Short Answer
Underlayment is a protective layer installed beneath the primary roof covering. It provides an additional layer of moisture protection.
Detailed Explanation
Underlayment is the secondary water-shedding layer installed directly on the roof deck, beneath the shingles. If water gets past the shingles — from wind-driven rain, ice dams, or damaged shingles — the underlayment provides a backup barrier that helps prevent water from reaching the deck and entering the home. There are different types of underlayment: synthetic underlayment (lightweight, durable, tear-resistant), asphalt-saturated felt (traditional, lower cost), and self-adhering membrane (ice and water shield, used in vulnerable areas). The type and extent of underlayment used affects both the cost and the performance of the roofing system.
Why It Matters
Underlayment is the difference between a roof that handles wind-driven rain and one that doesn't. Omitting or under-specifying underlayment is a common way contractors reduce price at the expense of performance.
Common Mistakes
- ✕Not asking what type of underlayment is included
- ✕Assuming all underlayment is the same
- ✕Choosing a proposal that omits underlayment upgrades to save cost
Questions to Ask Your Contractor
- ?What type of underlayment is included?
- ?Is synthetic underlayment or felt being used?
- ?Where will ice and water shield be installed?
- ?Is underlayment included in the entire roof or just the eaves?