The exterior wall finish for our tiny home is a nontraditional cladding system known as a rainscreen. A rainscreen's most functional capacity is that it takes advantage of a ventilated air cavity to keep the building's vapor barrier and cladding system dry, reducing home maintenance and providing longevity to building materials.
We chose to install a timber rainscreen on our tiny home for primarily aesthetic purposes. We wanted to ensure that the cladding system on the tiny home gave it texture and was appropriately proportioned to its size and scale. Wood was a natural option, as we could be very explicit in dictating its dimensional size. We chose to use very thinly proportioned wood planks, oriented vertically, in order to give emphasis to the vertical proportion of the home. Also, if we had gone with a horizontal orientation, the planks at the high side of the mono-pitch roof would have terminated awkwardly.
While cedar is possibly the most expensive hardwood we could have chosen for our rainscreen, we knew it would ultimately be the most cost- and time-effective in the long run. Cedar's natural properties make it inherently pest- and weather-resistant, meaning that we could install it untreated and it would last for decades with no maintenance.
Our original intent for the cedar was to torch it using the ancient Japanese method of shou sugi ban. Burning the wood makes it pest- and weather-resistant, but more importantly for us, would give the home a sleek, sexy, and unique modern appearance to the whole home. Unfortunately, however, the shou sugi ban method is incredibly time-consuming and delicate. As time progressed and the finish date for the home kept advancing further into the future, we made a tough, critical decision to not torch the wood and instead, let it weather a soft, cool grey over time. While disappointing, nothing functional was compromised, and the grey weathered cedar would still fulfill our broader aesthetic intent.
We chose to go through a local lumber yard to source the cedar for our exterior rainscreen. They agreed to plane and strip the planks down for us to our custom .75" x 1.5" dimension, all 2000 8'-long pieces. That's 10,000 linear feet, folks. While it cost only a small amount more to have this done, it saved us days, if not weeks, of time and tedium (and potential error).
In a rainscreen system, the cladding finish material never touches the massing of the home directly; a series of battens (in our case, 1" x 3" lumber) separates the exterior sheathing and weather barrier from the cladding finish, which creates the ventilated air cavity. For both vertical and horizontal timber rainscreen systems, battens should be installed approximately 24" apart - this is adequate for both structural and ventilation purposes. You'll notice in the photos above that on some walls the battens are installed with their broad face against the exterior sheathing, and their narrow face in others. This is the result of needing to disguise some exterior MEP elements behind the rainscreen, such as the bathroom fan exhaust and the mini-split wiring; if their depth was greater than 3/4", then a larger cavity was accommodated. These varying depths would not be perceptible once the cedar timber is applied.
The above image demonstrates the application of Prosoco, the fluid-applied weather barrier product, being applied also to the rainscreen battens and window flanges. The pine timber battens needed to be treated for pest- and weather-resistance, so we chose to use the Prosoco for two reasons: it is a highly effective product that we happened to have extra of, and it provided aesthetic consistency to the surface behind the cedar rainscreen finish.
As seen in the image above, our cedar was very knotty, and there was a critical concern around the timber warping over time. In order to mitigate this, we installed horizontal cedar battens every 6" so that the vertical timbers would be nailed and secured as tightly and frequently as possible. You'll notice that horizontal battens have been placed at the very top and bottom of the vertical timbers, as the end conditions are the most susceptible to warping.
You'll also notice that there is not one constant joint datum for the vertical cedar timbers; they vary in where they terminate vertically. This condition exists for two reasons: A) the cedar from the local lumber yard only came in 8'-long planks, and would require two timber pieces to complete each vertical 'line', and B) by not making the joint for the vertical timbers uniform, we prevented a potentially obvious warp datum at the end conditions of the planks, and we are able to use cedar plank scraps more efficiently and flexibly.
We chose provide a 1/2" gap between the vertical cedar timbers for two reasons: A) to reduce the amount of finish cladding material (and its associated weight), and B) to create texture and depth.