Understanding Underlayments

Underlayments are installed under your shingles and provide your home with a second layer of protection. The primary function of the underlayment is to provide a moisture barrier.  Underlayments also act as a temporary insurance policy, protecting your roof deck from exposure in the event of hail, wind or other storm related damages.

The majority of roof-covering materials are not waterproof, but water-resistant. They are designed to be installed over a waterproof or water-resistant membrane of some type.

Many homeowners are confused when it comes to choosing the right underlayments for their roofing system. Understanding the building code requirements and manufacturer’s recommendations is an important part of selecting the right material. Below we outline the purposes of different roofing underlayment types.

The 2 main major types of underlayment are felt paper and ice and watershield. Within these types there are many variations, with the biggest difference being if the underlayment is waterproof or water-resistant. 

Felt Paper – Water Resistant protection for the main body of your roof

Black, asphalt saturated felt paper is one of the most common types of underlayment used in residential roofing. Felt underlayment is water-resistant, but not waterproof. The most commonly used felt is a #15 non-perforated underlayment. Different weight categories including 15 lb. and 30 lb. are used to define the strength and weight of a felt paper. Some manufacturers have re-enforced their felt papers using fiberglass to create a stronger, flatter lying product.

Synthetic underlayment types are becoming increasingly popular. All are light-weight and provide superior resistance to tearing and wrinkling compared to traditional asphalt felt. Synthetic underlayments are immune to fungal growth since they don’t absorb moisture.  They are also very resistant to UV damage and some can be left exposed to severe weather for months at a time. Synthetic underlayment is a relatively new technology to the residential roofing industry and it is often used to differentiate a sales proposal. Although they do offer premium features, there is no real world evidence that they will enhance the longevity of your roofing system. Some of the most commonly used synthetic underlayments in Windsor Essex Include:
Rhino Roof Strength of a synthetic underlayment at an affordable price. Designed and priced competitively with standard 15 lb felt alternatives.
Titanium UDL 30 Premium Synthetic protection with 30 lb characteristics. Used with many premium roofing materials, such as rubber and metal roofing.
GAF Deck Armor The only true BREATHABLE underlayment. Deck Armor’s state of the art technology maximizes your homes energy efficiency, but cannot be left exposed as long as alternatives.
Certainteed DiamondDeck Scrim-reinforced, water-resistant underlayment that can be used beneath shingle, shake, metal or slate roofing. 

Ice and Water shield – Waterproof protection for the detailed areas

Ice and Water Shield or “leak-barriers,” typically have adhesive on one side, which is protected by a peel- off membrane, making them self-adhering. Rubber-like qualities make these underlayments self-sealing, meaning that they seal well around fasteners, such as staples and nails. Building code and roofing manufacturers recommend you install ice and water shield at your eave edge, in all valleys, and in any delicate areas of your roof including low sloped areas and flashings.

Stone coated leak barriers, such as GAF WeatherWatch, have a granulated finish and are designed for most areas where ice and water shield is required, including your eave edge and valley areas.

Film surfaced leak barriers, such as GAF Storm Guard, have a smooth finish that allows the overlapping edges to seal to each other. Film surfaced leak barriers are a better choice for more critical areas, such as low slope sections and difficult sidewall junctions. There is no reason that film surfaced leak barriers cannot be used for all areas where ice and water shield is required. However, they are more expensive than their stone coated alternatives.

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