There can be many reasons for a roof leak. Leaks can be the result of poor system installation, mechanical damage, plugged drains, material failure, HVAC problems; and on and on. The source of a leak can be quite distant from where it actually shows up. For example if there’s a hole in your shingles and the water gets in this hole, and then has to run along the top of the underlayment (15Lb felt paper) until it finds a hole there. Then it runs along the top of the decking until it reaches either a hole in the decking or a seam. Then it drops down in the attic and will run along the top of the ceiling until it reaches a hole or seam in the drywall, plaster, etc. The distance can be lengthened even further if you have more than one layer of roofing on your home.
Chasing a leak isn’t always as easy as it would appear to be. Inspect any drains near the leak area. If they are plugged or draining slowly, then there is a strong chance that they are the reason for the leaks. Drains are rarely waterproof if they are plugged. They are generally designed and constructed for water to flow in one direction only and that is down.
Inspect any material seams in the area of the leak. Just because you see "tar" or adhesive sticking out under a lap, it doesn’t mean that the material is adhered properly. Take a flat blade about 2 inches (5 cm) long (like a pocketknife blade), and gently run it along under the lap. Look closely at expansion joint seams. These are often faulty. Check for splits in the area. Do this by walking the area with your feet close together and taking many small steps, turning in all directions. If there is a split, you’ll see the material separate between your feet. If the leak occurs near the edge of the building, check the edge metal. It can separate at the seams and tear the membrane in the process.
Check under debris. A lot times, if debris has been sitting for a long period of time, then it can hold water which will expedite deterioration. Bird, rodent, and other vermin nests have been found under piles of debris. If you get a bad rain storm that dumps large amounts of water in a short period of time, and all of a sudden you have half a dozen leaks where before there were none, don’t get overly excited. Most roofs are not designed or constructed to handle that much water all at once.
If you look carefully, and find nothing, then check your attic or ceiling space. What is mistaken for a roof leak can sometimes be a problem with the plumbing or air conditioning lines sweating that have been routed through the attic space. These can be re wrapped with the correct insulation and solve the problem. And another problem that is frequently mistaken for a roof leak is a poorly designed roof-mounted HVAC unit that can have faulty pans in them which will permit water to enter the building during a rain storm.
Look at all roof penetrations in the leak area closely for holes and / or damage. Look for nails that were not covered by the following course of roofing material. If left exposed too long, many nails will rust, leaving a hole and causing leaks and the heat from the sun will actually start to draw the nail out if it was not driven into the decking properly.
Look at the mortar on chimneys and although it’s rare, damaged mortar can cause leaks.If your building has stucco, then cracks in the stucco, especially along the tops of walls, can be the source of leaks.
Check to make sure that all drain details are functioning and that your gutter is not full of debris. If your edge details and gutter details are not done correctly, water can back up over the top of the fascia, run along the soffit, and down the inside of the wall where it enters your building.
Finally, if you are not able to determine the causes for your leak and fix it, please consult a professional roofing contractor in your area as water damage is one of the most destructive processes a home can experience and working on a roof is very hazardous.
Note: Due to the ever changing building codes, it is important to check with your local building department to do all repairs and re roof projects according to code requirements!!
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