How to Replace Underlayment on a Tile Roof

Replacing the underlayment on a tile roof is a critical maintenance task that restores weatherproofing and prolongs roof life. This guide explains when to replace underlayment, how to plan the job, the step-by-step replacement process, safety and cost considerations, and tips to ensure proper installation. Homeowners And Contractors will find practical, actionable guidance to tackle this project on clay, concrete, or slate tile roofs.

Item	Typical Range	Notes
Estimated Cost Per Square Foot	$1.50 – $4.50	Varies by material and labor
Typical Project Time	1 – 5 Days	Depends on roof size and complexity
Common Underlayment Types	Felt, Synthetic, Ice & Water	Choose by climate and code

When To Replace Tile Roof Underlayment

Tile roofs can outlast their underlayment, so the underlayment may need replacement even if tiles appear intact. Replace underlayment when there is visible rot, extensive leaks, significant UV damage on exposed areas, or when re-roofing or reroof deck repairs are planned.

Other triggers include the roof age (felt underlayment older than 20–25 years), repeated patching, persistent interior staining, or building code changes requiring upgraded materials. An inspection after severe storms or prolonged exposure can identify hidden deterioration.

Types Of Underlayment And Which To Choose

Selecting the right underlayment affects durability, water resistance, and cost. The main options are asphalt-saturated felt (15# or 30#), synthetic underlayment, and ice-and-water shield for vulnerable zones.

• Asphalt Felt: Economical with decent water resistance but prone to tearing and absorbing moisture over time.
• Synthetic Underlayment: Lighter, stronger, and more UV-resistant; often recommended for tile roofs due to longevity and lower water absorption.
• Ice And Water Shield: Self-adhering membrane used at eaves, valleys, penetrations, and rakes for superior leak protection.

Local building codes and climate considerations should guide the final choice. In freeze-thaw or heavy-rain regions, pairing synthetic underlayment with ice-and-water shield in critical areas is common practice.

Planning And Preparation

Proper planning reduces time on the roof and improves safety. Start with a thorough roof inspection to assess tile condition, deck integrity, flashing condition, and ventilation. Determine if tiles can be removed and reset or if partial replacement is needed.

Obtain necessary permits and check local code for underlayment type and fastening requirements. Order materials: underlayment rolls, ice-and-water shield, fasteners, batten or hook replacements if using batten systems, and new flashings if corroded. Rent or acquire scaffolding, roof jacks, toe boards, safety harnesses, and tile lifters.

Safety And Roof Access Best Practices

Working on a tile roof presents slip and fragile-surface hazards. Prioritize safety with fall protection, roof anchors, and non-slip footwear designed for steep roofs. Avoid walking directly on tiles when possible; use crawl boards or roof jacks to distribute weight.

Tile removal and replacement may require two-person teams to carry tiles and operate equipment safely. When reroofing over 25 feet high or on steep pitches, hire a licensed roofing contractor experienced with tile systems.

Step-By-Step Underlayment Replacement

1. Remove Or Shift Tile

Carefully remove the tiles where underlayment will be replaced. Save intact tiles in neat stacks for reuse, labeling sections to aid reinstallation. Use a tile lifter or pry bar to unhook batten-secured tiles.

2. Inspect And Repair Roof Deck

Expose the deck fully and inspect for rot, nails pops, or damage. Replace any compromised deck boards or sheathing and ensure a smooth surface for underlayment attachment. Repair or replace framing as needed before proceeding.

3. Install Flashing And Details

Before underlayment, verify and replace flashings around chimneys, vents, and valleys. Proper flashing integration prevents leaks at transitions. Use corrosion-resistant materials compatible with tile systems.

4. Lay Ice-And-Water Shield In Critical Areas

Apply ice-and-water shield at eaves, rakes, valleys, and around penetrations. Self-adhering membranes should be lapped properly and adhered to a clean, dry deck for maximum effectiveness.

5. Roll Out Main Underlayment

Start at the eave and roll up toward the ridge. Align the edges and secure per manufacturer instructions. Overlap courses according to the underlayment specification—commonly 2–4 inches at horizontal laps and 4–6 inches for vertical laps with synthetic products offering wider tolerances.

6. Fastening And Sealing

Use approved fasteners and spacing to hold the underlayment without creating stress points. Do not overdrive nails; create a flat hold while avoiding ripping the material. Seal penetrations and laps with compatible tapes or adhesives if required.

7. Reinstall Or Replace Tiles

Reset tiles following original patterns and fastening systems. Replace broken or excessively worn tiles to restore proper interlocking and drainage. Check clearances and batten alignment to ensure tiles sit correctly.

Special Considerations For Different Tile Systems

Clay and concrete tiles are heavier and often installed on battens or directly on the deck. When battens are present, ensure battens are secure and not hiding rot beneath them. For flat-laid tiles without battens, underlayment must provide continuous coverage and proper adhesion.

For slate roofs, work is more delicate—slates can be brittle and require specialized hooks or fasteners. Consider hiring a slate specialist for underlayment replacement.

Common Mistakes To Avoid

• Skipping Deck Repairs: Installing new underlayment over a damaged deck leads to recurring failures.
• Poor Flashing Integration: Improper flashing causes persistent leaks despite new underlayment.
• Using Incompatible Materials: Mixing adhesives, tapes, or fasteners that aren’t compatible can reduce lifespan.
• Insufficient Overlaps: Not following overlap recommendations compromises water shedding.

Costs, Labor, And When To Hire A Pro

Underlayment replacement costs vary by region, roof pitch, size, and complexity. Expect material and labor combined to range from $1.50 to $4.50 per square foot for underlayment replacement alone, excluding tile repair or replacement and flashing upgrades.

Hire a licensed roofer when working on steep slopes, high elevations, or when extensive structural or flashing repair is needed. Professional installers bring warranties, experience with local codes, and safety compliance.

Maintenance After Replacement

After the underlayment is replaced, schedule periodic inspections every 2–5 years and after major storms. Watch for tile displacement, cracked tiles, and damaged flashings, and address small issues before they become leaks.

Maintain attic ventilation to reduce heat and moisture that can accelerate underlayment aging. Keep gutters clean to avoid water backup at eaves that can undermine underlayment performance.

Frequently Asked Questions

How Long Does New Underlayment Last?

Life expectancy depends on material: asphalt felt typically lasts 15–30 years, while quality synthetic underlayment can last 30–50 years under tiles. Environmental exposure and ventilation influence longevity significantly.

Can Underlayment Be Replaced Without Removing All Tiles?

Yes, spot replacement or working in sections is common. Complete replacement requires removing and resetting tiles across the roof for full coverage and warranty compliance in many cases.

Does New Underlayment Improve Energy Efficiency?

Some synthetic underlayments reflect heat and stabilize roof deck temperatures, modestly improving energy performance when combined with proper attic ventilation. Insulation and ventilation upgrades offer greater energy benefits.

Resources And Codes

Consult local building codes for underlayment types and installation requirements. Manufacturer installation guides are authoritative for overlaps, fasteners, and compatible accessories. Industry organizations such as the National Roofing Contractors Association (NRCA) provide best-practice references for tile roofing work.

For complex roofs or historic tile systems, engage roof inspectors or structural engineers to confirm deck capacity and compatibility with modern underlayments.

Replacing underlayment on a tile roof restores protection and extends roof life when performed with proper materials, attention to flashing details, and safe installation practices. Careful planning and adherence to manufacturer and code requirements ensure a durable, leak-resistant tile roof system.