One of the most common places to find a leak in a flat roof is along the flashing. The reason for this can vary from incorrect installation to normal weathering. Water that runs behind the flashing can cause a leak even if the rest of your roof is in good condition. Repairing the flashing will depend on what type of problem it has.
Flashing around a Stair House
Some flat roofs will have a stair house that provides access to the roof from the building below. These stair houses should have siding, and problems can arise where the siding and the flashing meet. Contractors should put an L-shaped flashing around the bottom edge of the siding. If this flashing is placed on top of the siding, water can run down the siding and leak behind flashing even if the top edge is sealed or when the seal wears out.
On the other hand, if you place the flashing behind the siding, any water will run down the siding and meet the solid body of the flashing, so there is no chance of a leak. If you find incorrectly installed flashing around a stair house, you have no choice but to tear out the old flashing and replace it with correctly installed flashing.
As metal flashing heats up it will expand and then contract as it cools down at night. This cycle of heating and cooling can pry out the nails that hold the flashing in place and break down the caulking that seals the top edge of the flashing. Water can then run down vertical protrusions on top of or along the edges of your roof and create leaks. To repair the flashing, you should replace the nails with screws — make sure the screws are made from the same metal as the flashing to prevent corrosion. Once the flashing is back in place, reseal the top edge of the flashing with a bead of caulk.
If a leak manifests itself in the middle of your ceiling, you might think that you have a leak in the middle of your roof. This is not necessarily the case. Instead, a leak might start at a vent pipe or stair house, then run under your roofing for a few feet before it starts leaking through to the building below. Thus, when you look for leaks in your roof, you need to take into account the flashing and make repairs as necessary.
Talk with a roofing contractor like RTN Roofing Systems if you have specific questions about flat roof repairs and maintenance issues.