Advanced Home Renovation Visualization Tools

How to trace water leaks on a flat roof

“NOTES TO THE NEIGHBORS”                                                                     September 2016





I hope that my house maintenance tips last month were helpful to you; here is some more useful information for you. If you have any misc questions, feel free to email me ----


This month I will cover how to trace water leaks on a flat roof.


A roof with a pitch of less than 4:12 is considered a low slope roof. This means 4" of vertical rise to 12" of horizontal run. Shingle manufacturers never installing shingles to a roof less than 3:12. These are considered to move into the flat roof category. It is necessary to use a membrane type of roofing material when the surface has such little pitch. I strongly recommend that if you replace your roof, do a complete tear off and replace the flashings too. A leaking roof can be one of the most difficult repairs to complete properly. It takes patience, knowledge of weather patterns, some trial and error to locate them. Most flat roof leaks happen as the roof material is near the end of its useful life. Leakage can also be created by using the wrong sealants, lack of flashings, improper installation to wall and sloped roof junctions and penetrations. Falling branches from trees hanging over the flat roof can penetrate the roof material as they impact. Roof leaks are common and often overlooked. Flat roofs in our area are mostly synthetic rubber EPDM (ethylene propylene diene terpolymer). It comes in widths ranging from 7.5-50'. It is available in two thicknesses, 45 and 60 mils. It is normally fully adhered but it can also be mechanically attached. The seams are sealed with specially formulated tape or adhesives.


It will be necessary to use a ladder to inspect the entire perimeter. During this portion of your inspection look at how the roofing materials outer edges are terminated. If they lap over downward about 2" and have a drip plate metal trim screwed into fascia, this should be sufficient. If the roof has a gutter attached, it should be below this drip plate.  It may be necessary to walk it to inspect the surface. Have a professional do this if you are not comfortable up there. Move slowly and be cautious of soft spots so that you do not step through the roof. Look for ponding after a hard rain. Mark the areas by circling them with chalk. When the surface is dry inspect for lifting seams, tears, deteriorated sealants and areas that are bubbling. Bubbling is caused by applying the rubber roof material before the solvents in the adhesive have a chance to flash off. This means the roofing was applied before both surfaces had a chance to become tacky, and nearly dry to the touch. When looking at the areas where your rubber roofing meets another roof section, it should travel up the roof slope uncovered for approximately 1-2' and then terminate beneath the asphalt shingles. Where it meets the house walls you should notice that it is installed beneath the first row or two of siding. Areas without siding should have a metal term bar trim screwed to the wall and sealed over. If your flat roof has railings installed, the leaks may be located under or near the newel posts. Newel posts are the heavy vertical post portion of railing systems. They are most commonly spaced within 4' - 8' of each other to provide strength to the railing system.


Flat roofs usually do not allow for inspecting from the inside without removing the ceiling material beneath them. I find that difficult roof leaks are best traced from the inside after it has just rained. I use an infra red camera and moisture meter when inspecting the underside materials. If staining, flaking, or moisture beading is evident on the plaster or drywall ceiling, it may be time for some investigative work . Keep a bucket beneath the area to be worked on. Drill a hole at the low point of the ceiling in an oval shape to allow the water to escape. This will help to preserve the building materials. If the ceiling is opened up, look for clues such as dark areas on the roof deck and rafters compared to the surrounding materials. Cover the open ceiling with heavy clear plastic after the insulation has been removed and the first inspection has occurred. Allow the area to dry out and watch it during following rain storms with wind coming from different directions. Keep a journal to track weather such as wind speed and direction will assist you to trace the leak.  Do not repair a ceiling without verifying that the leak has been addressed and eliminated. Leak verification testing at the pin pointed problem area should also be done after the roof leak has been repaired. This will ensure that the leak has been terminated.


Keep in mind that excessive sealants and tar applied to flat roofing is usually a patch covering a defect. Most flat roofs require a new piece of the same material cut in and lap joint sealant. This is not like regular roof tar such as blackjack. It will self level and seal the seams tightly where they meet. It is difficult and takes time to locate flat roof leaks and it is costly to make the repairs to the damaged areas beneath. This is my advice, if your flat roof is older than 25 years and is leaking, don't bother patching it, your money is best spent fully replacing it. When properly installed, the newest materials and flashing methods will eliminate your concerns for leakage and mold growth.



Jim Houghtaling                                                                  


        Renew View Custom Trim LLC

Stands for Quality Craftsmanship