Blog / Underlay: What You Didn’t Know

Most homeowners think of their roof in terms of the materials seen from the outside. Shake, shingle, tile, and other materials serve aesthetic and protective purposes in a roofing system. Many people forget about what resides underneath those materials: underlay. While not visible at first glance, underlay provides the protection, integrity and security every roof system needs. Read on to find out more about the underlay on your roof.

Materials
A relatively recent improvement in underlay is the use of SBS (Styrene-Butadiene-Styrene) Asphalt rubberized felts. This lightweight, malleable, and durable material has a long life and is dependable. The asphalt in the outer layers of the felt is waterproof, and the fiberglass mesh layer in the middle reinforces the felt against rot and deterioration. The fiberglass mesh also expands and contracts with temperature changes. On shingle roofs these felts keep oils from leaching out of the wood and into the wood on your rooftop.

Installation
Roofing felts come in 70-80 pound rolls, which are placed over the wood on the housetop. Wood battens, which support the outer layer of the roof, separate each strip of underlay.

Temporary Roof Covering
It is always better to install the external layer as soon as possible, but if needed, underlay can be a temporary roof covering for up to three months.

Guard Against the Elements
Despite outdoor conditions, underlay is designed to adapt to all types of weather. Asphalt provides a waterproof barrier while continuous coverage of the roof makes a watertight layer. The sidelays do not curl up, which makes it wind resistant. Expansion in hot weather and contraction in cold weather helps the felts to not break down in changing weather conditions.

Durability
Underlay has been tested, tried, and found to have a 30-year lifetime. Its elasticity makes it tough enough to withstand roofing nails and any foot traffic (though this should be kept to a minimum).

Integrity
Each part of the roof system has its own role in the roof’s structural integrity. Though more durable against strong weather conditions, the outer roofing layer alone will not stand without help. For this reason, underlay is a national roofing requirement. Insurance and realty companies factor in the quality of the roof when determining house value and rates.

Roofers Love it!
Believe it or not, roofers like underlay. Since it is lightweight, it is easy to manage. Many brands of underlay have an external peel with glue on the backside, which makes installation a breeze. It adheres to wood and concrete. Because it is installed in strips, it is easy to replace and repair. Also, with its long life, we know that we are installing a quality roof.

A good roof withstands the test of time, traffic and trial. The right underlay felts make the time longer, the traffic less hazardous, and the trials…well…less difficult.


Is your underlay in good condition? Schedule a free estimate to check.