Flashing & Insulation

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!

Getting started. These are the first few pieces being attached.

We've since put the all-weather duct tape over the foil tape underneath the trailer to ensure that its all sealed.

The pups hanging out with us while we work.

Here's a closer look at a smaller area at the rear driver's side corner.

Here's a closer look at the edge of the trailer.  This is all filled with insulation now.

Finished! Foil taped, all sealed up, and waiting for insulation.

Insulation Installation

The process of adding in the insulation was straightforward and fairly easy compared to flashing. The dimension between the c-channel to fill with insulation was 2.5", so between each crossmember we installed one layer of 1" insulation and one layer of 1.5" insulation. We opted for the more expensive, but most effective rigid insulation. This material also seemed to be the easiest type of insulation to work with. The three days we spent installing insulation consisted of Mike cutting each piece to size with the table saw, while I, Jen, followed up with installing each piece in the proper place. Once I got the first layer in, I applied PL Premium to all edges and gaps, followed by a strip of all-weather duct tape to ensure that it was completely sealed. Once we were almost finished with the larger crossmember insulation installation (say that three times fast, hah!), we finally nailed down the best and most effective cutting method of insulation.  Cutting notches on all edges made for easy installation by allowing us to slip the insulation in-between the cross members and still fill up every gap, making sure it was tight in its place. Every cut was a little better than the last, and we had it perfect by the end! That definitely seems to be a trend. Once we filled in every gap, we were ready for plywood flooring!

Mike getting it done on the table saw that we bought very cheap at a garage sale.

Glueing for the top layer of insulation.

Almost done! 

This is how we notched out the edges so we could fit the insulation all way into the c-channel steel crossbeams.

We used a razor to open finish the cut so that we could fit the insulation into the c-channel.

The final product of the notched out insulation.

Jen prepping for a piece of insulation to go in.

Final product! It looks so pretty! ...but maybe that's just because we spent so long working on it.  It felt good to finish this step.

We learned a lot during this part of the build.  We learned about drilling techniques, insulation options, using a table saw, different types of glue and many other construction related things.  It's been so fun to learn about these things, overcoming small obstacles and problem solving on the fly, but we've also noticed that while working together on this big project, we're learning more about each other.  We're learning about each other in ways that we hadn't expected.  We're learning to communicate more efficiently.  We're learning to help each other avoid irrational frustration.  We're learning to argue respectfully and to work through conflicts more easily.  We're learning to love each other better and keep our focus on glorifying God through our interactions with each other and our tiny house project in general.  We're thankful for the opportunity to be spending this summer building our tiny house but we're also learning to be more thankful for this great opportunity to work on our relationship and build a foundation for our lives together, ultimately in pursuit of helping each other become more Christ-like.

-Mike & Jen