Recommended Free Tools
Some links on this page are affiliate links: if you buy through them we may earn a commission, at no extra cost to you.
Asphalt shingles need an underlayment over the roof deck. Asphalt-saturated felt is an established option, but the correct product, number of layers, fastening method, and exposure limits depend on the locally adopted building code, roof slope and assembly, and the shingle manufacturer’s instructions. The Asphalt Roofing Manufacturers Association (ARMA) cautions that asphalt shingles should not be installed directly on a wood deck and says to check both code and the shingle maker’s requirements before selecting underlayment. Felt is water-resistant and helps separate the shingles from the deck, but a roll labeled No. 15 or No. 30 is not automatically compliant for every roof.
This guide explains what felt does, how Type I and Type II labels relate to No. 15 and No. 30 felt, when low-slope rules change, and how to plan installation without treating one jurisdiction’s rule as universal.
As an Amazon Associate I earn from qualifying purchases.
Quick wins for a faster PC:
Scan for outdated or missing drivers - takes under a minuteDriver Scan →Repair Windows errors before they cause bigger problemsFix Now →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Do asphalt shingles need felt underlayment?
Yes. Underlayment is installed over the roof deck and beneath asphalt shingles. It is part of the roof assembly, not an optional sheet added only when the deck looks vulnerable. ARMA’s steep-slope underlayment guidance specifically warns against installing asphalt shingles directly on a wood deck.
“Felt” normally means asphalt-saturated organic felt. The asphalt content makes the sheet water-resistant, while the organic reinforcement still permits some vapor movement and can absorb moisture. That combination explains why felt has been used for decades, but it also means the material must be selected and covered according to the roof’s conditions. Do not describe ordinary felt as a permanently exposed waterproof membrane.
Popular on Amazon
- Ergonomically Designed: Work in tight areas with a compact design that gets into tough spots
- Both tools are designed to fit into difficult to reach spaces
- Complete a wide range of applications with a high-performance motor that delivers up to 300 UWO, and an impact driver delivering up to 1,400 in-lbs of torque
- Both the DEWALT impact driver and drill driver feature integrated LED work lights with a convenient 20-second delay, ensuring enhanced visibility in dimly lit or challenging work areas
- One-Handed Loading - Keep one hand free with a 1/4 in. hex chuck that accepts 1 in. bit tips
Underlayment supports the shingle system by providing a secondary water-resisting layer and a consistent surface between the deck and shingles. It does not erase defects in the deck, incorrect flashing, poor shingle fastening, or a mismatch between the product and the code-approved assembly. The shingles, flashings, deck, ventilation and underlayment have to work as one system.
What are No. 15 and No. 30 roofing felt?
ARMA identifies two traditional categories: Type I, commonly known as No. 15 felt, and the heavier Type II, commonly known as No. 30 felt. Those names are useful shorthand, not a universal instruction that every roof needs the heavier sheet.
The Tool Desk
Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →| Label used in the trade | ARMA category | What the label tells you | What it does not tell you |
|---|---|---|---|
| No. 15 felt | Type I | A lighter asphalt-saturated organic-felt category | Whether it is permitted on your roof, how many layers are required, or which fasteners and laps apply |
| No. 30 felt | Type II | A heavier asphalt-saturated organic-felt category | That it is automatically “better,” code-compliant, or interchangeable with another manufacturer’s Type II product |
Product names can conceal important differences in reinforcement, labeling and installation instructions. Before purchase, read the roll’s standard and type markings rather than relying on a retailer’s search term. A listing that says “No. 15” or “No. 30” is not, by itself, proof that the roll meets the requirements for your jurisdiction or shingle system.
How do building codes decide which underlayment is allowed?
There is no single felt rule for every roof in every location. Start with the building department or code official for the project address, then read the shingle manufacturer’s installation instructions for the exact product. ARMA summarizes the priority clearly: “Always consult local building codes and the shingle manufacturer’s requirements regarding underlayment product selection and installation methods.”
Also popular on Amazon
- Valued Carpenter Pencil Set: You will get 2 pcs solid carpenter pencils with 26 piece 2.8 mm refills, 1 replaceable sharpener, 1 plastic storage box.The complete carpenter pencils combination allows you to finish your work faster and more easily
- Deep Hole Marker Pencil: The deep-hole construction pencils adopts 45mm elongated tip design, which is more convenient to mark in the small hole or in other tight areas that other carpenter markers cannot reach
- Carpenter Pencils with Sharpener: The sharpener is screwed into the top of the work pencil, which won't get lost either. Built-in pencil sharpener that keep the lead with pointed and smooth to Improves line of sight in fine work
- Stronger Solid Lead: This work pencil is matched with a 2.8 mm thick lead , which is much thicker and stronger during the drawing process of construction work, it will not break or damage easily
- Marks on Various Surfaces: 3 colors solid construction pencil can marks on various surfaces,such as metal, plastic, wood, paper etc. Ideals for woodworkers, contractors, craftsmen, builders, merchants and masons
The code references below show why checking the adopted edition matters:
- The 2025 Residential Code of New York State, Chapter 9, requires underlayment for asphalt shingles and includes material-standard, labeling and installation provisions. It also presents alternative pathways, including self-adhering polymer-modified bitumen and mechanically fastened underlayment. The state’s adopted text and amendments control a New York project, not a generic summary of the model code.
- The 2024 International Residential Code, Chapter 9, is a model-code reference. A municipality may adopt it with amendments, adopt another edition, or use a different code, so the book on a contractor’s shelf is not necessarily the enforceable rule at the job site.
- A Commonwealth of Massachusetts design guideline says to follow the shingle manufacturer’s recommendations for asphalt-impregnated 15 lb felt and calls for double-layer roofing felt on roofs pitched 3 in 12 or lower in that guideline’s context. It also says to cover installed felt with shingles the same day. That is a Massachusetts guideline recommendation, not a universal rule for every state or roof.
Codes can change the permitted material, required layers, attachment method, or treatment of valleys, eaves and other roof areas. Manufacturer instructions can be stricter than a minimum code path because the shingle warranty and wind or weather performance depend on a particular assembly. Keep the code section and the shingle instructions with the project record so the installer, inspector and owner are working from the same documents.
Should you choose felt or another underlayment?
Felt is one option among several. A code-permitted self-adhering polymer-modified bitumen product or another approved underlayment may be appropriate, but alternatives are not automatically interchangeable with asphalt-saturated felt. Compare the complete assembly rather than choosing by the material name alone.
| Decision factor | Asphalt-saturated felt | Self-adhering polymer-modified bitumen | Other code-permitted underlayments |
|---|---|---|---|
| Code status | Permitted only where the adopted code and project details allow the selected type and layers | May be an explicit alternative pathway in some codes | Must meet the applicable code and product-standard provisions |
| Attachment | Commonly mechanically fastened, subject to the code and manufacturer instructions | Self-adhered when the approved assembly calls for it; installation conditions matter | Can be mechanically fastened or installed by another approved method |
| Roof slope and exposure | Layer count and exposure limits can change with slope and weather conditions | Suitability still depends on slope, climate, deck and the shingle system | Use only where the product’s listing and the adopted code cover the assembly |
| Compatibility | Must match the shingle maker’s approved roof assembly | Must be listed or accepted for the shingles and substrate | Do not assume compatibility from a generic “underlayment” label |
The practical choice is the one that satisfies all five checks: code compliance, product-standard labeling, compatibility with the shingle instructions, suitability for the roof slope and weather exposure, and a workable installation sequence. A contractor may recommend an alternative for a specific assembly, but that recommendation should be traceable to the adopted code and the manufacturer’s written requirements.
Also popular on Amazon
- 【Great Compatibility】This Katerk 1/4 inch hex shank bit holder is specifically designed for 1/4 inch hex shank drill bits. It's compatible with most 1/4 fast hex handles, hex sockets, various electric screwdrivers, and handheld screwdrivers. The bit holder makes it a valuable addition for any handyman.
- 【Secure and Safe】Built with a secure backup nut design, each drill bit holder securely locks onto your bits, ensuring they stay firmly in place. Additionally, our bit holder incorporates a high-quality steel ball rolling design that holds up to several kilograms of weight, ensuring your various drill bits don't fall off.
- 【Easy One-Handed Operation】The bit holder for impact driver allows you to change bits single-handedly, simplifying your workflow. Its multi-color design further allows for quick identification of the drill bit you need.
- 【Compact and Convenient】Thanks to its compact size, this 1/4 inch bit holder is easy to carry around. The bit holder allows for easy attachment to various tools, making this a convenient addition to your construction accessories. The Katerk bit holder is cast from high-quality alloy material, promising a long product lifespan. Despite its rugged strength, the bit holder remains lightweight, making it portable.
- 【Cool Christmas Gift For Men Stocking Stuffers】 This screwdriver bit holder, driver bit holder, impact bit holder, can be given as a gift to your loved one, especially for anyone involved in construction or electrical work. It's a must-have for stocking stuffers for men and women, tools gifts for dad, tech gadgets for men, gifts for dad, gifts for him, gifts for husband, gifts for boyfriend, cool gadgets for men, and cool gifts for dad.
How do you install felt under asphalt shingles?
The exact overlaps, fastener schedule, side-lap treatment and special details belong to the applicable code and shingle instructions. The following sequence is a planning framework; it does not replace those tables or the manufacturer’s diagrams.
- Identify the controlling documents. Confirm the code edition and amendments adopted at the project address. Obtain the shingle manufacturer’s current installation instructions and any underlayment instructions referenced by them. Resolve conflicts with the code official or manufacturer before material is delivered.
- Confirm the roof conditions. Record the roof slope, deck material and condition, areas exposed to weather during construction, and any locations where the code calls for a different underlayment treatment. A low-slope section may require more than a standard steep-slope detail.
- Prepare the deck. The deck must be sound, dry and ready to receive the specified underlayment. Replace or repair damaged areas before covering them; felt is not a substitute for structural or sheathing repairs.
- Verify the roll before opening it. Check the product type, labeled standard, manufacturer instructions and any required markings. Make sure the roll is the type named by the code path and shingle instructions, not merely a product with a similar trade name.
- Install the first course and subsequent courses exactly as specified. Follow the required direction, laps, end joints, fastening pattern and treatment at edges, penetrations, valleys and transitions. The permitted method may be mechanically fastened felt, a self-adhered product, or a combination of approved materials; do not substitute one method because it is familiar.
- Keep the surface flat. Work in manageable sections and avoid trapping debris or leaving loose, wrinkled sheets beneath the shingles. Wrinkles can telegraph through the finished roof and create poor shingle support.
- Sequence the shingle work promptly. Massachusetts guidance says to install only as much felt as can be covered by shingles the same day because prolonged exposure can cause wrinkles and poor installation. If weather interrupts the work, protect the roof as directed by the product manufacturer and inspect the underlayment before shingling continues.
- Complete a pre-shingle inspection. Check that every required area is covered, laps and fasteners match the approved detail, edges and penetrations are treated correctly, and no section is damaged or exposed beyond the permitted period. Photograph the completed underlayment and retain the product labels for the project record.
What changes on a low-slope roof?
Lower slopes are a common reason a standard felt detail cannot simply be copied from another roof. Water drains more slowly, so the adopted code or shingle manufacturer may require additional layers, a different product, or a different installation method.
What’s actually slowing this PC down?
Pick the symptom - the matching free tool is one click away.
Massachusetts’ August 2022 guideline is a useful example: in the context covered by that document, it recommends double-layer roofing felt for a pitch of 3 in 12 or lower. That figure should alert you to check the local rule; it should not be converted into a nationwide requirement. The 2025 New York code and the 2024 IRC also contain roof-condition and slope-dependent provisions, but the applicable text is the version adopted and amended for the project location.
When a roof has multiple slopes, treat each area according to its own approved detail. Do not assume that a steep main plane authorizes the same underlayment on a porch, dormer or addition with a lower pitch.
Also popular on Amazon
- Toolwiz 17-inch magnetic sweeper maintaining a load capacity of up to 8.8 pounds provides a perfect solution to the problem of clearing small ferrous metal objects, such as nails, tacks, bolts, and metal shavings from workshops or garage floors.
- Convenient and portable：17” is good for home, small workshop, or small yard as it is space-saving and more reachable for narrow areas. Perfect for collecting nails or small parts in the car, under the table, and in other nooks or crannies.
- Upgraded Handle Design: The handle features a sturdy, non-telescopic design to completely prevent slipping during use. By simply adding or removing the extension poles, the height can be adjusted to 3 different lengths: 18.9" (48 cm), 32.5" (82.5 cm), and 42.5" (108 cm) from ground to top. This customizable height helps prevent back bending and muscle strain, making your cleaning tasks effortless
- Flexible wheels: Upgrade wheel screws to avoid being too tight to spin or too loose. More comfortable 3-inch rubber wheels roll smoothly on carpet, grass, concrete, and hardwood floors. Just push and pull this rolling magnet-sweeper to pick up metal nails easily.
- Lightweight materials: The magnetic nail sweeper's compact and lightweight design makes the sweeping can be done anywhere you want, Push or pull it under the furniture, passing through the workshop floor, driveway, mud, grass, and gravel.
How long can felt stay exposed?
Exposure time is a job-sequencing issue, not just a scheduling preference. The Massachusetts guideline advises covering installed felt with shingles the same day because extended weather exposure can produce wrinkles and lead to poor installation. Other products and jurisdictions may state different limits, so read the roll instructions and code requirements before leaving a roof partially covered.
If rain, wind or a delivery delay stops the job, do not shingle over visibly wrinkled, torn or contaminated material. Follow the manufacturer’s repair or replacement direction, and ask the code official or manufacturer how to document a condition that exceeds the stated exposure period.
What mistakes most often cause underlayment problems?
- Installing shingles directly on the deck: ARMA says asphalt shingles should not be installed directly on a wood deck.
- Treating No. 15 or No. 30 as a universal prescription: The labels identify Type I and Type II categories; they do not determine layer count or permission for a particular roof.
- Using a code from the wrong jurisdiction: A Massachusetts guideline, New York code chapter or model IRC provision cannot be applied wholesale to a different location.
- Ignoring the shingle manufacturer’s assembly: The approved product, attachment method and special details may be narrower than a generic roofing practice.
- Leaving felt exposed too long: Weather can wrinkle the material and undermine the flat surface needed for shingle installation.
- Buying by online title alone: A retailer’s “No. 15” or “No. 30” description does not prove the roll carries the required standard marking or is accepted by the local code.
- Mixing installation methods without approval: Mechanically fastened felt and self-adhering polymer-modified bitumen follow different installation procedures. Use a combination only when the code and product instructions permit it.
How should you verify an asphalt roofing felt roll before buying?
Use this short verification checklist:
- Read the roll label for the product type and applicable ASTM or other required standard marking.
- Confirm whether it is Type I/No. 15 or Type II/No. 30, without assuming the label alone settles the choice.
- Match the product to the underlayment option named in the locally adopted code.
- Compare the product instructions with the asphalt-shingle manufacturer’s roof-assembly instructions.
- Check the roof slope and any special low-slope or weather-exposure provisions.
- Ask the building department or code official to resolve any uncertainty before installation.
These checks matter whether the roll comes from a roofing distributor, a lumberyard or an online marketplace. Compliance is established by the product’s documentation and the approved assembly, not by a search result or a familiar number printed in a listing title.
What is the practical answer for a homeowner or builder?
Plan on an underlayment beneath asphalt shingles, and treat asphalt-saturated felt as a code- and assembly-dependent option rather than a universal recipe. Type I/No. 15 and Type II/No. 30 describe traditional felt categories; they do not tell you, by themselves, which roof needs one layer, two layers or a different material. Confirm the adopted code, roof slope, deck and shingle instructions first, then install and cover the selected underlayment within the allowed exposure period.
Also popular on Amazon
- APPLY TO MOST DRILLS : 6 pieces screw extractors work with any drill and all the screw size or bolt (3-12mm), These extractor tools are used to reverse the damaged screw counterclockwise until it is released
- The DIY Tools for Men-Men won't know they need screw extractor set until they have one! This screw extractor set is GIFTS WRAP AVAILABLE, can be gifted to your loved ones as it reflects a fresh trend with fun and practical. Amazing and Unique tool gifts for men women. The must have stocking stuffers for men, gifts for dad, husband, father, him, guy teens, adult, Boyfriend, son on Birthdays, Christmas, Fathers Day or anniversary. Perfect Holiday Gifts Guide
- HIGH QUALITY - This damaged screw remover tool kit is made from High-Speed Steel H.S.S 4341# , which have high hardness of 63hrc, it's durable and easily to remove any damaged screws.
- EASY TO USE: Just two simple steps to get the job done - drill a hole with a cutting size using the right size screw extractor and easily remove the screw or bolt using the removal tool Hardness 63-65HRC: Titanium hardened steel material, more durable than most screw extractors on the market, better hardness and durability than others, buy with confidence and complete peace of mind
- Cool Gadgets for Men Dad Christmas Birthday Gifts for Men and Women - Men won't know they need screw extractor sets until they have one! Every screw has the potential to rust and break, which can create a situation where it cannot be removed. Owning it, there will be no anxiety about rusty screws. This screw extractor set is GIFTS WRAP AVAILABLE, can be gifted to your loved ones as it reflects a fresh trend with fun and practical. Amazing and unique tool gifts for men women. A must have stocking stuffer for men on birthdays, Christmas, Father's Day or anniversaries, a gifts for dads, husbands, fathers, him, adults, boyfriends, sons. The best and most practical and surprising Christmas gifts
For background on roof-assembly approaches, the Pacific Northwest National Laboratory Building America Solution Center guide to asphalt shingle roofs is a useful companion to the governing code and manufacturer documents. Those project-specific documents remain the authority for the work.
Frequently Asked Questions
Is No. 30 felt mandatory for every asphalt-shingle roof?
No. No. 30 is the common trade name for ARMA’s heavier Type II organic felt, but the required type and layer count depend on the adopted code, roof slope, exposure and shingle manufacturer. A heavier roll is not automatically the correct or required choice.
Can self-adhering polymer-modified bitumen replace felt?
It can be an approved alternative in some code pathways, including provisions described in the 2025 New York residential code. It is not universally interchangeable with felt; verify the product listing, installation method and shingle-maker approval for the exact assembly.
What should I do if weather arrives before the shingles are installed?
Stop and follow the underlayment manufacturer’s exposure and protection instructions. Before shingling resumes, inspect for wrinkles, tears, displaced fasteners or contamination and repair or replace material as directed rather than covering damaged felt.
Does a product listing that says “No. 15” prove the roll is code-compliant?
No. The trade label identifies a felt category, not complete compliance. Check the roll’s standard marking and technical instructions, then confirm that the selected product and installation method are accepted by the local code and the shingle manufacturer.
