Why Does Old Roof Underlayment Need To Be Replaced?

The underlayment is an unseen yet essential part of every roofing system. While it’s not exposed to the elements, you may be wondering why roofers tear it down along with the rest of the roof during roof replacement. In today’s post, local roofing contractor Shine Construction Inc. discusses why old roof underlayment has to be replaced.

What Is Underlayment?

The underlayment is a type of moisture barrier that’s installed between the decking and the outer layer of shingles or other roofing material. It serves as a secondary layer of protection against water infiltration if the roof’s outer layer is punctured or otherwise damaged. Traditional underlayment, also known as “organic” underlayment, is made of paper pulp soaked in asphalt, while synthetic underlayment is made of woven polyethylene or polypropylene. The latter is more commonly used in today’s roofs.

Why New Roofs Need New Underlayment

It’s important to note that underlayment removal is part of the standard roof replacement process; keeping it is the exception. Some homeowners and DIYers are known to keep underlayment to cut roofing costs down, or if the old underlayment appears to be undamaged. The following are some of the reasons why old underlayment has to be replaced:

• Lower risk of leaks. The outer roofing material — asphalt shingles and metal, in particular — are fastened all the way to the roof deck. This means old underlayment will have holes in them once the old roofing is removed. Unless the roofer is able to install fasteners precisely where the old holes were, keeping old underlayment would defeat its purpose.
• Decking repairs. Keeping the old underlayment sidesteps a crucial part of roof replacement: inspecting the condition of the roof deck. Issues such as moisture damage won’t be repaired, which can lead to bigger problems over time. While it is possible to inspect the decking from the attic, it won’t be as thorough, especially if insulation is installed on that side.
• Limited roofing selection. Most roofing manufacturers require new underlayment as part of their roofing system. This can severely limit your choice of roofing products, along with exclusive warranties.

Planning on getting a new roof before the fall season? Get in touch with our team at Shine Construction Inc. at (508) 278-3300. You can also fill out our contact form to schedule a consultation.