Ensuring your roof is in good shape is essential for preventing water from leaking into your attic and helping the roof to last as long as possible. While the type of shingles or other roofing materials you use is important in this regard, the type of roof underlayment can be equally as important. Here, we’ll explain exactly what role underlayment plays in a roofing system and discuss the pros and cons of each type of underlayment.
Understanding the Components of a Roofing System
Roofing systems are more complex and have more components than you may realize. The underlying component is the roof structure, which consists of all of the trusses or rafters and the wooden roof deck. Once the deck is in place, the roofers then completely cover it with the roof underlayment.
The next step is to install metal flashing around all intrusions in the roof, such as exhaust pipes, the plumbing vent pipe, skylights, etc. Flashing is also used to cover the channels where two different slopes come together as well as along all of the edges of the roof. The flashing is usually nailed or screwed down to the deck, and the edges and nail or screw holes are then sealed with silicon. Finally, the roofers then install the roofing shingles, tiles or metal sheeting.
The Purpose of Roof Underlayment and Flashing
Roof underlayment and flashing are the two primary components of a roofing system in terms of preventing leaks. While water normally drains straight off a roof, it can sometimes end up getting underneath or leaking through the shingles, tiles or metal sheets. This is where the underlayment and flashing come into play since they help to ensure that the water can’t seep into the wooden roof deck or leak into the attic. If water does get underneath the overlying roofing materials, the underlayment helps to ensure it drains straight off the roof into the gutter.
Pros and Cons of the Different Roof Underlayment Materials
There are three distinct types of underlayment you can use when replacing or installing a new roof—felt paper, rubberized asphalt and synthetic. For many years, felt paper was the only option available. While it is still sometimes used, most roofers have moved away from it in favor of one of the other two types. Each type has some unique advantages and disadvantages that are important to consider when deciding which one to use on your roof.
Asphalt-Saturated Felt Paper
Felt paper is made from either natural cellulose or fiberglass, which is then soaked in asphalt to make it more water resistant. Felt paper is available in thicknesses of 15 and 30 pounds. The 30-pound paper is stronger and more durable, meaning there’s less of a chance of the roofers damaging it when installing the flashing and roofing materials over the top of the underlayment. The thicker felt paper also lasts longer and helps decrease the chances of the roof leaking if water gets underneath the roofing materials.
The main advantage of felt paper is that it’s less expensive than the other two types. The 15-pound felt paper is the cheapest type of underlayment available but also the least effective. The main concern with either type of felt paper is that it is only water resistant and not fully waterproof. That means you don’t end up with as effective of a moisture barrier with felt paper as you do with the other two options.
Synthetic Underlayment
Synthetic underlayment is made from either polyethylene or polypropylene plastic. This makes it fairly lightweight while at the same time being strong, durable and resistant to tearing. The lighter weight makes it easier to install than the other two types as well. Another advantage of synthetic underlayment is that it’s highly UV resistant, meaning it can be left exposed for longer without sustaining damage. The surface of the underlayment is also slip resistant or non-skid, which helps make it safer to walk on when installing roofing materials over it.
Two of the biggest benefits of using synthetic underlayment are that it’s fully resistant to mold and fungal growth and fully waterproof. The fact that it’s waterproof and doesn’t absorb any moisture is one of the main reasons why it’s now the most commonly used option. Synthetic underlayment is usually considered the best choice since it offers the best balance in terms of price and performance.
By using synthetic underlayment, you can create an extremely effective moisture barrier that greatly decreases the chances of roof leaks. However, as with felt paper, it’s essential that synthetic underlayment is installed correctly to ensure effectiveness. That means fastening it securely with staples or plastic caps to reduce the chances of water leaking in around the fasteners. It’s also important to overlap each piece far enough or else water may still leak underneath where the pieces meet.
Rubberized Asphalt
As the name suggests, this type of underlayment is made from various types of rubber polymers mixed with asphalt. This combination ensures the underlayment can handle extremely high temperatures without degrading and also creates an effective moisture barrier. The higher heat resistance is why this type of underlayment is usually the best option for a metal roof in places that experience hot summers.
There are various types of rubberized asphalt available that are designed for specific purposes. For instance, some have polyester or polyethylene added to the top to create a non-slip surface. Others have fiberglass mixed in with the rubber and asphalt to increase strength and durability. One of the most common options is modified bitumen, which has various polymers added to the bitumen asphalt. This makes the underlayment more flexible, further improves its strength and makes it last longer and be more resistant to damage.
One unique thing about this type of underlayment is that it’s self-adhering, meaning it can be installed without using any type of fasteners. The underside of the underlayment is fully coated with a strong adhesive and then coated with a sheet of plastic. To install the underlayment, the roofers just need to peel off the plastic to expose the adhesive and then press it securely onto the roof deck. Many products also have an adhesive edge along one side of the top surface. This edge helps to create a fully watertight seal where one sheet overlaps the sheet below it.
Rubberized asphalt is also self-healing. That means it naturally seals around the nails or fasteners used to secure the roofing materials to the deck to help ensure water can’t leak in around the fasteners. Underlayment made of rubberized asphalt is a great choice for places that experience heavy rains or lots of snowfall. Nonetheless, it’s also quite a bit more expensive than the other options, which is why many people still opt for other materials instead.
Contact Us Today
When you need a trustworthy residential roofing contractor in Columbus, OH or the surrounding areas, turn to the pros at The Roof Detective. We’ve been in business since 2012 and are dedicated to providing the best roofing repair and installation services available. Our roofers work on residential and commercial roofs and with a wide range of roofing materials. You can also count on us when you need any siding or gutter services. Whether you need a professional roof inspection or anything else, give The Roof Detective a call.
