Roof underlayment types: three basic materials
- asphalt-saturated felt;
- rubberized asphalt;
- synthetic roof underlayment non-bitumen.
Black, ashphalt-saturated felt paper is one of the most prevalent kinds of roof underlayment used in housing, steep-slope applications. Around 15 years ago, it was the most common option. The implementation of synthetics began to be substituted. This material consists of different blends of cellulose, polyester, bitumen and asphalt, frequently known as “felt paper” or “tarpaper.” Every material has a base mat, which is the flexible base layer and is saturated with water resistance asphalt in this case.
Felt underlaying can be produced from organic substrate or fiberglass substrate, although organic substrate is much more prevalent.
Felt classes of at least 19 inches shall overlap with low-slope roofs, which include 2:12 to 4:12. The underlay over the entire ceiling is double layered. The upper felt underlaying paths should overlap at least 2 inches in steep pitch rooves (4:12 and steeper).
Felt can also be fitted with plastic caps in high wind regions. Plastic caps provide a stronger strength than staples to the wind, and help avoid leakage through the fasteners, hole.
Roof underlayment: Edge Metal Laps
The underlay on the edge of the edge metal should overlay the eaves and be overlaid on the rakes with edge metal.This also applies to the underlay of rubberized asphalt but not necessarily to synthetic products.
Why does felt underlayment fail?
Asphalt saturated felt may fail for several reasons, but mainly because the roofer would use a poor quality one / unbranded.
There are several ASTM standards that give asphalt-saturated felt requirements.
Many companies manufacture “Underlaying,”
“15-lb” or asphalt saturated paper.
When referring to asphaltic roofing materails, the words’ modified bitumen’ are often used. The word “bitumen” is a generic name that is applied to different combinations of hydrocarbons, sometimes it is shortened to “mod-bit.” The underlying asphalt, the asphalt shingles, and built in roofing form one of these mixtures. In the roofing sector, this is a popular word.
Bitumen is sometimes altered with materials that provide it with plastic or rubber-like properties, depending on the method, to increase diverse features such as strength and elasticity. Polymers are materials made of molecules that have the particular characteristics of the material. In order to improve their resistance to damage and deterioration polymers are used for many distinct kinds of roofing products.
The word “cross-linked polymer” can also be heard. In cross-linked polymers, molecules effectively connect with each other at the atomic level; they share electrons, significantly increasing the material’s power.
The rubber-mounted asphalt rolls on one side of the roll can be fitted with a jelly rim. The jungle rim is intended to create a strong and water resistant screen along the corners of the rolls. When roof underlayment is mounted on courses across the ceiling, the jagged edge should always be at the top.
This is the most expensive roof underlayment type, and this is because it contains higher percentages of asphalt and rubber polymers. This mixture makes it completely waterproof.
Rubberized asphalt roof underlayment usually comes with a sticky back and a protective membrane that is removed before installation. This backing is the waterproof seal that separates the underlayment from the clean roof deck. Is the preferred underlayment option for valleys and roof protrusions.
Non-bitumen synthetic roof underlayment is produced of polypropylene or polyethylene.
The synthetic polymers are also used to produce a wide range of other goods, ranging from food storage containers to textiles.
Synthetic roof underlayment is the most common material available today and is used by most building and roofing professionals. The synthetic basepiece is saturated in asphalt and has an extra fiber glass blend to increase the tear resistance and product strength. High-quality synthetic underlay includes a shaft enhancement that decreases slip even when wet.
The use of synthetics has both benefits and disadvantages, like other roof underlayment products. They have lightweight and high power among their benefits. They are usually unskid as well.
Since they do not absorb moisture, synthetics are fungal resistant to development and free of wrinkles. Although it can be intended as humidity-permeable, the humidity obstacles are typically regarded. It is also extremely resistant to UV harm and, depending on manufacturer suggestions, can be left exposed to weather for a period of six months to a year.
Synthetic underlayment problems
Some synthetic underlaying issues exist as of 2010.
According to the Association of National Roofing Contractors: There are no ASTM standards relevant to these goods to date. The use of these underlayments can void certain manufacturers ‘ material safeguards for certain roof coverings (e.g. asphalt shingles). Many roof underlayments do not fulfill present construction code requirements.
Concerns from other sources include:
- wicking can be a problem rather than a felt underlay. With certain kinds of synthetics, the installation along the roof eave is distinct. If the installer does not read and obey the manufacturer’s setup directions and instead installs the felt humidity issues.
Although underlay manufacturers can also produce housewraps of the same kind, underlaying demands of roofing do not fulfill housewrap. A faulty system is Housewrap mounted as a sublayer. Smaller than homewrap generally is thicker.
The pitch constraints of synthetic material will differ according to the maker. For low-slope roofs some indicate an increased overlap, and others do not.
A lot of synthetic underlayments have been designed to wrap the roof edges and protect the edges of the roof covering in order to avoid wicking moisture problems. The rim metal is mounted on both the eaves and the rakes over the bottom.
Clamping is usually performed with plastic caps or clothes. It is discouraged to use staps because synthetics do not auto-scell. In short, roofing underlayment is an essential component in order to resist the elements, protect the interior of a house and prolong the life of the roofing materials. The more an inspection officer understands the components of a roof, the better he can identify inspection problems and deficiencies.