Wrapping the House: Do's & Don'tsInstall it right, and housewrap
works well to keep water out;
lap it wrong, and you're better off without it
To some extent, houses have always leaked. But in recent
years, using new materials like panel sheathing, housewrap, and
flanged windows, we've tightened up construction to the point
that houses no longer dry well. During the same period, there's
been a decline in traditional methods of carpenter training.
One result is that houses are going up without proper attention
paid to building paper and flashings. Once these new tight
houses leak and the insulated framing cavities get soaked,
they're more likely to stay wet and rot than the airy,
"breathable" houses of the past.
In more than 20 years of building, repairing, remodeling,
and inspecting homes, I've found that even the most critical
flashing details are often installed wrong or overlooked
altogether. These errors are common to expensive custom homes
and inexpensive modular houses alike. Often, it's evident that
the carpenters made a conscientious effort, yet still the
details are wrong.
Again and again, flashing and papering mistakes come back to
one overriding principle: Get the layers right so that water
flows out on top, not behind, the housewrap and flashing. A
second important principle: Don't rely on the siding to stop
the water. I tell customers that the purpose of siding is to
look good, and that, yes, it sheds most of the water off the
house. But it also lets water past it, so the backup system of
housewrap and flashings must deflect that water and allow it to
weep or drain back out from behind the siding before it soaks
the sheathing and framing.
Materials of Choice
Tyvek and Typar interchangeably (my carpenters tend to prefer
Typar because it's quieter and easier on the eyes.) Properly
installed, we get good performance from either material.
The housewrap debate.
There is some research that indicates that housewraps don't
perform well when they're subject to persistent wetting.
However, in my inspection work, I've never come upon a
situation where there was rot behind housewrap that I couldn't
trace to a water intrusion higher up - for example, a roof
leak, a rip in the housewrap, a backwards lap, or a missing
I don't claim to have seen everything, but it's my strong
opinion that if you get the details right, the brand of
housewrap you use is not important. If you just can't bring
yourself to trust housewrap, use tarpaper - it's been around
for a long time and still performs well.
Eaves membrane. Any areas
subject to a lot of moisture - splashback zones, areas below
intersecting roofs that dump accumulated rainwater, or tall
beachfront houses, for example - can benefit from extra layers
of tarpaper or self-sticking eaves membrane (commonly referred
to on the job site as "bituthene") in addition to the
housewrap. Just make sure that wherever you use it, the top
edge of the membrane or tarpaper is behind the housewrap
For the 36-inch-wide rolls of bituthene, we use one of
several available brands, including Grace and Certainteed. For
the narrow flashing rolls, we prefer to use Grace's Vycor.
Although this stuff is very sticky, it adheres best to clean
surfaces, and sticks poorly to dirty housewrap.
Get a brake. If you're
serious about keeping water out of the houses you build, you
should invest in a metal brake and learn to use it. With a
brake and a roll of coil stock on hand, we can bend the
necessary flashings as we go, and not have to rely on a roofer
or metalworking sub who may or may not be at the site when we
Don't rely on chemistry.
Don't substitute the stickiness of bituthene for proper
layering. The same goes for housewrap tapes and caulks. In
time, chemical bonds can break down, but properly lapped layers
will not move.
Sequence Is the Culprit
The photos that follow illustrate common leak spots that occur
from installing housewrap improperly. Some of these mistakes
result from nothing more than carelessness. But a root cause of
many problems is the construction sequence that's common on job
sites today: The frame gets sheathed and wrapped, then
everything else - doors, windows, decks, and flashings - gets
put on top. Immediately you have a layering problem - unless
you do something about it.