---
title: "Roof Underlayment Types for a Lasting Roof | NEMA Roofing"
description: "Roof underlayment types compared: felt, synthetic and self-adhered membranes, what the code allows under shingles, tile and metal, and how laps help it last."
url: "https://nemaroofing.com/roofing-installation/roofing-installation-built-to-last-backed-by-experts/"
updated: "2026-09-30"
---

**The main roof underlayment types are asphalt-saturated organic felt (ASTM D226 and D4869), felt made with inorganic fibers (ASTM D6757), synthetic polymeric sheets that are nailed or stapled down (ASTM D8257), and self-adhering modified bitumen membranes (ASTM D1970).** The California Residential Code lists which of them each roof covering may use and how they must be lapped, and getting that layer right is a large part of what makes a new roof last. To talk through the underlayment on your installation, call NEMA Roofing at [866-631-3366](tel:866-631-3366).

## What does underlayment do on a finished roof?

Shingles, tiles and metal shed most of the water, but not all of it. Wind drives rain under laps, tiles crack or slip, and water backs up at valleys and walls. The underlayment is the sheet on the deck that catches that water and sends it down to the eaves before it reaches the wood. On a tile roof it does most of the waterproofing, because tile is laid loose enough for water to pass between pieces. It also keeps the deck dry during the job, between tear-off and the day the covering is finished.

## How do the main underlayment types compare?

| Type | Standard | What it is | Trade-offs |
| --- | --- | --- | --- |
| Organic felt | ASTM D226 (Type I lighter, Type II heavier); ASTM D4869 | Paper-based felt saturated with asphalt, the traditional “tar paper” | Familiar and accepted under every steep-slope covering; heavier and easier to tear, wrinkles when it gets wet |
| Inorganic-fiber felt | ASTM D6757 | Felt reinforced with glass or other inorganic fibers | Listed in the code for asphalt shingles; ask whether the shingle maker accepts the exact product |
| Synthetic | ASTM D8257 | Woven or spunbond polymer sheet, mechanically attached | Light, strong and slip resistant for installers; exposure limits and fasteners vary by product, so the maker’s instructions govern |
| Self-adhered membrane | ASTM D1970 | Rubberized (polymer modified) asphalt sheet with a sticky back | Seals around nails; used in valleys, at walls, around openings and on lower slopes; costs more and must suit the deck and ventilation |

Every underlayment that must meet one of these standards has to carry a label showing the standard and type (CRC R905.1.1), so you or an inspector can read what went on the roof.

## Which underlayment goes under which roof covering?

In areas where wind design is not required, the code’s underlayment table allows:

- **Asphalt shingles:** D226 Type I or II, D4869, D6757, D8257 or D1970.
- **Clay and concrete tile:** D226 Type II, D2626 (coated felt base sheet), D6380 Class M (mineral-surfaced roll roofing), D1970 or D8257. The heavier choices reflect how much of the waterproofing the underlayment does under tile.
- **Metal panels on solid sheathing:** D226 or D4869 felt; in wind-design areas the list also includes D1970 and D8257.

Where wind design is required, the lighter felt types drop out of the table (for example, D226 Type II or D4869 Type III or IV for shingles). For more on the tile side, see our [tile roofing service](https://nemaroofing.com/our-services/tile-roofing/).

## How must underlayment be installed to last?

The code ties the method to the slope. Under asphalt shingles:

1. **2 in 12 up to 4 in 12:** two layers. A half-width starter strip goes along the eave, then full sheets overlap each other by half a sheet plus 2 inches.
2. **4 in 12 and steeper:** one layer, run parallel to the eave and lapped 2 inches, shingle fashion.
3. **End laps:** 4 inches, staggered 6 feet from the laps in the course below.
4. **Alternative:** one layer of D1970 self-adhered membrane, installed to both the underlayment and shingle makers’ instructions for that deck, ventilation and climate.

Clay and concrete tile between 2 1/2 in 12 and 4 in 12 also needs a double underlayment (CRC R905.3.2). Wrinkles and bulges are more than cosmetic: the code says distortions in the underlayment must not keep shingles from sealing. Drip edge at the eaves and rakes (CRC R905.2.8.5) finishes the edge so water leaves the underlayment and falls clear of the fascia. Our [step-by-step roofing installation guide](https://nemaroofing.com/roofing-installation/roofing-installation-a-step-by-step-guide-for-homeowners/) shows where this fits in the order of work.

## Which underlayment mistakes shorten a roof’s life?

- **Left exposed too long.** Each product states how long it may sit uncovered in the sun; past that, it can degrade before the covering goes on.
- **Wrong laps.** Short side laps or end laps lined up course over course give water a straight path to the deck.
- **Tears and loose fasteners.** Rips from foot traffic or wind, or too few fasteners, leave the sheet unable to carry water down the roof.
- **No extra protection where water gathers.** Valleys, wall intersections, chimneys and skylights need more than the field sheet, usually a self-adhered membrane plus metal flashing.
- **Mixing products without checking.** A self-adhered membrane under the wrong covering or over an unvented deck can trap heat and moisture; the makers’ instructions settle what may be combined.

## How can you check what your new roof is getting?

- Ask the estimate to name the underlayment product and its ASTM standard, not just “underlayment.”
- Ask where self-adhered membrane goes: valleys, walls, penetrations, low-slope sections.
- Ask for photos of the underlayment before the covering hides it.
- Check that the underlayment is one the covering’s manufacturer accepts, since manufacturer warranties expect the roof to be installed to their instructions.

We provide detailed estimates and clear contracts; ask us to point out the underlayment line in yours. For the other details that decide a roof’s life, read [roofing installation designed to improve durability and performance](https://nemaroofing.com/roofing-installation/roofing-installation-designed-to-improve-durability-and-performance/).

NEMA Roofing crews install roofs in all five counties we serve (Santa Barbara, Ventura, Los Angeles, Riverside and [San Bernardino](https://nemaroofing.com/service-areas/san-bernardino-county/)), working from locations in Santa Barbara, Oxnard, Woodland Hills, Tarzana and Downey. See our [roof installation service](https://nemaroofing.com/our-services/roofing-installation/), or call [866-631-3366](tel:866-631-3366) to plan your new roof.