Tag Archive for: Evergreen Park Roofing

SYNTHETIC VS. FELT ROOFING UNDERLAYMENT: PROS & CONS

SYNTHETIC VS. FELT ROOFING UNDERLAYMENT: PROS & CONS

When most people think of roofs, they typically think of shingles or metal roofing. But what some may not know is there’s another layer of protection directly on top of the roof deck and under the roof covering that performs a critical role in protecting your home from moisture damage. It’s called roofing underlayment.

Find out more about this critical component of your roof’s structure.

What Is Roofing Underlayment?

Roofing underlayment is what lies between the shingles and the roof sheathing, or roof deck, which is typically either plywood or OSB. It’s installed directly on the roof deck and provides a secondary layer of protection from the elements, including rain, snow, and wind.

Types of Roofing Underlayment

There are two main types of roofing underlayment:

  • Felt
  • Synthetic

Each product has its pros and cons, and the type you choose may depend on your geographical area, roofing materials used, roof design, budget, and what your roofing contractor may suggest.

Felt Roofing Underlayment

Felt roofing underlayment is one of the oldest types of roofing underlayment. It’s created by saturating paper or fiberglass mats with asphalt.

Felt roofing underlayment is typically available in two types: No.15 felt and No. 30 felt. Compared to No. 15 felt, No. 30 felt is typically thicker, stronger, and may be less prone to tearing or ripping off during installation or weather events.

Pros

The main advantage of using felt roofing underlayment is cost. Felt underlayment tends to cost less compared to the synthetic underlayment, which is why it’s often the go-to for budget-conscious homeowners.

Cons

There are several disadvantages to using felt underlayment on a roof. One disadvantage of traditional felt roofing underlayment is it generally can’t be left exposed for more than a few hours. The material may dry out or leach oils in the heat.  This would impact the felt’s ability to protect against moisture.

Other drawbacks of felt underlayment include:

  • Prone to tearing in high winds and during the strain of installation.
  • If exposed to moisture, the mat can absorb water and wrinkle the felt, making it harder for the shingles to lay flat.  Therefore, shingles should be installed immediately after felt roofing underlayment is installed if possible to ensure optimal protection.
  • Felt underlayment also weighs more, which can make it harder for roofing contractors to drag rolls of it up a ladder and onto a roof.
  • It also has a slippery surface, which can sometimes make it more difficult to install.
  • The weight also leads to less material per roll.  This means more potential seams instead of a single course with no laps.

Felt Roofing Underlayment and Warranties

If felt underlayment is installed it may also prevent you from being protected under the manufacturer’s warranty, which may require synthetic underlayment.

Synthetic Roofing Underlayment

For enhanced water resistance and protection from the elements, many roofers are choosing to go the route of synthetic roofing underlayment. These products are usually made from long-lasting polymers, which provide added strength and longevity. This type of underlayment is typically moisture-resistant, and when it’s installed correctly, it offers better protection from the weather compared to felt.

Synthetic roofing underlayment materials are not standardized, so different manufacturers may make their products differently, and therefore may have different levels of performance. Be sure to do your research and talk with a trusted contractor who can help guide you in selecting the right roofing materials to protect your home.

Pros

There are four main advantages to installing synthetic roof underlayment rather than felt. Compared to felt, synthetic roofing underlayment is:

  • Tough
  • Fast to install
  • Safe
  • Repels water
Synthetic underlayment has a tough and durable construction with an extremely high tear strength compared to felt.

Synthetic roof underlayment is extremely durable. It typically doesn’t tear and is suitable for extended UV and moisture exposure in some cases, which is especially helpful if there’s a bit of lead time before your roof covering is installed.

Synthetic underlayment also stands up to boot traffic, which is important when your roofing contractor is walking around on its surface as it’s being installed. At Owens Corning Roofing, we call this “use after abuse” — the product can still perform as designed even after the abuse it takes during installation.

Synthetic roofing underlayment also tends to be:

  • Lighter* – Up to four times lighter in some cases
  • Fast to install – Because there is more material per roll compared to felt (synthetic roofing underlayment comes in wider and longer rolls), it results in fewer trips up the ladder for your roofers, saving them time and perhaps helping the job move along faster. For instance, a typical 2700-square-foot home might require three rolls of synthetic underlayment compared to 14 rolls of No.30 felt to cover the same area.
  • Safe – Synthetic underlayment is also advantageous for worker safety — the surface of many synthetic roofing underlayments, including those offered by Owens Corning, features a variety of slip-resistant surfaces for enhanced walkability. It’s also usually well-marked with overlap guides and indicators of where fasteners should be placed, helping to improve consistency and accuracy during installation.
  • Moisture-resistant – Where felt products tend to absorb water, synthetic roofing underlayments are built to repel water. This is important for homeowners concerned about moisture infiltration, especially if they plan to leave the underlayment exposed for a prolonged period.

Because it’s made of plastic, synthetic underlayment is typically resistant to mold growth, a definite advantage over felt.

Cons

Many synthetics are competitively priced, but when compared to felt, the main drawback of synthetic roofing underlayment is the cost. The upfront investment in higher-quality roofing materials, however, could save you money down the road. You can’t put a price on the peace of mind of knowing that your roof is sufficiently protected from moisture.

The Right Underlayment for Your Roof

Whether you’re embarking on a reroofing project or new home construction, there are many factors to consider about the type of underlayment to use. Synthetic roofing underlayment has many advantages over felt and may be a worthwhile investment to protect your roof and home from the risks of water and moisture infiltration.

Learn more about our selection of roofing underlayment products and find an independent roofing contractor in the Owens Corning Roofing Contractor Network near you.

*9 (2 sq.) rolls of standard #30 felt compared to 2 (10 sq.) rolls of Owens Corning® Deck Defense® High-Performance Synthetic Underlayment. Individual product weights may vary.

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Roofing Ventilation 101

1

Why Ventilate?

There are four main reasons to ventilate your
home’s attic space.

• Reduce Heat Gain and Reduce Energy Bills in the Summer
Radiant heat from the sun warms the roof and radiates into
the attic. If not properly vented out, it could radiate into the
living space affecting the comfort level inside the house
and contributing to higher utility bills (because appliances
such as fans/refrigerators/air conditioners may have to work
harder to keep your home cooler).
• Reduce Moisture and Condensation in the Winter
In northern climates, heated air from the home escapes into
the attic through openings in the walls or ceilings (such as
recessed lights, electrical chases, the attic access door, etc.).
Some of this moisture vapor rises to the colder/dryer attic
where it can potentially condense if not properly vented. If it
condenses, it could dampen the attic insulation (which could
weaken the R-value of the insulation), contributing to wood
rot, mold, mildew and poor indoor air quality.
• Fight Ice Dams
Ice Dams are formed when in winter conditions, heated air
from the home migrates into the unheated attic through
the ceiling, under insulated areas and through bypasses,
such as light fixtures or exhaust systems found in kitchens
and bathrooms. This creates warm areas on the roof
and unevenly melts the underside of the snow that has
accumulated on the roof. The melted snow flows down the
roof until it reaches a colder spot, such as the eaves, where it
refreezes, forming a back up of ice commonly called an ice
dam. The ice dam is a result of energy loss from inside the
house, which could cost a homeowner hundreds of dollars
or more. It could also lead to rotted roofs and rafters, ruined
insulation, moisture inside the walls, mold and peeling
paint. Proper attic ventilation can help prevent the conditions
that contribute to ice dams.
• Prolongs the Service Life of the Building Materials
Finally, the shingles and decking of your roofing system may
deteriorate prematurely due to heat and excessive moisture
buildup. By reducing the surface temperature of the shingles
and the existence of moisture on the underside of the
decking by properly ventilating the attic space, a homeowner
may be able to extend the life of both of these materials.

2

How to Ventilate

Effective Ventilation is achieved by providing
intake ventilation at the lower edge of your roof
and exhaust ventilation at the upper portion of
your roof. The flow of air from the lower portion
of the roof to the upper portion the upper portion

through these vents is often called the “stack effect,”

which is similar to how a chimney works.

3

How to
Ventilate
Common
Mistakes
to avoid

Contractors and homeowners are urged to check
the following:
• Make sure two different types of exhaust vents are not on
the same roof of a common attic, so as to avoid possible
short-circuiting of the system (see Section 2 above).
• Make sure the intake vents are not covered with insulation.
To avoid this possibility be sure to insert attic insulation
baffles keeping the insulation away from the intake vents.
• Check that the intake vents have not been painted shut.
If they’ve been painted over that could restrict or reduce intake airflow.

4

Sealed
Versus
Ventilated

If you’re considering sealing your attic instead
of ventilating your attic be sure to ask your
contractor these important questions:
• Where will all the internal moisture go?
• How can I visually inspect for a roof leak if the underside
of the deck is sealed with insulation?
• Will I have more of a threat with mold and mildew?
• How does this impact my shingle warranty?
• Will this cause more ice damming?

5

Attic
Ventilation
IS Green
Effective ventilation is achieved by providing
intake ventilation at the lower edge of your roof
and exhaust ventilation at the upper portion of
your roof. The flow of air from the lower portion
of the roof to the upper portion through these
vents is often called the “stack effect,” which is
similar to how a chimney operates.
Contractors and homeowners are urged to check
the following:
• Make sure two different types of exhaust vents are not on
the same roof of a common attic, so as to avoid possible
short-circuiting of the system (see Section 2 above).
• Make sure the intake vents are not covered with insulation.
To avoid this possibility be sure to insert attic insulation
baffles keeping the insulation away from the intake vents.
• Check that the intake vents have not been painted shut.
If they’ve been painted over that could restrict or reduce
intake airflow.
• If using vented soffit panels for intake ventilation (typically
made by siding manufacturers) check the net-free area
rating of the panels to ensure they allow proper intake
airflow.
• Make sure bathroom, kitchen and dryer exhaust fans are
properly vented to the exterior of the house and not into
the attic cavity as this practice will add excess moisture
inside the attic.
If you’re considering sealing your attic instead
of ventilating your attic be sure to ask your
contractor these important questions:
• Where will all the internal moisture go?
• How can I visually inspect for a roof leak if the underside
of the deck is sealed with insulation?
• Will I have more of a threat with mold and mildew?
• How does this impact my shingle warranty?
• Will this cause more ice damming?
…and it’s contractor tested and trusted. A balanced
ventilation system allows fresh, dry air to flow into
your attic structure through your intake vents. As
this occurs, warm moist air is drawn through your
exhaust vents to the outside. This is what is known
as a passive ventilation system and is one of the
most energy-efficient systems in the industry, as it
requires no energy to run and can help reduce your
cooling bills in the summer time.

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Sealants: The Magic Touch

Shingle Sealants Bond Your Roof Together
With ever increasing performance expectations for asphalt shingles designed to
withstand high winds and heavy rains, manufacturers have responded by producing
increasingly higher-performing shingles. When properly installed, asphalt shingles are
manufactured to bond securely to each other, forming an integrated roof-covering
system designed to protect your home from the elements.
What is the secret ingredient? Asphalt-based bonding
sealants create the tie that binds!
How Are Shingles Attached to the Roof Deck?
Asphalt shingles are manufactured as individual units and are installed in courses
along the roof. When properly installed, the shingles adhere to each other to form a
cohesive roof-covering. Initially, make sure that the wood deck is in good condition,
then, assure that the right underlayment material is properly attached to the roof
deck. The underlayment provides extra protection for roof decking materials, and
keeps the shingle materials from adhering directly to the deck over time.
Nails and the Roof Deck
The best way to ensure that asphalt shingles are properly attached is to follow the
manufacturer’s installation instructions. As each asphalt shingle course is laid out, roofing
nails secure the shingles to the roof deck. Here are a few nailing practices recommended by
many shingle manufacturers.
It is important to make sure shingles are attached to the deck by using the proper type, size
and quantity of nails. Make sure the nails are in the right place by driving them in the
indicated “nailing zone.” Always ensure that nails in laminated shingles are driven through
the double thickness overlap area as indicated in this diagram.
How Does the Sealant Work?
Once each course of asphalt shingles is attached to the roof deck, every subsequent
shingle course will bond with the previously installed course, with the asphalt-based
sealant fusing the shingles together. The bonding sealant is factory-applied on the
shingle (front or backside), so following the manufacturer’s instructions regarding
spacing and alignment are critical for a proper sealant bond. Heat and UV rays from the
sun activates and softens the sealant to create the necessary bond needed to provide
good wind resistance for the finished asphalt roof covering system. Once sealed, the
bond is designed to hold the asphalt shingles together as a complete system.
What Are Sealants?
An asphalt based, heat activated, viscous
bonding material formulated to retain
bonding strength in all weather conditions,
once initial bonding has occurred. Sealants
are used on asphalt shingles to bond the
individual unit shingles together.
The Importance of Proper Installation
Recent research conducted by the University of
Florida’s College of Engineering1 has concluded
that proper installation is an important and very
critical factor to ensure that the shingle sealant
bonds the shingles together as designed.
Industry performance standards for asphalt
shingles include testing of the sealant bond
under laboratory conditions. These tests are
intended to simulate the resistance of the shingle
to uplift forces created during wind events.
Selecting a shingle that meets or exceeds local
wind-speed requirements in the building code
will help your roof covering withstand
windstorms and protect your home. Asphalt
shingle design has to ensure compliance to everchanging building code requirements. Shingles
have always worked as an effective windresistant roof covering, and now, thanks to the
use of bonding sealants, they work even better to
keep out the elements.
1Masters, Forrest J. Ph.D., P.E. (FL) (2013). Phase II Report: Investigation of the Wind Resistance of
Asphalt Shingle Roof Coverings (SERRI Report 90100- 02). Florida: University of Florida.
How Can I Make Sure the Sealant Does its Job?
Be aware of these key elements…
• Local code requirements matter. Manufacturers test asphalt shingles to the
requirements of local building codes. Check with the manufacturer to verify the
shingle you select is appropriate for use in your area.
• Schedule your roofing project to consider weather conditions. Asphalt shingles
can be vulnerable to wind forces until the sealant bonds, so it may be best to
install your roof when the temperatures are well above freezing. Heat and UV rays
from the sun activate the sealant to bond the shingles together. Check to make
sure that severe weather, including heavy rain, dust storms, snow and high winds,
are not in the forecast.
• The manufacturer’s installation instructions are your guide to a properly-attached
asphalt shingle roofing system.
How Can I Make Sure the Sealant Does its Job?
• Proper sealing starts with proper nailing. Always follow the manufacturer’s
instructions and use the right fasteners for the job, and make sure the shingles are
properly placed. Be sure that the nails are placed within the prescribed nailing
zone and are driven flush with the top surface of the shingles as required by the
manufacturer.
• For more information about Florida Building Code Requirements for asphalt
shingles, click here to read the ARMA Technical Bulletin.
What about that mysterious little cellophane strip?
Asphalt shingles are packaged for shipping in bundles, so most
manufacturers apply a strip of material between the shingles to
keep them from adhering into one big shingle brick! Once the
shingles are separated, the strip is in an area that will have no
effect on the performance of the shingle.
It is not necessary or desirable to peel off those strips.

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Tag Archive for: Evergreen Park Roofing