Initial Conversations

“Yack, yack, yack,” said the subfloor generic lipitor.
“Wait a minute. What do you mean?” responded Chris.
“Bolts, maybe.”
“Maybe?”
“Sure.”
“Have you heard of steel hold downs? What are they?”
“Ya, ya, all the time. They’re steel. They hold down stuff, ya idgit.”
“I give up.” Chris concluded.

Thermodynamic Obscenities

Common sensibly, fastening your house to the trailer needs to be well engineered and figured out.  After consulting countless tiny house builders’ experiences, I found 2cycle2gther’s article and the Tiny House Blog’s Phase 1: Subfloor Sandwich System to be extremely helpful.  Although we wanted to incorporate that precious 6 inch space between the steel trailer’s framing members, Michelle, a building science graduate student, informed me that steel framing (studs) destroy your insulating capacities where you’d want it: under your toes in the winter. Joe Lstiburek, building science guru, states, “insulating between steel studs is a thermodynamic obscenity.” Because there’s no way to fully enclose the trailer’s hitch from the elements, the trailer frame space wouldn’t be a part of our subfloor.

Redundancy Employed

Exemplifying redundancy, we’re combining an altered sandwich system with 2cycle2gether’s sheathing to trailer screwing as well as screwing the entire subfloor to the trailer with Teks #12 (wood to metal 2 3/4 inch screws). We will also weld 16 bolts to the trailer to hold down the sill plate and entire subfloor to the trailer.  No chances have been taken! Why choose some approaches when you can employ every single one?

Longest Sandwich Creation of My Life

Bottom Bun: Galvanized Steel Flashing

The bottom bun of our subfloor is galvanized steel flashing (seemed like the stronger and better option than aluminum although it was a little more pricey). As I understand it, the flashing will keep out insects and provide some water protection. You can skip the flashing and paint the 3/4 inch plywood layer with a strong and nasty marine grade of paint…if you’re into nasty.  What’s strongly stated with flashing types is aluminum reacts poorly to the chemicals used in pressure treated lumber. Our bottom T&G 3/4 inch plywood is treated, so aluminum was a no go; however, galvanized steel isn’t flawless according to the web, so for safety, we used tar paper in-between the plywood and flashing.  As always, better safe than sorry.

Portobello Slider: 3/4 Inch T&G Plywood

The 3/4 inch tongue and groove provides a lot of structural integrity. Having it or one side of it treated supplies extra durability if water penetrates.

Tomatoes and Pickles: Glulams and Foam

On top of the 3/4 inch plywood will be the framing of the subfloor. I will use homemade glulams and 2x4s and glue and screw them to the 3/4 inch plywood underneath. Additionally, 90 degree steel hold downs will secure everything to everything. Insulation will be foam boards–and all remaining seams will be spray foamed in. I’ll use 16 inch on center joists–this may be a waste of wood–but I’m playing all of my structural integrity cards.

Top Bun: 1/2″ plywood

On top of the framing will be only 1/2 inch thick plywood. Because the insulation is rigid, 3/4 inch plywood on top wasn’t necessary. All seams and joints will be caulked or siliconed for top notch air sealing (one of the most important, if not the most, energy efficient measures for a house).  This plywood layer will be glued and screwed to the framing.

Side of Chips: The Welded Threaded Rod

Choosing the way to bolt the trailer was stressful. We didn’t use bolts because our steel is 6 inches thick and the subfloor was 6 1/2 inches; buying 13 inch bolts would have been expensive; however, it’s a good way to prevent welding cost (unless you weld them yourself–threaded rod is cheaper). We placed the bolts in obvious spots: corners, near the wheel wells, and in-between those areas. We decided to weld the bolts (threaded rod) for added strength. We’ll use Simpson’s HTT5 hold downs with the bolts, so that’s a huge cost in itself. Although on a tight budget, these were the areas we wanted to spend our money.

Future post will have detailed specifics on each of these sandwich steps. Yum, yum.

The reins are ours,

Chris

Helicopter Lumberer

The lumber yard delivered our wood for free, but before they did we wondered, “Should we go and inspect every piece of wood and pick up the lumber?” Our answer was yes…until we decided no.  Because we’d have the option to return pieces of wood, we felt like it wasn’t necessary to inspect everything. As the lumber yard clerk assured me, “We don’t sell wood to have it returned.” That being said–horror lumber delivery stories are out there.

Figuring Out the Count

I used our Tiny Tack House plans to make adjustments and estimate all of the lumber that we’d need. Their plans list the amount of boards and sizes that you’d need, but we have changed a few things and our trailer/floor will be a different size (22 x 8.5 ft), so it was a little work to figure everything out. Obviously, it’s smart to add a few boards on to your total estimate, anticipating miscalculations and warped wood. Lumber yards could lend you a hand figuring everything out, too.

For our planned 22 x 8.5 ft trailer and house, our final lumber count was the following:

Construction phases and wood original estimates (these changed):

Zip System Contemplation

We considered using the Zip System for our wall and roof sheathing; it would have been $330 more up front. Although more expensive, people claim the system actually saves you money and time from wrapping your house. We will spend $150 on Grace: Ice and Shield roofing underlayment and $120 on our house-wrap. This means we’ll only save around $60, but yes, it will take more work to install the underlayment and house-wrap; however, we’ll ultimately have better roof protection; the Zip System claims to eliminate felt paper whereas we’ll have a strong sticky underlayment.

Toxicity, Zips, and Regrets

Although Oriented Strand Board (OSB/Zip Panels) are generally cheaper and structurally as durable as plywood, they have more glues that off-gas, so more formaldehyde would be seeping into your house.  This was the main reason we chose the less but still “formaldehydy” plywood. Although plywood is not perfect, it does handle moisture a lot better than OSB. Tiny House Builder Ryan Mitchell chose the Zip System for his house, so check out his reasoning here. Upon further discovery, I have found non-formaldehyde plywood by Purebond and other companies. Thankfully, less toxicity is becoming more popular.

Save to Splurge

Instead of buying 4x4s (expensive), we will be sistering 2x4s for stud uprights (putting two together with screws) and creating glulams for the subfloor’s perimeter (two 2x4s and a strip of plywood glued and screwed together). This saved us $180. We used this money to splurge and instead of using 2x4s for the loft beams, we’ll have beautiful 4×4 cedar beams ($250 more). What will your save to splurge ratio be?

Doug from Liverpool Lumber

The delivery of our lumber was an emotional stew; throw in excitement, nervousness, anticipation, and disbelief and you get these tiny house builders. Our house was truly in motion! Was our preparation enough? Is everything figured out? It doesn’t matter–time to build.

Reflections, Hindsight, and Alterations:

• Thank the tiny house gods I added ten extra 2x4x8s and a few 2x4x12s. We used them all and miss-cut a few.
• Quite a few warped boards, but we found a place for them.
• Had to buy another cedar beam for $78. Ouch.