Main Floor Framing and Sheathing

Marc Bilodeau/ Building, Tiny House

With the subfloor complete, the next major step in construction is framing the main floor. This is certainly an exciting part of the project because it is starting to look like a tiny house.

The main floor in this tiny house on wheels consists of the bathroom, kitchen, and great room.

A drawing of the main floor of my tiny home
A drawing of the main floor of my tiny home

Although there are some minor changes to this floor plan, the layout of where the bathroom, kitchen, and great room areas remain the same.

Scope of Work

[more photos of this process]

Like the subfloor, it was easier to break down the job into smaller tasks. This insures each step is completed properly and accurately. The steps for this phase of construction are as follows:

  • Build and raise the wall in sections
  • Framing the main floor windows and doorway
  • Bolting it all together
  • Adding a header
  • Constructing the loft floor
  • Reinforcing the main floor framing
  • Sheathing the outside
  • celebrate!

Build and Raise the Wall in Sections

Although this is jumping ahead and showing the main floor nearly complete, it demonstrates how each wall is constructed in sections and assembled together.

different phases of tiny house rough framing of first floor
Demonstrates raising the main floor in sections

All rough framing is 2″ x 4″ x 8′ (38 mm x 89 mm x 2438 mm) studs. The main floor height is 8′ (2.44 m) from the floor to the top of the wall frame. The overall construction of the main floor took several days.

After the walls were partially raised, it became obvious that two tarps would be needed instead of one. However once the roof and sheathing are installed, one tarp will only be necessary until all the windows and doors are installed.

Framing the Main Floor Windows and Doorway

Before the framing of the window begins, it is important to know the rough opening measurements of the windows. This information is usually on the packaging of the windows.

Each of the 6 windows on the main floor in this tiny house contains the same basic elements that support the window in the wall frame.

Window Framing Method
  • The header is two 2″ x 6″ (38 mm x 140 mm) studs that go across the entire length of the window opening.
  • The header supports are two 2″ x 4″ (38 mm x  89 mm) studs that support the header. Between the header supports is where the window will be installed. The area between the header supports is the rough opening measurements of the window. It’s important to know those measurements before framing the windows.
  • The footer is two 2″ x 4″ (38 mm x 89 mm) studs that measures the same width as the rough opening of the window.
  • The footer supports are three 2″ x 4″ (38 mm x 89 mm) studs that support the window.
Windows showing headers and footers. Door showing header.
(Left) Door frame showing header. (Center and Right) Windows showing headers and footers

This construction takes pressure away from the window. When windows are under pressure, they can be difficult to open and close. Even worse, they can crack.

Bolting it all Together

Structural support is an important element to this stage of construction. Bolts are holding the walls to the trailer flange and the corners of the framing to each other.

Bolting the Frame Together
Bolts secure the walls to the frame and wall corners to each other

In total, eight bolts hold the frame corners together and fifteen bolts hold the frame to the trailer flange.

Adding a Header

The header is 2″ x 4″ (38 mm x 89 mm) studs that overlap the entire perimeter of the first floor framing.

Demonstrates how the headers install over each other
Demonstrates how the headers install over each other

When installing the header, the seams where the frames join together should never end at the same point. This provides additional support and helps hold everything together structurally.

Constructing the Loft

The loft is 6′ 8″ (2.03 m) from the subfloor. By lowering the roof height in the kitchen area, it provides additional head room in the loft itself. Like the floor and frame corners, carriage bolts are installed at each loft joist where it meets the wall frame.

In a few cases, a shim fits between the frame and loft joist in order to keep the frame joist exactly the same distances on both sides of the tiny house. This is critical to preserve structural integrity.

Bolts provide additional support for the loft joists
Bolts provide additional support for the loft joists. A shim fits between the frame and loft joist (right)

Make sure the loft joists do not stick out beyond the wall frame. Even the slightest amount will prevent the sheathing from fitting flush against the wall frame.

Reinforcing the Main Floor Framing

At this point, the entire main floor framing is reinforced with bolts attaching the frame to the trailer flange and at the corners of each wall where the frames meet. However for tiny houses that travel, it’s a good idea to add as much reinforcement as possible. Metal strapping is a good solution.

Metal Strapping reinforces the main floor framing
Metal Strapping reinforces the main floor framing

The metal strapping attaches to the base of the frame and angles up and over each corner of the wall frames. A nail holds the strapping in place at each frame stud. This helps keep everything together, for example, in case a sharp turn or jolt when moving the tiny house around. It is a minor expense that provides more piece of mind.

Sheathing the Outside

The outside sheathing uses ZIP System®. The original plan was to use standard OSB plywood and Tyvek House Wrapping. However after researching different options, ZIP System provides an all in one solution to sheathing in one panel for both walls and roofing. Flashing tape rolls easily over the seams and a rubber roller makes sure the adhesive sticks properly.

ZIP System Panels and Sheathing
ZIP System Panels and Sheathing

The toughest challenge in applying the sheathing is making the proper cut around the fender. Using a template helps determine the necessary cut for a snug fit.

Template for Sheathing Around the Fender
Cardboard Template for Sheathing Around the Fender

After the initial cuts, small trimming and adjustments were made to get the sheathing to fit properly. Before the two panels around the fender are nailed into place, Garage Door Bottom Seal Vinyl Replacement (RV9) is placed between the ZIP System Panel and the Fender.

The garage door bottom seal is cut in half the long way and tucked between the fender and wall frame. One 10′ (3.05 m) package is enough to do the job.

Seal between fender and sheathing
Seal between fender and sheathing

Celebrate

After 38 hours of work between two people, the first floor framing and loft floor is complete. With each milestone make sure to take the time to reflect and celebrate the work and treat any friends and family for their efforts.

The Complete Frame without Loft Floor

[more photos of this process]