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Examples of such stack pipes include:
- The plumbing stack vent, also known as the “plumbing vent” or “vent stack,” is a long, vertical pipe running from the foundation of a home to above the roof. All drains in the house connect to the plumbing stack vent, which regulates air pressure within the sanitary system and removes odor from the home.
- Type B and C gas vents. Type B vents are double-walled metal pipes that vent natural gas or propane-fueled appliances, such as furnaces, water heaters, and boilers. Type C vents are similar to Type B vents but without the double-wall construction.
Worn-out or damaged roof stack flashings produce leaks, water stains, and mold.
If your roof leaks, or there are water stains, mold, or mildew on the ceiling or walls, you may have worn-out or damaged roof stack flashings.
The above can affect your health and the structural integrity of the house or building.
We’ll discuss common signs of roof stack flashing issues and which flashing products efficiently seal each type of roof vent.
Signs of Damaged or Improperly Installed Roof Stack Flashing
The most common signs of damaged or improperly installed roof stack flashing include:
- Internal leaks.
- Stained or rotting ceilings.
- Too much daylight in the attic.
- Worn or damaged shingles.
- The attic insulation:
- Feels clumpy and crispy (more like cardboard instead of soft cellulose).
- Is displaced instead of evenly distributed.
- Musty or moldy smells in the attic.
Several factors inevitably damage flashings, especially those made of cheaper materials that rarely last 6-7 years. Some damaging factors are hail, vandalism, rapid temperature fluctuation, and wildlife (like squirrels, raccoons, and woodpeckers).
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While replacing damaged roof stack flashing is easy, avoiding the problem from the beginning guarantees better sealing.
Let’s look at the proper types of flashing to use on the different kinds of roof stacks.
Suitable Flashing for Each Type of Roof Stack
The following are some of the most common types of roof vents and flashing products to seal the penetrations efficiently:
Suitability is a matter of efficiency and high quality. Menzies is the leading roofing and building accessories manufacturer, and we’re committed to offering our customers the best products, so you can only focus on getting the right flashing for your specific vent and roof type.
Plumbing Stack Flashing for Flat Roofs
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If your roof is flat, use plumbing stack flashing manufactured as a single seamless piece. An example would be Menzies’ Plumbing Stack Spun Aluminum, which prevents any roof flashing leak caused by external influences or improper welding. Aluminum is highly suitable for roof flashing, as it forms a corrosion-resistant oxide layer that lasts a long time.
Follow these steps to install the plumbing stack vent on your new roof:
- Remove debris preventing the pipe flashing flange from laying flush against the roof surface, and use a high-quality caulking sealant. We recommend Menzies’ TITEBOND WeatherMaster Metal Roof Sealant.
- Lower the pipe flashing over the vent pipe.
- Secure the flashing flange to the roof deck with at least four round-head fasteners.
- Follow your roofing system manufacturer’s instructions for installing roofing material around the roof vent flashing.
- Seal the gap between the flashing and the pipe with any of the following:
- Menzies’ Econo Cap which acts as a counter flashing to seal the gap between the flashing and the pipe.
- Menzies’ Vandalproof Cap is pop-riveted to the aluminum stack to prevent removal.
NOTE: Refurbishing a flat roof will sometimes result in the plumbing vent pipe’s outlet being too low. When required, raise the height of the pipe with Menzies’ Plumbing Pipe Extension Kit, as demonstrated in the video below:
Plumbing Stack Flashing for Pitched Roofs
Since they adapt to any slope, welded flashings are the go-to option for sealing stack vents on pitched roofs.
The bead on the Menzies’ Plumbing Stack Aluminum Flat-Welded creates a homogenous joint that is more robust than the parent material, making this type of roof vent flashing completely watertight and resistant to torching.
Lead Plumbing Stack Flashings
Whether your roof is flat or pitched, you can use heavier, more durable lead pipe flashing for your plumbing stack vent. Lead pipe boots might not be visually appealing, but they are pliable by hand and can last the entire lifetime of your building.
Caps like Menzies’ Lead Cap can counterflash the lead pipe flashing with the plumbing vent pipe, but you can manually fold the lead pipe flashing over the edges of the vent pipe’s mouth.
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Gas Vent Flashing
Since B vent flue pipes exhaust gases from furnaces and HVAC, they get hot, even though they have double walls. Thus, the penetration should have enough clearance to keep the pipe safely away from the roof, especially wooden ones, to prevent combustion.
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Because of their wider penetrations, B vent flue pipes require cone-shaped flashing instead of cylindrical boots.
Menzies B vent spun aluminum is a seamless one-piece heavy gauge aluminum cone-shaped flashing that can securely resist the hot temperatures from the double-wall pipe. The boot can also withstand heat caused by torch-on roofing installations
The top part of the B vent flashing fits the flue pipe snugly, while the lowest, wider section makes the whole flange contact the roof for a watertight installation.
However, flue pipes expand and contract due to temperature changes, producing relative motion between the pipe and the flashing, wearing prematurely caulking applications.
To provide a waterproof seal, B vent flashings need a storm collar (just above the joint between the flue pipe and flashing) with a caulking bead all around it. Our Galvanized Storm Collar does this job perfectly.
At a slightly higher cost, there’s also a more robust option for areas where flying debris could be a menace: Menzies’ B Vent Flat Galvanized. It’s hot-welded to work well with torch-on roofing installations and is moisture-resistant.
Combating Roof Stack Condensation in Cold Climates
Condensation is destructive to plumbing and heating vent stacks in cold climates. When warm, moist exhaust gases reach their dew point before exiting above the roof, they condense inside the pipe and start building frost. The condensation and freezing can cause the pipe to rot below the roof deck line and vent dangerous hot gases into indoor areas.
We recommend using our Multi-Flash Insulated Flashing Spun over the vent pipe to prevent condensation. The multi-flash insulated pipe flashing has top and bottom moisture seals that create a dead air space between the pipes, insulating them from freezing temperatures and delaying condensation.
The seals have tear-out plugs to fit standard sizes of plumbing pipes, which reduce estimation and installation time.
Retrofitting Old Roof Stacks
Sometimes, you might have damaged or improperly installed roof stack flashing that’s difficult to remove or replace. In such cases, a retrofit may be the faster, cheaper fix.
These boots can be placed on the faulty flashing, creating a new, intact layer of weatherproofing for several years. These retrofit boots will accommodate most pipe sizes, roof pitches, and surfaces.
Our standard retrofit boot is the Dektite Retro Combo Black, which comes with clips to form a tight seal when flashing pipes on sloped roofs.
We also have the Dektite Retro Combo Silicone, an alternative for when black won’t look too good on your roof. The Dektite Retro Combo flashing is paintable with 100% high-gloss acrylic paint to match your roof.
For larger pipes and/or steeper roofs, we recommend the Dektite Premium Black, which has a larger square base and is much more forgiving for penetration openings.
Lastly, for shingle roofs, we recommend the Dektite Retro Combo SHR. Its proprietary polymer material is compatible with asphalt shingles and can accommodate pipes up to 152 mm outside diameters.
Other Roof Stack Flashing Accessories
For everything in between regarding your roof stack flashing needs, Menzies has accessories to ensure your roof stacks will be safe and weatherproof for many, many years.
For the terminations of round HVAC pipes, we have the End Cap/Plug Spun Galvanized, which is usable in two ways. The female side can go over the pipe end, while the male side can go into it.
We also have Small Insert Caps for use where a pipe of the wrong size has been installed
To flash roof stacks fast and on a budget, we recommend our 5-in-1 Plumbing Pipe Flashing. They’re designed for roof pitches from 3½:12 to 12:12 and can accommodate most common pipe sizes.
We recommend capping your B vents and other roof vent stacks with our China Caps. They’re made of heavy spun aluminum and rusting is never a problem.
Lastly, proper caulking application is part of a good roof stack flashing job. We recommend using our Twist Top Caulking Nozzle to help you properly apply those caulking beads. It’s adaptable to any tube with a detachable nozzle and allows straight silicon nozzle access to hard-to-reach spots.
Trust Menzies for All Your Roof Stack Flashing Needs
For over 40 years, architects and project engineers in North America have trusted Menzies for our superior materials and production processes. If roof stack flashing has always been a sore point for you, look no further than our extensive product catalog for your solutions.
If you’d like to talk to one of our representatives, we’d love to hear from you! Contact us today