Once your tiny house is framed, you face a critical decision: How do you keep the water out and the air in?
For decades, the standard answer was House Wrap (Tyvek). But in recent years, the ZIP System (green boards) has taken over the custom home building world.
For a stationary house, it’s often a matter of preference. For a Tiny House on Wheels (THOW) traveling down the highway at 60 MPH, the stakes are different. Let’s compare the two systems.
The Traditional Choice: House Wrap (Tyvek)
This system involves installing standard plywood or OSB sheathing first, and then stapling a plastic sheet (Weather Resistive Barrier) over the top.
The Pros
- Cost: Standard OSB + a roll of house wrap is generally cheaper than ZIP panels.
- Forgiveness: If you are a messy framer, you can cover a lot of ugly carpentry with a sheet of Tyvek.
- Availability: You can buy rolls of wrap and standard OSB at any rural hardware store.
The Cons for Tiny Houses
- The “Flapping” Factor: This is the biggest risk for THOWs. If you have to move your tiny house before the siding is installed, house wrap acts like a sail. Highway winds can shred it, rip out staples, and compromise your waterproofing before you even finish the build.
- Complex Detailing: Properly taping windows and seams on loose plastic requires skill. Wrinkles in the wrap can trap water or create air channels.
- Fastener Leaks: Every staple you drive through the wrap is a tiny hole. If not covered by siding or tape properly, these are potential leak points.
The Modern Contender: ZIP System
The ZIP System is an “integrated sheathing.” It is an OSB panel with a weather-resistant coating fused to the face during manufacturing. You install the panel, tape the seams, and you are done.
The Pros
- Road Durability: Because the barrier is fused to the wood, it cannot peel or tear off in the wind. You can drive a ZIP-sheathed tiny house down the highway without siding, and it will remain waterproof.
- Air Sealing: Taping flat, rigid seams is infinitely easier than taping wrinkled plastic. This creates a tighter air seal, making your tiny house easier to heat and cool.
- Speed: You skip an entire step. Once the sheathing is nailed up, you just tape the seams. No wrestling with 9-foot rolls of plastic in the wind.
The Cons for Tiny Houses
- Over-Driven Nails: This is the “Achilles heel” of ZIP. If you drive a nail too deep and break the green surface coating, you have created a leak point. You must go back and seal every over-driven nail with liquid flash or tape.
- Cost: The panels are more expensive per sheet, and the proprietary flashing tape is pricey.
- Weight: ZIP panels are slightly heavier than standard 7/16″ OSB due to the density and resin, though the difference is usually negligible for a whole house (approx. +50-80 lbs total).
Comparison: The Highway Test
Imagine towing your unfinished tiny house 500 miles.
- Scenario A (Tyvek): You must secure every inch of the wrap with cap nails and tape. Even then, wind can get under a seam and balloon the wrap, potentially tearing it away from window flashings.
- Scenario B (ZIP): The air flows over the smooth, rigid surface. The acrylic tape (once rolled) bonds molecularly to the panel and gets stronger over time. Nothing flaps, nothing tears.
Verdict: Which is Best for DIYers?
For a Tiny House on Wheels, the ZIP System is generally the superior choice.
Why?
- Risk Reduction: It eliminates the risk of your weather barrier tearing during construction or transport.
- Simplicity: Taping seams is a more foolproof way for a DIYer to get a perfect air seal compared to the “origami” required to properly fold and tape house wrap around corners.
- Rigidity: The structural adhesive in the tape helps (slightly) with the overall rigidity of the shell, which is great for a moving structure.
Stick with Tyvek if:
- You are on a strict budget.
- You are building the house completely indoors and won’t move it until the siding is fully installed.
- You can’t source ZIP panels in your area.
Pro-Tip: The “Liquid Flash” Detail
If you choose ZIP System, spend the extra money on their Liquid Flash for window openings. Instead of using tape, you spread this goo over the window sill framing. It creates a seamless, rubber-like waterproof boot that is impossible for water to penetrate—perfect for protecting your subfloor from window leaks.