Flashing: A Key Construction Concept

Flashing is the term applied to materials used to seal seams where building materials meet, and where water has the potential to get into your home and cause damage. It is a key concept as most water damage remains invisible for years and the cost of repairs increases as the scope of the damage gets larger. You always want to repair water damage as soon as it's found to keep repair costs to a minimum and avoid health issues due to mold.

The biggest challenge is knowing where flashing should be installed, and that it was installed properly which takes skill to determine. Here are the most common places for flashing, and don't get flustered when your contractor uses a different term, i.e. the flashing under the edge of a roof is called drip edge … but it's still flashing.

Where Flashing Is Used in Home Construction

Flashing may have many other names, like drip edge for the edge of a roof. Regardless of the name, flashing is a key component in almost any type of construction. Here is a list of the most common uses for flashing.

• Flashing is key on the roof where chimneys, skylights and vents for plumbing and air ventilation are found. Properly installed, flashing insures gaps are sealed and water has a watertight path to follow gravity to the ground.
• Your home's design may also require flashing where the roof meets a sidewall or another roof line, commonly known as a valley.
• At the lower edge of the roof is flashing known as drip edge. This flashing lets water from the roof run off the edge and not down the trim boards (fascia) directly underneath the roof, which can rot when made of wood. It also supports the piece of the shingle that extends beyond the roof sheathing. Drip edge is also installed on the gable ends.
• On the sides of your home, flashing is used where windows, doors and trim boards meet the siding, to insure that water doesn't penetrate the outer surface of your house. Flashing is most critical above windows and doors where any water that has gotten underneath the siding needs to be channeled around the windows.
• Flashing is also important at the base of window sills and door thresholds, to prevent water from entering your house at these intersections. Thresholds are most vulnerable as there is always a platform just 8 inches below any exterior door and water can splash up, a common handyman repair.
• Sitting immediately on top of your foundation is the sill plate which is made of wood and therefore vulnerable to wood rot. Flashing insures water running down the siding doesn't come into contact with the sill, which provides support for your homes framework.
• Decks are commonly attached to a house using a ledger board. As the deck interrupts the flow of water from above, flashing that channels water around the ledger board is critical.

The following diagram illustrates how extensively flashing is used throughout a home's construction. Water damage is costly so proper installation and maintenance of your home's flashing is cost effective compared to repair costs.

Read about a real deck wood rot problem and repairs by my handyman team.