“What roofing underlay should I use?” This question is becoming quite common lately. Some time back, underlayment wasn’t used on roofing. However, it has become a compulsory requirement in many regions. But before we answer the question, do you know what underlayment is?

If you have ever looked at your roof, you will have noticed a sheet of material that lies between the deck (framework of timber) and the shingles or tiles. It comes in form of a bituminous or asphalt sheeting or felt paper. This is what is known as underlayment. It can be made from organic, synthetic, or a combination of the two materials.

What Role Does it Play?

Underlayment though hidden plays a major role in roofing and includes the following:

  • -Waterproofing: The felt is made from waterproof compounds that prevent water and moisture from seeping through the roof and ruining the deck (rafters, ceiling joists, and other parts). Asphalt and bituminous products are the most common.
  • – Protect the deck: Areas such as valleys serve as waterways. Normally, even the best shingles or tiles will allow some moisture to penetrate through. Also, the shingle or tile may degrade and release chemical compounds that may damage the deck. Underlayment, which is placed over the deck, prevents this from happening.
  • – Protect roofing covers: Timber naturally releasing some sap and moisture which can be damaging to the tiles, shingles or any roofing material. This may lead to some sections corroding, disintegrating or losing their appeal. Underlayment stops the harmful compounds coming from the deck from reaching the shingles/tiles.
  • – Improve strength: Incorporating an underlayment makes the roof stronger and more long-lasting. It creates stronger joints between the rafters, provides a firm base for nailing the singles or tiles.
  • – Boosts breathability: While preventing water/moisture from reaching the deck, underlayment, which is semi-permeable, allows humidity and air to freely move through. 

Types of Underlayment

Underlayment commonly comes as asphalt-saturated felt or non-bitumen synthetic felt. Generally, they fall as either organic felt or synthetic felt. Organic type is made from natural materials while synthetic underlayment comprises mainly of artificial compounds. The following are the pros and cons of each type: 

Advantages of Felt Underlayment

  • More affordable than synthetic
  • – Thicker than synthetic
  • – Easy to install
  • – Environmentally-friendly


  • – Heavier than synthetic
  • – More affected by wrinkling compared to synthetic
  • – More prone to water absorption

Advantages of Synthetic 

  • – More weather-resistant than organic felt 
  • – Lighter and more portable
  • – Less prone to rotting and lasts longer than felt
  • -Doesn’t buckle as easily as organic felt


  • – More expensive than felt underlayment
  • – Not as eco-friendly as organic felt
  • – Requires more time and labour to install

Choosing the Best Underlayment

When searching for good underlayment, it’s critical to pay attention to the following:

  1. – Ease of installation: A good product is easy to install and won’t leave any air gaps that may allow water to pass through.
  2. – Weatherproofing: The best underlayment creates a good waterproof barrier but also allows for free movement of air.
  3. – Heat Resistance: this is very important especially when installing the felt in hot areas. Self-adhering membrane underlayment consisting of butyl-based adhesive has a heat resistance of up to 240 degrees Fahrenheit.
  4. – Labour Intensity: it’s important to look for products that are easy to install and take minimal time. This not only saves time but labour cost as well.
  5. – Durability: Underlayment is expected to last for as many as 30 years without failing or needing repairs. Synthetic type scores well in regard to longevity but there are still some organic types that also have a good lifespan.
  6. – Environmental friendliness: With more and more people getting concerned about environment destruction, global warming, and pollution, people are now opting for eco-friendly underlayment. This makes the organic type a preferred choice.


Although it may be one of the hidden parts of a roof, the underlayment is among the most important sections. It serves as a water barrier, makes the deck stronger, protects the deck roof, and also improves breathability. However, it’s important to note that not every underlayment will serve you well. Unfortunately, with so many types readily available, it can be a challenge to know what is right.

You can make life easier by dealing with a reputable and established roofing company that knows all about the underlayment. A firm such as Plymouth Roofers has been in this sector for many years and has installed many roofs for residents in Plymouth and beyond. It uses the best products, takes time to understand your needs, and also offers a guarantee on its products and service. For more information on underlayment, choosing a good product, or

Plymouth Roofers

visit these Roofers in Plymouth You can also call 01752 967500 to talk to a representative or receive a free quote.

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