The question of which roof underlayment is best is actually pretty controversial.
But, in our opinion, natural felt underlayment is the best for Arizona roofs.
This recommendation isn't just our opinion. If you check the Tile Roofing Institute's "materials needed" for installing a tile roof (the most common type in Arizona), you'll see a list a variety of felt underlayment options, not synthetic.
But why do we recommend felt? It's all about where you live.
The underlayment material should match your region's climate
Your roof's underlayment material needs characteristics that are compatible with the climate, according to the International Association of Certified Home Inspectors (NACHI).
You can divide climates in the US into four basic types:
- hot and dry
- cold and dry
- hot and humid
- cold and humid
Arizona is hot and dry like a convection oven. For our weather, a felt underlayment works well enough because:
- It's cheaper than synthetic, which is better for colder climates.
- Felt underlayment is water-resistant, but not waterproof. You don't need waterproof underlayment in Arizona since we don't have to worry about the water from melting ice dams.
What what about severe rain from monsoons?
It's true that Arizona roofs do need to be prepared for heavy rainfall from monsoon storms.
The solution? Simple: Just install 2 layers of a heavier felt underlayment, which is a best practice according to Department of Energy Building America. They say:
"If…felt is used in areas prone to severe rain, install two layers. The use of two layers was once common and provides better than twice the performance of one layer. By providing a double drainage plane, they offer increased resistance to leakage at fasteners and allow for more flexible installation." (Emphasis ours.)
This is pretty common practice in Arizona. AZcentral.com reports that, "The best roofers recommend an underlayment of two layers of 40-pound felt as well as modified bitumen roofing in valleys." (Emphasis ours.)