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The roof of a home is one of the most common areas for water penetration to occur. Can you identify the different signs and degree of roof failure? The following helps you do just that. From flashings to life expectancies, it’s all here.

Method of Inspection

There are several methods of inspecting a roof. Typically, it is walked on, checked from a window from above, by a ladder at the eave, or from the ground with binoculars. If at all possible, the roof should be walked on, unless it would damage the material, such as older slate, or it would be unsafe or dangerous to the inspector. As a minimum, a ladder should be placed at the eaves, and the evaluation performed from that location. Windows from above provide an excellent opportunity to evaluate as much of the roof as possible from that location. The last resort is inspecting it from the ground with binoculars.

Inspectors carry extension ladders in some markets. Florida communities are mostly ranch or one-story homes. Most home inspectors in Florida carry folding ladders. Many northeastern markets, such as Philadelphia, have mostly two-story homes, so many home inspectors carry extension ladders.

Townhouses and inner city houses frequently have flat roofs that are difficult to get on without an extension ladder. In many cases, there is a hatch on the second or third floor that provides access to the roof.

Roofing Characteristics

There are nine characteristics of a roof that you should consider in your evaluation:

  1. Slope
  2. Material type
  3. Maintenance
  4. Estimated Age
  5. Design Life
  6. Remaining Life
  7. Style
  8. Structure
  9. Flashings


Roof slope is determined by vertical rise over horizontal run, expressed in inches, the second number always being 12. For example, if a roof rises at a rate of 6 inches per foot (horizontal), it is a 6/12-slope roof.

Roofs with slopes of 8/12 or less can be walked on in most situations. Some people do not have any difficulty climbing almost any roof, while others have considerable difficulty. You should never walk or climb a roof that you do not feel safe climbing.

A roof that is flat, close to flat or has depressions, and allows water to collect or pond, may be a defect. This will depend on the extent of the ponding and the amount of water that collects. The National Roofing Contractors Association (NRCA) says that if ponding water evaporates within 48 hours of the time it stops raining, it can be considered acceptable.


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 and 30-year). The differences are the weight and design of the shingles. 30-year shingles generally do not have the 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. Reshingling 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:

  1. 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.
  2. 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.

Mineral surface 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 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. With 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.

Wood is a popular material for roof covering. 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 ˝ inches, 7 ˝ inches and 10 ˝ inches. 1×4 sheathing boards for wood shingles; 1×6 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.

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, is approximately $30.00 to $40.00 per slate with a minimum of $250.00 to $350.00.
  • 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.

Built-up roofs 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. Recoating 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.

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.

Cement tile, terra cotta tile roofs are found in most areas, however, they are most common in the southeast and the southwest. 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.

Cement asbestos shingles. These 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.

Maintenance and Life Expectancy


All roofs should be inspected and maintained. The type of maintenance and frequency varies (i.e., asphalt shingles do not need maintenance). Built-up roofing should be recoated every 4 to 5 years. The life of a roof can be significantly prolonged if maintenance is accomplished. (The maintenance activity for the various types of roofing materials is included in Attachment “A”.)

Estimated Age

Estimating the age of a roof can sometimes be difficult. On newer homes, the age of the roof is normally the age of the house. Check for multiple layers, which is a good clue. If the roof has: (a) several different materials; (b) the same material on different exposures; or (c) materials of different ages, each one of the differences should be evaluated separately.

Life Expectancy (Design Life)

The life expectancies of various roofs are included in Attachment “A”. The exposure of a roof to weather (i.e., sunlight) will significantly decrease its life expectancy. A south or west-facing roof very often is in a poorer condition than the north or east-facing surfaces on the same structure. Other major factors in the life expectancy of the roof are slope, shade, color, etc. A well-shaded, low-sloped wood roof on the north side of a property will very often gather moss, mildew, etc. and deteriorate more rapidly than one that is not.

Remaining Life

The remaining life of the roof is not necessarily determined by subtracting estimated age from life expectancy. It is possible to have a two-year-old roof with a life expectancy of 20 years and have zero life remaining due to a product defect. Many factors can affect this. They include the manufacture, installation, wear, maintenance, etc. The actual condition of the roof determines remaining life.

Roof Structure


A considerable amount of new construction utilizes manufactured trusses. These trusses are held together with gusset plates pressed into the wood, and consist of various web chords that are arranged to adequately support the roof system. Typically, these web chords are made from 2x4s. Some problems related to roof trusses are due to the way that they are stored and handled. Trusses should be stored in a vertical position. Typically, they are laid flat on-site. Any broken or missing member of a truss renders it ineffective, and because trusses are dependent on the accumulated strength of the truss components, the integrity of the roof system, or at least that truss could be compromised. Truss repairs are relatively easy to design, but for credibility and liability reasons, a structural engineer should be consulted to design any truss repairs or modifications.


The type of material used on the surface is a factor in determining the type of sheathing necessary. Wood shakes, clay, ceramic and cement tiles often have nailing boards upon which the roofing material is hung or fastened. Older houses may have one-inch dimensional lumber for sheathing. In the 1940s and 1950s, plywood became the material of choice. The plywood should have spacers between the sheets. Plywood should not be used as sheathing for wood shakes, as it may not allow them to breathe and could shorten their life. However, solid sheathing is required in areas that receive considerable amounts of snow, for shake roofs.

FRT Plywood

Fire Retardant Plywood is a material used in townhouse construction starting in the early 1980s. The purpose of the Fire Retardant Plywood was to eliminate parapet walls required between units. One indication that a building may have Fire Retardant Plywood is that the walls separating the unit are constructed with fire rated drywall. If Fire Retardant Plywood turns a coffee or darker color, it may be delaminating/deteriorating. Care should be taken when inspecting the roof. It is not recommended that you walk on a roof with Fire Retardant Plywood until you have determined that it is structurally adequate.


Flashings nailed into a wall or chimney and covered with tar or asphalt roof cement are not adequate. Flashings should be mechanical and permanent. The use of asphalt roof cement or tar for flashing is considered a “temporary repair.” If caulk or roof cement is used as flashing for a new roof, it should be considered unacceptable or not dependable.

Roof valleys can be either metal or woven shingles. The woven shingle valleys have a tendency to wear more rapidly than metal (aluminum).

Common Defects

  • Antennas – Mostly the attachment points
  • Solar panels – Leaks and roofing penetrations
  • Flashings – walls, roof, skylights and valleys
  • Worn material
  • Modified structures – conventional and trusses
  • Broken structural members – including deteriorated gusset plates
  • Deteriorated FRT Plywood
  • Improper pitch/slope for the roofing material used
  • Missing shingles or other roofing components
  • Chimney deterioration – interior of the flue and/or exterior components
  • Improper chimney height
  • No attic access – Reporting issue
  • Ponding water – judgement call
  • Sag in roof line or walls pushing out
  • Unacceptable amounts of deflection or bounce when walked on
  • More than 2 layers of shingles present (3 layers allowed in some areas)

Related Components


Skylights should be inspected from both the roofing side and the inside. Items to look at on the outside of the roof are:

  1. Skylights should have adequate curbs, whether they are manufactured units or not. Skylights without curbs or with inadequate curbs do not allow for proper step and counter flashings, and are destined to leak. Some adhesives/sealants are better than others, however, without proper flashings, the skylight seal would not be considered dependable and the installation of proper flashings should be anticipated.The skylight curb height on a sloped roof should be approximately 4 inches, for a flat roof; it should be 6 to 12 inches, depending on the potential for snow in the geographical area.
  2. The flashing detail around skylights, particularly those installed after the original construction, is frequently improper. The most common problems are improper or non-existent step and counter flashings, lack of adequate curbs and failed thermal seals.

Solar panels

Solar panels mounted on a roof are beyond the scope of an inspection, however, they are frequently defective, and responsible inspectors will be aware of the potential problems. The major problems with solar panels are:

  1. The areas where they are fastened to the roof are typically tarred over with roof cement, will eventually open up and leak.
  2. The framing (i.e., truss/rafter) beneath the solar panel may not have been reinforced to receive the areas that bear on the roof or to accommodate the additional weight.
  3. Leaks are relatively common. In some cases, these panels are drained and abandoned in lieu of repairs.


Antennas secured to a roof or chimney are vulnerable and may cause problems. The reason is that they are normally anchored to the chimney, roof and/or the structure with guy wires that may be stressed during high winds. And over time, they may create stress points at the fasteners, which may become loose and weak.

Chimneys above the roof

While on the roof, evaluate the chimneys above the roofline. The masonry chimneys may have multiple flues. If the chimney is only one brick or 4 inches thick, and without a liner, it is defective. To be safe, a one brick chimney must have a flue liner all the way to the firebox on the bottom. A chimney two bricks or 8 inches thick does not require a liner. Cracked mortar, spalling bricks, or cracked caps are very common defects.

The reason chimneys deteriorate at the top most quickly is that they heat up and then cool off during the winter months, in rapid succession, causing the bricks to crack, and allowing condensing water to penetrate. The penetrating water can then cause deterioration, or even worse, could freeze, expand and cause larger cracks. When possible, look down the chimney to ensure that the terra cotta liner or the brick is in good condition. Metal chimney flues, normally for gas or oil-fired heating plants, should also be inspected above the roofline. These metal units should have a weather cap installed on them, and should not be rusted out. The individual sections should be screwed together.

Large metal pans that are installed at the top of some metal chimney structures should be convex to assure proper shedding of water. In some situations, the metal chimney is hung from this pan, causing it to distort and become concave. There is a collar in the pan that goes around and is screwed to the metal chimney. This collar may likely keep the pan from leaking for 10 years or more, however, it may eventually fail, and all of the water that lands on the pan will fall into the chimney structure. Check the top of metal chimneys. If you are unable, inspect the area around and adjacent to the chimney for even remote water stains.

Overhanging trees

Overhanging trees or brushing on a roof are not a defect unless they are actually causing damage. If leaves are lying on the roof, they may be causing moisture damage to the roof sheathing. This typically will not be visible, so check the ceiling below the area that the leaves are located for even the most minor stain, and carefully try to walk the roof in the area that the leaves are located. If the house is older and it appears that the leaves lay in one area for months at a time, it is possible to have severely weakened sheathing. If shingle granules are worn off, it is suggested that the tree be cut back and the roof be repaired, if necessary.