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Roofing materials are made up of many elements in the present day. Everything from metal, to asphalt, to slate and others types, roofing material varies by cost, life and installation required. Getting to know the various kinds of roofs can be helpful when evaluating your home or searching for a new one.


Asphalt composition shingles are the most common type of roofing material used in the country today. They vary in weight, color and design. The weight of a standard asphalt composition shingle before 1973 was 240 pounds per square (of coverage); modern standard shingles weigh approximately 190 pounds, depending on the manufacturer.

The oil embargo of the early 1970s wreaked havoc in the asphalt shingle industry. The shingles, at that time, were composed of an asphalt-saturated cellulose matrix, and slate or stone granules adhered to the matrix to protect it. Due to the fact that asphalt is a petroleum product, the shingle manufacturers were at the mercy of the oil industry and its politics. In an effort to minimize the cost problems, they redesigned their shingles to be less dependent on the oil industry. The plan was to use less asphalt in the shingles without sacrificing strength and durability.  The product that evolved had a fiberglass reinforcement mat in the matrix for strength. This also reduced the weight and thickness of the matrix. But the early versions of the fiberglass-reinforced shingle had problems:

In some cases, the granules did not adhere properly to the matrix, due to temperature problems. Due to the thinner matrix and the fiberglass, the shingles could crack when applied in colder weather. The concussion of the hammer would fracture the fiberglass, since it becomes brittle when the shingles get cold. Nailing guns are somewhat less of a problem, however, the shingles still may crack. These cracks are visible at the nails and may extend horizontally from nail to nail to nail, all the way across the roof.

Modern shingles are sold by the length of their warranty (i.e. 20-year, 25-year, 30-year, 40 Year, and 50 Year). The differences are the weight and design of the shingles. 30-year shingles generally do not have joints between the tabs exposed to the weather.

Obviously, there are wide variations in asphalt shingle roofs. But by and large, asphalt shingle roofs have a life expectancy of 15 to 30 years, depending on the weight of the shingles, slope of the roof, exposure to the sun, color, and weather and climate conditions.

In southern climates, such as Florida, it is not unusual for asphalt shingles to fail in 12 to 14 years. In northern climates, such as Massachusetts and New York, higher sloped roofs with an eastern and or northern exposure can last 25 years. These shingles can be expected to deteriorate as the petroleum and composition fiber base, of which the shingle matrix is constructed, begins to dry out.  When this occurs, the shingles begin to curl, cup, split and lose their granules. Loss of granules between the shingle tabs is the most conclusive evidence you have for determining the condition of the shingles. This is normally the first place where failures occur.  Re-shingling can be done, either by applying another layer of shingles over the existing roof (as long as the existing shingles are laying reasonably flat or if there is only one layer of shingles on the roof) or by tearing off the existing roofing and applying new shingles. The concerns with two or more layers of asphalt shingles are: 

Weight, which can be considerable. Standard shingles weight approximately 190 pounds per 100 square feet (SF), or approximately 2 pounds per SF. A 15 or 16 square roof with 2 layers of standard shingles will have about 6,000 lbs of shingles. This will have more impact on shallow sloped roofs. Roof framing should be designed at 20 pounds per SF, so there is no danger of collapse, however, snow and wind loads may cause deflection. Heavy weight shingles can be 50% heavier than standard or 20-year shingles.

Longer roofing nails should be used to secure the shingles to the wood sheathing. Nails should penetrate the sheathing a minimum of 3/4 inch.

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Rolled Roofing

Rolled roofing or 90-pound roll roofing is fabricated the same way as asphalt strip shingles. It consists of a petroleum and composition fiber base, upon which crushed slate or stone granules are installed. Most of the modern felts are overlaid with fiberglass for added strength. Rolled mineral roofs are installed on relatively flat (2/12), and steep roofs. The NRCA considers mineral surface roll roofing steep roofing material. Asphalt roll roofing materials may be applied:

  • On 4/12 slopes or more, if applied parallel to the rake using the exposed nail method.
  • On 3/12 slopes or more, if applied parallel to the rake using the concealed-nail method.
  • On 6/12 slopes or more, if applied parallel to the downslope roof edge or eaves, using the exposed nail method.
  • On 2/12 slopes or more, if applied parallel to the downslope roof edge or eaves, using the concealed-nail method.

Asphalt roll roofing material should not be applied on roof decks with less than 2/12 slope, unless it is 19-inch selvage edge roll roofing. Selvage edge or double coverage roll roofing may be installed on slopes of 1/12 or more, provided the deck slopes drain. All water should drain off by gravity.

Roll roofing, however, is commonly used on low-sloped roofs, especially in the inner city, and functions reasonably well. Rolled mineral roofing material comes in 36-inch wide x 50 feet long rolls and is installed with a 2 to 4-inch lap. Exposed nails are not acceptable on roofs with 3/12 slope or less. Low slope roofs must be secured with a concealed-nail method.

Double coverage rolled mineral roofing is called Selvage roofing. The mineral surface is only on one half of a 36-inch roll. The other half is a heavy felt and is suitable for the application of tar or petroleum-based roof coating, which is used as an adhesive and sealer for this type of roof. The 19-inch selvage portion is lapped with the 17-inch granule-coated exposed portion. Both rolled mineral and selvage roofings are popular roof coverings for low-sloped roofs, such as you would see on inner city row housing. Selvage roofing is more dependable than (single layer) rolled mineral roofing, because it is two layers.

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Wood is a popular material for roof covering in some areas. Wood roofing comes in hand and machine split shakes, and machine-sewn shingles, both of which have approximately the same life expectancy. The quality of the shingles, the length of the shingles or shakes, exposure to the sun, the maintenance they receive and the slope of the roof impact the roof’s life expectancy. The lower the slope of the roof, the slower water drains off, and the more likely it is for water damage or deterioration to result from mildew or moss.

Wood shingles are typically installed on spaced or skipped sheathing, or solid sheathing, such as plywood. NRCA recommends No. 1 shingles and a slope of at least 4/12. The main drawback of wood roofs is the lack of fire resistance, although the wood can be pressure treated to achieve a class-C rating.

Air circulation under wood roofing systems promotes longevity of the wood roofing as it facilitates proper drying. Requirements for the roof deck over which wood shakes or wood shingles are to be applied are as follows:

  • Roof must be steeply sloped to provide relatively rapid runoff of water. Minimum of 4 inches per foot or 33% slope or as some manufacturers allow.
  • Spaced or solid sheathing is acceptable.
  • Spaced sheathing should be installed on centers equal to the reveal or weather exposure. Common exposures are 5 ½ inches, 7 ½ inches and 10 ½ inches. 1x4 sheathing boards for wood shingles; 1x6 for wood shakes.
  • Solid sheathing or plywood requires a minimum of 15/32-inch deck (1/2-inch plywood).
  • Sheathing should have 1/8-inch spaces to allow for expansion.
  • Solid sheathing or plywood should be APA rated or APA performance rated.

All panels should be rated for structural use. There is concern that some OSB and other non-veneer products could have potential fastener-holding problems.

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Slate varies in quality, depending on: the quarry it came out of; thickness; density; slope of the roof; and exposure to the sun. Its density and thickness generally dictate quality.  Some slate will be more expensive because it is harder to quarry and causes more wear on the cutting equipment than softer slates. Inexpensive slates have a life expectancy of 45 to 60 years on the southern exposure. This is fairly common for slate that is quarried from western Pennsylvania and West Virginia. Dense slate is more common from Vermont quarries. Good quality, dense and thick slates could last hundreds of years.

The most significant concern with good quality slates is the fasteners or nails that secure them to the roof. You should expect some nail failures when the roof is 50 to 75 years old. This will be an ongoing maintenance problem and may cause premature replacement if it is not maintained regularly or if this type of maintenance is a burden to the owner or responsible party.  Inspecting slate roofing should be done as follows:

Look for whitish stains on the slates. These stains will usually look like half moons and will be more prevalent on the southern exposures. The delaminating of the slates, due to the ongoing absorption and drying of water over decades of exposure, causes these stains. In most cases they can be seen from the street. Rain will wet and to some extent wash off the mineral stains.

Slates with whitish mineral stains may have considerable remaining life if they are 1/2 inch thick or more. 1/4-inch slates with delamination and mineral stains probably have little remaining life. Check to see if the corners of delaminated slates can be broken with your fingers. If you tap the slates with a coin, the delaminated areas may sound like cardboard and the areas that are not delaminated will sound like glass.

  • After you determine the condition of the slates on all exposures, you should determine if or how many slates are loose, missing or cracked/broken. Be careful because loose and broken slates may give way underfoot.
  • Periodic maintenance should be recommended on any slate roof more than 40 years old.
  • Loose, broken and missing slates should only be replaced or resecured by mechanical means. Repairs performed with roof cement or similar substances are to be considered temporary, not dependable.
  • Cost to repair slate roofing, depending on the geographic location can be expensive.
  • When it looks like maintenance will be too difficult or a burden, replacement should be anticipated.
  • Deteriorated metal valleys and/or flashings, typically the ones that have been patched with roof cement, should be replaced.

This type of roof must be properly installed and maintained by a professional who has experience with slate roofing. A contracting firm or person that has proper scaffolding and equipment is necessary when work is needed on these roofs. The slate roofing is easily damaged when repair work, such as shingle replacement, valley repairs or replacement or chimney pointing, etc. is needed.

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Built Up

Built-up roofs (BUR) are typically constructed of 2, 3, or 4 plies of 15 or 20-felt paper material, held or mopped with melted asphalt. Older installations may have been held down by ballast of either slag or gravel. Modern installations do not have slag or ballast and are called bald installations.

You can identify the number of plies or layers of roofing felt that are present by checking the spacing of the laps. The roofing felts come in 36-inch wide rolls. If you see lap joints every 18 inches, it is a two-ply roof and would be considered marginal. The most common built-up roofs are 3 and 4-ply roofs. Three-ply roofs will have laps at 12 inches. Four-ply roofs will have laps at 9 inches. Some roofing contractors install a base sheet to provide a fresh, clean surface under the new roof. This does not count as a ply or layer of roofing because it is used as a base or separator and is not part of the coated plies.

Determining the age of a built-up roof can be difficult, however, but here are some clues:

The top coat or flood coat generally lasts 4 to 5 years. When it is worn out, you will be able to see the felt paper or the fiberglass reinforcement. The flood coat is very black, and the exposed felt paper is a charcoal black, which has some gray in the black. If it is fiberglass-reinforced felt, you should see the fiberglass fibers. Re-coating is recommended every 4 to 5 years and will significantly increase the life expectancy of the roof.  The flood coat is the only waterproof part of a built-up roof.  When the flood coat is compromised, water will infiltrate and be absorbed into the matrix.

Check the short pent eve, or fire or party wall, on the north side that is exposed to the south sun. This is typically 90-pound rolled roofing, the granules become loose and expose the heavy paper matrix below in about 12 to 15 years, and is a good clue.


If you are on a row house or townhouse that join other flat roofs, there are additional evidences. Check the roll roofing lap over the firewall; the last roof to lap is the youngest roof. If there is a roof on each side you can compare all three. Use the same evidences outlined above to determine the age of the adjacent roof. By evaluating the ages based on all of these evidences, it will generally help you figure out the age of the subject roof.

Inspecting flat roofs:

Check the condition of the surface. Age, wear, flood coat, delaminations, flashings, ponding and projections. The condition of the flood coat will assist your maintenance suggestions. Delaminations are separations or bubbles that may occur in the roof surface when moisture or water gets trapped below the roof surface. The most common cause is moisture that was trapped in the older roofs that are below the newer or current roof surface. This is also caused by water entering at penetrations, seams, and flashings. A few delaminations do not necessarily render the roof failed. If it is a young roof with no evidence of compromised seams or flashings etc., the moisture was probably trapped in the older roof below. As long as the surface is intact, the delamination is not too serious and no one walks on it, there may not be a failure for five or ten years.If there are 5 or 6 or medium to large delaminations, you may have a condition that renders the roof marginal or poor due to the excessive vulnerabilities.

Ponding on flat roofs is always a concern. If the ponding water does not evaporate within 48 hours of rain stopping, it is likely defective. A small amount of ponding water is not a problem, assuming it will evaporate within 48 hours. Look for stains in low areas of the roof, adjacent to wall scuppers or roof drains, especially if it has not rained in 3 or more days.

Flashings at walls and projections, such as chimneys and skylights, account for the majority of roof leak problems. Check these areas carefully, as well as the ceiling areas below. Determine whether any stains are wet or dry. This is one of the best uses for a moisture meter.

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Metal roofing is normally one of two varieties, either flat seam or standing seam. A standing seam metal roof will easily last 75 to 100 years, if it is properly maintained.

Proper maintenance consists of periodic scraping and painting with rust-resistant paint. These roofs are frequently abused by the use of tar or asphalt patches or repairs. These materials have a tendency to trap moisture adjacent to the metal and accelerate rusting.

​An asphalt or tarred-over metal roof can be assumed to be in failure, because coating a metal roof with an asphalt material is not an acceptable practice. It may suggest that the roof had leaking problems and an inexperienced person may have performed the work.

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Terra Cotta

Terra cotta tile roofs are found in most areas, however, they are most common in the southeast and the southwest. This style of roof, tile, has been used for millenia. Everyone from the Greeks to Romans, to Chinese and Middle East have used them.

These roofs are long lasting, however, they are vulnerable to breaking. And when they are installed in a commonly used mortar bed system, they tend to slip and may need replacement in 10 years or less. It is easiest to check for slippage in valleys. If there are no valleys, check at the gutters, dormers and at the ridge for slippage.

Adding some flare to your home can be achieved if you're in the right climate and have the right style of roof germane to the area. Terra cotta tile style roofs certianly add character.

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Asbestos shingles come in 1/8-inch and 1/4-inch versions, with the 1/8-inch version being the overwhelming majority. They do not pose a health hazard, however, workmen are at risk when they remove them. The 1/8-inch shingles are dependable for about 40 years. After about 40 years, they tend to break easily, lose their strength, and need considerable maintenance, due to them breaking more easily.

They need replacement when the maintenance is difficult or a burden (i.e. if the roofer repairing the roof breaks more or almost the same number of shingles that he is replacing, the roof should be replaced). The 1/4-inch version will often last more than 70 years.

There are many other types of roofing, however, they are in the minority and will have to be addressed as needed, depending on the geographical location.

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