How difficult is it to wrap a house properly? Judging by the mistakes routinely found, it’s harder than you might think. Even some veteran builders get it wrong, which is a shame, because all it takes is a bit of attention to detail.
Why does it matter? Essentially, housewrap is a home’s first line of defense against air infiltration. In addition, it is a crucial layer for protection against moisture damage.
Why use housewrap? Consider these top three reasons:
1) It sheds bulk water that has penetrated through the façade.
2) It allows water vapor to pass through so the wall can dry out.
3) It retards airflow for added energy efficiency.
Many builders believe humidity problems in a house are caused by water vapor being wicked through a wall (diffusion). In reality, far more moisture enters through small holes in the building envelope. Think of housewrap as the hull of a boat. If there are holes in it, the boat is going to leak. Lots of little holes (commonplace in construction conditions) lead to big problems.
Mold, mildew, rotting window jams, drafts, and higher energy bills can result if housewrap is torn or improperly sealed during installation. Thankfully, these problems can be avoided by taking a little extra time and care.
Common Installation Mistakes
What follows is a listing of four of the most common errors found in housewrap installation practices. Getting it right the first time means a better-built house and fewer callbacks. For an illustration of correct installation practices, see “Housewrap Installation Details,” opposite page, bottom.
Mistake 1.
Start the housewrap in the middle of the sill plate, or better yet, don’t cover it at all.
Now, do it right: The bottom edge of the housewrap should fully cover the edge of the sill plate and overlap the foundation by at least 1 inch.
Mistake 2.
Tear out a hole for the windows and be done with it.
Now, do it right:? At each rough window and door opening, make an inverted Y cut (also called a modified I cut) in the housewrap. Then pull each of the flaps to the inside of the opening and fasten to the inside face of the framing. You should be able to see the housewrap inside the window and doorframes.
Mistake 3.
Any fasteners will do.
Now, do it right:? Use the proper fasteners. Plastic cap nails are best. Some housewrap manufacturers allow staples with a minimum 1-inch crown, but staples don’t create the same airtight seal..
Mistake 4.
What they can’t see won’t hurt them.
Now, do it right:? Before you put the siding on, repair all rips, tears and holes in the housewrap. Repair small holes or tears with code-approved contractor sheathing tape. Patch larger gaps with housewrap (use a 6-inch overlap and install like a shingle), then tape.
More Mistakes
A picture is worth a thousand words, and the following pictures demonstrate what can go wrong. Hopefully, this will be the last time you ever see these errors.
Mistake 5:
What we see: Look at the two tears above the window. This installer saw the top tear and tried to staple it together.
What we should see: Tape the tears and the horizontal seam; use plastic cap nails.
Mistake 6:
What we see: A housewrap seam flapping in the wind, with a 2-inch overlap.
What we should see: The top roll should overlap the bottom by 6 inches, and the seam should be taped to make a weather-tight bond.
Mistake 7:
What we see: Housewrap doesn’t reach jamb on door opening.
What we should see: Housewrap wrapped around the inside of the rough opening, so it’s visible on the inside.
Mistake 8:
What we see: The housewrap gets within 2 inches of the top of the wall.
What we should see: The housewrap should wrap up and over the top plate.