure an airtight seal for the whole top surface area of the floor, allowing for a good moisture barrier and a continuous radiant barrier.

100mm was wide enough to cover the beam and overlap it with the adjoining insulation boards. We also covered any parts in the PIR board which weren’t foil covered with this tape.

floor insulation - van conversion


quick look

Quick Steps Overview:


  1. Measure and mark PIR board
  2. Cut the PIR board
  3. Adjust and fit PIR board
  4. Cover gaps with aluminium tape