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Tiny House Subfloor: Flirtatious Beginnings: Wood Meets Metal

T&G: Tangible and Gnarly Plywood

After receiving our lumber, the plywood and wood needed to be acquainted, so we left the plywood on the trailer for a week to see if they liked each other…any gullible readers? I hope so. The first step was to correctly cut and lay out all of the plywood on the trailer without the obtrusive bolts complicating things (I’ll weld them on later). I mapped out two ways to lay the plywood efficiently. I did this before purchasing the lumber to help calculate my plywood count.  I ended up using a slightly adjusted “longitudinal” approach to make sure the plywood seams ended up on the trailer’s metal joists.

Trailer Dimensions:

Trailer Schematic
Trailer Schematic

Orientation Option 1:

tandg plan
Lateral Option

Orientation of Plywood Option 2:

Longitudinal Option

Confession: Permit-less Punks

If your trailer is a typical eight foot wide one, it’s a lot easier to lay out your plywood. Our trailer is wonderfully and awkwardly eight ft, four and 3/4 inches. With our roof overhangs we will be pushing the state’s limit of 8 ft, six inches. Because we rarely plan to move the house, we’re comfortable with pushing the width limit to gain as much interior space as possible. Will this “inch pinching” decision come back to haunt us? I hope not, gulp!

The Beginning of Endless Wood Cuts

Ignoring 100,000 demanding future cuts for the house, I emphatically engage with the initial large and heavy plywood puzzle.

Tools:

  • Circular Saw and Jigsaw
  • Powered Drill with Your Bolt Size Bit (5/8 in) *A little bigger
  • 4 ft and 2 ft Square
  • Cutting Guide with Clamps

Plywood Puzzle
Plywood Puzzle

Jigsawing the Wheel Well
Jigsawing the Wheel Well

It fits!
It fits!

Turmoil Already

Unbeknownst to me, after the wheel wells–the trailer starts to taper as you approach the angled hitch area! So, it wasn’t square and flush with my plywood’s factory edge pieces–which was really throwing me off. I thought the whole trailer might be out of alignment and warped. Panic anyone? Because my glass is half full, the trailer tapers only a half an inch on each side gradually over the last four feet–not so bad, so instead of moving the whole house’s frame inward, I tossed the dice, letting it hang over (the bottom plate will still be 85% on the steel frame and bolted to it). Surprisingly, the turmoil led to an idea.

Inch Pinchers Become Foot Pushers

“This overhangs. Why not gain some feet in the front? Extend the overhang!” exclaimed Chris.

“Wow. The extra feet would be nice! Would it effect turning and driving the trailer?” Michelle said.

“That’s what I was wondering about…I don’t know. If we only do two feet, it shouldn’t, but I don’t know. Should we go for it?” Chris said gazing at the hitch area while day dreaming about even more space.

“Yea!” Michelle said…day dreaming about more space.

Let’s hope our space ambitions really don’t haunt us–but yes, although in all of my tiny house research I have never come across any instances or examples of it, Michelle and I have taken the risk of expanding the house over the trailer two feet. This will give us 22 ft total. The angled steel framing near the hitch is four feet in length, so we’ll still have two feet–hopefully this is enough for all turning we’ll need to do on the road.

The Dice Keep Rolling: Extending the House
The Dice Keep Rolling: Extending the House

Bolt Holes

Finally, I drilled holes where I plan to weld the bolts. Had to buy a drill bit that was slightly larger than the 5/8 inch threaded rod. Initially, I was using a 5/8 inch bit and spinning it around to make a larger hole–not something my arm wanted to do sixteen times–doubt the drill liked it either.

Always ruining things with  holes!
Always ruining things with holes!

The reins are ours,

Chris

Reflections, Hindsight, and Alterations:

  • Although the extra space will be nice–the extra width may cause a lot of problems while driving–and it makes more wood waste because it’s over eight feet. Would have enjoyed an eight foot wide trailer for its simplicity.
Categories: Building, Design

Tiny House Subfloor Design: Bottom Up! Subfloor Evolutions

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

Our Sandwich System
Our Sandwich System. Yum.

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.

More Steel!
More Steel!

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.

It fits!
3/4 Inch T&G Pressure Treated Plywood

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.

Framing Style
Framing Style
No Decomposing Insulation
No Decomposing Insulation

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.

1/2 Inch CDX Plywood
1/2 Inch CDX Plywood

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.

Threaded Rod!
Threaded Rod!

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

The reins are ours,

Chris

Categories: Building, Design

Tiny House Lumber Calculation: Living in Lumber

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.

So many minute changes.
So many minute changes.

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

Lumber Cost

Construction phases and wood original estimates (these changed):

Wood Ballparking
Wood Ballparking

Zip System Contemplation

Sheathing Options: OSB, Zip Panels, Plywood
Sheathing Options: OSB, Zip Panels, Plywood

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.

Zip Panel Cost

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

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.

Why did you put me up here? I need to poop.
“This is all the wood? Wait, why did you put me up here? I need to poop.” Charlotte

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.
Categories: Building, Design