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Sealing Roof Penetrations

September 15, 2001

communication equipment, signs, machinery screens, safety railweakest point in any roof and the greatest source ings, and structural steel have created expensive and challenging of leaks. waterproofing problems for all commercial roofers. Commercial roofs are often riddled with penetrations. Although many sealing systems, such as witches’ hats, moldHeating
and air conditioning equipment, utility pipes, conduit, ed rubber boots, and elevated curbs have been tried, the traditional NRCAtype pitch pan, or some variation of it, is still the most common penetration sealing system in use today. Pitch pans are comprised of a flanged metal box four inches high. The box is secured with screws to the roof around the penetration and then filled with nonshrinking grout to a depth of four inches. When the grout sets, the top is usually filled with solventbased asphalt mastic. Mastic is often mounded up around the penetration to shed water and to compensate for volume shrinkage when solvent in the mastic evaporates. The flange at the bottom is flashed with appropriate material for the type of roofing system used on the job. A rain cap is sometimes installed on the penetration to keep water and weather off the top of the pitch pan. In the real world, pitch pans are seldom built to NRCA specifications. Sand, rocks, urethane foam, and old roofing materials are often used as base filler. Nonshrinking grout is usually substituted with a mortar mix that shrinks up to five percent.
Above: NRCA pitch pans on a Roofers often use whatever pans can become with a rain cap is close to very creative. NRCA specifications.
builtup roof. they can get their hands on and then top off the pan with asphalt cement. Under actual field conditions, the construction of pitch
All roofs have penetrations which are regarded as the
Right: This pitch pan
18 • Interface
September 2001
Because of low confidence in workmanship and high rates of failure, the NRCA discourages the use of pitch pans. They are defined as “perpetual maintenance items” by all roofing professionals. Until recently, few alternatives were available. Many consultants have even suggested banning roof penetrations altogether with such tactics as placing all HVAC equipment at ground level. The real world dictates otherwise.
With the advent of singleply roofing, the pitch pan evolved to a more streamlined form. The pan became a twoinchhigh metal flange filled with twopart urethane sealer. The SPRIapproved type metal pan is mechanically fastened and bonded to
the roof surface. Its outer
surface is then flashed with
Right: Penetration seals on machinery
an appropriate membrane,
screen over builtup roof.
thus sealing the flange and
preventing corrosion on
the metal box. The rubber
seal in this new pan has
proven to be more durable
than asphalt mastic and
does not shrink. Installation,
however, is very
labor intensive, with flashing
details taking up to
an hour.
Mixing the sealer is also
time consuming, and
improper mixing occasionally
leads to failure. The
use of a twopart rubber
sealer increases the
installed cost of the pan.
Excess mixed rubber is
Right: The space between the
penetration and roof deck
must be sealed with an
appropriate filler before
pouring the interior seal.
SPRIapproved pitch pan on EPDM.
often wasted. Success with this system is often dependent on efficient mixing of the rubber and the flashing skill of the roofer.
In the past few years, packaged “penetration seal” kits have emerged in which all the components of a modified singleplytype pitch pan are assembled as a readytouse unit. These kits include a mixing paddle, pourable sealer, gloves, and a finishing tool. The assumption is that if the contractor has everything he needs to do a job, he will do it right. The kits are described as penetration seals to distinguish them from traditional pitch pans.
An important feature of penetration seal kits is the replacement of the traditional square metal pan with round, precast curb components that are bonded directly to the roof surface with a moisture curing adhesive. The bonded curb components are two inches high and two inches wide and are comprised of either
hard structural urethane or polymer modified cement.
2001 Interface • 19
Because they are not subject to corrosion, these hard peripheral parts do not require flashing.
Straight segments and corner pieces permit the construction of various alternative shapes, such as squares, rectangles, and ellipses. The circular forms are the most efficient because they expose the least amount of surface area to the weather and require the least volume of rubber to fill and seal the interior cavity.
Although penetration seal kits cost a little more, the ease and speed of installation more than compensate for the expense. A penetration seal can be completed by an
Penetration seal
inexperienced roofer in under ten minutes.
Recent innovations in polymer technology have resulted in polyetherbased, singlecomponent, pourable sealants that can reduce the labor required to install a penetration seal to under five minutes.
Penetration seals contain no mechanical fasteners and are therefore totally dependent on the integrity of the chemical materials that hold them together and bond them to the roof and penetrations. Good bonds lead to very strong seals; poor bonds often result in problems. Here are some rules that will lead to success with penetration seals:
• Some roofing materials are not good substrates for a bonded penetration seal. Unacceptable substrates are TPO, Hypalon, and smooth APP Modified Bitumen. Smooth APP can be sealed only if a granulated “target” piece is heat welded around the penetration.
on builtup roof.

All bonding surfaces must be clean and free of any materials that would interfere with adhesion. Asphalt cement as a night seal where a penetration seal is scheduled to be installed is prohibited. Shrinkage from solvent loss will create voids beneath the seal. Also, solvent escaping from such mastics will undercut the seal and may damage the surrounding membrane.

Surface preparation requires that all bond surfaces be clean and sound. Asphalt, oils, cement, ice, loose paint, and dirt must be removed. Loose roofing granules will interfere with adhesion and lead to failure. To ensure adhesion, a coat of moisturecure adhesive, provided by the manufacturer, should be applied to the roof and penetration surfaces prior to installing a penetration seal.

The space between the penetration and roof deck must be sealed with an appropriate adhesive before pouring the interior seal. The poured seal must not be disturbed or subjected to movement for twentyfour hours after installation.
Following these rules, along with using proper considerations for weather and using commonsense workmanship, should guarantee that penetration seals should perform well on most singleply, mod bit, or BUR roofing systems. ■
BOUT THE AUTHOR Phil Georgeau has been an industrial chemist for over 30 years. He is currently president and principal shareholder of Chem Link Inc. His industry experience began as a product development engineer with US Polywood in its Weldwood Chemicals Division. He has continued in this field, with an emphasis on construction adhesives and sealants, at St. Clair Rubber, ContechSonneborn, Megaloid Chemical, Imperial Adhesives, and Chem Link. Georgeau holds six patents in the area of adhesives, sealants, and construction materials, including two patents for ChemCurb penetration seals. PHIL GEORGEAU
20 • Interface September 2001