I clad the exterior of the tiny house with red cedar, stained blue, and installed over a rainscreen gap to maximize its lifespan.

Cedar

I like the look of vertical wood siding - so that’s why I did that. Red cedar is a durable choice of wood species, as it has a high natural resistance to moisture, warping, rot, and insects. You can pay more to buy “clear” cedar with no knots, but I opted for knotty cedar as I prefer the look and it saves money. Win win.

Choosing a finish

There are many options for finishing Red Cedar (described in detail here). The choice boils down to a tradeoff between showcasing the natural beauty of cedar and providing longer-term protection against the elements. At one extreme, leaving cedar unfinished gives a totally natural look and relies completely on the weather resistance of the wood. But, while cedar may be more resistant to the elements that many other wood species, it will eventually degrade over time, and any sort of finish will extend that time. The most protective finish is paint, which completely hides the natural wood color and some of its texture.

I ended up between those extremes, choosing a solid stain - which offers a lot of protection from the elements but doesn’t obscure the texture of the wood. Cedar boards come with a rough side and a smooth side. I installed the cedar with its rough side out, which provides a much stronger adhesion for the stain for a more durable finish.

I’ve read conflicting accounts about whether primer is necessary before painting the rough side of cedar with a solid stain. It seems priming is a must if one wishes to stain with a light color, because woods like cedar have tannins that bleed darkly. But since I’m finishing with a dark solid stain, and cedar is already a durable wood, and because the Behr stain instructions state no primer needed, I skipped the primer and applied the stain directly. The stain still looks great one year in.

I stained both sides of my cedar boards before cutting, then stained the cut edges as I cut and installed them.

What’s a rainscreen gap?

A rainscreen gap is an air gap between the sheathing of a building and the exterior siding. It vastly improves the drying speed of the siding in a couple ways:

1. The gap pulls air through via the stack effect which speeds drying.
2. The gap allows water to drain and prevents wicking water up between the sheathing and siding.

Keeping the sheathing and siding dry prevents moisture damage and rot so your house lasts longer. There’s a super in-depth article on rainscreens on the Green Building Advisors website.

Here’s a side-view diagram of rainscreen gap. The top is open to air, but protected by the small eave to ensure water doesn’t flow into the gap.

Installing the fascia boards to protect the rainscreen gap

Guarding against moisture damage is a good idea in any situation, but it’s especially important for this tiny house. I designed the structure with no eaves to maximize the interior space while obeying the size constraint of a road-legal trailer (8.5’ in most states) and to minimize wind updraft forces on the roof during transport. The downside to no eaves is that the siding has no protection from rain. The siding will get wet relatively often, so it needs to be able to dry out quickly.

I used 3/8” thick plastic CedarVent furring strips from to create my rainscreen gap. They are corrugated so they still allow water and air to pass through when installed horizontally. I got some with an attached mesh to serve as the top and bottom strips to keep insects out of the gap.

Cedar Siding Installation

I attached the tongue and groove cedar by blind nailing with 2” 16-gauge stainless steel fasteners. I used a 16” O.C. fastening schedule (through each furring strip), plus 3 more spaced in between. I added those extra nails because aren’t regular studs in a SIP wall for the fasteners to bite into, only the outer 1/2” OSB skin.

Installation was generally straightforward and repetitive gruntwork. The only trick I had to develop was planning ahead to ensure the board joints ended up in the right place relative to the edges of windows and walls. Without this trick you end up with board edges that are not flush with a window, or are too thin so they splinter while working with them. There is about 1/16” of wiggle room when seating the tongue into the groove at a joint. Adding that wiggle room across a number of boards ahead it’s possible to control when the joint lands.

Install videos

Part 1. Part 2. Part 3.

Interface with windows

I installed my siding around my windows and doors without trim because I like that simple look. The siding easily clears the nail fin of all my windows because of my rainscreen gap. I left a 1/8” gap between the edge of my siding boards and the windows, which I caulked to prevent rain water from flowing from the outside of the siding into the rainscreen at the windows.

I didn’t keep precise track, but the whole process boiled down to about 10 full days of labor: staining, cutting, and installing (and re-cutting + re-installing pieces I messed up). I spent $2000 on cedar and $370 on the CedarVent strips to create the rainscreen gap.