How to Repair a Leaky Roof Vent Pipe Flashing

By |Last updated on |Plumbing, Roof|26 Comments

This tutorial explains how to diagnose and repair a roof leak caused by a cracked rubber boot around the plumbing vent flashing.

I became aware of the roof leak when I noticed a water stain on the drywall ceiling. The water stain occurred during a period of record rainfalls and extensive flooding in the metro Atlanta, GA region when 17 inches of rain fell over an 8-days period. That’s a lot of rain for a region that normally receives around 4 inches in September. With that much rain even a small roof leak is likely to be noticed:

Water Stain on Drywall Ceiling due to Roof Leak

Water Stain on Drywall Ceiling due to Roof Leak

Find the Roof Vent Pipe Leak

The attic is above the room where the water stain on the drywall ceiling. To locate the source of the leak, I went into the attic with a flashlight. The stain is the corner next to the exterior wall so I focused my search in that direction. The PVC vent pipe for the basement bathroom plumbing rises through the roof directly above the stain on the ceiling. The vent pipe became an immediate suspect.

Take care to walk only on the wood joists when working in the attic. The ceiling drywall will not support your weight and you can fall through.

PVC Vent Pipe to the Roof

PVC Vent Pipe to the Roof

This is the lower end of the vent pipe directly above the drywall ceiling. It’s covered by blown fiberglass insulation. The dark bits on the insulation are nut shells left by flying squirrels used to get into the attic during the winter before I had the roof replaced.

Leaky Roof Vent Repair: Plumbing Vent Pipe above the Drywall Ceiling

Leaky Roof Vent Repair: Plumbing Vent Pipe above the Drywall Ceiling

I moved the insulation away to reveal the bottom of the vent pipe and ceiling drywall. The insulation and paper surface of the ceiling drywall are damp. I’m getting close to finding the leak:

Leaky Roof Vent Repair: Water Leak on Drywall Ceiling

Leaky Roof Vent Repair: Water Leak on Drywall Ceiling

A closer inspection of PVC vent pipe penetration through the roof revealed daylight shining around the vent boot flashing. This is the source of the water leak! Rain water leaks through the cracked the rubber vent boot, runs down the vent pipe and drips onto the drywall ceiling. Persistent heavy rains caused enough water for the leak to soak through the drywall ceiling and be noticed inside the house.

On the positive side, the Oriented Strand Board (OSB) roof deck is dry and untouched by the leak. If the roof decking were rotted, the shingles would have to torn up and the rotted section of deck replaced – a major repair effort!

Roof Vent Pipe Flashing Leak: Cracked Rubber Vent Boot

Roof Vent Pipe Flashing Leak: Cracked Rubber Vent Boot

More rain was in the forecast and it might a take a couple of days to get a roofer over to repair the vent flashing. To minimize further water damage I tied a towel around the pipe to temporarily catch the rain water. This is only a band-aide solution:

Roof Vent Leak: Towel Tied to Vent Pipe to Catch the Water

Roof Vent Leak: Towel Tied to Vent Pipe to Catch the Water

An alternative is to place a pan on the drywall ceiling under the PVC vent pipe elbow to catch the leak.

Roof Leak: Cracked Rubber Vent Pipe Boot

The rubber vent pipe boot (or flashing) has cracked and split as highlighted in the next photo (red square). The rubber vent boot flashing must be seal tightly around the PVC vent pipe to make a watertight seal. The roof is about 10 years old and the vent boot has cracked from a combination of the UV rays from the sun, weathering, expansion and contraction from the heat and cold:

Roof Leak Caused by Cracked Vent Pipe Flashing

Roof Leak Caused by Cracked Vent Pipe Flashing

The 2″ PVC vent pipe with the cracked rubber boot is shown in perspective to the house. The roof is a steep 10/12 pitch and the house sits on a hillside. A 40 foot ladder is needed to reach vent pipe from the ground. Time to call a professional roofer to make this repair.

Roof Vent Pipe Flashing with Cracked Boot

Roof Vent Pipe Flashing with Cracked Boot

This repair is continued in How to Repair a Leaky Roof Vent Pipe Flashing – Part 2.

Hope this helps,

Bob Jackson

Copyright © 2019   Reproduction strictly prohibited.


  1. Jay Smith January 26, 2010 at 12:12 pm - Reply

    This is really helpful, thanks. I think I have a similar problem, and the roofer is quoting me $375 to change out the boot, fix some nails, and he’s not going to replace any of the decking. Sound like a deal?

    • Bob Jackson January 26, 2010 at 1:30 pm - Reply

      Sounds a bit high to me for a single pipe boot. I called two roofers and received the following quotes:
      1st Roofing Company: $225 minimum for a service call. Will replace two vent boots including materials at this price.
      2nd Roofing Company: $125 minimum for a service call. Price includes replacing one vent boot with materials. A 2nd vent boot would be $50 extra.

      Both companies said a lead pipe boot flashing would be extra.

      Also ask about the warranty, e.g. “guaranteed no leaks for 1 year”.

  2. brian burgess February 24, 2010 at 1:38 pm - Reply

    I have leaking through cracked boots on the roof vent pipes on my house which is 10 years old. A roofer with 25 years experience offered two options, 1. to replace the flashing and boots (would likely breakdown in 6-8 years), 2. to buildup and cover the existing boots with polyurethane which will work just as well and last as long as the current roof before needing to be replaced in 15 years or so. Please advise.

    • Bob Jackson February 24, 2010 at 7:59 pm - Reply

      I recommend option 3 or 4 – that is, none of the above.

      Option 3 (preferred): Install a lead pipe flashing. Lead flashing lasts forever and the top is folded into the PVC pipe for a leak free union. A lead book will cost ~$35 versus $7 for the Oatey plastic boot. This is what I would have done had there been more time to buy one before the next rain storm. See the lead flashing references in the article.

      Option 4: Install a new $7 flashing unit/boot like you have now but add a $5 rain collar. This is how I fixed mine. The rain collar provides extra UV protection for the plastic boot.

      It’s so simple and inexpensive to replace the entire flashing why bother with the polyurethane? Do use roofing caulk to seal the nail heads.


  3. Amy Fogelstrom April 1, 2010 at 1:23 pm - Reply

    I have EXACTLY the same problem. I just got an estimate for $2,225 dollars to replace the boot and to patch a bit of drywall (around a square foot) in the ceiling where the leak came through. Seeing this website is disturbing to me because I think someone may be trying to take advantage of me for being a female again.

    • Bob Jackson April 1, 2010 at 6:14 pm - Reply

      $2,225 just to replace the boot and repair a small area of drywall sounds like a scam.

      I show how to replace a water damaged section of ceiling drywall in How to Repair Drywall Ceiling Water Damage. To hire someone would cost $150 to $200 – mainly because it requires two trips to sand and apply a second layer of drywall mud.

      You can find reputable contractors and businesses in your area at

      Write back and let me know how your repair turns out.


    • Joanne seedorf November 2, 2017 at 12:25 pm - Reply

      I had the same thing happen to me with a ridge vent. One local guy quoted me $1,500 to replace the ridge vent. The second company replaced it for $400. That’s why I always get a few quotes. I never just pick the cheaper one but this roofing company did work for me before and had good reviews so I went with him. The leaking has stopped completely.

  4. bw January 4, 2013 at 4:16 pm - Reply

    Should this kind of repair be covered under the roof warranty?

    • BobJackson January 4, 2013 at 5:51 pm - Reply

      Generally speaking, any roof leak due to materials or workmanship should be covered by your new home warranty (if new construction) or roof replacement warranty. It all depends on the specific terms and conditions of your warranty, so read the fine print.

  5. Scott Jackson October 2, 2013 at 12:00 pm - Reply

    Same problem, 12 yr old weather cracked Oatley plastic boot, short term caulked with ‘All Purpose Polyseamseal’, more storms and didn’t leak..was going to put another boot over it but, because of minor hail damage to shingles, had new shingles and boots replaced..will add a ( rice paddy hat) stove pipe style ‘ tin collar flashing’ (above Oatley boot ) to direct sun & water away from boot so when it does age again – and it will – there will be no water contact..

    • Bob Jackson April 27, 2014 at 10:21 am - Reply

      I’m pleased to see more products for preventing vent boot roof leaks on the market.

      I’ve written about Perma-Boot which is also available Home Depot.

  6. Mike Biddle November 1, 2015 at 2:06 pm - Reply

    Can these cause a dripping sound even if there isn’t a leak if they are clogged etc? we here a dropping sound near where one of these vents is located but there is no moisture etc in the ceiling area.

    • Bob Jackson November 1, 2015 at 3:16 pm - Reply

      It’s highly unusual to hear water dripping inside the roof vent pipe because rain water will trickle down inside the pipe wall, where it will make it’s way to the sewer.

      While you’re not seeing evidence of a drip or water stain on the ceiling now, it’s probably a matter of time before you do as the leak will eventually soak through the drywall ceiling. If you inspect the roof penetration and attic area you’ll find a drip and puddle on the attic insulation or drywall.

  7. mark May 16, 2016 at 6:44 am - Reply

    I have been roofing for 25 years you people are leaving out what they will do when they install the vent flashing. When you rather pay a little more money to know that it’s installed correctly. Did you know that the felt paper doesn’t overlap the flashing underneath the shingles it will still leak.

    • Bob Jackson May 16, 2016 at 8:38 pm - Reply

      Did you mean to say that “[if] felt paper doesn’t overlap the flashing underneath the shingles it will still leak”? That not how the Oatey No-Caulk installation instructions says it should be done. I wouldn’t want a roofer pulling up the roof felt because it’s the last line of defense against leaks and you may end up cutting a new seam in the middle of the felt depending on where each row happens to overlap.

      When my roof was later replaced after a hail storm the new vent boot flashing was installed in the following sequence:
      1. Roofing felt
      2. Ice & Water Shield rubberized membrane; lower section overlaps the hidden section of shingles.
      3. Vent boot flashing
      4. Shingles over the up-hill, left and right sides of the flashing.

      See Hail Damaged Roof Replacement: Part 5 – Plumbing Vents for details. The Type B gas flue vent flashing was installed the same way.

  8. Jack June 25, 2016 at 10:27 am - Reply

    I have had a leak in my house for 9 months. I have had a roofing company come out 13 times! And have had an AC and heating company come out once to clean and take a look at the area. The AC guy blames the roof and the roofer says it’s caused by a double lined duct ( which appears to be where the water is coming from). The AC guy says it is very unlikely to be the duct because of its double lined wall and he says the piping and connect is looks good from the base to the roof. the leak was persistent throughout the late fall and winter, it was also leaking when the weather outside was below freezing. Has not leaked in the spring, and has since leaked once when we got 2 inches of rain in 3-4 hour period. I have had a handyman rip out the ceiling to expose the duct/pipe and still nothing appears abnormal. Should I just replace the duct? Is there something more?

    • Bob Jackson June 26, 2016 at 12:35 pm - Reply

      Hi Jack,
      I believe your Type B Gas Flue vent is leaking. Gas flue vents relay combustion gases from furnaces and hot water heaters to a roof vent and have double wall sheet metal pipe for insulation. The purpose of the double wall pipe is two fold: to limit the exterior surface temperature of the pipe for fire prevention and perhaps more importantly to keep the combustion gases hot enough to prevent condensation inside the pipe. Natural gas combustion gases are mainly carbon dioxide and water vapor.

      Typically the vent cap, storm collar or cone flashing rusts or a high temperature caulk joint opens allowing rain water to intrude. The rain water may run down the exterior of the vent pipe or may get inside the pipe. Either way it’ll appear as a leak at an elbow joint or horizontal section of pipe. The source of the leak can be challenging to locate because it may only leak when the rain blows from a particular direction or only during prolonged or heavy rain spells.

      Leak repair is possible but it’s a hit & miss affair, see How to Fix a Leaky Gas Flue Roof Vent.

      For about $75 in vent parts why not replace the entire vent to be certain the leak is fixed with no call backs. See Hail Damaged Roof Replacement: Part 4 – Gas Flue Vents.


  9. Sara July 5, 2016 at 7:55 am - Reply

    We have lived in our home for 6 years and have been stumped by a leaks on inside of the back wall of our unfinished basement. The leaks only come with a driving rain. After reading about these roof vent pipes leaking, I’m wondering if it possible ours is leaking? We had a new roof placed 2 years ago with no improvement. Our house, like the one in the post, is extremely tall and the vent pipe would be very dangerous to try to reach from the outside.
    IF the source of our leaks is a vent pipe, is it possible to ONLY see evidence in the basement and nowhere in the two stories above the basement??

    • Bob Jackson July 5, 2016 at 9:37 am - Reply

      It’s very possible water is trickling down two stories of vent pipe. Have you looked at the vent pipe and roof penetration in the attic for water trails and drips? Toilet paper tissue is an excellent tell-tale. Wrap some toilet paper snugly around the vent pipe in the attic and secure with tape over the fold. Next time it leaks check the toilet paper as it will reveal the smallest leak even if the paper has dried.

      When you had the roof replaced 2 years ago did the roofer replace the vent boots? The vent boots shouldn’t be leaking so soon and the roof may be under warranty. A roofer knows how to safely climb the steep roof to inspect the boots.

      Another possibility is there’s a PVC elbow or coupling in the vent pipe that’s leaking. You only notice during a heavy rains when a lot of water enters the outdoor vent pipe. Normally rain water would drain into the sewer pipe but may leak if an elbow or union wasn’t glued properly.

  10. Buddy Kavanagh April 4, 2017 at 1:09 pm - Reply

    please visit [Editor: website redacted]. My new product prevents damage from stack leaks.
    We are looking sales persons and installers. probably upto $500.00 per working day.

    contact me at [Editor: phone number redacted] Thanks Buddy

    • Bob Jackson April 4, 2017 at 6:50 pm - Reply

      Hi Buddy,
      Interesting invention which treats the symptom but not the cause of a vent boot flashing leak. In my opinion, it makes the situation worse by masking a leak until the roof deck has rotted.

      I’ve redacted your web site and phone number because:
      A. Your product creates open slots in the vent pipe which allows sewer gases to enter the attic.

      B. Venting in the attic probably violates the following 2012/2015 International Plumbing Code Sections:

      904.3 Vent termination.
      Vent stacks or stack vents shall terminate outdoors to the open air or to a stack-type air admittance valve in accordance with Section 918.”

      903.4 Prohibited Use.
      A vent terminal shall not be used for any purpose other than a vent terminal.”

      903.5 Location of Vent Terminal.
      An open vent terminal from a drainage system shall not be located directly beneath any door, openable window, or other air intake opening of the building or of an adjacent building, and any such vent terminal shall not be within 10 feet (3048 mm) horizontally of such an opening unless it is 3 feet (914 mm) or more above the top of such opening.”

      C. Your web site provides no information about Code compliance.


  11. Kawika April 20, 2017 at 8:59 am - Reply

    Hey Bob,

    I have a 4 inch vertical cast iron pipe exhaust vent for my bathroom exhaust fan. It is leaking water into the bathroom. I sealed the boot, surrounding shingles and flashing with geocel sealant. However, water is still leaking in somehow.

    My question: How often do you see rain water entering directly in the the mouth of the pipe as the cause of the leak? Is a pipe cap worth the while? (here is an example 4in pipe cap or

    Any thoughts are appreciated!

    • Bob Jackson April 20, 2017 at 12:04 pm - Reply

      Cast iron pipe for a bathroom exhaust fan is highly unusual. Is it an older home? Was the bath fan retrofitted some years later? I suspect the iron pipe is or was part of the Drain Waste Vent (DWV) system. Someone may have repurposed the iron pipe or tied into it.

      When a DWV pipe vents through the roof to the outdoors, rain water isn’t a concern because it runs down the vent pipe into the sewer line. The problem is when rains enters a roof vent pipe connected to a bathroom vent fan the water has no where to go and leaks. It’s a bad setup anyway you look at it.

      Go in the attic and trace the cast iron pipe to see how it connects to the bath fan duct. If the fan is connected by a Tee fitting it is improperly repurposed as an exhaust duct while it’s still functioning as a sewer vent. If the fan is connected by an elbow fitting and there are no other pipe connections then rain water is pooling inside the pipe and probably leaking at the fan duct connection.

      If the cast iron pipe is only serving the bath ran you may get by with one of the pipe caps you referenced – assuming it fit’s because 4 inch nominal iron pipe outside diameter is actually 4.30 inches. However, cast iron pipe promotes condensation which will pool inside the pipe causing leaks.

      I recommend reworking the bath fan duct and outdoor vent connection using insulated flex duct to either a soffit vent or new roof vent. These projects may be helpful:
      * How to Install a Soffit Vent and Ductwork for a Bathroom Vent Fan
      * How to Replace a Bathroom Exhaust Fan and Ductwork – Part 2
      * Panasonic WhisperFit EZ Fan Old Work Ceiling Mount and Junction Box Wiring

      If you decide to vent the bath fan through the roof, use an attic roof vent cap.

  12. B. Yoder June 23, 2017 at 10:56 am - Reply

    Thank you for this post!

    We recently bought a 1951 home with a deteriorating roof (cedar shake on top of asphalt shingle), and there is a leak around the vent stack; water runs down the stack all the way into the basement, and we have some water damage on the ceiling. We cleaned out around the stack, removed insulation, etc to help it dry out. We removed some of the shingles and caulked around the boot (it was raised a bit from the roof, and there were some holes as well.)

    We are going to have the roof replaced, and want to prevent more water damage inside while we are waiting (a month). Would it be crazy to use some of that expandable foam inside the attic around the stack to keep water from coming down the pipe?

    Thank you very much, this blog is very appreciated!

    B. Yoder

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