Is Roof Underlayment Necessary?
When installing a roof, most people focus on what they can see shingles, tiles, or metal sheets. But there’s a layer underneath all of that doing serious work behind the scenes. It’s called roof underlayment, and even though you don’t see it, it plays a major role in protecting your home.
Roof underlayment is not optional. It’s part of a complete roofing system. Even you’re building a new home or replacing an old roof, skipping underlayment exposes your structure to water damage, temperature swings, and unnecessary repairs.
What Exactly Is Roof Underlayment?
Roof underlayment is a protective barrier installed directly on top of the roof deck, before the final layer of shingles or panels. It usually looks like a thick paper or synthetic sheet, but its purpose is much more serious.
Even the most expensive shingles can’t fully block out wind-driven rain, ice, or melting snow. The underlayment acts as a second shield—catching any water that slips through the outer roofing material and stopping it from soaking into the wood underneath.
Besides moisture protection, underlayment also adds fire resistance, helps the shingles lay flat, and prevents resin from wooden decking from seeping into the shingles over time.
Different Types of Roof Underlayment
There’s no one-size-fits-all product here. Different homes in different climates benefit from different types of underlayment. Here are the main types and where they make the most sense:
1. Asphalt-Saturated Felt
Often called “felt paper”
Traditional choice used for decades
Offers basic water resistance
Heavier and more prone to tearing during installation
A budget-friendly option, but not the most durable
2. Synthetic Underlayment
Made from polypropylene or polyethylene
Lightweight and much stronger than felt
Resists tearing, even in high winds or when walked on
Excellent water resistance
Ideal for steep-slope roofs and extreme weather areas
3. Rubberized Asphalt
Fully waterproof layer with adhesive backing
Great for cold climates and ice-prone regions
Helps prevent ice dams and interior water leaks
Often used around valleys, edges, or full-roof coverage in high-risk zones
Premium option, but excellent for long-term protection
Each type of underlayment serves the same basic function—but some provide more durability, flexibility, and protection than others. The right choice depends on weather, budget, and your roofing material.
Read Also: Roof Maintenance Tips
What Happens If You Skip Roof Underlayment?
Skipping underlayment may seem like a way to save money, but the consequences are costly—often more than you’d expect.
Without underlayment, any missing or damaged shingle becomes an open door for moisture. Rainwater seeps into the decking, leading to:
Wood rot: Wet wood loses strength and can collapse over time
Mold growth: Moisture trapped inside creates the perfect environment for mold, which can spread quickly and harm indoor air quality
Interior leaks: Water stains on ceilings and walls can appear, especially after storms
Shorter roof lifespan: A roof without underlayment often fails years earlier than one that includes it
Many roofing warranties also require proper underlayment. If it’s not installed, and a problem occurs, the manufacturer may refuse to cover repairs or replacement costs.
Underlayment and Energy Efficiency
Though its main job is to block water, underlayment can also influence how your home handles heat and cold. Some synthetic or reflective underlayments help reduce heat transfer through the roof, keeping your attic cooler in summer. This reduces the load on your air conditioning system, lowering energy bills. In colder regions, underlayment adds a layer of insulation. It slows heat loss, helping your home stay warmer in winter without cranking up the heat. If you’re aiming for a more energy-efficient home, it’s worth choosing underlayment that supports that goal.
Local Codes and Roofing Requirements
Most cities and towns require roof underlayment as part of the building code. That means during roof replacement or new construction, an inspector will check to make sure underlayment is installed correctly. If it’s missing or incorrectly applied, your project might fail inspection and delay progress. It could also come up later when selling your home. Home inspectors will often point out roofing shortcuts, and buyers might ask for expensive repairs or price reductions if underlayment is missing. Whether required or not in your area, installing underlayment is a standard that reputable contractors follow without question. It’s not just about following code it’s about building a roof that lasts.
Conclusion: Yes, Underlayment Matters, More Than You Think
Roof underlayment might not be the part you see, but it’s a major reason your roof stays dry, stable, and strong. It protects your roof deck from leaks, boosts energy efficiency, and ensures your roofing system lasts as long as it should. Whether you’re building a new home or replacing an old roof, don’t skip it. Underlayment is a critical part of any well-built roof not an accessory, but a necessity.
Make sure your Roofing contractor explains what kind of underlayment they’re using and why. A few extra minutes of conversation now could save you years of stress later.