Why do we wrap?

If you ask most people why builders wrap a house, they’ll tell you it’s to stop air leaks. That’s true — but it’s only half the story. The other half is especially important when it comes to tiny homes.

The Chemical Problem Nobody Talks About

Modern construction materials are not inert. The oriented strand board (OSB) used for wall sheathing, the engineered lumber in your framing, and the composite materials in many siding products all contain adhesives, resins, and chemical binders — formaldehyde being the most common — that off-gas over time. In a conventional house with standard ventilation and plenty of cubic footage, this is a manageable concern. In a tiny home, where the volume of air is small and the ratio of wall surface to interior space is high, it’s worth taking more seriously.

House wrap — technically called a weather-resistive barrier, or WRB — creates a continuous membrane between your construction materials and your interior air supply. When fresh air enters your tiny home, it’s coming through intentional openings: doors, windows, vents. It’s not seeping through your walls, picking up whatever the sheathing happens to be releasing that day.

How Air Actually Moves Through a Tiny Home

A well-built tiny home is reasonably airtight, which raises an obvious question: where does fresh air come from?

The most immediate answer is the door. Every time you open and close it, you exchange a volume of interior air with outside air. So spending says on end inside your tiny home without ever opening the door is not really recommended. But it’s not very likely either.

Beyond that, cracking a window for a few minutes each day — even in winter — does more than most people expect. You’re not trying to heat the outdoors. A two-minute exchange replaces a significant portion of your interior air volume without meaningfully dropping the temperature in a well-insulated space.

For a more systematic approach, there are mechanical ventilation options worth knowing about. An HRV (heat recovery ventilator) or ERV (energy recovery ventilator) continuously cycles fresh air into the home while capturing most of the heat from the outgoing air — so you’re not just venting your warmth outside. These systems are common in high-performance homes and increasingly popular in tiny homes, where air quality per square foot matters more than in a larger space.

At minimum, most tiny homes include a bathroom exhaust fan and a range hood, both of which move air out of the home and create slight negative pressure that draws fresh air in through small gaps and intentional vents. It’s a passive system, but it works.

The Bottom Line

House wrap is one of those details that’s invisible once the siding goes on, which means it’s easy to skip or cut corners on. But the air inside a tiny home is the air you’re breathing every night while you sleep, every morning while you make coffee. Getting the envelope right — including a proper continuous WRB — is one of the less glamorous but more important decisions in a build.

At Mount Baker Tiny Homes, we wrap every build.

Mount Baker Tiny Homes builds custom tiny homes on wheels and van conversions in Bellingham, Washington. Get in touch if you want to talk through how we approach your build.