Aluminum Flashing Attachment
We began our first day of construction with much anticipation and a carefully thought out plan for what our first few hours of work would look like. We were quickly faced with halting obstacles, unanswered questions, and quite a bit of cluelessness.
Let's take a few steps back. When considering the beginning steps of the build, the first decision to be made regards the subfloor. Most tiny house builders choose to build their subfloor frame with 2x4s, similar to the way houses on foundations are built. We, however, opted to use our steel trailer frame itself as our subfloor. Using our trailer as the subfloor allowed us to gain a few inches of headspace, save money, be more weight efficient (our trailer is rated for only 10,000lbs), as well as save the time it would take to build a separate subfloor. We were able to do this because we designed our trailer with the cross-members flush with sides/edges, as well as spacing cross-members every 16".
The first step of our build was to apply aluminum flashing to the trailer. The flashing (sheet metal) is meant to keep small critters out from under the trailer, as well as serve as the first barrier to water and insects. Because we used the trailer frame as our subfloor frame, we couldn't put the flashing on top of the trailer as most tiny house builders do. We needed to flash underneath the trailer to allow room for insulation between the steel crossbeams below the top of the subfloor. This meant crawling underneath the trailer to attach the flashing directly to the underside of the trailer. Jen assumed this difficult/unglamorous job because she's a stud and also because her fingers are small enough to hold the screws while hammering.
Initially, we tried using self-tapping screws to attach the flashing but quickly realized that the 1/4" steel C-Channel Tubing was too hard to penetrate using the self-tapping screws we had. This was our first obstacle. Our solution, then, was to drill pilot holes in the 1/4" steel. We bought a couple of 1/8" drill bits and went at that trailer frame with blind aggression. I should note that I, Mike, took on the task of drilling the pilot holes while Jen had the more difficult job of cutting, placing, and attaching the aluminum sheet metal flashing. I didn't do much research about drilling through steel before I started. I mean, I read the back of the drill bit package noting that when drilling though metal, one should spin the bit at a higher RPM than most other materials. The first hole went well. The bit sunk into the steel frame slowly but effectively, eventually cutting through after about 5 minutes. Drilling the second hole was much less successful. It took a more strenuous 20 minutes of rigorously pushing the bit (now dull due to improper use) into the steel at full speed (~1300 RPM). I drilled these first two holes while laying under the trailer, pushing the drill upward. My arms hurt from pushing continuously for those few minutes but once the second hole was done, I tried putting a screw into one of the pilot holes only to break the head off while tightening it. Frustrated, I tried to remove the shaft of the screw to no avail. All of that miserable drilling with nothing to show for it but a couple of holes, one of which I had just rendered useless with a broken screw. This was during the late morning when there's no shade over the worksite and the temperature climbs rapidly. I thought of all the drilling I'd be doing from underneath the trailer. I quickly and angrily deduced that if one hole takes 20 minutes to drill, it'd take me a lifetime to drill the rest of the ~200 holes necessary to attach the aluminum flashing. Hot and irrationally frustrated, I went inside to report the hopeless situation to Jen. She was ready to solve the problem and eventually after researching steel drilling techniques, we realized that I'd been doing it all wrong. When drilling through steel, or any hard metals, one should spin the bit slowly and put little pressure on the drill, allowing the bit to work under its own cutting power. I was pushing hard and running the drill at a high RPM, the exact opposite of what I should've been doing.
Once I'd formed a game plan for more effectively drilling the pilot holes, I began again, this time using cobalt tipped drill bits, a lower RPM, cutting oil, and very little pressure on the drill. It worked like a charm! The bit stayed cool due to the reduced friction of the slower speed and the lubrication of the cutting oil. I also decided to drill downward from above the trailer instead of upward from underneath. The holes were at an angle due to the shape of the steel beams but the added difficulty of screwing in the screws from underneath was worth the added ease of drilling from above. Once I got into a groove, I was able to drill each hole at an average of about 5-7 minutes and only going through 6 bits in ~200 holes. Success!
I drilled the pilot holes while Jen slid under the trailer to attach each sheet of aluminum to the trailer after cutting each length of flashing to the correct size. We worked in the cool of the morning, broke during the hot noontime hours to research/plan for future building stages, and resumed working during the afternoon when the shade made working in the high temperatures bearable. This is how it went for 4 days until we finished flashing the whole underside of the trailer. Then, we taped every crease and overlap with a layer of foil tape and another layer of all-weather duct tape. After we'd sealed it all up, we were finally ready to lay in the insulation!