If there is one silent killer of tiny houses, it isn’t the wind or the highway vibration—it’s trapped moisture.
Many first-time builders assume that siding is waterproof. It is not. Siding is a “water shedder,” meaning it deflects most rain, but some moisture will inevitably get behind it (via condensation, wind-driven rain, or capillary action).
If you nail your siding directly to your house wrap and sheathing, that trapped water has nowhere to go. It soaks into the wood, breeds mold, and rots your tiny house from the outside in.
The solution? A Rain Screen.
This guide covers the essential details of installing a rain screen system using furring strips to ensure your tiny house dries out and lasts for decades.
What is a Rain Screen?
A rain screen isn’t a single product; it’s a system. It essentially creates a physical air gap (usually 1/4″ to 3/4″) between the back of your siding and your weather-resistive barrier (WRB/House Wrap).
This gap performs two critical functions:
- Drainage: Gravity pulls bulk water down and out the bottom of the wall.
- Drying: Air circulates through the gap, evaporating any residual moisture.
Choosing Your Furring Strips (H2)
The core of a rain screen is the “furring strip”—the batten that holds the siding off the wall. For a tiny house, weight and durability are key factors.
1. Pressure Treated 1x3s (H3)
- The Standard: These are cheap and rot-resistant.
- The Tiny House Caution: They are heavy and often come wet/warped from the store. If you use these, let them dry flat before installing, or they will twist your siding.
2. Rip-Your-Own Plywood (H3)
- The Risk: DO NOT rip standard CDX plywood into strips. The exposed edges will wick moisture and delaminate over time.
- The Exception: You can use marine-grade plywood, but it’s expensive.
3. Engineered/Plastic Battens (H3)
- The Pro Choice: Products like Cor-A-Vent Sturdi-Batten are made of heat-resistant plastic.
- Why for Tiny Houses? They are lightweight, perfect in dimension (won’t warp), and rot-proof. They often don’t split when screwed into, which is a huge plus for DIYers.
Installation Techniques: Orientation Matters (H2)
How you install your furring strips depends entirely on the direction of your siding.
Technique A: Vertical Siding (Board & Batten)
If your siding runs vertically, your furring strips generally need to run horizontally to provide a nailing surface.
- The Problem: Horizontal strips trap water. They act like little dams, holding moisture against the wall.
- The Solution: You must create drainage paths.
- The Shim Method: Place plastic shims behind the horizontal furring strips at each stud to create a gap behind the strip itself.
- The Kerf Method: If using wood strips, cut vertical “kerfs” (grooves) on the back of the strips every 16 inches to allow water to flow behind them.
- The Double Furring: Install vertical strips first, then horizontal strips on top. (Warning: This adds 1.5″ of width to your tiny house—watch your road width limits!).
Technique B: Horizontal Siding (Lap Siding/Shiplap)
If your siding runs horizontally, your furring strips run vertically.
- The Benefit: This is the easiest installation. The vertical channels naturally let water drain straight down. Align the strips directly over your wall studs (usually 16″ or 24″ on center) to ensure your siding nails hit solid framing.
The Critical Detail: Bug Screens (H2)
A rain screen creates an open gap at the bottom of your wall. Without protection, this is an open invitation for wasps, spiders, and mice to nest inside your walls.
Installation Steps:
- Install the Screen First: Before putting up furring strips, wrap the bottom edge of your sheathing with a high-quality insect screen or a specialized ridge vent mesh.
- Fold It Up: Let the screen hang down, install your furring strips, and then fold the screen up over the bottom of the furring strips.
- Secure: Staple it to the face of the furring strips. Now, air can flow in, water can flow out, but bugs are locked out.
Fastening Tips for Road Safety (H2)
On a stationary house, you might just nail furring strips. On a tiny house that hurtles down the highway:
- Use Screws: Use exterior-grade structural screws or ring-shank siding nails to attach furring strips to the studs.
- Penetration: Ensure your siding fasteners are long enough. They need to go through the siding, through the air gap (furring strip), and embed at least 1 inch into the solid stud.
- No “Floating” Strips: Never attach furring strips only to the sheathing (plywood). They must be anchored to the studs, or the wind load could rip your siding off.
Conclusion
Installing a rain screen adds a day or two to your build time and a bit of width to your trailer, but it is the single best insurance policy against rot. By using the right furring strip techniques, you ensure that when your tiny house gets wet (and it will), it has the ability to dry out, keeping your home healthy and mold-free.
FAQ: Rain Screen Details
Q: How thick should the furring strips be? A: A minimum of 3/8″ is required for drainage, but 3/4″ (nominal 1-inch lumber) is standard and recommended to provide better air circulation and nail holding power.
Q: Does a rain screen effect road width? A: Yes. Adding 3/4″ furring strips on both sides adds 1.5 inches to your total width. If you are building to the max 8’6″ limit, you must account for this in your floor plan design.
Q: Do I still need House Wrap (Tyvek) if I have a rain screen? A: Yes! The house wrap is your actual water barrier. The rain screen/siding is just the cosmetic skin that protects the barrier.