Underlayment is a crucial roofing component that every metal roof needs to have. Because a metal roof will be a large investment, you definitely want the best quality underlayment. 

Don’t get me wrong, the different types of underlayment do their job well and have their place in the roofing industry. However, there’s one type that’s best to use on a metal roof system. 

Here at Bill Ragan Roofing, we want to give you key information to ensure you get the most out of your metal roof investment. That’s why we’re going to break down the best underlayment for a metal roof, the proper way to install it, and how much it costs. 

Before we get to all that, let’s do a quick overview of what roof underlayment is. 

What is roof underlayment?

Roof underlayment is the roofing material that’s installed directly over your roof decking for extra protection from the elements. There are two different types of underlayment, felt and synthetic. 

Felt underlayment is the older of the two and comes in 15 lb and 30 lb rolls. The big difference between the two types of felt underlayment is that 30 lb is thicker, stronger, and less likely to tear than 15 lb. 

synthetic underlayment

Synthetic underlayment has been around for about 20 years and is made out of woven/spun polyethylene or polypropylene. I personally recommend synthetic underlayment. 

However, it’s up to you and your budget to decide which one is right for your roof. 

What is the best underlayment for a metal roof?

While felt and synthetic underlayment are great options for asphalt roofs, metal roofing needs something different. The expanding and contracting a metal roof goes through will destroy the integrity of the normal types of underlayment. 

Because of this, a metal roof needs something that can handle the metal panels going back and forth during thermal expansion. That’s where ice and water shield comes in.

high heat ice and water shield for metal roof

Your metal roof needs high heat ice and water shield as underlayment over the decking. High heat ice and water shield has cotton-like fibers that won't stick to the metal panels as they expand and contract. 

This prevents the underlayment from being destroyed and ensures your decking will be protected if water finds its way in. While metal roofing needs high heat ice and water shield as underlayment, it’s also used with premium roof systems (slate and cedar shake) to add extra protection. 

However, it will be more expensive than the other types of underlayment and adds to the cost of your roof replacement

The right way to install high heat and water shield on a metal roof

I always recommend hiring a qualified local roofing contractor to install your metal roof. However, if you're a DIY homeowner or are curious about the right way to do it, you need to know how high heat ice and water shield is installed correctly on a metal roof. 

The first thing installed for your metal roof system will be lock strips. They hold (lock) your standing seam metal panels to the edges of your roof (eaves and rakes) to keep them from flapping in the wind or strong storms. 

After the lock strips are installed, the high heat ice and water shield must be installed over the top of the lock strip at the eaves. If the lock strip is installed over the underlayment, the condensation under the ribs will run down the fascia board behind the lock strip, leave streaks on the fascia, and eventually rot it out. 

This will leave lines down the fascia board when the water starts running behind the lock strip and will eventually lead to a leak. You won't run into this problem as long as you hire a roofing contractor with experience installing metal roof systems. 

How much does ice and water shield cost?

The price of roofing materials fluctuates constantly and can be different depending on the area you live in. Because of this, it’s impossible to give you an exact cost number for any roofing material.

However, I can at least give you an idea of the budget you’ll need for high heat ice and water shield for your metal roof.  

High heat ice and water shield will cost around $125.00 per square (100 square feet). It will be the most expensive of the three types of ice and water shield

For comparison, granular or sand ice and water shield starts at $50.00 per row of material, while smooth ice and water shield costs around $100.00 per square (100 square feet of roof area) to go under a low slope roof.

Remember, these numbers aren’t exact. However, they do give you an idea of what to expect from a price standpoint.

The rest of your metal roof system’s roofing materials

Now you know the best underlayment for a metal roof, how it’s installed properly, and an idea of the cost. If you do get a new metal roof, be sure to ask the roofing contractor if they’ll be using high heat and ice and water shield. 

After reading this article, you know that underlayment is a crucial material for your metal roof system. However, there are even more crucial metal roofing components you need to learn about. 

That’s why we wrote another article breaking down the 7 materials that make up your standing seam metal roof system. 

Since 1990, the team at Bill Ragan Roofing has proudly helped homeowners in the Nashville area with all of their metal roofing needs. You can count on our metal roofing installation expertise to give you a new metal roof that’ll last for decades. 

Check out The Materials Make Up a Standing Seam Metal Roof System to learn the other crucial components that are part of your new metal roof.

which roofing material is right for you