By Lawrence Evensen
A combination
of drawings and specifications encompass the requirements
for a construction project. Although far more like a
technical paper than a novel, these combined documents
can in some ways be seen as the concise narrative detailing
the design and construction of a project. The goal of
the designer is to create comprehensive documents telling
the building's "story". Unfortunately,
some drawings and specifications leave out so many details
that they read more like a Sherlock Holmes mystery, but
without the "gotcha" finale to tie up the loose ends.
This can be particularly true when it comes
to roof penetrations.
In this case, the mystery is what component will provide
a watertight assembly for each of the various penetrations
shown on the roof plan. Without penetration details and
complete specifications, the story is incomplete and the
roofing installer is left to assume unfair responsibilities
or attempt to interpret the design team's intention.
An understanding of roof flashings and counterflashings,
and how they perform their waterproofing tasks, is a
necessity. This article concentrates on roof penetrations
and the methods of installing the aforementioned products
and systems to aid in comprehensive roof plans. Following
some of the practices suggested in this article should
result in a smoother-running construction project.
Specifying Dilemma
The building envelope designer must be extremely diligent
when writing the specifications for roofing details,
because the results of poor planning are confusion and
a higher risk of litigation. A roof membrane is a watertight,
non permeable cover unless damaged, penetrated, or bypassed.
In a perfect world, roofing contractors would not have
to deal with complications that typically arise during
the construction process, and there would never be any
leaks.
A dilemma is created for the design professional when other
trades such as electric, refrigeration, structural steel,
air conditioning, and other contractors install their products
and break the watertight cover in some way. Only clearly
written designs directed at each of the trades will place
waterproofing responsibility in the hands of the individuals
with the expertise and knowledge required to create failsafe
waterproof penetration solutions. When the chain of responsibility
for waterproofing a roof penetration is not clear,
conflicts result, since most subcontractors are concerned
with only the equipment or structure they have contracted
to produce.
It is imperative that subcontractors take responsibility
for the roof penetrations they create and start caring
about how their work affects the overall building envelope.
Only clearly written specifications put the responsibility
of proper waterproofing into the contracts
of each of the responsible parties. If specifications
and details are clearly defined in advance, the roofing
contractor is not placed in the impossible position of
creating details for penetrations that are proprietary
to the various subtrades. Closing this
gap goes a long way toward keeping water from bypassing
the monolithic roof cover and keeps the lawyers at bay.
Flashing Basics
Over the centuries, roof construction has evolved
to include two waterproofing techniques: flashings
and counterflashings. These materials create a rise in
the roof's membrane high enough to keep the elements
from entering the waterproofing membrane, with a cover
over the rise.
The roof rise feature, or flashing, facilitates
water runoff as long as weather conditions are not
extreme enough to overflow the rise. The cover of the
flashing, or counterflashing, is designed to allow water
to shed over or around the flashing opening. There are
many classes of roof flashings and counterflashings,
including those products specifically designed for:
- Bases;
- Chimneys;
- Copings;
- Eaves and fascias;
- Valleys, and
- Roof penetrations.
For each class of flashing, the law of gravity and the
rules of physics for the water's flow are the same. The
roof flashing is constructed to rise higher than the
highest expected water level from a weather event,
and is counterflashed to cap its opening, allowing gravity
to direct water away.
Potential Problems with Penetration
Flashings for roof penetrations, projections, and equipment
stands are designed with the flashing/counterflashing
methodology. Pipes, conduits, vents, and support legs
use a sleeve or 'jack' flashing to create the rise in
the roof's level.
As a general rule of thumb, roofing product manufacturers
follow the guidelines of the National Roofing Contractors
Association's (NRCA) Roofing and Waterproofing
Manual. In the third edition of its "Handbook
of Approved Roofing Practices," Sections 1 & 2
recommend using a metal flashing or inserting roof jacks
into the membrane for projections through the roof's
membrane no lower than 203 mm (8 in), and not higher
than 356 mm (14 in) above the finished roof level on
low-slope roof applications. In the 2007 Roofing
and Waterproofing Manual, the verbiage has been
replaced by a detailed drawing. The notes on the detail
include the following: "Penetration pockets are not the
preferred flashing method at the penetrations because
they may be a constant maintenance problem." (See
Figure 1.)
 |
| Figure 1
- NRCA penetration pocket drawing. |
Steep slope roof applications can have a rise as minimal
as 63.5 to 76 mm (2.5 to 3 in), since the grade virtually
guarantees that a water event will not be high enough
to overflow the flashing, even in extreme weather conditions.
Many penetrations through a roof covering can be waterproofed
using the respective manufacturer's standard details.
Round penetrations - such as plumbing vents, electrical
conduits, HVAC chiller lines, domestic water lines, and
natural gas pipes - can be matched to
a pipe flashing jack with the proper outside diameter.
Nearly all designers call out a flashing method at these
locations.
It is the responsibility of the general contractor to
ensure the appropriate installer provides properly sized
flashing for each of the roof penetrations on a project.
However, when the roof penetration is not a standard
round geometry or is not detailed on the drawings, or
when subcontractors do not provide the necessary flashing
as part of their work, the roofing professional is forced
to create a waterproofing detail on the fly. This is
complicated by the great variety of structures and mechanical
devices used on a roof.
For example, many structures have equipment located
on the roof. For safety or aesthetic reasons, this equipment
is often hidden behind screens. The screens are built
out of very solid material (e.g. structural
steel) to ensure their capability to withstand high wind
loads. It is not unusual for equipment screens to employ
several hundred roof penetrations made from square, angle
iron, or H-beam steel. The use of non-round steel support
structures at these locations makes standard details
difficult to write, creating a problem for the roofing
contractor that can be especially complex to solve.
Help From
Above for St. Luke's
To better understand the need for clarity in
waterproofing specifications, it can be useful to see
the lessons learned from a previous project. St. Luke's
Outpatient Center is a new medical facility located in
St. Louis, Missouri (see Photo 1).
 |
| Photo 1
- Front of St. Luke's Outpatient Center. |
In late 2007, Ryan Freeman, the job
superintendent of McCarthy Building Companies, discovered
the roof details provided by the roofing material's manufacturer
were inadequate. He was faced with 120 steel support
posts (102 or 152mm [4 or 6 in] tall) that were part
of the equipment screen. If the posts were improperly
waterproofed, the leaks would have been numerous.
The flashing detail included a site--fabricated
flashing to be created by the roofing crew out of the
white, single-ply roof product. The plan was to make
the flashing, seal the top edge against the steel post,
and draw it tight using a stainless steel band clamp.
The problem with this technique is that no matter how
much torque is applied to the clamp, there will be loose
gaps on the flat part of the square post. Square pegs
do not fit in round holes.
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In search of a better solution, Freeman
contacted RNC Enterprises' Ron Carter, a local technical
advisor for innovative construction products. Carter suggested
installing storm collars over the field--fabricated flashings
to provide the waterproofing that each square post required.
(NRCA approves storm collars for this design purpose.)
The steel support posts had already been installed, so
any counterflashing would need to be a retrofit design.
Choosing the appropriate product was the next challenge.
Any storm collar used for these posts had to fit certain
design criteria. The storm collar needed to be:
- A retrofit design (as the equipment screen posts
had already been installed),
- Installed using the existing roofing crew labor,
- Made of material compatible with the metal posts,
without worry of corrosion to the post or structure,
- Free of sharp edges,
- Able to spring back into place
in the event of disturbance by workers or pedestrians
walking on the roof, and
- Aesthetically in line with the building's white roof
covering.
Additionally, the storm collars had to have a life expectancy
of at least 20 years - the intended duration of the roof.
Carter used retrofit
storm collars made
of ethylene propylene diene monomer (EPDM) rubber as the
counterflashing. By ordering these products with square
cut-outs sized exactly to match the metal posts, he ensured
that the storm collars were suitable for the field-fabricated
roof detail. There were neither corrosion compatibility
issues nor sharp edges. Further, if the rubber is impacted
by pedestrian traffic, it bends and springs back automatically.
Installed using a simple nut driver, the "off-the-shelf"
collars can open up to wrap around myriad geometric shapes,
while creating the rise in roof level needed.
A/C Specifications
Are Not Always Cool
By utilizing the same roof rise and cover technique, one
can write almost all other odd or difficult roof penetration
waterproofing specifications.
The luxury apartments built by Trammell
Crow Residential at the corner of Walnut
Street and Colorado Boulevard in the city of Pasadena,
California, provide another example that illustrates how
a common problem can be solved. The project includes 265
luxury dwellings that are cooled using individual split
central air-conditioning systems. (See Photo 2.)
 |
| Photo 2 -
Trammell Crow Residential project in Pasadena,
California, seen from the air. |
A split system is made up of two copper
refrigerant tubes that are connected to an indoor coil
and an outdoor condenser heat pump unit. The smaller of
the lines is called a liquid line and the larger, a suction
line. The lines are filled with a chemical refrigerant,
which has a boiling point low enough that it evaporates
at relatively low temperatures and takes heat and moisture
out of the air as it passes through a coil that is installed
inside each apartment dwelling. The refrigerant travels
in a closed loop between the coil and the rooftop condenser.
In addition, a low-voltage wire inside
a watertight conduit provides an electrical connection
from the coil to the outdoor condenser. The two tubes and
conduit combination create a tightly grouped roof penetration
called a "line set". (See Photos 3 and 4.)
 |
| Photo 3 -
Closeup of a line set at the Trammell Crow project. |
The 265 heat-pump condenser units on the
Trammel Crow project were mounted on platforms located
on the flat areas of the multistory buildings' roofs.
Line sets are a prime source of water
intrusion, because it is extremely difficult to seal between
the groups of tubes. As a further complication, the large
suction-line tube is always insulated with soft foam as
an energy conservation measure. Water that gets inside
the insulation follows the tube like a highway through
the walls of the building, ultimately creating leaks in
apartments. The Walnut Street project had first-floor apartments
five stories below the roof decks, so a leak at the ground
floor could create hard-to- identify longterm problems.
Line sets need to be waterproofed!
|
Photo 4 -
Split central air-conditioning units on the Trammell
Crow roof. |
EPDM
storm collars again offer ideal solutions
for this roof penetration problem. In this case, the rise
in the roof level was created using a standard 37-mm to
50-mm (1.5-in to 2-in) diameter lead- pipe flashing jack
and covering the rise with an EPDM-molded storm collar.
The factory-made storm collars are pre-engineered to
accept three closely grouped tubes and include two 20-mm
(7/8-in) and one 10-mm (3/8-in) nipple holes. When the
three independent components of the line sets pass through
nipples molded into the rubber collar, each is separated
and secured by a stainless steel hose clamp. A bonus of
using rubber is that the
assembly has no bimetal contact and zero corrosion potential.
(See Photos 5 and 6.)
 |
| Photo 5 -
Worker with 12-inch Collar on equipment screen
footer. |
After demonstrating the storm collars
to the roof consultant and roofing manufacturer's technical
team, Joe Daniels, owner of D7 Consultants, Newport Beach,
CA, said, "These provide a simple solution to a common
problem we find on the roofs we work on. Let's use them."
The storm collars were approved.
 |
Photo 6 - Close
up of 6-inch angled Storm Collar. |
A plan was put in place to have each line
set enter the building through lead-pipe flashings, each
with 200-mm (8-in) high risers that were installed into
the roof system following the manufacturer's standard construction
details. The roof installed was a CertainTeed specification
number N-N-B5, 5-ply, built-up, smooth-surfaced roof installed
over a protective layer of rosin sheet. Because the team
used CertainTeed installation details CT-11 or CT-12, the
roof flashings were installed in a watertight manner, and
the result was a specification that allowed issuance of
the manufacturer's 20-year warranty.
After the roof jack flashing had been
completely installed, the rubber storm collars were placed
down onto the copper tubes by way of the pre-molded nipples.
The storm collars were located over the already installed
lead flashings, and the stainless steel hose clamps on
each of the three nipples permanently secured the storm
collars as covers over each flashing. Line-set storm collars
created a waterproof counterflashing umbrella for any type
of pipe jack, keeping the water on the roof.
Conclusion
The NRCA recommends
metal flashing or roof jack insertion into the membrane
for projections between 203 and 356 mm (8 and 14 in) above
the finished roof level. These flashing jacks can be fabricated
from many classes of materials, including lead, steel,
aluminum, and even single-ply materials. (The material
used is often determined through manufacturer preference,
design/construction professional experience, compatibility,
aesthetics, and cost.) All that is required is a storm
collar that attaches to the penetration or group of penetrations,
which acts as the counterflashing atop the flashing jack.
The installation of retrofit and standard
storm collars to solve these waterproofing problems is
an example of how innovative products can improve roof
penetration details. By adding storm collars to the roof
plan, each penetration becomes manageable, taking the mystery
out of inadequately written details.
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