Insulation and Ventilation

One of the first steps for most van builds is insulating. While it might not be necessary for many builds, spending some time insulating is relatively cheap and simple and will add A LOT of comfort to a van. While traveling along with a couple friends who had done a quick build and skipped insulating, my van was relatively comfortable in the morning after a few sub-freezing nights while theirs typically hovered a few degrees above the outside temperature. That’s without heat in either van and with two people in theirs compared to one in mine.

I opted for polyiso board on the flat surfaces of the floor and ceiling, and denim in the walls. Denim is a bit more expensive than widely used fiberglass, but is easier to work with and isn’t a skin and lung irritant like fiberglass. I’ve done a lot of insulating with fiberglass in my life and trust me, the upgrade to denim is absolutely worth it for the small amount necessary to insulate a van. I used 2 packs of batts almost exactly for my 144 WB. Under the denim on the metal surfaces of the van I used a layer of reflectix first. This provides a good radiant barrier to keep the heat out in the summer and in during the winter.

Prior to starting insulation, I took care of a few maintenance and prep tasks that are best accomplished while the van is stripped. My van had been well used by its previous owner, and had a fair amount of surface rust which I uncovered after tearing out the factory floor. I also found rust starting in the body panels under the penetrations for the clips which hold the exterior trim on. These are things that should absolutely be taken care of at this point in the build, as it’s not generally possible to access these areas after a van is built out.

Interior rust that needed to be taken care of

I took the rust down to bare metal with an angle grinder and abrasive pad where possible, and removed what I could by hand with a wire brush in harder to reach places. Then I used POR-15 on the bare metal and remaining rust. Make sure to read the directions, there’s more to it than you’d think. On my van there was a fair amount of exterior rust under the trim panels as well, so I took care of that while I was at it. This actually turned out to be quite a task, and I probably spent a week overall on rust repair and prep.

When I was ready to put the trim pieces back on, I applied a bit of silicone sealant to the surface of the clips before putting them back on. This should keep water from getting inside the wall cavities in the future. This may come back to bite me, as I figure it’s going to be extremely difficult to get those clips out if I ever need to remove the trim panels in the future. A non-setting sealant like vacuum grease might be a better option.

Next up was taking care of any external penetrations that needed to be added. One of my goals was to keep external connections to a minimum so my van doesn’t really look like a camper. Still there were a few places I needed to cut into my van’s perfectly good sheet metal, including to add a driver’s side window, a fan for ventilation, and a penetration for the cables going to the solar panels I’d be adding to the roof. Any wiring or other goodies going in the walls should obviously be done prior to insulating as well.

My van came with factory windows in the side and rear doors, but I still wanted to add a driver’s side window for as much natural light as possible. I opted for the simple to install CR Laurence window which opens for ventilation and matches the factory lines of the vehicle. If I had to do this over, I’d still add a window to that location but would go with a smaller one. As it stands now, the kitchen counter partially blocks my window, and by putting in such a large piece of glass I lost valuable kitchen wall space. The full writeup is here – CR Laurence Window Installation.

Driver’s side window installed

As I wouldn’t be adding AC to my van, having a ventilation fan at a minimum was crucial. I opted for the rain sensing version of the popular Fantastic Fan. Placing this over the bed is generally better for airflow to keep you cool at night, but there’s an extremely convenient flat spot in the Sprinter’s roof ridges near the front of the vehicle which makes installation very simple. So, that’s where I put it. I went ahead and mounted my solar panels at this point as well so I knew where the wiring would need to come through. I used one of these with some 3M VHB tape and lap sealant to seal the penetration.

Running the power cables for the solar panels

The penetration for the solar panel power cables all sealed up

After that, it was time to actually insulate. First I installed some Rattle Trap over the wheel wells and on some of the large flat spaces in the walls. This definitely helped with sound deadening prior to insulation, but after insulating it might not have really made much difference. After that I applied a layer of reflectix on every accessible surface of the exterior sheet metal in the walls (this wasn’t necessary on the floor and ceiling as the Polyiso has a reflective layer on it already). Spray on some 3M Super 77 to hold it in place. Next, I cut and tore pieces of denim to fit all the main cavities. Super 77 works great to get that to stay in place as well. For the small cavities that aren’t very accessible, I tore small pieces of denim and stuffed them into the cavities through whatever access hole was available. The pieces need to be small enough to not get stuck and hung up on protrusions inside the cavity, but large enough that you can push them into place with some type of implement. It’s an art, and it sucks. I used a small metal rod at first that worked ok, then eventually I switched to a piece of 3/8” PEX tubing that was just the ticket. The PEX had the right combination of flexibility and stiffness, was large enough to effectively push the insulation, and wouldn’t scratch anything! I highly recommend it. There were some spots like the ceiling ribs where this just wasn’t possible, so for those places I used expanding foam. Make sure to apply it in small batches so it cures properly.

Rattle Trapp applied to some key areas

Reflectix going in the wall cavities

In addition to the walls, I used denim above the headliner as well. This area is pretty easy to insulate, and can make a big difference in the overall effective R-value of the vehicle. The headliner is kind of a pain to put back in, so make sure to do any other work you’re doing in this area like running wires or adding a headliner shelf while you have it down.

Insulation above the headliner

Next up was the roof. The Sprinter roof consists of rectangular open sections separated by ribs. While the roof isn’t perfectly flat, I found that two pieces of ¾” Polyiso board (I think, it might have been ½”) provided enough flexibility to match the contour when installed on top of each other. The edges of the roof have a taper to them as well, so using two pieces allows the second piece to extend further than the first, providing better coverage. Again, 3M Super 77 does the job of holding them in place until the ceiling in installed.

Polyiso on the roof and expanding foam dripping out of the rib cavities before I trimmed if off

The floor of the sprinter has a plethora of ribs of differing heights, so to provide a uniform surface for the Polyiso to sit on I filled the low areas with ¼” thick strips of cork floor underlayment. In retrospect, this was probably overkill and just laying the Polyiso directly on top of the ribs would likely be ok. As far as thickness of the floor insulation, it’s a tradeoff between added thickness (and thus reduced interior height), and a higher R-value. I went with ¾” thick Polyiso. I found that the existing floor I’d taken out worked nicely as a template for cutting the floor insulation out.

Space between the ribs in the body filled with cork underlayment

One important thing I did at this point is worth pointing out. I wanted to use bolts to secure my subfloor down to the body. This would be primarily to help prevent warping, but also because I like to build things stronger than necessary. There are existing threaded holes in the floor that are perfect for this, so why not? To locate the holes, I got some threaded studs (M8 x ~60mm) and threaded them into the holes in the floor. I then aligned the cut out Polyiso board over them and pushed it down using the studs to puncture holes in the insulation.

Using the factory floor as a template – highly reccomended

After insulating the floor, I put the subfloor down right away to avoid having to walk on the insulation. Half inch thick plywood did the trick here. Again the old van floor was a great template. To locate the holes for the bolts here, I used the same method as before except I laid the plywood down in place and hit it with a mallet over the studs to leave an indentation where the hole needed to be. I then removed it and drilled out the holes. I glued the plywood to the insulation for added prevention against warping and squeaks – again, overkill probably. One note, I didn’t glue down the rearmost piece of the subfloor at this time, as I knew I wanted to be able to take it out while building the bed platform / gear locker.

The last step here was to put a vapor barrier over the denim insulation (the Polyiso is closed cell and impermeable, so doesn’t need a vapor barrier). I used 4 mil Poly and held it to the ribs with – you guessed it – 3M Super 77. I didn’t bother putting vapor barrier over every little spot, as some areas don’t lend themselves well to this (like the headliner). I’m guessing it will be ok.

That’s it! Now the van will stay nice and toasty, and is a heck of a lot quieter driving down the road. The next step for me was building the bed platform.