If you have a flat roof on your home, chances are good that it has one or more scuppers. These essential features need to function well to keep your roof from flooding; however, they occasionally are unable to work as designed, and that's when they will need repair. Below is how to identify scuppers, what they do, and how you can get them back in their original functioning condition:
Repairing the scupper - what you will need
Bitumen-based roof membrane - this product is a combination of asphalt, rubber and other materials. It comes in rolls and is available from hardware stores and home improvement centers.
Roof cement - this product consists of a sticky, petroleum-based mix; it can also be purchased from hardware stores or home improvement centers.
Propane torch - use a propane torch designed for burning weeds and other similar tasks. You will also need a standard-size propane bottle that is used with gas-fired grills.
Extension ladder or inside roof access
Repairing the scupper - step-by-step procedure
When working on a flat roof, or a roof of any kind, the first consideration is safety. Keep in mind that flat roofs may have electrical hazards, such as power lines; also, beware of fall hazards such as skylights and working near edges. Wear gloves to protect your hands from heat or flame, and be cautious when using the torch so that you don't cause a fire.
1. Identify the scuppers – scuppers are small openings placed along the inside edge of a flat roof. Rainwater or melted snow drains into scuppers, and the water is then carried away down a gutter. Along with interior drains, scuppers are essential for preventing water from pooling on top of flat roofs.
2. Inspect the scuppers – ideally, the bottom of the scupper should align with the surface of the roof. However, it is not unusual to find a scupper that is much lower than the roof surface; as roofs age and are resurfaced, layer upon layer of roofing materials are added. If roofers don't cut-away material around the scupper, the roof surface eventually becomes high enough to obstruct the scupper. When you locate scuppers in this condition, you will need to cut away material to provide access to the water.
3. Cut excess material – using a utility knife with a sharp blade, cut away the layers of roofing felt, tar, paper and other materials that are blocking the scupper opening. Cut away a rectangular-shaped section that measures about 12 inches away from the scupper. Extend the ends of the rectangle about 3 inches from each end of the scupper.
Keep cutting until you reach the same level as the scupper. Be careful not to damage the wooden underlayment as you continue downward. Remove as much debris as possible from the area and clean up the edges of the rectangle with your knife.
4. Measure and cut the roofing membrane – measure the length and width of the rectangular-shaped section you just cut, and add 12 inches to each side. For example, if you cut out a rectangle that measures 14 inches long by 12 inches wide, you will need to lay out a rectangle on the membrane that is 26 inches by 24 inches. Cut out the rectangle with your utility knife.
5. Spread roof cement – use the trowel to spread a layer of roof cement about one-quarter of an inch thick inside the area where you removed old roofing material.
6. Heat the back of the roofing membrane – use a propane torch to heat the black backing of the roofing membrane piece you cut in step 4. Heat the membrane to where the backing starts to bubble and become tacky, but be careful not to ignite it.
7. Place the roof membrane – immediately after heating the roof membrane, center the roof membrane over the area where you made the cut and placed roof cement. Carefully push it into position so it adheres, and use the trowel to push down the edges.
8. Cover the edges of the roof membrane – with the trowel, apply a layer of roof cement underneath the edges of the roof membrane so it is completely sealed.
9. Inspect your work – after allowing the roof cement to cure for a day, inspect your work to be sure all the gaps are covered. If you see any location where water can penetrate underneath the membrane or between the membrane and the scupper, fill it with additional roof cement.
If you don't have the time or tools to do commercial flat roof repair, contact a professional in your area.