Best Tile Roofing Underlayment

Irene writes:  Our house in Los Angeles is 25 years old. One roofer recommended removing the composite roofing tiles and replacing the old underlayment with 90-pound paper. Then they will replace the roofing tiles. Another roofer recommended the same approach, but with two layers of 30-pound felt as the underlayment. Please explain the differences between paper and felt and the differences between using the 90-pound paper and the 30-pound felt? Is one better than the other?

Steve Bliss, of, responds: With a tile roof, the underlayment and flashings are critical as they create the primary water barrier. The tiles are mostly for aesthetics and to help protect the underlayment. Since the tiles, themselves, should last 50 years or more, the underlayment should be of similar quality. More often than not, the tile roofing outlives the underlayments and flashings.

The terms “paper” and “felt” are used interchangeably and refer to organic felt paper, which is impregnated with asphalt and fillers to make roofing shingles and underlayments. Some products use fiberglass mesh rather than felt as the substrate.

The term “90-pound paper” usually refers to gravel-coated roll roofing, which is a low-quality product that rarely lasts more than a few years when exposed to the elements. It weighs about 90 pounds per square (100 sq. ft.) because of the heavy gravel surface. I would not recommend it for anything other than a utility shed as the quality today is very poor.

Two layers of  ASTM 30-pound asphalt-impregnated felt is the minimum you should use under tile and should last 20 to 30 years. For a little more money, you can upgrade to a double layer of heavy-duty,  SBS-modified asphalt underlayment such as VulcaSeal G40 (Fontana), Layfast SBS T35/43 (MB Technology), or Right Start UDL (Malarky Roofing Products). The fiberglass mat, SBS (synthetic rubber) additives, and 40-pound weight can increase the lifespan of the underlayment by 50 to 100%. Torch-applied membranes of organic or modified felt are commonly used as the second layer (the “capstock”) in wet areas like Florida, but are probably overkill in an arid region like southern California.

ASTM-rated roofing felt must comply with D 4869 or the older D 226 standard.

ASTM No. 30 roofing felt is far better than unrated “30 pound” felt, which may weigh as little as 15-20 pounds. Courtesy of Tamko.

There is a distinction between standard “30-pound”  felt, which actually weighs 15 to 20 pounds per square and ASTM-rated #30  felt which weighs closer to 30 pounds and is of higher quality. ASTM-rated felt (under ASTM D4869 or the older D226) is manufactured to strict specifications, while standard 30-pound felt varies in quality from one manufacturer to another. Both are made with an organic felt mat impregnated with asphalt and various fillers. Some premium asphalt underlayments use a fiberglass mat instead of felt paper.

Many roofers now prefer synthetic underlayments, which are lighter, more tear-resistant, and easier to work with than felt paper. There are wide variety of these with different warranties and projected lifespans. As with any new product, however, how long they will really last is unknown and manufacturing standards have not yet been established.

Whatever underlayment is used, the installation is as important as the specific material. Most important are proper sealing and flashing at all penetrations for chimneys, skylights, pipes and roof vents. Valleys are also a problem area that need special treatment. I prefer an open valley design using a self-sealing flashing membrane (such as Grace Ice & Water Shield) as the underlayment, covered with a heavy-duty metal flashing. Avoid aluminum flashing as it is will fail long before your tiles.

Q&A Index


  1. G40 vs. 30 Pound Felt

    Hi, I am comparing quotes for replacing the underlayment of my concrete shake roof in Los Angeles. What is the price difference between two layers of G40 and regular 30-pound felt. ( I have a total roof area of 3700 sq. ft.) How long would two layers of G-40 last compared to two layers of 30-pound felt for a Los Angeles home? Would you recommend two layers of G40 or 30 lbs felt ? Thank you !

    • buildingadvisor says:

      The weak link in tile roofs is the underlayment and metal flashings, which often fail before the tiles. Tiles can last 50 years or more, but underlayments often fail in 20 to 30 years.

      Fontana VulcaSeal G40 underlayment is definitely a better product than “regular” 30-pound felt because it is manufactured to ASTM standards, and is much heavier. ASTM 30-pound felt can weigh as little as 26 pounds per square, while standard #30 felt can weight as little as 15-20 pounds. Also G40 uses a fiberglass base and SBS-modified asphalt, which make it more flexible and durable than standard asphalt-felt underlayments. SBS is synthetic rubber, which gives the asphalt greater elasticity and seals better around nails, although these products are not technically self-sealing.

      Similar SBS-modified underlayments with fiberglass mats are made by Malarky (Right-Start UDL), a 40-pound product, and Layfast SBS TU35/43, which comes in two weights – 37 and 43 pounds. All things being equal, a heavier underlayment can be expected to last longer.

      Predicting how long any roofing product will last is a tricky business and is a function of the material, installation method, and climate. The roof color and slope also play a role, as does the maintenance of the roof. Cracked tiles and the build-up of organic debris can also shorten the life of the tile and underlayment.

      G40 and Layfast SBS both offer 20-year warranties for two-layer installations, while Malarky offers a 10-year warranty. However, it is reasonable to expect 30 years-plus with good installation and roof maintenance. Technical reps at the three firms confirmed this, but stressed the importance of proper installation and maintenance. For example, plastic cap roofing nails should be used on the underlayment, never staples.

      Whatever you use in the field, make sure you use a self-sealing, fully-adhered flashing membrane at any valleys, roof transitions, and around openings such as skylights.

      Related Product Links:    Fontanta G40    Layfast SBS TU35/43      Malarky Right Start UDL

  2. Clay vs. Concrete Tile, Synthetic Underlayment?

    I have a Mediterranean-style custom home and currently have authentic one-piece clay S-tiles. I had fumigation done because of termites and the roof was extensively damaged. I am not sure should if I should go with concrete tiles or the same clay tiles. Also what kind of double underlayment is recommended? I have been recommended Fontana G40 for underlayment or synthetic Sharkskin. I have been reading about concrete tiles that their color will fade over time, are heavy, and are 30% less expensive than clay tiles. The 30% extra cost is not an is an issue. I just need the right advise because overall it is an expensive project. I would appreciate your response at your earliest.

    • buildingadvisor says:

      You are smart to focus on the underlayment as that is the true waterproofing layer on a tile roof. The industry-standard minimum underlayment for a tile roof with a slope of 4:12 or greater is a single layer of ASTM-rated #30 felt paper. Cheaper felt paper without an ASTM rating, widely sold in home centers, is much thinner and should not be used. (The ASTM standards are D226 Type II or D4869 Type IV for organic felt; D6757 or D4601Type II for fiberglass products.)

      A double layer of underlayment provides twice the protection and longevity as a single layer and is, therefore, highly recommended. Many tile roofing systems have outlived their felt underlayments, requiring expensive repairs. No sense in putting a 10 year underlayment on a 50-year roof! The specific underlayment used should be suitable for the climate. Freezing weather, extreme heat, and windblown rain require appropriate materials and installation.

      Nowadays there are many more options than asphalt felt – primarily rubber-modified asphalt (SBS) products and synthetics, such as the Sharkskin and Titanium lines of products.

      Adding synthetic rubber (SBS) to asphalt generally improves its flexibility, its performance in cold and hot weather, and its overall durability and longevity. Modified asphalt has been widely used in self-adhesive flashing membranes such as Grace Ice & Water Shield and is used on many premium roofing underlayments such as Layfast SBS TU35/43. Fontana G40 is basically a high-quality 30-pound asphalt underlayment with a fiberglass base, which lays flatter than traditional “organic” felt. It meets ASTM Standard D6757 for 30-pound fiberglass underlayment and provides a 20-year warranty for a two-layer installation.

      There are also a number of newer synthetics on the market made from a variety of materials. Some, like Sharkskin, carry very long warranties. But like most roofing warranties, they don’t really cover much. For example, Sharkskin’s 50-year-warranty and Titanium’s lifetime warranty cover only the original cost of the material, not its installation. This might cover 10% of the actual cost of repairs.

      Some of the synthetic underlayments provide a Class A fire rating, improved walkability on steep slopes, and easier installation due to their light weight and resistance to tearing. The easy installation makes them popular with many roofing contractors. How well they will last over the long haul is unknown, however, and manufacturing standards have not yet been established.

      Personally, I would choose two layers of G40 over Sharkskin as the material has been around longer and has a proven track record. I would also consider an upgrade to an SBS-modified product such as Layfast TU43, which is bit heavier, but still only carries a 20 year warranty for two layers. Whatever you choose, make sure you use a self-adhered flashing membrane at valleys and transitions and around skylights or other openings.

      Sounds like you have done your homework about clay vs. concrete tile. As you point out, concrete tiles are less expensive and lighter, but will fade somewhat over time. Also because they are more porous, they can get stained. Clay tiles will keep their color pretty much forever whether natural or with a ceramic finish. If you are in a freezing climate, however, concrete tiles are a better choice as they are less prone to cracking.

      Good quality concrete tiles should last 30 to 50 years, while clay tiles may still be going strong in 100 years, well after you and I are long gone. Best of luck with your new roof!

  3. Composite Roofing Tiles

    Are composite roofing tiles very popular in California? I love the look of slate tiles and I thought that these were common in California. How durable are they?

    • buildingadvisor says:

      As far as I know, traditional clay tiles are still the most common (and most expensive) roofing material on the West Coast, followed by concrete tiles, and then composite tiles.

      Good quality concrete tiles should last 30-50 years. Clay tiles may last much longer. Composite tiles vary in their composition and lifespan.

      Composite tiles are made from a variety of materials so it is hard to generalize about quality and longevity. They are lighter weight than concrete or clay and less costly. They use various combinations of fiber-cement, plastics, polymers, synthetic rubber, and various fillers.

      If you go with composite, I would look for a product and company with a good track record and products that have been in the field, in your climate, for 10 to 20 years. Check the product online for consumer complaints, lawsuits, etc. A lot of composite roofing and decking products have not lived up to expectations and ended up being pulled from the market.

      Look for a strong warranty, which shows some level of confidence in the product. But remember that most roofing warranties are for materials only, are prorated by years of use, and require that the product be installed exactly as the manufacturer specified. And the company has to still be around when you make the claim. So, in reality, roofing product warranties are usually not worth very much.

  4. SBS-modified 40 or 90 lb felt is much higher quality than 30 lb paper. Two layers of unmodified 30 is cheaper than 1 layer of modified 90. I was disappointed to read your answer. I disagree with many specifics you gave, including the lack of the term “modified” and the actual weights vs names. Please refer to Malarkey Building Products for accurate information.

    • buildingadvisor says:

      I agree that SBS-modified asphalt underlayment is, in general, a much better product than unmodified asphalt felt, and stated that above. And also pointed out, that underlayments with manufactured to ASTM standards are much better than unrated products.

      Different companies offer different formulations and different weights, so I’m not sure what you find incorrect. For example, MBTechnology offers 37-, 43- and 70-pound SBS-modified underlayment. Your company, Malarky, and Fontana both offer premium 40-pound SBS-modified underlayments as well. You can find links to these products here.

      Since the nominal weight with any of these products does not always match the actual weight, it’s always a good idea to check the product specifications before purchasing. Also confirm that it meets the appropriate product standards and pay attention to the installation instructions or risk poor performance and a voided warranty.

      • Brad -- A Roofer in Findlay says:

        I thought you answered the question pretty accurately. I too have moved away from the 90 pound paper to go with a different type of material like you mentioned. Thanks. Brad, Findlay Roofers, Findlay, OH



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