Asphalt shingles are classified by their weight. Shingles are rated by their weight per roofing square. A roofing square is a 100 square foot area of the rooftop. Lightweight shingles weigh about 215 pounds per roofing square. Heavyweight shingles weigh about 350 pounds per roofing square. Most asphalt shingles have a fiberglass mat instead of an organic type of mat. Asphalt-Fiberglass shingles have a typical life expectancy of 18 to 22 years. If a heavy weight shingle is used, then the life expectancy can be 30 years. This is because the roofing will stand up to the elements better. Quality roofers give warranties for these shingles as long as 20 to 30 years. As asphalt roofs age, they begin to cup and curl. You'll see these shingles fraying at the edges when they get old. You'll also see pitting of the granules. This is caused by the exterior of the shingle beginning to wear away. These granules are needed to protect the shingle from the sun and weather.
Check to see how many layers of shingles are currently on the roof. Most local building codes only allow up to two layers of asphalt shingles on a roof. If there are more than two layers, tell the client to find out if this is a building code violation. Three layers of shingles on a roof adds too much weight to the structure. You should only recommend that there be two layers as a maximum. Also, when shingles are placed over an existing layer, they can have a poor cosmetic appearance. The bumpy appearance of the roof is caused by the layer underneath which has cupped and curled from aging. Furthermore, placing roof shingles over an existing layer cuts down the life expectancy of the top layer of shingles.
If the house has two layers of shingles presently, then tell the client that they're going to have to strip these layers off during the next reroofing. This is a much more expensive repair.
If the house has two layers presently, then tell the client to budget for the next reroofing. They're going to have to strip these layers of shingles off and probably install new sheathing during the next reroofing. This is much more expensive than just having a new layer put over the existing shingles. Especially, if the roof sheathing has to be replaced as well. To determine the number of layers of shingles, look at the visible edges of the roof. If you see two or three shingles, then the roof probably only has one layer. This is because an extra layer of shingles is installed at the edges to keep rainwater from being blown underneath the shingles. Sometimes a roofing contractor will place a strip of aluminum flashing along the edge of the roof shingles. This will prevent rainwater from getting under the shingles but it also prevents you from seeing the number of layers of shingles.
To determine the age of the roof shingles you have to use some basic math and your own judgment. This is a good example of where the owner's answers to your preinspection questions come in handy. For instance, the life expectancy of average weight asphalt shingles is about 20 years. Let's say you are inspecting a house that's 30 years old and the roof doesn't show signs of aging. If you see four or more shingles at the exposed edges of the roof, you can assume the top layer is about 8-10 years old. It's just basic math: the first layer lasted about 21 years before a new roof was installed over it.
Be careful when evaluating roofs on houses that are about 20 to 25 years old. If there are heavyweight shingles the roof might not show clear signs of aging yet. If you don't check for the number of layers, you could incorrectly assume it's the second roof. This would cause the client to think he has another 15 years of roof life when actually there's only 5 years left. I made a mistake like this on one of my first home inspections in this business. The roof of the house had heavyweight shingles that were in excellent condition. There was no way to get close to the roof with my ladder. This house was located on a slope and my ladder couldn't reach near the roof edge. I did check the sides with binoculars and saw an extra layer of shingles along the edges. As a result, I thought the roof was relatively new since it was in excellent condition. The extra layer of shingles on the edges gave the indication that a second layer of roofing was installed within the past five years or so. Yes, I was wrong on that one. However, Lady Luck was on my side. The client had a friend who was a general contractor come by the house before the closing to give him some price estimates. The estimates were needed for some of the problem conditions I identified in other parts of the house inspection. Fortunately, the contractor had a long ladder that reached up to the roof line. He noticed that this was not a second layer of roofing shingles even though the shingles were in great condition. The client called me and told me about the mistake I made. I felt terrible that I missed this one and offered to refund his home inspection fee. However, the client was happy with the overall inspection I did and the problems I was able to identify. He said he would still recommend me to other people for home inspections.
You also have to be careful when inspecting houses that have sections of roofing that are different ages. For example, some homeowners will only replace 1/2 of a roof when a leak develops. Also, if an addition is installed to the house, this roofing will be newer. So don't just look at one side of the roof and assume that all the shingles are the same age. View all areas of the roofing shingles. On occasions you'll come across sections of a roof that were replaced at different times. This happens when a homeowner only wants to pay for part of the roof to be replaced. It's more cost efficient in the long run to reroof the entire house at the same time. However, if the homeowner cannot afford this, they'll only replace the shingles that are leaking water. Due to this possibility, you have to make sure you evaluate the roofing shingles from all sides of the house. Also, you may find "woven valleys" on some asphalt shingle roofs. A woven valley is shingles installed to overlap one another where roof sections meet. This is done for cosmetic purposes so the valley flashing is not visible.
Wood Shingle and Wood Shake roofs have a typical life expectancy of about 40 years. The lifespan will vary depending upon the maintenance given to them. They should be sprayed about every 4 years with a water repellant stain or sealant. This will prevent the wood from drying out and splitting. Wood shingle and wood shake roofs are more expensive to install than asphalt shingle roofs. As a result, they're usually only found on higher priced houses. Often you'll find asphalt shingles installed over a wood shingle roof. This is because the homeowner wanted to save money when reroofing. They did not want to pay the higher cost to install new wood shingles when the first layer needed replacing.
The difference between wood shingles and wood shakes is that wood shingles are sawn when they're manufactured. This gives them a smooth surface. Wood shakes are split when they're manufactured. Therefore, they're thicker and have a rougher surface. Wood shingles are spaced about 1/4 inch apart so they can expand and contract with the temperature changes. However, there shouldn't be any open gaps allowing water into the attic. Wood shingles and wood shakes are usually made from cedar or redwood. The reason for this is that these woods are more rot resistant and have less knots. Check for any signs of dry or rotted shingles that indicate a need for repairs.
Slate roofs are very expensive to install. Because of this, they're usually only found on older houses or very high priced newer houses. Slate roofs will only have one layer of shingles on the roof. This is due to their being very heavy and brittle. Do not walk on a slate roof; you'll damage the shingles. The life expectancy of a slate roof can be anywhere from 50 years to 150 years or more. The lifespan will depend upon the quality of the slate and the installation of the shingles. If the roofing nails are intact then the thicker the slate shingles, the longer they will last.
When slates are shaling (flaking) and excessively falling off the roof, it's an indication that repairs are needed. The slate shingles will have to be removed carefully so they aren't damaged. After that, new tar paper needs to be placed over the roof sheathing to provide a weather covering. Then the slate shingles will be reinstalled with copper nails. Don't take any chances with a slate roof; they're extremely expensive to reroof. If you're not sure of it's condition, tell the client to get an estimate from a roofing contractor.
You'll usually find a few fallen slate shingles. However, you're looking for an excessive amount of shingles that have fallen off the roof. This is an indication that the roofing nails are all corroding. The only way to correct this problem is to remove each slate and reinstall it with copper nails. In northern climates where there's snow, you might see snow guards along the bottom rows of slate shingles. Snow guards are small metal fins that stick up from the slates. Their purpose is to stop snow from falling off the roof so it doesn't drop to the ground with excessive force. Large amounts of falling snow could hurt someone or damage cars and other objects located below the roof line.
Tile roofs are similar to slate roofs. They're very expensive to install and are usually only found on older houses or very high priced newer houses. Tile roofs will only have one layer of shingles. This is due to their being very heavy and brittle. Do not walk on a tile roof; you'll damage the shingles. The life expectancy of a tile roof can be anywhere from 50 years to 100 years or more. The lifespan will depend upon the quality of the tile and the installation of the shingles.
As with slate roofs, you're looking for any shaling or an excessive number of falling tiles from the roof. Don't take any chances with a tile roof as well; they're very expensive to reroof. If you're not sure of it's condition, tell the client to get an estimate from a roofing contractor. There are concrete roofing shingles that look identical to slate and tile shingles. The purpose of these concrete shingles is to give the home an expensive roof appearance. In reality the cost can be far less than installing an actual slate or tile roof.
Flat roofs usually consist of asphalt rolled roofing material. Asphalt Rolled flat roofs generally are the least expensive type of roofing to repair or replace. Flat roofs have to be monitored by the homeowner, more often than other types of roofs, to make sure they're watertight. The reason for this is that they don't just shed water like pitched roofs do. Flat roofs have a tendency for ponding water conditions. The life expectancy for an asphalt flat roof is about 8 to 10 years. There are rubber material flat roofs that are superior to asphalt rolled roofing. These rubber roofs have a 30 year life expectancy.
As with asphalt shingle roofs, flat roofs can be installed over existing layers when a new roof is needed. You should try to determine how many current layers there are when evaluating these roofs. You won't be able to see an exposed edge like on a pitched roof. Just use some basic math and your own judgment based upon the age of the house and the owner's answers to the preinspection questions.
Check for any ponding water conditions on a flat roof. Ponding water will decrease the life expectancy of these roofs and must be repaired to help prevent leaks. If you see a flat roof bubbling in areas, it shows the roof covering is near the end of its life expectancy. As a result, the roof will need to be replaced.