Patch a Leaky Flat Roof in 5 Steps

Lead Image
  • 2-4 hours
  • Beginner
  • 10-20
What You'll Need
Large broom
Drilling with screwdriver bits
Tin snips
Tape measure
Small brush
Garden hose
Roof flashing
Roofing cement

A flat roof must be checked frequently for any leaks to prevent extensive damage. Determining the exact location of the leak is the most time consuming and challenging part of the procedure since it can be several feet away from the damaged part. Once the spot is located, patching a leaky flat roof is quite easy. Remember to be very careful when working on a damaged roof to prevent possible accidents.

Follow these 5 steps to do the job of preventing water from leaking inside yourself, instead of hiring and paying a professional to do it for you.

Step 1 – Sweep the Roof

Before you begin, sweep the roof clean to remove any debris or dirt so the leak is visible. There may be more than one leak, so inspect the entire area thoroughly to avoid repeating this step. Also, the roofing cement you will apply to patch any leak will not stick to a dirty surface.

Look for an area where the water will seep through the layers or puddle up and mark it with chalk, or for any damaged, loose or split flashing. Also, check the aluminum trim around the edge of the roof for any holes and mark them for patching

Step 2 – Remove Damaged Flashing

Use a drill with screwdriver bits to remove any leaking flashing. Pry it open with a chisel and hammer if it is stuck. Put your gloves on and clean the entire area with a stiff brush to locate the exact site of the leak. Also, look for cracks in the roofing material underneath the flashing.

If there is a part of the roofing material that is totally soaked or damaged, cut it carefully with a razor knife in a square or rectangular shape.

Step 3 – Apply Roofing Cement

Spread a layer of roofing cement under the flashing with a trowel, forcing it down into any cracks or holes. Spread the cement 3 inches around the repaired area to secure the leaked patch. Wait 15 minutes for the roofing cement to set in place.

If you have cut out a layer or more of roofing material, you need to replace that before applying cement. Place the cut piece over the replacement patch and cut it in the same pattern, adding an inch to it all around.

If you removed more than one layer of roofing, cut enough patches to make sure the new section is line with it’s surrounding. Apply roofing cement to it and insert it into the hole. Nail the other layers over it and apply cement to the top layer to hold it in place.

Step 4 – Replace Flashing

Cut your new flashing at least 2 inches bigger all around than the patch you want to repair with a pair of tin snips. Drill it tightly into place using long nails that will not come loose with high winds.

Step 5 – Water Repaired Area

Follow the label instructions on the roofing cement for drying time before watering the patched area with a garden hose for 5 to 10 minutes.