Roofing Underlayment Decision
Traditional asphalt-saturated roofing felt can still be a legitimate underlayment for some asphalt-shingle roofs, but “install felt” is not a complete project specification. The right choice depends on the roof covering, slope, local code, wind exposure, manufacturer instructions, expected weather exposure during construction and whether vulnerable areas require a different waterproofing layer.
Start With the Project
Roofing felt can be a reasonable choice when the roof system, schedule and local requirements actually support it.
Roofing felt is a secondary water-shedding layer installed over the roof deck and below the finished roof covering. It is not insulation, and it is not a substitute for the shingles or other primary roof covering. Its job is to add a secondary layer of protection during construction and beneath the finished roof assembly.
#15 vs #30 Roofing Felt
The familiar “15-pound” and “30-pound” names are useful shorthand, but they are not enough information for a modern roof specification.
Roofing crews and suppliers still commonly use terms such as #15 and #30 felt. Historically, those names were associated with approximate material weight per roofing square, but modern products should be evaluated by their actual labeled standard, classification and manufacturer instructions rather than assuming the trade name tells you every performance characteristic.
| Decision factor | Lighter felt commonly called #15 | Heavier felt commonly called #30 | What matters to the homeowner |
|---|---|---|---|
| Material thickness / robustness | Thinner, lighter field material. | Heavier and generally more robust. | Heavier felt generally tolerates handling and jobsite traffic better. |
| Tear resistance | More vulnerable to tearing. | Generally better resistance to tearing. | Wind during installation and crew traffic can matter before shingles are installed. |
| Material cost | Usually lower. | Usually higher. | Compare the total roof-system proposal rather than saving a small material amount without considering performance. |
| Handling | Lighter rolls. | Heavier rolls and less coverage per comparable roll format. | Labor and material handling can influence what contractors prefer. |
| Wind-design context | May not satisfy the underlayment classification required for the project. | Heavier classifications may be required depending on code and assembly. | The applicable standard and type matter more than the nickname. |
| Best decision rule | Do not approve either solely from “15 lb” or “30 lb” language. | Ask for the labeled ASTM classification and confirm it against the roof covering, local requirements and manufacturer instructions. | |
The dedicated technical owner for the material itself is felt roof underlayment. This page focuses instead on how to make the selection decision.
Felt Specification Decoder
A homeowner should be able to identify more than the color and weight nickname of the roll.
Current residential building-code language references recognized underlayment standards and type classifications rather than relying only on traditional “pound felt” terminology. That distinction becomes important when wind design, roof covering or another project condition changes which underlayments are acceptable.
Confirm that the contractor is actually proposing asphalt-saturated roofing felt rather than synthetic underlayment or self-adhered membrane.
Ask which applicable ASTM standard the product is labeled to meet. Traditional asphalt-saturated underlayments commonly appear under standards such as ASTM D226 or ASTM D4869, depending on the product and application.
The type classification matters. Current IRC tables distinguish which underlayment types may be used for particular roof coverings and wind-design conditions.
Underlayment requirements are not independent of the material installed above them. Asphalt shingles, tile, metal, slate and other systems have different approved assemblies.
Slope can change underlayment application requirements. Low roof slopes may require different layering or another system altogether.
Fastener type, spacing and lap configuration must follow the applicable code and product instructions rather than a generic installation rule copied from another felt product.
Underlayment is not intended to become the permanent exterior roof covering. Verify how long the exact product may remain exposed during construction and what happens if weather delays exceed that limit.
Know When Felt Stops Being the Obvious Choice
Traditional felt, synthetic field underlayment and self-adhered membranes solve overlapping—but not identical—problems.
A homeowner does not need to upgrade automatically because a newer material exists. But the project should not stay with felt automatically merely because it is familiar or cheaper.
Traditional felt
Most defensible when the roof covering permits it, the project is straightforward, exposure before covering is short, budget matters and the actual code-required classification is satisfied.
Synthetic field underlayment
Worth stronger consideration when tear resistance, lower roll weight, jobsite handling, dimensional stability or longer allowable construction exposure matters.
Self-adhered membrane
Often used when the assembly requires a sealed waterproofing layer or enhanced protection in vulnerable locations. It should not be treated as merely “premium felt.”
If your actual decision is whether to stay with traditional felt or move to modern synthetic field underlayment, use the dedicated synthetic vs felt underlayment comparison.
Field Coverage vs Vulnerable Areas
Choosing felt for the main roof field does not answer what should happen at eaves, valleys and other high-risk areas.
A common homeowner misunderstanding is that one underlayment decision applies uniformly to every part of the roof. In real roof assemblies, the broad field layer and localized waterproofing details may perform different jobs.
Main roof field
Felt or another approved field underlayment is installed over broad areas of the deck below the primary roof covering.
Eaves and cold-climate exposure
Some climates and codes require enhanced protection where water can back up behind ice dams. The exact requirement depends on local design conditions.
Valleys and penetrations
Concentrated drainage and roof transitions can justify additional waterproofing details beyond the field underlayment itself.
The distinction between these two protection jobs is covered in underlayment vs ice and water shield.
Construction-Phase Risk
The best felt choice can change when the roof may sit exposed before the final covering is installed.
Underlayment experiences its harshest exposure before the permanent roof covering is complete. Wind can lift loose material, crew traffic can tear it, moisture can affect felt, and sunlight can degrade products that remain uncovered longer than intended.
Same-day or rapid covering
When the contractor removes only what can be safely dried-in and the roof covering follows promptly, traditional felt has less time to be exposed to wind, rain and jobsite traffic.
Possible multi-day delay
A project exposed to weather delays, inspection scheduling, material delivery problems or complicated phased work puts more importance on tear resistance, water behavior and the manufacturer’s exposure limitation.
Where Felt Sits in an Asphalt-Shingle Roof
Underlayment is important, but it is only one component of the water-management and fastening system.
Roof deck
The deck provides the substrate beneath the underlayment and receives the fasteners for the roofing assembly. Damaged or unsuitable decking should not simply be concealed beneath new felt.
Underlayment
Felt or another approved underlayment provides secondary protection between the deck and the primary roof covering.
Leak barrier where required
Self-adhered protection may be used or required in specific high-risk locations depending on climate, code and system specification.
Starter and shingles
The visible asphalt-shingle system becomes the primary weather-shedding layer.
Flashing
Valleys, walls, chimneys and penetrations depend on deliberate flashing details; underlayment alone does not replace them.
Ventilation and moisture control
Roof-covering replacement does not automatically solve attic moisture or ventilation deficiencies.
Proposal Check
“Install new roofing felt” is not a scope-complete underlayment line item.
Weak proposal language
Install roofing felt.
Install new shingles.
The homeowner still does not know the felt type, standard, classification, lap/attachment basis, vulnerable-area protection or what happens if the material is damaged before the shingles are installed.
Better scope language
Vulnerable-area membrane: [identify locations] Damaged decking: [allowance/change-order method]
The exact wording will vary, but the proposal should give enough information to compare the same assembly across competing bids.
Replacement Scope
Underlayment is easiest to evaluate before the replacement contract is signed—not after the old roof has already been removed.
Once tear-off begins, homeowners have less time to research an unexpected underlayment change. A stronger roofing proposal identifies the intended underlayment system, vulnerable-area protection and decking assumptions before work begins.
If the larger project is an existing roof being removed and rebuilt, continue with the complete roof replacement planning guide.
Before the Final Specification
Six conditions should be verified before a contractor locks traditional felt into the project.
Contractor must verify
Slope can affect underlayment layering and approved roof-covering applications.
Underlayment must be compatible with the specific shingles or other covering installed above it.
The model IRC is not automatically the governing code in every jurisdiction.
Current model-code tables distinguish some underlayment requirements where wind design is required.
Roof covering and underlayment installation instructions remain part of the approved assembly.
The contractor should know how the deck stays protected if installation is interrupted.
Hiring Decision
The goal is not to tell the roofer which roll to buy. The goal is to understand what assembly is included in your price.
Ask the contractor to put these answers in writing.
Roofing Felt FAQ
Questions homeowners commonly ask before approving felt under shingles.
Is #30 roofing felt better than #15 felt?
Heavier felt commonly called #30 is generally more robust and more resistant to tearing than lighter felt commonly called #15. However, the correct project choice should be based on the product’s labeled standard and classification, roof covering, slope, local code and manufacturer instructions—not the weight nickname alone.
Does “15-pound roofing felt” actually weigh 15 pounds per roofing square?
The #15 and #30 names are traditional trade terminology and should not be treated as precise modern material-weight specifications. Modern products vary, so the labeled ASTM standard, type and product data are more reliable ways to identify what is being installed.
Is roofing felt waterproof?
Traditional roofing felt should be treated as a secondary water-resistant underlayment, not as the finished waterproof roof covering. Its performance depends on the product, installation, laps, fasteners, weather exposure and the finished roof system above it.
Do roofers still use felt under shingles?
Yes. Traditional asphalt-saturated felt is still used on residential roofing projects where the roof covering, project conditions and applicable requirements permit it. Synthetic underlayment has become common because of advantages such as lower roll weight, stronger tear resistance and product-specific construction-exposure capabilities.
Is synthetic underlayment always better than felt?
No material is automatically best for every project. Synthetic underlayment generally improves handling, tear resistance and moisture behavior during installation, while felt can remain a lower-cost compliant option in appropriate assemblies. The meaningful comparison is the complete roof specification, not the material name alone.
Is roofing felt the same as ice and water shield?
No. Traditional felt is a mechanically attached field underlayment. Products commonly described as ice and water shield are self-adhered waterproofing membranes designed to bond to the deck and provide a different level and type of protection.
Can roofing felt be left exposed before shingles are installed?
Only within the conditions allowed for the exact product and assembly. Felt is not a permanent roof covering. Wind, rain, sunlight and crew traffic can damage exposed underlayment, so the contractor should follow the product’s exposure limits and inspect or replace damaged material before covering it.
Does roof slope affect underlayment requirements?
Yes. Roof slope can change how underlayment must be applied, including layering and overlap requirements for some roof coverings. The applicable code and roof-covering instructions should control the project rather than a generic felt-installation rule.
What should a roofing estimate say about underlayment?
A useful proposal should identify the proposed underlayment sufficiently to compare bids: product or material type, applicable standard/classification where relevant, vulnerable-area waterproofing, deck-repair assumptions and the roof covering installed above it.
Should I choose the underlayment myself or let the roofing contractor choose it?
The contractor should design and install an appropriate compliant assembly, but the homeowner should understand what is being proposed. Ask why the selected underlayment fits the roof, whether alternatives were considered, what product is included in the price and what conditions could change the specification after tear-off.
Technical Reference
Underlayment requirements vary by roof covering, adopted building code, wind-design condition and manufacturer instructions. The 2024 International Residential Code identifies multiple recognized underlayment standards and type classifications and distinguishes certain requirements for areas where wind design is required.
Always verify the code adopted by the actual jurisdiction; model-code language should not be assumed to be the exact local requirement.
International Code Council — 2024 IRC Chapter 9: Roof Assemblies
Here's a list of criteria compiled by handyman roofer experts to help you choose the best roofing felt material:
Durability: Select a material known for its longevity and resistance to wear and tear. The ability to withstand harsh weather conditions is crucial. - 9.8
Water Resistance: Ensure the roofing felt is highly resistant to water to prevent leaks and water damage. - 10
Weight and Thickness: Consider the weight and thickness of the felt. Thicker materials usually offer better durability and insulation but may be heavier. - 9.9
Ease of Installation: Some materials are easier to install than others. Choose a type that aligns with your installation skills or the expertise of your roofer. - 10
Compatibility with Roof Type: Make sure the roofing felt material is compatible with your existing roof structure and material. - 9.7
Cost-Effectiveness: Balance quality with affordability. The most expensive option is not always the best, but extremely cheap materials might be less durable. - 10
UV Resistance: If your roof is exposed to a lot of sunlight, look for materials with UV protection to prevent degradation. - 10
Eco-Friendliness: Consider environmentally friendly options, especially if sustainability is a priority for you. - 9.7
Brand Reputation: Research brands and choose one with positive reviews and a good reputation in the industry. - 9.3
Warranty and Guarantees: Look for products with warranties or guarantees, which can provide peace of mind and protection against defects. - 10
9.8
Score:
By considering these factors, you can make a well-informed decision on the best roofing felt material for your needs.
I found the section on durability to be particularly helpful. It’s important to choose a material that can withstand harsh weather conditions.
Great article! I had no idea there were so many factors to consider when choosing roofing felt material.
I’m curious about the cost differences between different roofing felt materials. Are there any options that are more budget-friendly?
Thanks for mentioning the importance of considering the environmental impact of roofing felt materials. Do you have any suggestions for more sustainable options?
Overall, this article has given me a good starting point for choosing the right roofing felt material. Thank you!
It would be great if you could include some recommendations or specific brands to consider.
Could you provide more information on the different types of roofing felt materials available?
I was hoping to see some information on the installation process for roofing felt. Is it difficult to install yourself?