Problems with Synthetic Roof Underlayment and How to Solve

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When most people think of roofing, they usually think of metal roofing or shingles. However, some people may not be aware that there is a protective layer on top and directly below the roof, which plays a vital role in protecting your home from damage caused by the humidity. This is called a roof underlayment. There are two main types of roof underlayment: felt and synthetic. Learn more about this important part of the roof structure.

During the California Gold Rush, prospectors covered the roofs of temporary shacks with felt, also known as felt or tar. The roofing felt has been the most popular roofing material for 170 years (currently used as an underlayment). However, this may soon change. Over the next few years, more homes in the United States are likely to reach the tipping point where they will be covered with a synthetic underlayment rather than roofing felt. What is this synthetic underlayment, how does it differ from the roofing felt and why does the builder change their mind? What is the problem with synthetic roof underlayment?

What Is Roof Underlayment?

What Is Roof Underlayment

The roof underlayment is between the shingles and the roof sheathing, or roof deck (usually plywood or OSB). It mounts directly to the roof deck and provides a second level of protection against elements such as rain, snow and wind.

Types of Roof Underlayment

Types of Roof Underlayment

There are two main types of roof underlayment:

  1. Felt roof underlayment
  2. Synthetic roof underlayment

All products have their advantages and disadvantages. The type of roof underlayment you choose depends on your territory, roofing materials, construction, budget, and the contractor’s advice.

Felt Roof Underlayment

Felt Roof Underlayment

To understand why synthetic underlayment can replace felt roof underlayment, you need to know what felt roof underlayment is. The felt roof underlayment is made of fiberglass fleece or polyester fabric, which is used in some cases. It is 15 pound thick and 30 pound thick, which is called No.15 felt and No. 30 felt. It weighs 15 pound and 30 per square foot, but that’s actually less than what the label says. Compared to No.15 felt, No. 30 felt are usually heavier and more durable, will not crack or break during installation or some weather conditions.

Pros: Felt roof underlayment has been around for decades and has changed little. Felt roof underlayment are used by every roofer, so it is easy to find the roofer. In addition, felt roof underlayment are expected to absorb water and liquid droplets. Felt roof underlayment is cheaper than synthetic roof underlayment. Absolutely better price than synthetic roof underlayment.

Cons: Felt roof underlayment are heavier, making it difficult for roof builders to drag rolls from the ladder to the roof. Because the roof can absorb water, which can put high pressure on the roof when the building is wet. The abbility to retain water will shorten the life of the fabric, you may need to replace it.

Synthetic Roof Underlayment

Synthetic Roof Underlayment

Synthetic roof underlayment has been designated for roofing to improve water-resistance and safety. These products are made from a solid polymer for strength and durability. This type of roof is almost water resistant and, if properly installed, can provide both appearance and weather resistance. Since the synthetic roof underlayment material is not standardized, different manufacturers offer different products and performance levels. Of course, do your research and contact a reputable contractor who can help you choose the right roofing materials to protect your home.

Pros: Unlike felt roof underlayment, there are many options for looking at synthetic roof underlayment, which allow you more flexibility to choosing the right material. Synthetic roof are easier to install and have a longer life than felt roof. This helps pay off other expenses, extending the life of the home. The synthetic underlayment is very lightweight, making it ideal for large shingles. In some cases, it can be 4 times lighter.

Cons: The main disadvantage of synthetic roof underlayment is their cost. For a low-budget building, the cost of a synthetic underlayment may be higher, but as a cost-effective building, it will extend the life of the roof. Many roof builders think they can repel more water and moisture than felt roof underlayment. In other words, if there are cracks or holes in the underlayment, the synthetic roof can’t handle water seepage problem.

How Much Does Synthetic Roof Underlayment Cost?

How Much Does Synthetic Roof Underlayment Cost

Each roofing quotes includes a standard 15# felt, so there is no additional charge. However, the price for a good roll is usually $20.00-$30.00 and covers around 400-440 square feet. Synthetic underlayment vary by brands, job applications, and quality. Many asphalt roofs can be installed with products that cost between $150-$175 to install a roll. However, each roll covers 1,000 square feet. Of course, these prices may vary depending on the application. So make sure you receive the exact price for the upgrade.

Problems with Synthetic Roof Underlayment in Canada

Problems with Synthetic Roof Underlayment

The advantage of synthetic roof underlayment is that it is lightweight and weather resistant. In the United States, roofs are left exposed to the weather for several weeks, so it is best to use it. In Canada, roofs are not left exposed to weather, so the market in Canada does not get all the benefits. Some synthetics require plastic cup nails, while others require regular nails or staples only if the underlayment will be covered during two days. Ensure that the contractor follows the correct procedure and has proper authority.

There are several brands of synthetics, such as CertainTeed Diamond Deck, BP Deck Guard, IKO Cool Gray, Owens Corning Deck Defense, Rhino Roof U20, Grace Sin 15, and Elco Shield 15. All these products have in common that they are not breathable and are considered as a moisture barrier.

Roofing and construction industry are concerned that installing a non-breathable synthetic underlayment or moisture barrier on the roof will cause problems due to rising humidity and wood rot. Due to the limited history of the Canada market, no one is convinced that this product is effective.

We know that all synthetic manufacturers state that synthetic trap water in a structure. Therefore, install synthetic only on the ventilated roof thoroughly. Many buildings in Canada are not well maintained for construction. Therefore, in this case, do not use the synthetic roof underlayment as recommended by the manufacturer.

We also know that polyethylene is waterproof and make a vapor barrier, which have been used many times in the past, was removed from the general building code because they retain moisture and make the roof deck rot. We are not sure that installing a vapor barrier in the eaves can be harmful, but is it worthwhile to install a vapor barrier on the entire roof?

We think it is important to consider the benefits of synthetic roof underlayment with the problems of non-breathable underlayment may cause. Until these products became proven in the roofing industry, felt was the best choice as a roof underlayment. Felt breathes, has been around for decades, works reliably, and there is no risk of vapor barrier on the roof. Felt absorbs water and allow moisture to evaporate, preventing wood from decaying.

Breathex and Deck-Armor are two breathable synthetic products. If you insist on using synthetic underlayment, you should consider these product. It is the only synthetic breathable lining on the market today. Not surprisingly, these products are more expensive than generic non-breathable synthetic products.

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