Your Roofing System | Part III: What is The Purpose of Flashing?

7/24/2017

In part III our roofing system guide series, we’re covering a common question: What is the purpose of flashing?

Shingles cover the majority of the roof, but there remains plenty of seams and openings that shingles can’t cover. These areas, if left uncovered, provide excellent pathways for water and other harmful elements to enter your home. A roofing system is not truly complete until all areas of the roof are protected. Flashing helps achieve this goal, and is key for a properly functioning roofing system.

The concept and purpose of flashing is rather simple–a barrier

Flashing is a barrier, usually made of metal or plastic, that aids in the redirection of water that otherwise would seep into the small cracks and openings of a roof. Whether building a new home or repairing the roof of an existing home, flashing is vital in preserving your home’s structural integrity.

Roof flashing is an integral part of your complete roofing system

Where is roof flashing applied?

Flashing is applied on roofs in areas where there is an increased chance of water infiltration. These areas include, but are not limited to, valleys (the meeting point of two downward-sloping roof planes), ridges (the apex where two upward-sloping roof planes meet), chimney walls, vents, pipes, skylights, and dormers. At these locations, your roof is more vulnerable due to the proclivity of water to settle in these areas and the natural gaps present where these areas meet the roof. This means that special protection is required in these areas to prevent water from infiltrating the roof, damaging the interior of the home, and possibly leading to indoor mold problems.

Careful consideration needs to be taken when choosing a roof flashing material

The three main factors to consider when selecting flashing are weatherability, durability, and elasticity. Depending on where you live, the priority of these 3 factors may change.

Weatherability – It is important for all types of flashing to be able to stand up against the weather. This doesn’t just mean the wind and the rain. Flashing needs to be able to withstand the sun’s punishing rays as well. Flashing can be damaged by the sun over time, leaving your roof and home at risk.

Durability – Just like all roofing materials, flashing must be durable, however some flashing is more durable than others. If you don’t want to worry about repairing or replacing your flashing in the near future, a more durable flashing made from copper may be the right choice for you.

Elasticity – As the seasons change and temperatures go from hot to cold and back again, your roof experiences a series of expansions and contractions. To keep moisture from infiltrating your roof during these periods, the flashing must have a degree of flexibility to allow it to expand and contract with your home. This factor is not as important in regions that do not experience great temperature change, however even minute temperature changes can cause your roof to expand and contract so this factor should not be completely discounted.

The flashing material that is best for your roof is contingent upon which of the above 3 factors are most important to you. Below are the 3 most common flashing materials and their pros and cons.

Rubber – Inexpensive. Fair weatherability and elasticity. Poor durability.

Plastic (Most commonly PVC) – Inexpensive. Fair durability and elasticity. Poor weatherability.

Metal

• Galvanized Steel – Inexpensive compared to other metal flashing. Great durability. Fair weatherability (Prone to rusting unless coated), Fair elasticity.
• Aluminum – Great durability and elasticity. Fair weatherability (Prone to rusting unless coated).
• Copper – Great weatherability, durability, and elasticity. Can be expensive.

Your roof is your home’s first and last line of defense against the elements and if it were not for flashing, your roof would be fighting a losing battle more often than not. Flashing is crucial to the proper functioning of your roofing system and proper consideration needs to be made when replacing or repairing flashing.