Flashing - a necessary defense against leaks

The Old House Web
Flashing is perhaps one of the disappearing crafts in the world of modern materials that seem to suggest simple installation,"no-worry" performance, and low maintenance.

An emphasis on quick installations often comes at the expense of flashing. Good flashing installations take time -- but it is time well invested. So, if flashing is to be installed, it is best to invest the effort to make sure it's done right.

Rules of Thumb and Tips

  • Flashing is necessary for proper drainage plane performance in walls and for roofing systems.
  • Most leakage problems are related to improper or insufficient flashing details or the absence of flashing.
  • All openings in exterior walls and roof penetrations must be flashed.
  • Caulks and sealants are generally not a suitable substitute for flashing.
  • Water runs downhill, so make sure flashing is appropriately layered with other flashings or the drainage plane material (i.e., tar, felt, or housewrap).
  • Water can be forced uphill by wind, so make sure that flashings have recommended width overlap.
  • Sometimes capillary action will draw water into joints between stepped flashing that is not sufficiently lapped or that is placed on a low pitch roof; take extra precaution in these situations.
  • Avoid joint details that trap moisture and are hard to flash.
  • Treat end joints of exterior wood trim, railings, posts, etc. prior to painting; paint end joint prior to assembly of joints; if pre-treating, be sure the preservative treatment is approved for use with the type of paint or stain being used.
  • Minimize roof penetrations by use of ventless plumbing techniques, such as air admittance valves, side wall vents, and direct vented appliances (check with local code authority for approval).
  • Use large roof overhangs and porches, particularly above walls with numerous penetrations or complex window details.

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