When you build a stationary home, windows just need to sit there and look pretty. When you build a Tiny House on Wheels (THOW), your windows are essentially subjected to a continuous 60 MPH earthquake every time you move.
Many DIY builders try to save money by buying standard residential vinyl windows off the shelf at a big-box store. This can be a dangerous mistake.
This guide explains why Tempered Glass is non-negotiable for THOWs and what features you need to look for to ensure your windows survive the highway.
The #1 Rule: Use Tempered Glass
If you take nothing else from this guide, remember this: Tiny homes on wheels should utilize tempered glass for all windows.
What is Tempered Glass?
Tempered glass (or safety glass) is heat-treated to be up to 4 times stronger than “annealed” (standard) glass.
- Standard Glass: When it breaks, it shatters into large, jagged shards that can decapitate or severely injure someone.
- Tempered Glass: When it breaks, it explodes into thousands of small, dull cubes (like car window glass).
Why is it Required for THOWs?
While residential building codes (IRC) only require tempered glass in hazardous locations (like bathrooms, doors, or low to the floor), a THOW exists in a legal gray area between a house and a vehicle.
- Road Debris: A rock kicked up by a semi-truck at 65 MPH will shatter standard glass instantly, spraying your living room with razor-sharp shards. Tempered glass is much more likely to deflect the rock without breaking.
- Vibration: The flexing of a trailer frame can torque the window frame. Standard glass is brittle and cracks under this stress. Tempered glass has higher tensile strength.
- DOT Standards: Vehicles are required to have safety glazing. If an accident occurs on the highway, standard glass poses a massive liability risk.
The Altitude Problem: Don’t Blow Your Seals
Most tiny houses utilize double-pane windows for insulation. These windows are sealed units filled with Argon gas.
If you build your tiny house at sea level and then tow it over the Rocky Mountains (or any pass above 4,000 ft), the atmospheric pressure drops, but the pressure inside the window pane stays the same. The result? The window balloons out and explodes.
The Solution: Capillary Tubes (Breather Tubes) If you plan to travel, you must order your windows with capillary tubes. These are tiny metal straws inserted into the seal that allow the pressure inside the window to equalize with the altitude outside, preventing blowouts.
Window Operation Styles: What Stays Shut?
Not all opening mechanisms are created equal when it comes to 60 MPH winds.
Best: Casement and Awning
- Mechanism: These crank out to open.
- Why they are safer: When closed, the latch pulls the sash tight against the frame. The force of the wind pressing against the front of the tiny house actually pushes the window tighter into its seal. They rarely vibrate open.
Worst: Single/Double Hung and Sliders
- Mechanism: These slide up/down or left/right on a track.
- The Risk: Gravity and vibration are enemies here. It is very common for double-hung window latches to rattle loose on the highway, causing the window to slide down and slam open violently.
- The Fix: If you use these, you must install secondary travel locks or cut “travel sticks” (dowels) to wedge in the tracks during transit.
Installation Tips for Road Vibration
How you install the window is just as important as the glass itself.
- Leave a Gap: Never fit a window tight into the rough opening. You need at least a 1/4″ to 1/2″ gap all the way around. This allows the wall framing to flex and twist as the trailer moves without crushing the rigid window frame.
- Use Flanges: Always use “nailing fin” (new construction) windows, not “replacement” windows. The flange provides a secure structural connection to the sheathing, which is far superior to screwing through the jambs.
- Don’t Over-Shim: Place shims only at the fastener locations. Over-shimming the header (top) can transfer roof loads directly onto the glass, causing cracks.
Conclusion
Windows are one of the most expensive line items in a tiny house build, so the temptation to buy cheap, standard glass is strong. Don’t do it.
Spending the extra ~15-20% for tempered glass and capillary tubes is cheap insurance against road accidents, shattered glass, and failed seals. Your tiny house is a vehicle first and a home second—glaze it accordingly.
Checklist: Ordering Your Windows
- [ ] Tempered Safety Glass (All units)
- [ ] Capillary/Breather Tubes (If crossing mountains)
- [ ] Nailing Fin/Flange included
- [ ] Screens included (Hard to find aftermarket sizes)
- [ ] Crank-out style (Preferred for air seal)