Siding gets all the glory, but Trim does the heavy lifting. Corner boards, window surrounds, and fascia are the first line of defense against water intrusion. They also take the brunt of the sun and rain.
For decades, wood (Cedar or Pine) was the king. But in the modern tiny house movement, Cellular PVC (plastic) has become a top contender.
This guide breaks down the pros and cons of each material to help you choose the right frame for your tiny home.
The Contender: Cellular PVC (Azek, Veranda)
Cellular PVC is an extruded plastic that looks and cuts exactly like wood, but it has no organic fiber in it.
The Pros
- 100% Rot Proof: You could bury PVC trim in a swamp for 50 years, and it wouldn’t degrade. For a tiny house that might face varying climates, this is huge peace of mind.
- No Knots or Warping: Every board is perfect. It doesn’t cup, twist, or split like wood does.
- Waterproof: It doesn’t absorb water, so paint doesn’t peel due to moisture cycling from the inside out.
The Cons
- Thermal Expansion: This is the big one. PVC expands and contracts significantly with temperature changes (much more than wood).
- The Fix: You must glue joints with special PVC cement (like plumbing) and leave expansion gaps at the ends of long runs. If you nail it too tight without room to move, it will buckle.
- Paint Limitations: You generally cannot paint PVC dark colors (Black, Charcoal) unless you buy specialized heat-reflective paint. Dark colors absorb too much heat, causing the plastic to warp.
- Plastic Look: Even with a “wood grain” texture, it still looks a bit synthetic up close.
The Champion: Solid Wood (Cedar/Redwood)
Natural wood is the traditional choice, specifically rot-resistant species like Western Red Cedar or Cypress.
The Pros
- Paintability: You can paint wood any color you want—jet black, bright red, or clear coat. It handles heat absorption much better than plastic.
- Stainable: You cannot stain PVC. If you want the natural, rustic tiny house look, you must use real wood.
- Rigidity: Wood is structurally stiffer than PVC. It creates a more solid corner board that resists impact better in very cold weather (PVC can get brittle below freezing).
The Cons
- Maintenance: Wood moves moisture. If you don’t back-prime (paint the back side) before installation, it will absorb water, causing the paint on the front to blister and peel.
- Rot Risk: Even Cedar will eventually rot if it touches the ground or if water gets trapped behind it.
- Cost: High-quality, knot-free (clear) Cedar is now often more expensive than PVC trim.
The Verdict for Tiny Houses
Choose PVC If:
- You are painting your trim White or Off-White.
- You want a “Zero Maintenance” exterior.
- You are building in a wet/humid climate (Pacific Northwest, Florida).
Choose Wood If:
- You want dark black/charcoal trim (very popular on modern tiny homes).
- You want a natural stained wood look.
- You are sensitive to the use of plastics/chemicals in your build.
Installation Tip: The “Pocket Hole” Trick
Regardless of which material you choose, assemble your window casings (the 4 pieces of trim around a window) on the ground using pocket screws (Kreg jig). Then, install the entire square frame onto the wall at once. This ensures tight corners that won’t open up as the tiny house vibrates down the highway.