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Installing Roof Flashing | How To Avoid Two Common Mistakes

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If you have residential roofing formed out of asphalt shingles, then you likely have some flashing on the structure as well. Flashing is a metal material made from either steel or aluminum, and it is adhered to the roof to prevent water and ice from leaking into the home. Flashing must be placed over seams for the best protection, and you may find the flashing on your roof falls into a state of disrepair far more quickly than the shingles themselves.

It is in your best interest to repair or replace the flashing when you see it is no longer in good shape. When you do this, you should try to avoid some common mistakes that some inexperienced individuals make, like the following things. 

Forgetting to Add the Correct Membrane

When an asphalt shingle roof is installed on your home, professional roofers will generally place felt material over the plywood before the shingles are secured. The felt helps to keep moisture from reaching the wood roof base if rain find its way underneath the shingles. This is ideal to keep the plywood materials from rotting.

Some people choose to place the same type of felt underneath flashing. Unfortunately, the felt does not stand up well against water and ice that sit for long periods of time and tend to flow underneath flashing materials. Water is more likely to seep under the flashing in valley areas where two separate parts of the roof form a trench. If flashing is replaced across a valley, then you will need an ice and water shield material instead of regular roofing felt. 

Ice and Water Shield

Ice and water shield material is made out of an asphalt and rubber mixture, where the felt is made from fiberglass and asphalt materials. The rubber helps to form an impenetrable barrier and the glue that lines the back of the product allows you to secure the material in place with little difficulty. You can even add roofing nails to the membrane and the rubber will create a seal around the hole to prevent leaks. When you use the ice and water shield, just make sure to overlap the membrane wherever there are seams.

Overlooking the Caulk

When you add flashing to your roof, you will likely place a thick layer of adhesive around the inside edge of the metal before sticking it in place. Roofing nails are also needed to ensure the secure placement of the flashing. However, polyurethane materials can shrink over time and nails can come loose. This can leave openings where water can move under the flashing.

To prevent this, make sure to add caulk around the very exterior of the flashing where it comes into contact with the roofing shingles, the chimney, or the side of your home. You will need to purchase gutter and flashing caulk for this job, since this material can withstand both extremely hot and cold temperatures. 

Other Flashing Securing Techniques

If you live in an area that sees a great deal of rain, snow, and ice, then you may want to add some extra protection to make sure that your flashing will not leak or become dislodged in some way. You can do this by securing a special adhesive underneath the flashing before you add your caulk. The best adhesive is made to withstand hurricane winds and torrential downpours and it is called hurricane force flashing adhesive. This adhesive does not contain a lot of water or solvent materials, and this means it is thicker, stickier, and stronger than other adhesives. This allows the material to withstand 400 pounds per square inch of pressure without becoming damaged.


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