There does not appear to much out there on the interwebs documenting window installation into a box truck with aluminum studs and skin. Therefore, I am attempting to document my build to a deeper level of detail.

First, here is the finished result:

Background

My truck uses aluminum Z-purlin studs which are riveted to the outer skin. They do not appear to be carrying any load from the roof and purely stiffen the outer wall. However, they are really flimsy without the inner plywood sheathing and will deflect in/out without much force and will very easily twist along their axis.

For windows, I ended up settling on surplus frameless type windows off of ebay. I like the frameless windows because they can be left open while it is raining, and give a clean look. Unfortunately, they do not let in as much airflow as a slider window would have.

These windows install from the outside and have an inner ring which clamps the window’s outer flange onto the wall. This appears to be pretty common for RV windows and there are plenty of youtube videos covering the installation into a preexisting hole.

This window measures 16×18 inches and doesn’t really fit well between the studs in the truck. I also would rather it be moved over a bit from what will be the bathroom wall. This meant that I would be needing to cut through one of the studs in the wall. Also the window really needs a stiff surface to clamp onto that will ensure the outer flange of the window is sealed against the skin. These factors meant that I cannot merely cut a hole through the wall and poke the window through without creating some structural issues.

Installation

Before getting to the window installation I had already torn out what was the desk, moved the drawers, and pulled off the plywood sheathing. After much contemplation I decided to recycle some of the plywood strips that had been pulled out for the frame.

The frame was fashioned so that the plywood layers were perpendicular to the sheathing. this offers the greatest stiffness to the wall deflecting. The 3/4 inch strips were already doubled up and magically were the right width to match the thickness of the wall.

The frame was cut so that one end would slip under one Z and over the other Z. After fit testing the frame it was painted with primer to increase the water resistance.

Painting frame to help with ingress Lift gate makes a great standing table to. Here you can see the frame construction and relation to Z purlins

I spent some time optimizing the vertical location of the window so that the remaining rivets did not interfere withe the outer flange of the window

The interfering stud was cut back to be snug with the outside of the frame using a sketchy body panel saw from Hazard Fraught Tools.

The cut does not go through the skin and cutting the part of the Z purlin flush with the skin was done by hand with a hack saw blade and completely a pain in the ass…

I’ll have to find something better for the other windows. I was then able to drill out the rivets and pry off the section of purlin in the way of the window.

After a couple fit checks, the opening in the skin was marked and cut out using my jigsaw. With the holes cut, the skin is very floppy.

Oh yeah….Since the water heater is also in the kitchen area I had to make this opening as well. The frame was similarly constructed except it does not cut through any studs.

Holes Cut! Yep its a hole Outside view Frame in, beer break Close Up of frame attached right before inner sheating

The frame was a snug fit and it was first glued to the skin with a construction adhesive. Next, three inch angle brackets were screwed in to tie the studs to the frame. Then, I filled the wall with insulation. Wiring was run for the plumbing systems. Lastly, the inner sheathing was cut to match the window opening. The sheathing covers the entire opening area and really stiffens the structure of the wall.

At this point of the construction it is getting early, so things start getting less documented

I installed the window into the opening using butyl tape to seal the outer flange and #6 self drilling screws to attach the inner clamp ring to the window. This is also when I discovered the water heater opening was slightly undersized. At that point I decided fuck it, and installed the water heater from the inside. If I ever have to pull the water heater out then I will have to remove the Styrofoam insulation…oh well.

After letting the window sit for a day so the extra butyl tape could squeeze out I cut off the extra and applied silicone around the lip. I also had to trim the water heater cover to fit around the rivets before gluing it on.

Other Bits

The windows I purchased from tristatesurplusllc are 16×18 and 48×22. I was really skeptical of buying windows from someone in Wisconsin and having them shipped to Texas. These guys did a great job packing them and the windows showed up fine and quick. Compared to the other options I was looking at they were very cheap.

The 48 inch windows are going to cut through at least 3 studs and will not allow a single piece of sheathing to span on the inside. So, I am going to have to use a different method to frame them in I think. Still mulling that one over.

Another thing I did was to drill a small hole in the window frame and run wire for a future switch that will indicate if the window is open/closed. Because the windows open out, they do not like to be open at highway speeds.