Not that long ago, plastic housewraps like Tyvek and Typar
replaced organic felt paper as the standard siding
underlayment. Now there's a new generation of synthetic roofing
underlayments poised to displace felt paper up on the roof. To
find out whether their advantages justify their higher prices,
I recently gathered together as many of these roofing membranes
as I could find.
Along with roofing contractor Martin Elle, who's a strong
advocate of 30-pound felt-paper underlayment, I designed a
simple field test to compare roofing underlayments from an
installer's point of view and get an idea of how they
Why Not Stick With Felt Paper?
The primary job of any roofing underlayment is to keep the roof
deck dry before the final roofing is installed. Underlayments
also provide a secondary weather barrier in the event of
wind-driven rain or damage to the roofing, and they improve
Clearly marketed as replacements for 15- and 30-pound roofing
felt, synthetic underlayments have proven to be far tougher and
more durable than organic felt when exposed to wind and sun,
and they're a lot lighter. Some of them, like Tri-Flex 30, have
been around for many years, but most are relative newcomers to
the United States, if not to Europe and Canada. Distribution is
improving, but — based on my experience simply tracking
them down for this survey — some underlayments may be
hard to locate in your area.
Material. These underlayments are
composed primarily of polypropylene (PP) and polyethylene (PE),
synthetic polymers used to make everything from Tupperware to
long underwear. Some manufacturers start with a layer of
spunbonded PP, a nonwoven fabric, while others use a woven PP
or PE fabric and then add extra coatings or laminations for
better traction, UV and abrasion resistance, and other
Because most types of PE have a much lower melting point than
PP, underlayments made with PE fabrics or coatings tend to be
more temperature-sensitive than their all-PP counterparts. When
choosing an underlayment, it's important to consider shrinkage
and expansion, particularly in hot climates, since this cycling
can stress and elongate fastener holes.
a woven polypropylene fabric with a waterproof backing, comes
in black or gray. Our rolls measured 4 feet by 250 feet, but
smaller, 100-foot rolls are also available. Code compliance,
manufacturer information, and lap lines are printed on the
fabric; fastener locations are not.
While FelTex has a skid-resistant coating, I suspect that
the weave of the fabric itself contributes most to traction.
When I run my hand over the surface, it feels smoother along
the length of the roll than across it, which feels quite rough.
Also, the product feels hard underfoot, with no give to
Although I used a section of FelTex diagonally above a valley
and had no trouble walking on it, it's definitely designed to
be installed horizontally. Perhaps more important, we found
that the shiny, woven surface of FelTex won't take a chalk line
We noticed minor wicking at the laps on the mockup, with more
where the FelTex lapped over the smooth peel-and-stick
membrane. No weathering was apparent on the mockup. The FelTex
never wrinkled on the mockup or on my roof.
Some manufacturers make products in lighter colors to help
reduce surface temperatures during installation in hot
climates, which should also help reduce cycling. And at least
one manufacturer claims that because dark colors tend to show
ice better and warm up faster, black underlayments are a good
choice for colder climates.
Cost. Synthetic underlayments are
more expensive than 30-pound felt, but not prohibitively so.
Depending on variables like transportation costs and volume,
prices range nationwide from $10 to $14 per square, with one
exception (see chart). A few extra dollars may be worth it for
an underlayment that won't rot or tear like felt paper.
* Warranties are typically limited to materials only; check
with manufacturer for terms and conditions.
Don't Use Staples
It's tempting to treat these new roof wraps like housewrap. I
made this mistake at first, using 3/8-inch stainless steel
staples in my T-50 stapler to hold my first roll of
RoofTopGuard II down on a small house of my own that I was
remodeling. Contrary to the manufacturer's instructions, I also
lapped the roof wrap over — instead of under — the
On the same project, I ended up short of material and finished
off a small dormer on the front of the house with some leftover
After a couple of months of Pacific Northwest winter rain and
wind, the felt disintegrated and blew off the dormer, while the
roof wrap remained intact. I replaced the felt with Tri-Flex 30
and FelTex, and relied on these two roof wraps to protect the
dormer roof deck for the rest of the winter. By May, when we
finished roofing the house, all three underlayments were still
in good shape.
Still, I learned that these manufacturers aren't kidding when
they say not to use staples as fasteners. This isn't
necessarily because the staples will tear through the roof wrap
or pull loose from the decking; it's because water — a
lot of it — can get through the staple holes via
capillary suction, commonly known as wicking.
The problem starts when a little water gets inside the holes
and comes into contact with the slick underside of the roof
wrap and decking. Adhesive intermolecular forces between the
water and the two smooth surfaces create a gravity-defying film
that draws more water in through the holes as it spreads
outward. This happens with felt, too, but not to the same
I discovered how serious the wicking can be when I pulled back
several sections of roof wrap in search of the source of some
water leakage. Blobs of butyl caulking (compatible with
RoofTopGuard II) smeared on the staples solved the problem, but
I was glad I'd left a large tarpaulin spread out inside the
attic during tear-off, because it prevented leaks into the
living space below. Instead of staples, you should use plastic
or tin caps to hold these underlayments down.
Wicking at other locations. This
house also had a pair of low-pitched shed-roof dormers, which I
had covered with peel-and-stick membranes. I ran the membranes
up the 8/12 slope of the main roof, then lapped the
RoofTopGuard II over them. Wicking was a problem here, too,
which I solved by caulking the lap with butyl caulking, leaving
a few weep holes for drainage.
• Polyprotector UDL is a polyolefin-based,
multilaminate underlayment sold in 39 3/8-inch-wide rolls (the
shortest in our survey), each of which provides 948 square feet
of net coverage. The distinctive light-adobe-colored woven top
layer is printed with lap lines and fastener locations; it
provides good traction, and shows and holds a chalk line well.
On the underside, a fuzzy white spunbonded poly layer gives the
roof wrap a grip on the roughness of the decking and just a
little cushion, making this underlayment very comfortable to
Polyprotector UDL is supposed to hold up for 180 days when
left exposed, but it didn't in our mockup. Our sample curled at
the laps in the first few weeks, exposing the fuzzy underside,
which is not UV-resistant. The fuzz held water and carried it
up the underside of the roof wrap a bit, and eventually the
fuzz at the laps disintegrated in the sun.
RoofShield consists of a spunbonded layer of polypropylene
coated on both sides with additional layers of PP. It comes in
a number of colors and roll sizes. We used a bright green roll
measuring 59 inches wide that provided about 800 square feet of
The top surface is coarse, with a waffled pattern, making the
material easy to walk on in wet or dry weather. The fuzzy white
spun-poly layer on the underside grabs the decking and prevents
wicking. Preformed corners for dormers and skylights are
available, as are seam tape and adhesive. With a perm rating of
86.7, this underlayment is definitely vapor-permeable, and it
shows and holds a chalk line well.
Installed on a 12/12 roof in a high-traffic area, our sample
showed virtually no wear, and the roofers reported no trouble
walking on it. And while the maker recommends leaving this
underlayment exposed for no more than four months, that number
seems conservative: Our mockup looked like it would never wear
out, even after seven months of exposure. This is a premium
product, which is reflected by its premium price.
Manufactured in Finland by Rosenlew RKW, this five-layer
polyethylene/polypropylene fabric has a slick underside and a
fuzzy, spunbonded polypropylene topside for better foot
traction. The fabric is imprinted with top and bottom lap lines
and fastener locations.
We found that this roof wrap shrinks a bit when exposed to the
sun, so it will wrinkle in the cool of the day; if it is
installed in cool weather, it should be left loose in the
valleys. It can be pulled tight without distorting, and it will
hold a chalk line.
If there is a weakness in this product, it lies in the fuzzy
traction surface. While it tends to keep water from wicking at
the laps by breaking the capillary action, it also can scuff,
especially in high-traffic areas. The scuffs form woolly
rollers, and when you step on them, down you go. This tendency
to scuff increases with weathering, of course, but I noticed it
even during installation. By the time I finished the shingles,
I was really fed up with the scuffing.
Wicking also occurred where I had lapped the roof wrap over the
metal drip edge at the eaves. Again, out came the caulking gun.
Most roof-wrap installation instructions require that you
extend the lower edge of the first course at least the
thickness of the decking beyond the edge of the decking at the
eaves. You then install the eaves metal over the roof wrap,
bending the latter down to form a protective cover for the edge
of the decking.
Unlike felt, roof wraps won't crack when you fold them, and
they won't rot, so the roof wrap will probably outlast your
eaves metal, especially if you're using galvanized steel. Only
with Tri-Flex 30 do you install the drip edge under the roof
There are a few other twists to working with these
underlayments. First of all, put away your hook-bladed roofing
knife: It won't cut these roof wraps properly, and using it can
even be dangerous. Instead, use a utility knife. If you keep a
sharp blade in the knife, the roof wrap will cut effortlessly,
just like housewrap. In fact, you have to be careful not to cut
a piece you've already installed; the cuts can be so clean
You'll also need to give up roofing cement and other
asphalt-based products; they aren't compatible with these
synthetics. Use a compatible caulk specified by the
manufacturer, and follow the instructions for lapping.
are two Sharkskin underlayments: Comp and Ultra. Unfortunately,
we discovered them only after completing this study, so we were
unable to test them in the field.
Sharkskin Comp, directed at the asphalt-shingle roofing
market, comes in 48-inch-by-250-foot 30-pound rolls. This
light-gray underlayment is made with 100 percent polypropylene,
which the manufacturer claims will neither expand nor contract
with changes in temperature. The company also says the product
can tolerate six months of UV exposure. Like the other
underlayments, it installs with plastic or metal cap nails.
It's imprinted with 5 5/8-inch layout lines, which should help
increase shingling speed.
Intended for use under tile, metal, and slate roofs, Sharkskin
Ultra is thicker, heavier, and more expensive; a
4-foot-by-250-foot roll weighs 45 pounds and allegedly delivers
12 months of UV resistance. Unlike the other underlayments in
our survey, Sharkskin Ultra can be installed with 3/8-inch
roofing nails, which means the fasteners won't telegraph
through a metal panel or get in the way of a batten
Both versions of Sharkskin have a patented nonslip surface,
which the maker claims provides better traction than the
surface of other underlayments. We hope to verify this in a
future field test.
With one exception, these synthetic underlayments aren't
vapor-permeable and should be used only on roofs with
ventilated attic spaces. Nor should they be substituted for
housewrap on exterior walls. The exception is VaproShield's
RoofShield, which is designed as a breathable waterproof
membrane. (Actually, it's the same product as the company's
The other underlayments are classified as vapor retarders, with
a perm rating of less than 1.0. (For reference, 15-pound
organic felt paper has a minimum perm rating of around 5,
though this number can rise in high-humidity conditions.)
• A coated, woven polyolefin
fabric manufactured in Canada, Titanium-UDL comes in black,
white, and gray. Rolls are available in 3- and 4-foot widths
and feature a 1/4-inch grid texture on the top surface for
better traction on steep roofs. While we found that the
textured surface worked well on the 5/12-slope roof we
installed it on, we would have liked to have tested it on a
steeper slope in wetter conditions.
We found that this roof wrap will take a chalk line, but it
can be rubbed off, leaving only a trace on the grid texture.
The texture seems to prevent any serious wicking from occurring
— although there was some wicking on our mockups where
the roof wrap lapped the slick peel-and-stick membrane.
InterWrap offers a companion peel-and-stick underlayment
— Titanium-PSU — for low-pitched areas, which
apparently has the same surface texture. We didn't test it, but
I suspect it would help reduce wicking.
We found that Titanium-UDL lays flat and stays flat, and that
it easily holds up to at least six months of UV exposure. Its
plywood mockup still looks as good as the day we built
• Manufactured and
marketed by Flexia Corp. in Canada for nearly 25 years,
Tri-Flex 30 was purchased by W.R. Grace in 2004. Since then,
it's been sold in the U.S. under the Grace name.
At 41 1/2 inches by 300 feet, each Tri-Flex 30 roll contains
1,037 square feet and provides a full 10 squares of coverage.
Code compliance and lap lines are printed on the material's
face. The product comes in black, gray, and — for use in
hot climates — a reflective white.
The spunbonded polypropylene fabric is coated on both sides
with layers of UV-stabilized polypropylene. A "tackifier"
coating on the topside enhances traction and the underlayment's
ability to hold a chalk line. However, the snapped line may not
remain entirely accurate: We found that this roof wrap tends to
belly and distort if it's pulled too tight, and it seems to
expand and contract a little — like felt — so that
it doesn't always lie flat.
While the surface coating started to show wear in the
heavy-traffic areas of our mocked-up ridge, the panel showed no
weathering at all. Wicking was not a problem.
Code Approvals and Warranties
All of these underlayments are approved for use under most
applicable building codes, but a prudent builder will still
want to verify that a specific product and use (for example, a
severe-climate application) complies with local code. Shingle
warranties and fire ratings are unaffected by their use,
according to the shingle manufacturers we contacted.
Testing the Roof Wraps
To test the membranes under controlled conditions, we built a
series of mockups using 4-foot-by-8-foot plywood sheets nailed
to 2x3 "rafters."
After fastening roof-wrap samples in place, we tipped the
plywood mockups on end, so their bottom edges were held off the
ground by the 2x3s, and leaned them up against a wall facing
We also formed a simulated ridge by nailing some plywood strips
together and applying sections of all the roof wraps to them;
we placed this structure on a walkway to Martin's shop. He and
his workers could walk over it as they went to and from the
shop, which would allow us to check the underlayments' traction
Typar RoofWrap 30 • If the
sizes and specs for Typar RoofWrap 30 and Grace Tri-Flex 30
seem similar, it's no coincidence. These two roof wraps are
manufactured in the same Canadian facility, using the same type
of spunbonded polypropylene fabric for the core.
We found the working characteristics of RoofWrap 30 and
Tri-Flex 30 to be virtually identical, although both Grace and
Reemay assured us that there are proprietary differences
between the two products.
Of all the underlayments, Tri-Flex 30 and RoofWrap 30 look,
behave, and feel more like felt than any of the others
Finally, we sent samples of each roof wrap to job sites where
Martin's roofing company was working. The intention was to
install these swatches on the part of the roof that would
receive the most traffic during the roof installation. It may
seem that this was the most important part of our experiment,
but in actuality it was the least consistent. The conditions
for each roof — especially the pitch — varied, as
did weather conditions.
Moreover, since Martin rarely leaves underlayments exposed on
the roof for more than two weeks, they weren't exposed to the
elements for very long.
After seven months of exposure to the weather and hundreds of
trips across the mock ridge, we evaluated our test mockups. The
results of the ridge traffic test were impressive: While there
was some wear on all of the roof wraps, they remained
watertight despite more foot traffic than they would ever
actually receive on a job site.
As for the panels, even after seven months of exposure, none
showed significant degradation.
In some cases, our roofers noted that it's easier to walk on
these roof wraps when they're wet than when they're dry —
though that may be attributable to Portland's air pollution,
which seems to put oil in the air.
As one of Martin's roofers put it, "These things aren't harder
than felt paper to walk on — they're just different. You
just have to learn how to do it."
John Nicol is an architectural designer and remodeler
in Portland, Ore.