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Roofing underlayment is a membrane applied to the deck of the roof before the
shingles are installed.
Your roof needs an underlayment because of the following reasons:
from permeating on the roofing deck
It prevents chemical mixture of shingles from leaking onto the roofing deck,
to save the roof from an expensive repair
It works as a secondary ambient barrier, optimizing the heat and sound
It acts as a water barrier and prevents precipitation or external water vapor
Types of Roofing Underlayment
Constructing a roof demands significant investment and so it is important to choose
the right types of roof, material and underlayment. Choosing the right products has a
huge impact on the overall maintenance cost of the structure. It is always
recommended to seek the advice of a reputable roofing company in Florida or the
one in your city before you start with the installation work.
Let’s look at the three common types of roofing underlayment options your roofing
company might recommend and the difference between them:
Asphalt Saturated Felt
A sheet material impregnated with asphalt, it is one of the most common types of
roofing underlayment used for residential structures. Organic and inorganic are the
two types of felt underlayment that are commonly used. The base material of
organic felt is made of rag or cellulose fiber while the inorganic felt has fiberglass or
polyester as the base material.
The thickness of the felt paper varies, the most common one being 15lb and 30lb.
The 15 lb paper has a perm rating of 5 but the number can rise with increasing
humidity. The 30lb paper is more resistant to damage during the installation process
and provides better protection to the roof.
The asphalt saturated felt is usually fastened with staples but if you live in a
hurricane-prone area, it is recommended to use plastic windstrips along the edges of
the felt. It is advisable to attach plastic caps to felts as they provide better wind
resistance as compared to staples.
When Does Asphalt Saturated Felt Fail?
underlayment fragile and moisture absorbent
If the felt underlayment somehow gets exposed to direct sunlight, UV rays
increase the deterioration process
Volatile components in asphalt dissipate over time which make the
Rubberized Asphalt Underlayment
Rubberized asphalt underlayment is made of regular asphalt concrete and crumb
rubber procured from recycled tires. It is a peel-and-stick product that adheres to the
roof deck. It seals around fasteners such as nails and staples because of its
rubber-like quality. A rubberized asphalt underlayment might have:
Polymer film bonded to weather surface
Mineral coating on the weather surface
Polyethylene bonded to the upper surface to provide weather-resistant
Rubberized asphalt underlayment is vapor impermeable which makes it highly
recommended for hurricane prone areas. In addition to this, rubberized asphalt fully
adheres to the substrate and adjacent sheets on the side and end laps, which makes
it highly resistant to air pressure.
Non-bitumen Synthetic Underlayment
Polypropylene or polyethylene are the two synthetic polymers used to make
non-bitumen synthetic underlayment, which is lightweight and has a high strength.
Some of the additional features include resistance to fungal growth, non-skid surface,
moisture absorbance and high resistance to UV damage. The non-bitumen synthetic
underlayment is generally fastened with roofing nails and plastic caps. It is
recommended to avoid the use of staples because synthetics don’t have self-sealing
Although, non-bitumen synthetic underlayment costs more than the felt roofing
underlayment, but it provides better protection against seepage. Felt and rubberized
asphalt are sticky to work with and slippery to walk on during the installation process,
but non-bitumen synthetic underlayment is easier to install.
A roofing underlayment has significant role in increasing the ability of the roofing
materials to withstand external elements and protect the structure. While choosing
roofing underlayment take into consideration some essential elements such as
weight and ease of installation, durability, safety, waterproofing and long term
maintenance cost to get value for your money.
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