Van Build Post 4: SUBFLOOR

What is a Subfloor?

Okay, you have removed and prepped your floor and your sound deadening is done, which means it’s time to build the subfloor. The subfloor is important because it allows you the chance to insulate your floor. The subfloor also acts as an anchoring system for the rest of the build. We screwed each piece of “furniture” straight into the subfloor, so that nothing shifts as we drive. As always when building out a van, you have to take into account both weight and structural stability. When building, we chose to create a grid frame out of 2x2s, and insulated with 1″ XPS foam board and Great Stuff (Spray Foam). We used the same plywood/plastic factory flooring that came with the van to put over the top of our insulated grid.

What Materials do I Need?

First, you will need wood (2x2s) and some sort of insulation. We got 12 8ft 2x2s and 3 sheets of XPS board. For the 2x2s, you can buy either treated or untreated wood. The treated wood is more water resistant, but it is much heavier and more expensive. If we were doing this again, we would have bought untreated wood. The rest of our van is made out of untreated wood. For our 159″ WB Promaster, 12 8ft 2x2s was the perfect amount. We had about 1/3 of an XPS board left over, which are ~4′ x 8′. We also used a Kreg Jig, Kreg screws, regular 1.5″ screws, and lots of construction adhesive (4+ tubes, Loctite or Gorilla brand). Remember, as we said in post 1, the upfront cost of tools can be daunting, but there are certain tools in a van build that you cannot do with out. The first one is a good drill. We have the Milwaukee Drill and Impact Driver set with bits. It is expensive, but worth it. You will also need a good saw. Throughout the build, we used a chop (miter) saw, a table saw, and a jigsaw. You will also need a razor knife to cut the foam board, markers (Metallic and Black), pen and paper, safety goggles, a straight edge, a tape measure, extension cord, work gloves, caulk gun (for construction adhesive), saw horses, clamps, and construction adhesive, and cinder blocks.

A Note About Insulation and How We Know What’s a “Good” Insulator

Firstly, let’s talk about insulation, how it works, and how we can tell what is a good insulator, and what is not. When we insulate our homes (or vans), we do it to keep in heat in the winter and keep heat out in the summer. How “good” a product is at insulating a space is measured via an R-Value. The higher the R-value, the better a material is at insulating, and vice versa. So, for example, something with an R of 15 is better at keeping heat in/out than a material with an R of 5.

R-Value is measured per inch of thickness, so if a piece of foam board has an R-value of 3, it means that 1″ thickness of foam board is R3, 2″ thickness of foam board would be R6, 3″ would be R9, and so on. Based on this article and video from Home Depot, floors in a regular home should be at least R13. We however, bought 1″ XPS board with an R-Value of ~4.3. This means, if we wanted to get the R13 that normal homes get, we would need a little over 3″ of foam board to get to that value….. And do vans REALLY have that space? NO! So, this was a roundabout way of saying that your floor is likely never going to be properly insulated (i.e. very cold in the winter) unless you are willing to give up quite a bit of your valuable space. This brings us to our next point: find an insulation option that you feel good about!

Subfloor Insulation Options and Alternatives

There are many options when insulating your van and subfloor. We used XPS foam board for the subfloor, but there are also other options including spray foam, wool, and cork, among others. Looking back now, and knowing that our floor was not really every going to be properly insulated, we would have picked an insulation material that was more eco-friendly. XPS board is basically styrofoam, and knowing what we know now about sustainability, we would prefer to have insulators that are more natural. Two of the options that we had looked into in the past that were cork and wool– the only reason why we didn’t go with them originally was because we had to order them offline, instead of pick them up at our hardware store.

We used and currently have XPS board insulating our floor, which has the highest R-Value per inch thickness of 4.7. However, Havelock wool batts are 3.6 and blown in wool is 4.3, and cork is 3.6-4.2. Regardless though, you will not be getting to that R13 in the small amount of space you have for the floor, so go with an insulation that makes you feel best. Your floor is going to be cold no matter what– invest in slippers!

Starting Your Subfloor- Wooden Frame

To create the frame for the subfloor, we used the 2x2s and the Kreg Jig to create a wooden frame, which you can see in the picture below. This frame acted as studs that allowed us to screw in the factory flooring, but also allowed us to anchor any of our furniture to the floor as well.

As we planned out the frame, we made sure that the 2x2s sat within the grooves of the metal floor. In addition, as we cut our 2x2s with a table saw or chop saw, we labeled each piece of wood and wrote on the floor where each piece went, so that we could keep track. Believe me, those pieces all start to look the same after a while! We suggest getting yourself a Milwaukee Marker to label. We got ours from our friends Georgia and Justin back in June of 2021 and that bad boy is still going strong (It’s August 2022 now)! Plus it is supposed to be able to write through dust and all sorts of other things. Also, while naming your pieces, have fun with it! In order to screw the 2x2s together, we used one of our most favorite tools of the whole van build, the Kreg Jig. This basically allows you to screw two pieces of wood together at a 90 deg. angle without having to go in from the end or having to make a toenail. It’s a very elegant solution, and as I have said many times, Kreg (Craig?) must be a very rich man!

Adhering the Wooden Frame to the Floor

Before adhering the frame to the floor, make sure that you have closed up any holes in your floor with JB Weld Steel Stick. Ideally, this would have been done when prepping your floor back in step 1, but make sure it’s done, because your metal floor is about to be covered up!

We screwed the whole wooden floor frame together before construction adhesive-ing it to the floor. Once we added the construction adhesive and got the frame situated on the floor, we put our factory flooring on top of it, and used 12 cinder blocks to evenly distribute weight on it while the adhesive dried overnight. If you do not have a factory floor, you will have to make a paper or cardboard template of your floor and then make your subfloor top out of plywood. There are many YouTube videos about this. After about 24 hours of drying, we removed the cinder blocks and the factory floor and added our XPS board insulation.

XPS Insulation

There isn’t anything too crazy about this, but once you are done making your wood frame, you will want to insulate it. After building, you will have a whole bunch of slots open which will need some sort of insulation. We used XPS foam board which is basically large sheets of rigid styrofoam. We first “named” each slot and the piece that fit in there so it was easier for us to put each piece in the right place. We cut down XPS board with a razor knife, and glued it down with construction adhesive. We also made sure to mark which sides were meant to face towards the back doors and face towards the cab as these were not perfect rectangles. In our YouTube video, you will see these referred to as the “Northside” and “Southside”. Any cracks/ holes can be filled with Great Stuff or some other spray foam.

The Factory Floor

If you have a factory floor, great! If not, you will have to create your own subfloor out of plywood. I would think that 1/2inch plywood would be fine. There are many videos on YouTube about how to do this, but the gist of what I have seen is that you will need to make a cardboard or paper template of the inside of your van, trace this template onto the plywood, and then cut it out with a jigsaw. If you have a Ram Promaster Factory Floor, keep reading.

Zak and I found that moving our factory floor in and out of the van was very difficult because it was extremely heavy and hard to grip. Therefore, we decided to cut it in half with a jigsaw. To cut it, we set the floor on top of two saw horses and clamped a piece of wood to it to create a straight edge. Cutting the floor in half made moving it easier, and it gave us the benefit of seeing our frame below and marking it on top. Marking where the frame/studs were allowed us to know where to later drill into the subfloor for maximum security. We used a straight edge, a tape measure, and a metallic marker to mark where our frame/ studs were. The only annoying thing about having the floor in 2 pieces was that it was mildly uneven later, and also, we couldn’t screw anything in down the line that we had cut. After gluing the frame down, we also decided to cut off the back inch or so of the factory floor. This made the factory floor flush with the frame, which made everything look much cleaner. Once we were done with the cutting, shaping, and marking of the studs on the floor, we screwed the factory floor into our wooden frame. We made pilot holes and then used 1.5″ screws to hold the floor in place.

The Video!

Okay, so I think that’s the end! Here is the video of us doing it, and all of the foibles that come along with it. If you have any questions, please feel free to message us!