Choosing the Right Metal Roof Underlayment

By Anna Lockhart.  

Underlayments are important in protecting a building from harsh weather and water damage.  

A quality underlayment can protect the integrity of a building both during and after construction. Underlayments protect against water infiltration, shedding the water away from the roofing system and the layers underneath. There are multiple kinds of underlayment products on the market, though in this article we will focus on the main three types and how well they work with metal roofing: felt paper, peel & stick synthetic and mechanically attached synthetic underlayments.  

Felt paper underlayment 

Felt paper underlayments are manufactured using fiberglass and wood which have been coated with an asphalt-like substance that aids in repelling water. In the past, felt underlayments with an asphalt coating were the standard for most roofs, however, in recent years, they have faded from popularity as contractors switched to newer products.  

Felt paper underlayments are a good option for building owners looking for the most cost-effective option. However, by going with felt paper, it must be taken into consideration that the felt paper underlayments are considerably heavier than other options on the market and therefore take longer to install, leading to higher labor costs. Another downside to felt paper underlayments is that they are quicker to break down and have a shorter lifecycle than other materials. The roofing experts at McElroy Metal advise that asphalt-based underlayments are not recommended for use under metal roofing.  

Mechanically attached synthetic underlayments 

Mechanically attached synthetic underlayments have become a popular option in the last twenty years, and offer many advantages compared to traditional felt paper underlayments.  Synthetic underlayments are up to 15% stronger than felt paper and a single roll covers five times more area than a roll of felt paper. The mechanically attached synthetic underlayment requires the use of capped nails, which can be a downside as the nails may telegraph to the roof and create issues with proper sealing.  

Peel & stick synthetic underlayments  

Synthetic underlayments have made their way into the market in recent decades and are a popular option. Peel & stick synthetic underlayments are made with three main layers: the top layer of laminated polypropylene and plastics, a middle layer of modified bitumen and a bottom layer consisting of heavy-duty adhesive. This multi-layer design is ideal under metal roofs and offers a greater product thickness compared to other underlayment options, which gives the roof system and building better protection. Peel & stick underlayments offer strong protection, multiple color options, longevity and durably. Easy to install, this underlayment is a great product for quick and efficient installation for contractor teams. A downside to this, however, is the cost as it does usually run at the highest price compared to other underlayment types. This is why it is often only used on critical areas such as rakes, valleys, eaves, ridges, hips and chimneys. 

Underlayments are a major factor in protecting a roof, and the professionals at McElroy Metal have an extensive knowledge in the different underlayment options that work best for metal roofing. Read their blog post about underlayments to learn which kind is best for metal roofs!