New Roofing Underlayment Offers Light Weight, Good
Coastal roofers may want to take a look at the newest
contestant in the expanding world of synthetic underlayments: a
membrane combining woven and non-woven polypropylene, with a
fuzzy, slip-resistant walking surface, that calls itself "Opus
Roof Blanket." The new fabric comes from Propex, a company with
extensive experience in geosynthetic membranes and fiber
reinforcement for concrete.
One coastal roofer who approves of Opus is
custom roofing contractor who works on Cape Cod and Boston's
South Shore. After trying out the new product, compliments of
the manufacturer, Bennette told Coastal Contractor, "My guys
loved it. It's a really good product." Some other synthetics
have been more trouble than they're worth, says Bennette
— "they're slippery, or they wrinkle when you lay them
down. But this stuff is fuzzy, it's walkable, you can write on
it, you can chalk-line it, and it lays flat. It's kind of like
a totally different animal than some of the other synthetic
felts on the market, I think."
The International Codes specify asphalt-impregnated felt as
the approved underlayment for most roofing materials, including
fiberglass-asphalt shingles, metal roofing, slate, and tile.
The plastic-based synthetic membranes aren't mentioned in the
code. So for code acceptance as a substitute, manufacturers
need to obtain an Evaluation Report from the International Code
Council's Evaluation Service (ICC-ES). A number of suppliers
have done that — to view the code reports, you can
” page on the ICC-ES site .
But even with Evaluation Reports, comparing the synthetic
felts with traditional asphalt paper — or even with
other synthetics — can be a tricky apples-to-oranges
problem. One huge advantage for the synthetics is their light
weight — a roll of synthetic membrane that will cover
8 or 10 squares may weigh less than a roll of asphalt felt that
can barely cover one square. Roofing can be backbreaking labor,
and anything that lessens the load is welcome.
But asphalt has the ability to seal nail and staple holes,
at least partially. Most synthetics won't. In a 2006 article in
Synthetic Roofing Underlayments
," by John Nicol —
JLC 5/06), remodeler John Nicol recalls learning the hard way
that "water — a lot of it — can get through
the staple holes via capillary suction, also known as wicking"
when synthetics are left exposed to the rain. That's why
manufacturers call for cap nails to attach the products to the
roof." (That's not a problem for Jim Bennette, who says, "We
always fasten all underlayment with buttons, including asphalt
And some synthetics can be very slippery when wet. In a
2006 JLC Online forum thread
, a contractor described an
encounter with a fog-slicked synthetic surface: "It was like
ice and one of our guys slid down the roof and landed 20' down
on the ground." [That's the hazard that Opus Roof Blanket is
trying to overcome with its fuzzy slip-resistant surface.
(According to Opus' product literature, Opus is the
highest-friction synthetic on the market.)
On the other hand, unlike asphalt felt, synthetics can be
left exposed on the roof for long periods. In fact, an Opus
product rep told JLC editor Dave Holbrook at the JLC Live expo
in March, 2010, that Opus could be left exposed on the roof for
up to 30 months. Of course, for a product that has only been
introduced to the market this year and that still is only
stocked in a handful of lumberyards, that claim has yet to be
field-tested. And it's unlikely that most builders would
consider leaving a roof unshingled for months, let alone years.
Still, you can imagine a situation where you'd be glad you
don't have to start over with fresh asphalt paper, just because
the rain has kept you off the job for a couple of weeks.
In the short term, you may not see Opus showing up in your
local marketplace. However, you can order the material by phone
at 877-315-6669, or try the company website: