How to Patch Up a Leaking Rubber Roof in 8 Steps

Patch up that leak in no time

Ben Kissam
Written by Ben Kissam
Reviewed by Ami Feller
Updated July 27, 2022
A house’s flat rooftop with installed vents
Photo: Michael Kai / The Image Bank / Getty Images
Difficulty

Intermediate

Perfect for handy homeowners.

Time to complete

2 hours

Cost

$100–$250

Doing the labor yourself goes a long way

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What you'll need:

TOOLS

  • Utility knife
  • Power drill
  • Paint brush and/or paint roller
  • Ladder
  • Tape measure
  • Caulk gun
  • Marker

SUPPLIES

  • New rubber roof section
  • New substrate section
  • Fiberboard or scrap piece of wood (for cutting on)
  • Contact cement
  • Rubber membrane cleaner
  • Lap sealant

Many homeowners choose to install rubber on their home over other types of roofs because they help protect against rough weather. But even the best rubber roof can spring a leak from time to time, causing water to drip in your attic or even rooms inside your home. 

Fortunately, the fix isn't too complex. You'll need some common tools, a replacement piece of rubber and substrate, and a few more supplies you can pick up at a hardware store. Read on for eight steps to patch up your leaky rubber roof.

  1. Climb Your Roof Safely

    A quick disclaimer—roof climbing isn't for everyone, so make sure you have the strength, coordination, and confidence before climbing on top of yours.  If you’re not comfortable getting on your roof, it’s best to outsource it to a local rubber roofing contractor

    Never climb on a roof during inclement weather (high winds, snow, rain). Also, never make a repair when the roof is wet, because products won’t adhere properly. Be sure to practice good ladder safety by climbing slowly and having a friend or family member hold the base. Ideally, you shouldn't complete this task without assistance, even if it's just having someone to keep an eye on you.

  2. Identify Where the Leaks Are

    Without being on top of your roof, you can't know exactly where the leak is. But you can probably pinpoint the location, or at least get an idea by looking for all the spots water is seeping into your home first. After all, leaks are one of the most common rubber roof repairs needed.

    If it helps—especially if there are multiple areas leaking—draw a small diagram to bring with you when you get up on the roof to patch it up so you don't miss one.

  3. Cut the Damaged Area With a Utility Knife

    Once you're safely on your roof with the tools you'll need to complete the job, locate the first leaking section. It'll most likely appear damaged, dented, wrinkled, or could even be missing.

    Cut a square around the entire damaged portion of the roof using a utility knife. You might use a board or piece of fiberglass to keep the cut as straight as possible. Set the damaged piece aside.

    This is a less expensive option than the cost to install a new roof coating, which can cost up to $2,500.

  4. Remove the Substrate

    Underneath most rubber roofs you'll find screws holding down a piece of substrate. This is what your rubber roof is adhered to and offers both insulation and water protection. If your roof is leaking a lot, this may need replacement, too. 

    Remove the screws (and caps) holding the substrate down and set them aside. Use your utility knife or power saw to remove the damaged substrate section. Below it you'll find exposed wood. Use your hands to remove any excess pieces so the section is clear before continuing.

  5. Fit a New Piece of Substrate and Rubber Roof to the Hole

    Roofing membrane rolls on a flat rooftop
    Photo: Doralin Tunas / iStock / Getty Images Plus / Getty Images

    Line up your replacement rubber roof section (and substrate, if needed) over the hole. Use a permanent marker to mark a section that'll fit snug over the gap. Use that piece of fiber board or scrap wood to keep the cut straight. You'll need to cut the new piece larger than the actual hole so that you have overlap of at least two to three inches. The manufacturer installation instructions should provide you with the exact overlap amount.

    Repeat this step with your new piece of substrate, if needed. Screw the substrate piece back into place afterward to cover the wood.

  6. Use Scrap Roofing to Even Out (If Needed)

    In some cases, especially if your rubber roof is older, the new substrate piece may be slightly thinner than what's installed on the rest of the roof. If this happens, lay a scrap piece of rubber roof—either any that's leftover from the piece you just bought, or the old piece folded over itself if it isn't too damaged—down to even it out. This will add a little thickness to help even it out.

  7. Clean the New Rubber Mat, Then Attach With Contact Cement

    Take your paint roller and dip it into a rubber cleaning solution, available for $10 to $15 at home improvement stores. Run this along the piece of substrate or extra piece of scrap roofing, as well as the side of the new rubber roofing that will face down. 

    Once dry (it won't take long), add contact cement to both the top layer of substrate/scrap rubber and half of the new rubber mat. Roll it into place gently and press firmly to seal on all parts of the mat. Repeat the process on the other side.

  8. Apply Caulk or Lap Sealant Around the Edges

    Finally, lay a bead of rubber silicone caulk or lap sealant around the edge. Lap sealant is more expensive ($20 to $25) as compared to silicone caulk. If you opt for basic caulk, make sure it's one that's suitable for rubber and rated for outdoor use.

    Repeat steps 3 through 8 as needed on other areas of your roof.

Patch a Leaking Rubber Roof DIY vs. Hiring a Pro

If you’re not experienced with this type of repair, it’s best you call in the professionals. It's not worth an accident or further damaging your roof, which could be quite costly—far more than you'd pay to simply have someone who knows what they're doing tackle the project. More extensive roof repairs cost anywhere from $400 to $2,000 depending on the scope of the project.

Need professional help with your project?
Get quotes from top-rated pros.