2022 Flat Roof Leak Repair Guide

Typical Price Range To Install new Flat Roof Average: $6,980 - $9,720
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A flat roof repair costs $400-600, which is significantly cheaper than the cost of full replacement.

Moreover, having a pro repair your flat roof can easily extend its service life by at least 3-5 years. However, in some cases, trying to fix a leaking roof membrane might be a futile effort and a complete waste of money.

Often leaks, water damage and other issues may be the result of faulty installation, poor maintenance, or old age of the roof itself.

We will go through the common flat roof problems and signs that warrant repair vs replacement, so you can figure out the most cost-effective and lasting solution for your roof.

If you are ready to repair your flat roof, contact your local roofing pros for FREE Estimates!


Average Flat Roof Cost:

Low End
$6815
Mid Range
$8769
High End
$11211

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When To Repair Your Flat Roof

If your flat roof has been properly installed and maintained on a regular basis, and it started to leak, repairing it is best.

However, if the roof is old, has sustained major damages to due a natural disaster, or continues to leak despite the fact that repairs have already been done, replacement may be warranted.

If your roof is relatively new, look at your warranty paperwork. You may be able to have your roof repaired for free or at a discounted rate, depending on warranty terms. Most flat roofing materials carry a warranty of 10-15 years.

There are a couple of repair options to consider:

1) If you have EPDM rubber and don’t mind getting your hands dirty, you can purchase a DIY repair kit. It comes with an adhesive and tape for making localized repairs. This is also a quick and inexpensive option, if you are not planning to keep the property for more than a year or two.

2) If you don’t want to get yourself into an endless cycle of repairs every few months, get an EXPERT contractor to do the job. You may pay a few hundred dollars more, but you will save yourself thousands of dollars, as well as avoid stress associated with recurring problems in the long run.

3) If you have modified bitumen, you will most likely need a pro, as it requires torching to repair.

4) If you have a leaky tar and gravel roof, finding the source of the problem is very difficult. Even the most skilled pro will have a repair success rate of less than 50%. Consequently, it will most likely need to be replaced.

5) If you have a single-ply membrane, stay away from roof coatings. They are:

a. Expensive

b. Only last 2-3 years. Afterwards, the coating starts to peel, chip and crack. If your roof still leaks, it becomes virtually non-repairable.

Flat Roof Leak Repair

Flat roofs have inherent design and installation peculiarities that often lead to performance issues and a shorter life span.

A leak is the most frequent and common issue on any type of a flat roof. It usually happens as a result of ponding water that puddles for more than 48 hours, after the most recent rain.

Typically, water penetrates at the seams or flashings. It may also come from drains, chimneys, skylights, parapets and other penetrations. It is very rare to have a leak due to a puncture.

If water gets under the membrane, into the sheathing, mold and rot can occur. This is especially likely in areas with high moisture and frequent rain storms.

Flat Roof Materials Shrinkage

One of the most common repairs for a flat roof, such as EPDM membranes results from membrane shrinkage.

When a rubber roof shrinks, it can pull off parapet walls, drip edge or a chimney.

This is more likely to occur on a large building, and on one where the membrane has not been properly attached.

Flat Roof Damage Due To Foot Traffic

Another leak problem, especially for flat roof decks and commercial properties is heavy foot traffic.

Maintenance personnel (mainly HVAC contractors) and other random visitors going out on the roof, dropping tools, walking over fasteners, etc.

All these actions can accidentally puncture the membrane and causing other damages that need to be repaired.

Cost To Repair A Flat Roof Leak

The average cost of professional repair for a leak is $350-600. It entails things like:

– Patching a few small sources of leakage
– Patching a couple of puncture holes
– Fixing a chimney, skylight, or pipe flashing

Bigger jobs can run significantly more, and will depend on the scope and complexity of the work. Typically, contractors charge $75-100 per hour, plus materials.

How To Fix A Leaking Flat Roof DIY

If you are handy, doing a DIY roof repair will save you about 50%, compared to hiring a pro.

An EPDM rubber roof is the easiest and cheapest to repair on your own. You will spend $200-300 on materials, if you buy a roofing kit, like this:

EPDM Rubber Roof DIY Repair Kit

As you can see, this kit is made specifically for fixing a roof leak yourself, and has just the right amount of all required materials.

Otherwise, you would need to go to a supplier and get very large quantities, that will cost you at least 3 times more.

This is because single ply membrane parts and accessories are only sold in commercial size quantities, needed for contractors. For example, you would have to purchase 100 ft of flashing, 1 gallon of primer, 1 gallon of cleaner.

Its not really possible to DIY a TPO or PVC repair because, both of these require heat – welding equipment. Moreover, you will only be able to get large amounts of other necessary materials, as there are no DIY kits for homeowners.

Locating The Source Of A Leak On A Flat Roof

Before you can start the actual repair, the most important step is to find the source or multiples sources of leaks on your flat roof.

Pro Tip: did you know that if you have water damage on your ceiling, the actual source of leak may NOT be directly above it on the roof membrane?

This is because the water that seeps in through the exterior membrane can travel as much as a few feet until it penetrates a weak spot in the sheathing and leaks inside.

This means that discovering the real source of the leak may be a bit tricky and will require some careful examination of the roof.

Here are a few tips:

1. First look for the most obvious points of water penetration. Examine the roof for any holes, punctures, popping screws, rips or tears, visibly worn out areas, raised or separated seams, etc. Once you discover any of these, you will know that is where you will need to patch up the membrane.

2. If you don’t see any obvious damage on the membrane itself, look at flashings and caulking around your vents and other exterior roof structures. Often, leaks are located in these areas, because the original installer did not do a good enough job caulking all the penetrations.

3. In case you can’t locate the source of the leak on the roof itself, but have water spots on your ceiling, measure the distance from this spot to the nearest walls. Go back to the roof, and use those measurements to narrow your search area.

4. If your roof is leaking and you can’t find the source, contact a roofer to do an inspection and repair the roof.

How To Patch A Flat Roof Leak

Once you pin point all areas where your roof is leaks, its time to patch them up.

Small holes are the easiest and fastest to fix up. You can simply applying a rubber sealing directly to the puncture. Another option is to apply a peel and stick flashing patch to the area (be sure to follow the instructions).

If you discover blisters on your membrane, these will be a lot more challenging to repair. First, use a utility knife to cut through the blister. Use towels to dry the wet area under it (you can also use a propane torch). Once the area is completely dry, apply a peel and stick patch.

When it comes to blisters, one of the biggest mistakes DIYers can make is cutting too deep into the membrane when trying to cut through the bubble. If you are not sure how to do this correctly, its best to call a pro.

Last but not least, your roofing membrane can have a few big rips or tears. These can also be repaired using a peel and stick patch. However, this will require a lot more experience and skill. First, you need to remove all the damaged material.

Be sure to prepare a completely clean and dry surface before applying any new patches. There are various sizes of EPDM rubber rolls that range from 3 to 50 inches, so you can get one most appropriate for your needs.

As mentioned earlier, all other types of flat roofs, such as modified bitumen, tar and gravel, PVC and TPO are a lot more challenging to repair, require special tools and expert knowledge.

When Should You Replace A Flat Roof?

Flat roof replacement is a costly and time consuming option, and it should really be your last resort.
Just because your roof has had a few leaks does not mean it its time for it to go.

There are really only two scenarios that warrant a new install:

1.Old ageWhen the original material has reached the end of its service life, your best bet is to replace it. Depending on the roof you have, local weather conditions, as well as maintenance, this life-cycle may vary, as we have discussed above.

Since EPDM has seams that are prone to water infiltration, they will cause a lot of problems in areas with heavy and frequent rain storms. TPO may not live up to their fullest service life in areas with very high heat and drastic temperature fluctuations.

2. Faulty installation

Unfortunately, problems with installation happen all too often. In fact, this is the Number 1 source of all other issues, including leaks.

If you constantly need to fix a relatively new roof, it most likely means that it was incorrectly installed. Some of these can be fixed by a pro, but others cannot be. This is why getting a thorough inspection is so critical.

In case installation errors cannot be eliminated, the best course of action is replacement. Otherwise, you will just keep dumping money into a product that will never preform the right way.

Keep in mind, that if it turns out that there is wet insulation, it cannot dry out on its own and can cause mold issues and structural damages.

These are much more expensive to fix than putting on a new roof, or replacing a large section of the original one.

If you have enough money, opt for a premium material such as PVC. While it costs more that other single ply options, once you install PVC roofing, you will not have to worry about leaks and other problems again.

PVC roofing has hot air-welded seams that will never come apart, and will remain impervious to moisture.

It is also an Energy Star rated, cool material, that will reflect the sun’s heat, and save you hundreds of dollars on energy costs.



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This roofing guide is presented by Leo B.

I've been a roofer for 15 years, and specialize in Metal Roofing and Flat Roofing.

Have a roofing question or issue? Ask me any roofing question!

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37 comments on “2022 Flat Roof Leak Repair Guide

  1. Recently, my roof starts leaking and I acquired the services of roof replacement inc. I must say that it is very heartening to see the professionalism.

  2. Excellent and well written Leo. As a new roofing contractor starting out in Canada it’s nice to see a fellow contractor break it down so well and the longevity of roofs and that Roof Inspections are very important in my opinion to do to ensure your roof is at an optimal and functional state. To make sure it is doing what it is supposed to do and that it protects your home from the elements. I believe you should do a visual inspection from the ground as an owner once a year and especially after winter to see the condition of any roof whether its residential or commercial.
    Keep up the great work from your neighbour in Canada

    Costa Moutzouris 🙂

  3. I never took into account the fact that a flat roof would get damage from heavy foot traffic. My uncles’ apartment roof is flat. I wonder how often it gets damaged from foot traffic.

  4. The fact that most of the biggest problem that a homeowner will have when trying to perform roof leak repair is finding where the water is coming in from. The failure to find the wellspring of the break can prompt the mortgage holder fixing the off-base components of their rooftop. What I did is I called professionals to check on my roof to make sure to be inspected properly.

  5. I liked how you talked about getting an expert to work on the repairs if you don’t want to keep doing repairs every few months. I never thought about how this might happen if the job isn’t done expertly. It’s definitely something that I’ll pass on to my friend so that she can get her roof properly repaired.

  6. Living in an area with heavy hail makes it regular that we have someone knock on our door and tell us that we should consider roof repair. I was unaware that 40% of all homes need roof repair. Next time we have a hail storm, I’m going to call a roofing repair service to come and inspect our roof.

  7. Roof replacement is important. If your roof is already over 50 years of age is it recommended to have roof replacement. It may not be leaking but there may be some problems you are not aware of your roof has. Thank you for sharing this great post!

  8. I want a roof that I can spend time on. Thank you for letting me know that I should, make sure that you hire a pro, because a general contractor or a residential shingles guy will not know all the nitty-gritty details and complexities of these materials.” I’ll need to find a great service that I can rely on.

  9. Thank you for your article. We have had damage to our flat metal roof from Winter Storm Riley. We have had 3 roofing companies give us estimates to replace the roof with different methods and materials. They all say they work on slate, flat roofs, and shingled roofs, but have crews that specialize in the rubber or slate.
    One wants to remove the metal, inspect the decking and repair if needed then install 1/2″ HD ISO guard insulation. They want to install a fully adhered 60 mil. EDPM over the insulation. Warranty is for 3 years only.
    Another wants to “retrofit” the roof, removing the old metal drip edge, install 1/2″ fiberboard over the metal deck and fiberglass base sheet on the entire deck. Then he installs either Firestone 160 & 180 modified torched down rubber OR EDPM 60 mil. glued down rubber. He will replace the old drip edge with stainless steel. Warranty is 10 years labor 20 years materials.
    Please give us your honest opinion. I asked why the second fellow would not remove the old metal and he said it was not necessary and the insulation would protect the new roofing material from any old roofing nails etc. Thank you

    1. @P. Jackson,

      First, what state are you in?

      So I’d say both methods would work with one big exception, which you might have picked up by reading my articles. I’m absolutely against installing EPDM rubber. It’s a junk product that will fail after 7-10 years, because the seams will come apart.

      If you are doing a new roof, go with a thermoplastic membrane such as PVC or TPO. I personally prefer PVC, and the cost difference is either minuscule or non-existing (for materials), and installation is identical. So the installed cost difference is gravy for contractor.

      As for your project – it’s ideal to have old roofing removed and fix any rotted wood. That said, if you can get into attic and inspect substrate / confirm there is no rot, going over is an option (though not ideal).

      In both cases, get more insulation. 1/2″ ISO is nothing. Get 2-3 inches – it will pay off. Fiberboard is not insulation.

      Also definitely stay away from Firestone modified / torch-down. Modified is one of the worst flat roofs out on the market, and is only loved by old-timers 🙂 It is only good for one thing – puncture resistance, but as far as waterproofing, its as bas as rubber… just different.

      My honest opinion – get quotes for PVC or TPO from companies that specialize in it. You can get a cost estimate for PVC/TPO here: https://www.roofcalc.org/flat-roof-calculator/

      Best of luck – let me know which way you decided to go.

  10. I found it interesting that you said damage could be caused by foot traffic or people being too rough causing punctures in the membrane. I didn’t think that that could be a cause for that much damage. I will be researching this more.

    1. Well, if you think service techs or other people going onto a commercial roof, cannot cause damages, think again.

      We did a repair job on a 22 story building in Cambridge, MA, with 100+ punctures / patches, from idiots cleaning snow with ice picks.

  11. In this fast running life, we often see about roofing suppose if we are looking for any touch up at home we will spend money but 95% among us we never look after the roof.

    As you mention it’s a great point you made about price list(Avg.).So many of us want budget roofing so this thing will help them to fix the budget for their roof.I can say VERY INFORMATIONAL article.Keep Writing.Thank You!!

    1. Rick,

      I’m not sure what you are trying to say, besides “very informational” part … I’m also not sure how this relates to flat roofing.

      Finally, this site is not a place to get free mentions of your company by posting meaningless comments (no offense). If you want more exposure for your company, you should sign up for a listing in our FREE local roofing contractors directory.

      So please, next time, if you do post a comment – make it useful or interesting (preferably both).

      Sincerely, Leo

  12. It’s good to know that flat roofs require you to clean the drains often. My current roof has gotten to be old and I’m starting to notice signs of cracking along the perimeter. I feel like we should have it completely replaced with a flat roof to give our home more of a modern style.

    1. Stanley

      Definitely not. It’s against building regulations in EVERY state. Also you are trapping moisture and a lot of weight with 3 layers on the roof, which may result in roof collapse! I’m not kidding – watch this:

  13. I have a flat roof and need to get it fixed since part of it is starting to sink. I agree that you should get help from an expert so that you don’t have to pay for repairs every month or so. Something else to do is to get your flat roof inspected once a year so that you can catch any leaks early.

  14. A month ago my rooftop began leaking. It was under warranty. It was a lot of stress. My companion recommended that I file a claim. It worked out and now the roof is leak-free.

  15. I had my roof replaced last year. I have a mission style house in WPB FL. The drain is on the back parapet wall in the center and has great pitch. The gutter drain on the wall was not replaced and my roof leaks inside or around the drain. I asked when they were replacing the roof if they were putting new valley pans in the area and was told they couldn’t find a gutter to replace it and that it was in great condition. 1 year later I have a leak inside my bedroom closet. Are the roofers who did the work responsible for this damage? Thanks

    1. Nick,

      If the leak is from the gutter drain and it wasn’t part of the job, then they are not responsible. If they had to fix it, then they would be responsible… I’m not sure what valley pans have to do with gutter.

      So the best way for me to answer would be with pictures – take a few shots of the roof drain and gutter drain and wherever you think the leak may be and email to leo@roofcalc.org – then I can better “diagnose” and help you out.

      Leo

  16. That’s interesting that if there is a leak in a tar or gravel roof, the success chance is around 50%. I would say you should just get a new roof. Luckily, I don’t have such a roof. Unlucky for me, I do have a leak. Hopefully, it will be a successful repair.

  17. Ryan Johnson,

    You are so right! My husband has been a flat roofer and flat roof serviceman for 37 years. Old school is the best, if done by qualified skilled contractors and flat roofers. I read a comment a while back from another contractor who may have said it best- that these new supposedly better roofs are a gift to roofers because they do not hold up. And one last comment from me- just what is going to happen when all the older skilled flat roofers retire? A lot of the younger guys getting into roofing are there for a paycheck, unlike a lot of the older guys who, although the money is good, take a lot of pride in a job well done.

  18. Ya, i’m not a big fan of the flat roof. It always seems like they find a low point and the water starts to drip in. I would definetly recommend having at least a little bit of a pitch. Good article!

  19. My cousin has a shed in his back yard the roof has been leaking a lot of water on to the contents of the shed. You mentioned most flat roofs leak at seams or flashing and leaks are often due to ponding water. Do most roofing contractors prefer a certain material for flat roofs that may be more water resistant? It seems getting it replaced may be a good option.

  20. I have a flat rubber EPDM roof that the drip edge has rolled up and rotted the fascia board and some of the rafter tails I can sister the rafter tails replace some of the substrate and put on new gutters but where I splice the new EPDM with the old will that hold? The rubber roof is good 15 20 years old but is in good shape all scenes are tight except for the edges on the east side of the house there is A2 foot taper off the peak on the North and South sides of the house they used a j-channel over a drip edge which is turned up slightly but on the west side of the house where are they used the same material above the gutter 90% of that age curled up inch 1/8 foot length of fascia rotted and a two-foot area where there is a corner in the middle also has a leak on the corner near the edge of the house it’s a two foot overhang so what I was thinking of doing it rolling back the rubber roof patching the substrate and rafters then reattaching the roof will this work or should I cut off the rubber that eyepatch under and put on new EPDM either way there will be a seam

  21. I can see how you would want a flat roof expert. I probably would have just asked any normal roof contractor. Great tip. It makes sense that flat roofs would have more leakage problems, but I’m sure it’s more economical than putting an A-frame on an industrial sized building. Thanks for the info!

  22. We have a warehouse in Toronto, Ontario, Canada. Flat Roof size approximately 5,500 sq.ft. On roof is a bill board, a HVAC and for air Cooler cum heater unit in the show room-the main unit is on top of roof. Roof is about 15 so years old (not sure). After heavy snowfall , water flooded the office area and in warehouse.

    Please suggest what alternative we need to go by. I read your article, gave me lots of insight about the roofing.

    Thanks

    Sat

    1. Sat,

      I don’t suppose you know what type of roof material is there now?

      At any rate – 15 years is often the end of life for many flat roof systems (definitely end of warranty for most).

      So you can try patching it and see what happens – hopefully insurance company covered the damages. But since now you have a claim, I’d use it to the fullest. Take claim money install a new PVC roof (IB / Sarnafil / Duro-Last).

      Here are some insights into filing a claim.

  23. We have an EPDM flat roof on my home. I never realized that shrinkage could be such a problem. For now, the roof drains properly and has no problems. I’ll have to make sure that I keep an eye on it so there aren’t any future problems.

  24. You say that you should replace your flat roof when it’s reached the end of its service life. Is there a way of knowing how long the service life is? I don’t know what my roof service life is, but I’ve had it for about ten years.

    1. Hi Kenny,

      This depends greatly on the material you plan to use for your flat roof. If material is Tar & Gravel or modified bitumen or EPDM rubber, you will need at least 1/12″ roof slope, which can be achieved with tapered insulation.

      If you are using a thermoplastic roof such as TPO or PVC, you can go below 1/12 slope. In fact, premium PVC membranes such as IB or Sarnafil can withstand ponding water! But this is not recommended because it will create additional stress on the framing.

      So best advice is to use 1/4″ tapered insulation (1/12″ slope).

      Tapered insulation can be installed as a pyramid, with highest point in the center, but this will create a lot of waste … somewhere in 40% range … best is to slope from one end of the roof to another, and compensate with wider edge metal.

      Hope this helped. Good luck and let us know how you made out and what material you ended up using (as well as how much it cost you)

      Best regards, Leo

  25. Our office building has been around for several years, and we are trying to determine if it needs to be re-roofed anytime soon. I’m glad that I read this, as it appears that rolled asphalt roofs should be replaced at about 5 years. Thanks for sharing this with us, and we will be investing into a new one here in the next month or so!

  26. Traditional felt roofs, especially the domestic type, are more likely to leak on the board joints due to thermal movement, causing the felt to split.
    I would’ve thought this was more common than leaking seams.
    A flat roof is only as good as the person who lays it, and as a highly qualified and experienced fixer, I still don’t see why the traditional method with elastomeric materials isn’t promoted as much. I have never had to return to a job in 25 years, so really the “new and improved” materials such as PVC were only introduced because of the amount of cowboys and under-qualified operatives out there.