The roof of a home carries a heavy burden, both figuratively and literally. It must perform equally well in a structural capacity as it does with its aesthetic impact. When the roof is tiny it is even more important to maintain this balance between form and function.
A single ridgeline with roofing at a 12/12 pitch could bare a considerable load, but would severely cut down on the interior volume. This 45 degree roof is the iconic shape drawn by children all over. A single ridgeline with a pitch of about 5/12 or 22 degrees would not be able to withstand as heavy of a load, but expands the interior volume significantly and also allows room for the addition of extra windows to let in more light. I chose to design Arborion with a split roofline. In this way I gain some of the benefits of each roof pitch while minimizing their individual down falls. On the plus side I gain the strength and simple appeal of the steeper roof pitch on the ends of the house and stay away from the caboose-look that a continuous low pitch would create. I also gain the interior volume in the center of the house and part of the sleeping loft where I can use it most. This gives the small space a much larger feel. While the split roofline is a more complicated build, I feel that of the many options and arrangements I’ve considered, this is the best of all worlds for me.
Although it is important to minimize weight on a trailer foundation, I want to be sure that the roof is well-built to the best of my ability. Special attention was given to make sure that the rafters all line up with studs in order to better transfer the weight through the single 2×4 top plate. There will be a combination of hurricane straps, ties, and custom plywood cutouts to tie the rafters securely to the walls and connect to the ridge.
The roof will be vented with openings in the soffit. A channel will be created between the plywood of the roof and the 2″ rigid insulation. The specialized rigdecap allows venting through an air-permeable butyl membrane while keeping out rain.
Here are the roof layers from outside inward:
1. Metal roofing
2. 30# Tar paper
3. 3/4″ plywood
4. Structural grade 2x4s
5. Air channel for venting
6. 2″ rigid insulation (R13)
7. 1/2″ maple plywood (interior ceiling)
Next up – Back to the 3D Drawing Board
I will discuss 3D computer models and physical scale models and the advantages and disadvantages of each.