Roofing Underlayment: An Overview

RefurbishmentWhether you are replacing your shingles or building a new house, choosing which materials to put on your roof is an important decision. Most people concentrate on the shingles during roof repairs for Jacksonville homes; however, what goes under them is just as important.

Your roof is several layers of materials that protect the home from water, heat, and weather. Plywood is often used as a decking and is nailed to the struts. Shingles or a metal is often the most visible part of the roof. But because water can seep into the tiniest holes, there needs to be something else to protect the decking and the interior of your home from moisture, heat, and weather damage. Underlayment is a layer of protection between the roofing shingles or metal roof and the plywood decking. Depending on the material used, it can serve several purposes:

  • Water resistance
  • Thermal barrier
  • Fire retardant
  • Anti-slip technology (with certain products)

There are many different types of underlayment, and some are more durable than others. Additionally, some underlayments have features that help homeowners save money. Currently there are three types of underlayment used.


Felt is the traditional underlayment currently used by roofers. It is a cellulose base covered with asphalt and sometimes fiberglass. It has two weights, a lighter 15# and heavier 30#. The heavier 30# weight resists tears and lasts longer. Felt underlayment is rolled out on the roof and stapled or nailed to the decking. One of the many advantages of felt underlayment is its ability to self seal. This means that staples or nail holes will seal and not allow water through those small holes.

Rubberized asphalt

Rubberized asphalt is a newer product. By layering rubber, asphalt, and other materials, roofers have a variety of advantages: improved temperature resistance, moisture resistance and a non-skid surface. Rubberized asphalt is often used under metal roofing because it can handle higher temperatures than traditional felt underlayment.


Synthetic underlayment uses the same material that is used in food containers. They are water-resistant, lightweight, and strong. Many of these products can withstand UV damage for up to six months, and, on occasion, this product is left to protect the roof before shingles can be put up.


Underlayment is important for every roof, and even though these products have been used for years, they do have some disadvantages.

While felt has been the traditional treatment for roofs for many years, it does deteriorate over time. Felt underlayment is also easy to tear, so installers must use caution while installing. In future years, felt underlayment might be a thing of the past as oil refining is limiting the amount of asphalt produced for roofing materials.

As of 2010, there has been debate over whether or not synthetic underlayment meets certain building standards. Because such standards have not been established, some shingle manufacturers could void the warranty on the shingles if synthetic underlayment is used.


Installing most underlayment isn’t difficult. Because the material is in rolls, a two-person system works best. One person rolls out the material while the other secures it. Always consult the manufacturer’s instructions before beginning a project of roof repairs for your Jacksonville home. Synthetic underlayment may need to be wrapped around the roof edge to help protect the edges of the roof. Also, the pitch of the roof will determine the amount of overlap needed for each row.

The roofing experts at A.J. Wells Roofing Contractors can help you decide what kind of roofing underlayment you need to complete your roofing repair in Jacksonville.


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