My house will be 20 years old next year and I am considering replacing the wood shakes with a synthetic material.  There are no problems with the roof but is there is a “magic number” of years after which it should be replaced?   J.C. Fremont

While there is no “magic number” for roofs in general, each particular type of roof covering does have an average life span.  The four most common types of roof covering used in California are tile (clay, cement and metal), wood shake and shingle, composition shingle, and finally, tar and tar and gravel. Each of these roofs require periodic maintenance to maintain their serviceability.  After the first five years of age, roofs should have a professional inspection every two to three years to determine what repairs may be necessary.

In order to understand how long a roof covering lasts, it helps to understand how a roof is designed to work.  Roofs are basically designed to shed water without leakage.  All of the roof coverings that I have mentioned above, require an underlayment called roofing felt.  Roofing felt is a thick black sheet of material that is installed under the roof covering.  The felt is what truly ensures that the roof remains water-tight.  The actual roof covering, whether it is tile, wood shake, comp shingle, or tar and gravel, merely protects this felt from the damaging effects of the sun’s ultra violet rays. 

Therefore, the life of a roof depends upon many things, the quality of the roof covering and felt, the amount of direct sun exposure, and the quality of routine maintenance.  Since the sun is a primary source of deterioration, roofs tend to wear out fastest on the southerly and westerly sides of the house because of the increased sun exposure.  Also, low-sloped roofs and flat roofs tend to wear out faster than steep roofs, again because of the increased sun exposure.    

A medium grade, wood shake roof covering has an average life of 18 to 22 years.  This is about how long it takes wood shakes to begin to break down and deteriorate from the sun’s ultra violet rays.  However, throughout the life of the roof covering, the shakes are wearing thin, splitting or slipping out of place, exposing the felt.  Exposed felt can develop into leaks within several months. That is why periodic maintenance is so important. 

Most people are not aware that roofs can leak two to five years before a water stain appears on the ceiling. This is usually because the roof leaks onto the ceiling insulation in the attic which can retain a tremendous amount of moisture before it finally seeps into the ceiling sheetrock.  Properly maintaining a wood shake roof covering can prevent expensive repairs and extend its life upwards of 25 years.

If you have not had your roof inspected or serviced lately, now is probably the best time to have that done.  A 20 year old wood shake roof is definitely getting towards the end of its life.  With winter and the rains approaching you will want to be sure that your roof is water tight and able to last through the wet season.   

When you finally decide to replace your roof, I would suggest that you thoroughly research the different types of roof coverings that are available.  Tile roof covering generally has the longest life span of approximately 50 years.  Single layer composition shingle roof coverings have a 15 to 20 year life span, and the dimensional composition shingles have a 25 to 40 year life, depending upon the quality that you buy.

Each type of roof covering has advantages and disadvantages that you should be aware of before making your final decision.  Things to consider are the weight of the material, the ability to walk on the roof and make repairs, and the maintenance that is required to keep the roof water tight.

A reputable roofing contractor would be able to discuss the pros and cons of each type of roof covering for your particular house.  When shopping for a new roof, be sure to get at least three bids, and only deal with licensed roofing contractors.  Most cities require that a permit be obtained when a new roof covering is installed.  Be sure to find out if your building department does.

Finally, don’t be surprised when after selecting your contractor, he tells you that his first available opening is not for three months.  It has been an extremely busy year for the construction industry.

John R. Schneider is a licensed general building contractor and a certified residential code specialist. He is president of All About Homes, a residential inspection company, and has been performing code and construction consultations since 1985.  Readers may address their comments to John Schneider ,  24326 Mission Blvd. Suite 7, Hayward, Ca 94544, or at www.allabouthomes.com.  Schneider will answer questions of general interest in the paper. He reserves the right to edit the letter for brevity and clarity. Readers are encouraged to contact a competent contractor or code consultant for specific information regarding questions they may have about their homes.

Copyright 2002, John R. Schneider, all rights reserved