Concept
Tyvek
What it is
Tyvek is DuPont’s brand of house wrap: a synthetic weather-resistant barrier (WRB) installed over the exterior sheathing before the siding goes on. It’s water-resistant from the outside but vapor-permeable from the inside, which means moisture that does get into the wall cavity can escape rather than rot the framing. Different from plastic vapor barriers that stop moisture both ways and can trap it inside walls.
Why it matters
Wall assembly failures kill houses. Water gets in through siding gaps, through windows, through bad flashing. If the WRB is missing or installed wrong, the framing rots, mold grows, and the structural bill goes up fast. Tyvek done right is cheap insurance: a few hundred dollars of material and an afternoon of labor protecting a house worth hundreds of thousands.
Also the workaround move for asbestos siding. In a lot of markets, especially back in Colorado, Ross would leave asbestos siding in place: “You would just put plywood right over the top of it and re-wrap the house in plywood, put new Tyvek or house wrap on it, and then put new siding over the top of that. Same thing with floors, just you go right over the top instead of trying to tear the stuff out of there.” Covering is legal in most cities; removing asbestos is expensive and regulated. Tyvek over plywood over the old siding is the clean exit.
How it shows up
Install overlapping horizontally, seams taped, integrated with window flashing per manufacturer spec. This is one of the details where pro diy work goes wrong. Homeowners install it upside down, or without seam tape, or they forget to integrate with the window flashing and water pours in behind the wrap and rots the framing.
On any gut job where siding comes off, inspect the WRB. If it’s torn, aged, or missing, replace it before the new siding goes on. Small line item compared to what it protects.
On asbestos covers, the order is: plywood over the asbestos, Tyvek over the plywood, new siding over the Tyvek. You’ve now encapsulated a hazardous material legally and given yourself a fresh exterior.